Chemistry chapter 9 and 10

which set of elements is arranged in order of increasing electronegativity? a) O<S<As<Ge b) Ge<As<S<O c) S<O<As<Ge d) As<O<Ge<S

B

use bond energies from table 9.3 to determine triangleH(rxn) for the reaction between ethanol and hydrogen chloride. CH3CH2OH(g) + HCl (g) --> CH3CH2Cl(g) + H2O (g) a) -1549 Kj b) 1549 c) -12 d) 12

C

which pair of atoms form the most polar bond? a) N and O B) C and O c) C and F d) N and F

C

Of the following molecules, the only one with no permanent dipole moment is: Water, H2O Acetone, CH3COCH3 Carbon dioxide, CO2 Sulfur dioxide, SO2 Chloromethane, CH3Cl

Carbon dioxide, CO2 Although it is true that the C(double bond)O bonds in CO2 are slightly polar, their dipole moments are equal and opposite in direction and thus cancel each other out

Which response contains all the characteristics listed that should apply to PF3? a) trigonal planar b) one unshared pair of electrons of P c) sp^2-hybridized phosphorus atom d) polar molecule e) polar bonds 1) a, d, and e 2) b, c, and d 3) a, b, and d 4) b, d, and e 5) a, c, and e

4) b, d, and e The electron-group geometry is tetrahedral while the molecular geometry is trigonal pyramidal. There is one unshared pair of electrons on the phosphorus. The bonds are polar and their dipole moments do not cancel, so the molecule is polar.

which compound has the lattice energy with the greatest magnitude? a) MgS b) CaS c) SrS d) BaS

A

which pair of atoms forms a nonpolar covalent bond? a) C and S b) C and O c) B and O d) Na and Cl

A

which set of compounds is arranged in order of increasing magnitude of lattice energy? a) CsI<NaCl<MgS b) NaCl<CsI<MgS c) MgS<NaCl<CsI d) CsI<MgS<NaCl

A

which is the correct lewis structure for magnesium bromide?

check in book! its C

consider the reaction 2HCl(g) + 185KJ --> H2(g) + Cl2(g) which of the following is true? a) the chemical bonds in the products are weaker than those in the reactants b) if thermally isolated, the reaction mixture will get cooler as the reaction proceeds c) the HCl has a negative heat of formation d) the reaction is endothermic e) all of these are true

e) all of these are true. reaction is endothermic -if assume all of reaction enthalpy change due to bond breaking and reformation, can conclude that total bond enthalpy in the products is higher (less negative) than that of the reactants, indicating stronger bonds in reactants) -although rxn endothermic, not necessary to add heat from the surroundings to cause it to proceed -if isolated, reaction will simply get cooler as the reaction proceeds -reaction is reverse of the formation reaction for 2 moles of HCl. that means that the formation of reaction is exothermic and that the enthalpy of formation of HCl is negative

what is formal charge? equation? -what does the "best" skeletal structure normally have? rules when calculating formal charges?

fictitious charge assigned to each atom in a lewis structure that helps us to distinguish among competing lewis structures (charge it would have if all bonding e-s shared = between bonded atoms) -FC=# valence e- - [nonbonding e- + ½ bonding e-] -sum of all the formal charges in a neutral molecule=0 (in an ion, total = charge) -"best" skeletal structure usually has the least EN atom in the central position 4 rules apply when calculate formal charges: 1) The sum of all formal charges in a neutral molecule must be 0 2) The sum of all formal charges in an ion must = the charge of the ion 3) Small (or zero) formal charges on individual atoms are better than large ones 4) When formal charge cannot be avoided, negative formal charge should reside on the most electronegative atom.

what is measured as the lattice energy in regards to the formation of a crystal lattice? is it endothermic or exothermic? what does lattice energy depend on? how does the born-haber cycle work? for a metal atom(g) --> cation(g), what is triangleHof? for a nonmetal atom(g) --> anion(g), what is triangleHoF? MAKE SURE YOU UNDERSTAND THIS!

lattice energy is the energy released when the solid crystal forms from separate ions in the gas state: -energy associated with the formation of a crystalline lattice of alternating cations and anions from the gaseous ions. -always exothermic (energy emitted as heat as lattice forms) -lattice energy depends directly on the size of charges and inversely on distance between ions. born-haber cycle: -hypothetical series of steps that represents the formation of an ionic compound from its constituent elements. The reactions are chosen so that the change in enthalpy of each reaction is known except for the last one, which is the lattice energy. for a metal atom(g) --> cation(g), triangleHof= first ionization energy for a nonmetal atom(g) --> anion(g), triangleHoF= electron affinity

a lewis structure for the acetate ion is shown here. which structure is the best resonance structure for the acetate ion?

look in book D

CCl4, BeF2, SbCl5, XeF4 which of the following does NOT describe any of the molecules above? a) linear b) octahedral c) square planar d) tetrahedral e) trigonal bipyramidal

octahedral

why does lewis theory predict that ionic compounds should have high melting points and boiling points? the stronger the attraction, the ___ the melting point what is the reasoning behind the fact that ionic compounds have high melting points?

predicts ionic compounds should have high melting points and boiling points because the breaking down the crystal should require a lot of energy -the stronger the attraction (larger the lattice energy) the higher the melting point -modeled ionic solid as lattice of individual ions held together by coulombic forces that nondirectional (as move away from center of ion, forces = strong in all directions). To melt solid, forces must be overcome which requires significant amount of heat hard and brittle crystalline solids (all solids at room temp), melting points generally >300 C, liquid state conducts electricity (solid state doesn't conduct electricity), many soluble in water (solution conducts electricity well).

what arrangement of charged particles has the lowest PE? what is polar covalent bonding? what are metallic bonds? how does this relate to ionization energy? what is the electron sea model?

-arrangement in which negatively charged particle lies between two + charged ones has lowest PE → - charged particle interacts most strongly w both of + charged ones Polar covalent bonding: covalent bonding between unlike atoms results in unequal sharing of the electrons. Metallic bonds: the relatively low ionization energy of metals allows them to lose electrons easily. Electron sea model: simplest model for metallic bonding- all atoms in metal lattice pool valence electrons. when metal atoms bond together to form a solid lattice, each metal atom donates 1+ electrons to an electron sea -electrons delocalized throughout the metal structure

as two atoms approach each other, how do they interact to form molecular orbitals? why are the molecular orbitals more stable than the separate atomic orbitals

-as two atoms approached, the half-filled valence atomic orbitals on each atom would interact to form molecular orbitals (regions of high probability of finding the shared electrons in the molecule.) -the molecular orbitals would be more stable than the separate atomic orbitals because they would contain paired electrons shared by both atoms (the PE is lowered when the molecular orbitals contain a total of two paired electrons compared to separate one electron atomic orbitals)

difference between lewis model and nature on how e-s in molecule localized or delocalized:

-in lewis model, e-s localized either on 1 atom (lone pair) or between atoms (bonding pair) -in nature, e-s in molecule often delocalized over several atoms or bonds, which lowers e-s energy and stabilizes them.

what does lewis theory predict in terms of ionic solids conducting electricity? do ionic compounds conduct electricity in liquid state/when dissolved in water?

-to conduct electricity, material must have charged particles that are able to flow through the material --> in ionic solid, ions cant move -lewis theory predicts that ionic solids shouldn't conduct electricity -ionic compounds conduct electricity in the liquid state or when dissolved in water. Conductivity of NaCl: in NaCl(s) the ions are stuck in position and not allowed to move to the charged rods. In NaCl(aq), the ions are separated and allowed to move to the charged rods

What are the 3 common ways of predicting how atoms combine to form molecules?

3 common ways of predicting how atoms combine to form molecules (approximations needed because solving Schrodinger's equation exactly is not possible.) 1) Valence shell electron repulsion (VESPR): qualitative approach, treats all valence e-s the same, as belonging to the molecule as a whole without considering orbital shape. 2) Valence bond theory: semi quantitative approach using quantum mechanics, treats atoms as if they are described by quantum mechanical atomic orbitals. Predicts some properties better than VESPR. Takes into account shapes of atomic orbitals 3) Molecular orbital (MO) theory- construct orbitals for the molecule as a whole (molecular orbitals). Construct trial molecular orbitals and select one that minimizes energy. Predicts some properties better than valence bond theory

consider the halogenation of ethene, where X is a generic halogen: H2C(double bond)CH2(g) + X2(g) --> H2XC--CH2X(h) use bond energies to determine which halogen produces the most exothermic halogenation reaction with ethene. The C--F, C--Br, and C--I bond energies are 552 Kj/mol, 280 kJ/mol, and 209 kJ/mol. Look up all other necessary bond energies in table 9.3 a) flourine b) chlorine c) bromine d) iodine

A

electron group geometry: -maximum of __ bonding electron groups -how many basic arrangements of electron groups around a central atom does it matter which resonance form you use for molecules that exhibit resonance? what is geometry about in terms of separating between electrons?

Electron group geometry: -5 basic arrangements of e- groups around a central atom -based on max of 6 bonding e- groups (though there may be more than 6 on very large atoms, very rare) -each of these 5 basic arrangements results in 5 different basic e- geometries. -in order for the molecular shape and bond angles to be a "perfect" geometric figure, all the e- groups must be bonds and all the bonds must be equivalent -for molecules that exhibit resonance, it doesn't matter which resonance form you use as the e- geometry will be the same -all geometry about maximizing separation between electrons

what predicts the number of valence e- pairs around the central atom? -each lone pair of e-s constitutes one electron...... -each bond constitutes one e- group...

Electron groups: -the lewis structure predicts the number of valence e- pairs around the central atom(s) -each lone pair of e-s constitutes one electron group on a central atom -each bond constitutes one e- group on a central atom, regardless of whether it is a single, double, or triple

Which of the following provides the best evidence that all of the carbon compounds listed below are tetrahedral and NOT square planar? a) Only one CH4 compound is known and its nonpolar b) Only one CF4 compound is known and its nonpolar c) Only one CH3F compound is known and its polar d) Only one CH2F2 compound is known and its polar e) Only one CHF3 compound is known and its polar

FIND ANSWER

four electron groups: tetrahedral electron geometry: -bond angle? five electron groups: trigonal bipyramidal electron geometry: -bond angles?

Four e- groups: tetrahedral e- geometry: again, allowing max separation among the groups -when there are 4 e- groups around the central atom, they will occupy positions in the shape of a tetrahedron around the central atom. This results in the e- groups taking a tetrahedral geometry. Bond angle=109.5 5 e- groups: trigonal bipyramidal electron geometry: The positions above the below the central atom are called the axial positions -the positions in the same base plane as the central atom are called equatorial positions -the bond angle between equatorial positions=120 -the bond angle between axial and equatorial positions=90

Covalent bonds? How does this connection to ionization energies? when nonmetals bond together, it is better in terms of PE for the atoms to....

Nonmetal atoms have relatively high ionization energies, so it is difficult to remove electrons from them. When nonmetals bond together, it is better in terms of PE for the atoms to share valence electrons (PE lowest when the electrons are between the nuclei) -when nonmetal bonds w another nonmetal, neither atom transfers e-s to each other; two atoms share e-s. Shared e-s interact w nuclei of both bonding atoms, lowering PE (and resulting in covalent bond)

what is octahedral electron geometry? bond angle what is electron geometry? what is molecular geometry?

Octahedral e- geometry -when there are 6 e- groups around the central atom, they will occupy positions in the shape of two square-base pyramids that are base-to-base with the central atom in the center of the shared bases -this results in the e- groups taking an octahedral geometry (called octahedral because the geometric figure has 8 sides) -all positions equivalent -bond angle 90 -electron geometry: the geometrical arrangement of the electron groups -molecular geometry: the geometrical arrangement of atoms

molecules that have planar configurations include which of the followers? I) BF3 II) XeF4 III) NH3 a) I only b) III only c) I and II d) II and III e) I, II and III

I and II

what is an ionic bond? what happens when a metal atom loses electrons and a nonmetal gains electrons? How does this process lower the potential energy and create an ionic bond?

Ionic bonds: when a metal atom loses electrons it becomes a cation (metals have low ionization energy, making it relatively easy to remove electrons from them) When a nonmetal atom gains electrons it becomes an anion: nonmetals have high electron affinities, making it advantageous to add electrons to these atoms -the oppositely charged ions are then attracted to each other, resulting in an ionic bond -metal atom becomes cation and nonmetal atom becomes anion. Positively charged ions attract one another, lowering overall PE (resulting in ionic bond)

what happens when there are 2+ interior atoms? how do you describe the shape around each central atom?

Larger molecules may have 2+ interior atoms Multiple central atoms: -many molecules have larger structures with many interior atoms (we can think of them as having multiple central atoms.) when this occurs, we describe the shape around each central atom in sequence.

According to the lewis bonding theory, why do atoms bond? what creates a more stable configuration (according to potential energy?) How to use lewis structures to represent a transfer of electrons from a metal atom to a nonmetal atom? How to allow ions to form a crystalline lattice?

Lewis bonding theory: atoms bond because bonding results in a more stable electron configuration. More stable=lower potential energy. -octet rule -lewis symbols can be used to represent the transfer of electrons from a metal atom to a nonmetal atom, resulting in ions that are attracted to each other and therefore bond. -move e- dots from lewis symbol of metal to lewis symbol of nonmetal and allow resultant ions to form crystalline lattice composed of alternating cations and anions.

how does the actual geometry of the molecule compare to the electron geometry? what can affect the molecular geometry around the central atom? What do molecular geometries tend to not be perfect?

Molecular geometry: -the actual geometry of the molecule may be different from the e- geometry. -when the e- groups are attached to atoms of different size, or when the bonding to 1 atom is different than the bonding to another, this will affect the molecular geometry around the central atom. -lone pairs also affect the molecular geometry (occupy space on central atom but not "seen" as points on the molecular geometry) → lone pair electrons typically exert slightly greater repulsions than bonding electrons. Not quite perfect geometry: because the bonds and atom sizes are not identical in formaldehyde, the observed angles are slightly different from ideal. The double bond repels more than single bonds

which of the following species has a lewis structure similar to H3O+? a) NH3 b) HCO3- c) CO3 2- d) ClF3 E) NF3

NH3

the lewis structure for each of the following contains at least one double bond except: a) CS2 b) NO+ c) C2H4 d) N2H2 e) O2

NO+

how do polar and nonpolar molecules have different properties? How does molecular polarity affect solubility in water?

Polar and nonpolar molecules have different properties → water and oil don't mix bc water molecules polar and molecules that compose oil generally nonpolar -polar molecules interact strongly with other polar molecules because the positive end of one molecule attracted to the negative end of another. Molecular polarity affects solubility in water: -polar molecules attracted to other polar molecules -because water is a polar molecule, other polar molecules dissolve well in water (and ionic compounds as well) -some molecules have both polar and nonpolar parts -nature uses surfactants to make cell walls

polyatomic molecules:

Polyatomic molecules: when many atoms combined together, the atomic orbitals of all the atoms are combined to make a set of molecular orbitals, which are delocalized over the entire molecule -gives results that are better match real molecule properties than either lewis or valence bond theories

what are some problems with the valence bond theory?

Problems with valence bond theory: -predicts many properties better than lewis theory (bonding schemes, bond strengths, bond lengths, bond rigidity), but still many properties of molecules it doesn't predict perfectly (magnetic behavior of O2) -in addition, doesn't consider phases of wave function

in which of the following species is the octet rule violated by the central atom when the central atom has a formal charge of 0? a) H2S b) SOCl2 c) CCl4 d) N2F4 e) PF3

SOCl2

Sp3 hybridization: what does it indicate?

Sp3 hybridization: indicates that the hybrid orbitals are mixtures of one s orbital and 3 p orbitals. Hybrid orbitals degenerate. -atom with 4 e- groups around it: tetrahedral geometry, 109.5 degree angles between hybrid orbitals -atom uses hybrid orbitals for all bonds and lone pairs

what is bond energy? is it endothermic or exothermic? what do chemical reactions involve regarding breaking and forming bonds? what is the average bond energy? -in general, the more e-s two atoms share, the.... -in general, the shorter the covalent bond, the.... periodic trends of covalent bonds?

The amount of energy it takes to break 1 mole of a bond in a gas phase=bond energy -each atom gets half of the bonding electrons -always positive (takes energy to break bond), endothermic -chemical reactions involve breaking bonds in reactant molecules and making new bonds to create the products -average bond energy- average of the bond energies for that bond in a large number of compounds. stronger the covalent bond (must be comparing bonds between like atoms ) stronger the bond (must be comparing similar types of bonds) Br--F (237 kJ)>Br--Cl(218 kJ)>Br--Br(193 kJ) -bonds get weaker down column -bonds get stronger across the period

how much space to done pairs take on the central atom? -what are the relative sizes of repulsive force interactions? how does this affect the bond angles? why are lone pairs more repulsive?

The effect of lone pairs: -lone pair groups "occupy more space" on the central atom because their e- density is exclusively on the central atom, rather than shared like bonding e- groups. -relative sizes of repulsive force interactions as follows: lone pair-lone pair>lone pair-bonding pair>bonding pair-bonding pair -this affects the bond angles, making the bonding pair angles smaller than expected -the bonding electrons are shared by two atoms, so some of the negative charge is removed from the central atom. The nonbonding e-s localized on the central atom, so the area of negative charge takes more space → therefore lone pairs are more repulsive

How to use bond energies to estimate TriangleHo(rxn) bond breaking is endothermic/exothermic bond making is endothermic/exothermic when weak bonds break and strong bonds form, reaction is exothermic/endothermic When strong bonds break and weak bonds form, reaction is exothermic/endothermic

Using bond energies to estimate triangleH0rxn (enthalpy change of a reaction) -the actual bond energy depends on the surrounding atoms and other factors -we often use average bond energies to estimate triangleH0rxn -works best when all reactants and products in gas state -bond breaking is endothermic (triangleHbreaking=+) -bond making (forming) is exothermic (releases energy) (triangleHmaking=-) Reaction exothermic when weak bonds break and strong bonds form Reaction endothermic when strong bonds break and weak bonds form triangleH(rxn)=sum of triangleH(bonds broken) - sum of triangleH(bonds formed)

trends in lattice energy: ion size how do lattice energies change with increasing ionic radius? what about ionic charge? trends in lattice energy: ion charge larger charge=stronger...=larger=

Trends in lattice energy: ion size -lattice energy decreases as move down column -a ionic radii increase as move down column, ions cannot get as close to each other and therefore don't release as much energy when lattice forms -lattice energies become less exothermic (less negative) with increasing ionic radius -lattice energies become more exothermic (more negative) with increasing magnitude of ionic charge Trends in lattice energy: ion charge -the force of attraction between oppositely charged particles is directly proportional to the product of the charges. -larger charge=stronger attraction -stronger attraction=larger lattice energy

What is the electron-pair geometry of the central oxygen atom of ozone (O3)? Linear Trigonal planar Tetrahedral Trigonal bipyramidal

Trigonal planar It will be a bent shape

steps for writing lewis structures of molecules

Writing lewis structures of molecules: 1) Write correct skeletal structure for molecule a) Hydrogen atoms always terminal b) The more electronegative atoms are placed in terminal positions 2) Calculate total number of e-s for lewis structure by summing valence e-s of each atom in the molecule 3) Distribute the e-s among the atoms, giving octets (or duets if hydrogen) to as many atoms as possible a) Begin with bonding electrons b) Lone pairs on terminal atoms c) Lone pairs of central atom 4) If any atoms lack an octet, form double or triple bonds as necessary to give them octets

what are the main concepts of the valence bond theory? -where do the valence electrons of the atoms in a molecule reside? -when does a chemical bond result? -the shape of the molecule as in VSEPR is determined by..... why do some atoms hybridize their orbitals? -what is hybridizing? can the same type of atom have different types of hybridization?

Valence bond theory main concepts: -valence e-s of the atoms in a molecule reside in quantum-mechanical atomic orbitals. The orbitals can be the standard s, p, d, and f orbitals, or htey may be hybrid combinations of these -a chemical bond results when these atomic orbitals interact and there is a total of 2 electrons in the new molecular orbital (e-s must be spin paired) -the shape of the molecule as in VSEPR is determined by the geometry of the interacting orbitals Hybridization: -some atoms hybridize their orbitals to maximize bonding (more bonds=more full orbitals=more stability) -hybridizing is mixing different types of orbitals in the valence shell to make a new set of degenerate (same energy) orbitals (Sp, sp2, sp3, sp3d, sp3d2) -same type of atom can have different types of hybridization (carbon may have sp, sp2, or sp3 depending on the type of bonds to be made)

What is the valence bond theory of H2? what is equilibrium molecular separation determined by? when two hydrogen atoms are far apart, what is the interaction energy? as the atoms get closer, what happens to the interaction energy? what if they are too close?

Valence bond theory of H2: describes bond formation as the overlap of two half-filled atomic orbitals. The chemical bond exists in the region of maximum overlap between the two orbitals. Equilibrium molecular separation determined by balance between attraction of electrons to nuclei and repulsion of equally charged nuclei. This type of representation is called a potential energy diagram. -when two hydrogen atoms far apart, interaction energy nearly 0 because two atoms don't interact to any significant extent -as atoms get closer, interaction energy becomes negative -if atoms too close, interaction energy begins to rise because of mutual repulsion of 2 positively charged nuclei.

steps when trying to find the magnitude of lattice energy

When trying to find magnitude of lattice energy: 1) First, look at ionic charges. If lower ionic charges, smaller magnitude lattice energy 2) Then, look at ionic radius of individual ion in one ionic compound and compare it with that of the other ionic compound → if larger ionic radius on ion, then lower magnitude lattice energy on ionic compound.

determine the formula change of nitrogen in the structure shown here:

look in book A

use formal charge to choose he best lewis structure for CH3SOCH3

look in book B

which is the correct lewis structure for CO3^2-?

look in book B

which is the correct lewis structure for nitrogen triflouride?

look in book C

what is hybridization? what is the concept of hybridization in the valence bond theory? how do hybrid orbitals minimize the energy of the molecule?

-concept of hybridization in valence bond theory is essentially a step toward recognizing that the orbitals in a molecule are not necessarily the same as the orbitals in an atom -hybridization: mathematical procedure in which the standard atomic orbitals are combined to form new atomic orbitals called hybrid orbitals that correspond more closely to the actual distribution of electrons in chemically bonded atoms → still localized, but shapes/energies differ from those of standard atomic orbitals. -hybrid orbitals minimize the energy of the molecule by maximizing the orbital overlap in a bond

what are the problems with lewis theory?

-generally predicts trends in properties but does not give good numerical predictions (for ex, bond strength and bond length) -lewis theory gives good first approximations of the bond angles of molecules, but usually cannot be used to get the actual angle -lewis theory cannot write one correct structure for many molecules where resonance structure is important -lewis theory often doesn't predict the correct magnetic behavior of molecules (ex: O2 is paramagnetic, although the lewis structure predicts its diamagnetic) Lewis structure and VSEPR theory: Valence bond theory and molecular orbital theory about finding mathematical wave functions that describe the space regions where valence electrons reside in molecules.

what does lewis theory predict the hardness/brittleness of compounds should vary depending on? what does the lewis theory predict about molecular solids and liquids w electricity conduction? what does lewis theory predict; as the number of electrons two atoms share increases, the bond becomes... (bond length and strength)

-hardness and brittleness of molecular compounds should vary depending on the strength of intermolecular attractive forces (the kind and strength of the intermolecular attractions vary based on many factors) -lewis theory predicts that neither molecular solids nor liquids should conduct electricity (there are no charged particles around to allow the material to conduct) Lewis theory predicts that the more electrons two atoms share, the stronger the bond should be. ex: C(triplebond)C(120pm)<C(doublebond)C(134pm)<C-C(154om) Lewis theory predicts that the more electrons two atoms share, the shorter the bond should be (when comparing bonds to like atoms) -bond length determined by measuring the distance between the nuclei of bonded atoms

if the vectors sum to 0, then the molecule is.... if the vectors sum to a net vector, then the molecule is.... how does vector addition work? 1 dimension vs 2+ dimensions?

-if vectors sum to 0, molecule nonpolar -if sum to net vector, molecular polar One dimension: to add 2 vectors that lie on same line, assign one direction as positive. Vectors pointing that direction have + magnitudes. Vectors in opposite direction=- magnitudes. Then sum vectors 2+ dimensions: draw parallelogram to which 2 vectors form 2 adjacent sides. Draw 2 sides of parallelogram parallel to and same length as 2 original vectors. Draw resultant vector.

what is the hardness of ionic solids in comparison to most molecular solids? why does Lewis theory predict ionic solids will be brittle?

-ionic solids relatively hard (compared to most molecular solids) -lewis theory implies that if ions displaced from their positions in the crystal lattice, repulsive forces should occur. This predicts the crystal will become unstable and break apart. Lewis theory predicts ionic solids will be brittle

how does lewis model account for why covalent bonds are highly directional? how do the strength of molecular interactions differ from interactions between molecules in covalently bonded molecular compounds to bonding interactions within a molecule ? melting and boiling points of molecular compounds? -in molecular compounds: ____ covalent bonds within molecules, _____ intermolecular forces between molecules

-lewis model accounts for why covalent bonds highly directional → in contrast to ionic bonds, which are non directional and hold together an entire array of ions, each covalent bond links just one specific pair of atoms. Therefore, lewis theory predicts covalently bonded compounds will be found as individual molecules (rather like an array like ionic compounds). -in covalently bonded molecular compounds, interactions between molecules (intermolecular forces) generally much weaker than bonding interactions within molecule (intramolecular forces) Predictions of molecular formulas by Lewis theory: oxygen more stable when it is singly bonded to two other atoms. -lewis theory predicts that the melting and boiling points of molecular compounds should be relatively low -this involves breaking the attractions between the molecules but not the bonds between the atoms -the covalent bonds are strong, but the attractions between the molecules are generally weak -in molecular compounds: strong covalent bonds within molecules, weaker intermolecular forces between molecules

what are resonance structures? when are they relevant? the actual structure of a molecule is a combination/average of.... what is this called?

-lewis theory localizes the electrons between the atoms that are bonding together -extensions of lewis theory suggest that there is some degree of delocalization of the electrons; concept resonance -delocalization of charge helps to stabilize the molecule Resonance structures: relevant when 2+ valid lewis structures can be drawn for the same compound. One of 2+ lewis structures that have the same skeletal formula but different e- arrangements. -when there is more than 1 lewis structure for a molecule that differ only in the position of the e-s, called resonance structures -actual structure molecule is a combination/average of the resonance forms- a resonance hybrid -the molecule does not resonate between the two forms, though we often draw it that way -if have resonance structures: resonance structure #1 ←> resonance structure #2

when two atoms approach each other, what happens to the electrons and nucleus within the atoms. -if the energy of a system is lowered because of interactions, what happened? What is hybridization on the valence bond theory? what does the kind of interaction depend on?

-when 2 atoms approach each other, e-s and nucleus of one atom interact w e-s and nucleus of another atom → if energy of system lowered because of interactions, then chemical bond forms. If energy of system raised by interactions, then chemical bond doesn't form valence bond theory: hybridization -applied principles of quantum mechanics to molecules, and reasoned that bonds between atoms would occur when the orbitals on those atoms interaction to make a bond. The kind of interaction depends on whether the orbitals align along the axis between the nuclei sigma bonds or outside the axis (pi bonds)

what does lewis theory say about why regions of electron groups should repel each other? how are the position of atoms surrounding a central atom will be determined by.... positions of e- groups will be determined by... what is the VESPR theory? what is it based on? what determines the geometry of a molecule? -when will electron groups around the central atom be the most stable

-lewis theory says that these regions of e- groups should repel each other, because they are regions of negative charge -this idea can then be extended to predict the shapes of the molecules -position of atoms surrounding a central atom will be determined by where the bonding e- groups are -positions of e- groups will be determined by trying to minimize repulsions between them VESPR theory: based on idea that electron groups (lone pairs, single bonds, multiple bonds, single electrons) repel one another through coulombic forces) -repulsions between electron groups on interior atoms of a molecule determine geometry of molecule -electron groups around central atom will be most stable when they are as far apart as possible (max separation=preferred geometry) -Called valence shell electron pair repulsion theory. Because e-s negatively charged, they should be most stable when they are separated as much as possible -the resulting geometric arrangement will allow us to predict the shapes and bond angles in the molecule.

the number of standard atomic orbitals added together= the total number of orbitals is _____ -what determines the shapes and energies of the hybrid orbitals formed? what particular kind of hybridization occurs?

-number of standard atomic orbitals added together always equals the number of hybrid orbitals formed. Total number of orbitals is conserved. -the particular combination of standard atomic orbitals added together determines the shapes and energies of the hybrid orbitals formed -the particular type of hybridization that occurs is the one that yields the lowest overall energy for the molecule. Since the actual energy calculations are beyond the scope of this book, we use electron geometries as determined by VSPR theory to predict type of hybridization

what is an issue with hybridization? how does the valence bond theory deal with the situation more accurately ?

-one of the issues that arises is that the number of partially filled or empty atomic orbitals did not predict the number of bonds or orientation of bonds -valence bond theory deals with the situation more accurately by postulating that the valence atomic orbitals could hybridize before bonding took place. unhybridized C orbitals: -one hybridization of C is to mix all the 2s and 2p orbitals to get 4 orbitals that point at the corner of a tetrahedron -although would predict that carbon and hydrogen should form molecule with formula CH2 and bond angle 90, actually know that stable compound formed is CH4, which has bond angles 109.5.

what do the properties of molecular substances depend on? what does molecular geometry depend on?

-properties of molecular substances depend on structure and shape of molecule Molecular geometry depends on: Number of electron groups around central atom How many of those electron groups are bonding groups and how many are lone pairs.

what is the geometry of a molecule determined by? what is the number of electron groups determined by? if the lewis structure contains resonance structures, which of the resonance structures do you use to determine the number of electron groups? what counts as a single electron group? what is the geometry of the electron groups determined by? How can bond angles vary from idealized angles? what causes them to vary?

-the geometry of a molecule is determined by the number of electron groups on the central atom (or on all interior atoms, if there is more than one) -the number of electron groups is determined from the lewis structure of the molecule. If the lewis structure contains resonance structures, use any one of the resonance structures to determine the number of electron groups -each of the following counts as a single electron group: lone pair, single bond, double bond, triple bond, or single electron -geometry of the electron groups is determined by their repulsions as summarized in table 10.1. In general, electron group repulsions vary as follows: Lone pair-lone pair>lone pair-bonding pair>bonding pair-bonding pair -bond angles can vary from the idealized angles because double and triple bonds occupy more space than single bonds (bulkier even though shorter), and lone pairs occupy more space than bonding groups. The presence of lone pairs usually makes bond angles smaller than the ideal angles for the particular geometry

the number of standard atomic orbitals combined= why can't H hybridize? what determines the shape of the hybrid orbitals? what kind of hybridization occurs? why do hybridized orbitals readily form chemical bonds?

-the number of standard atomic orbitals combined=the number of hybrid orbitals formed (combining a 2s with a 2p gives two 2sp hydrid orbitals). -H cannot hybridize as its valence shell only has 1 orbital -the number and type of standard atomic orbitals combined determines the shape of the hybrid orbitals -the particular kind of hybridization that occurs is the one that yields the lowest overall energy for the molecule -hybridized orbitals readily form chemical bonds because they tend to maximize overlap with other orbitals.

what does chemical bonding involve? what is it trying to attain? which electrons are most important in bonding? How to determine the number of valence electrons in the atom?

-valence electrons held most loosely (most imp) -chemical bonding involves the transfer or sharing of electrons between 2+ atoms to attain stable e- configurations for the bonding atoms -lewis theory focuses on the behavior of the valence electrons Determining the number of valence electrons in an atom: -the column number on the periodic table will tell you how many valence electrons a main group atom has. Transition elements have 2 valence electrons

What are valence electrons represented as in lewis structures? How do you "give out" and place the dots for valence electrons? what is the exception to the octet rule?

-valence electrons of main-group elements= dots surrounding the symbol for the element (also known as electron dot structures). -symbol of the element=nucleus and inner electrons. Lewis structures of atoms: dots around symbol represent valence electrons (in main-group atom) -pair first two dots for the s orbital electrons. -put 1 dot on each open side for the first 3 p electrons -then, pair the rest of the dots for the remaining p electrons. Helium exception: 1s2, He: -lewis symbol only contains 2 dots (duet) → represents stable e- configuration

seesaw shape, t-shape, and linear shape

-when 5 e- groups around central atom and some lone pairs, will occupy the equatorial positions because there is more room -when e- groups around central atom and 1 lone pair, result is called seesaw shape (aka distorted tetrahedron) -when there are 5 e- groups around the central atom and two lone pairs, result is T-shaped -when there are 5 e- groups around the central atom and 3 are lone pairs, result linear shape -bond angles between equatorial positions less than 120 degrees -bond angles between axial and equatorial positions less than 90 degrees -linear=180 degree axial to axial trigonal bipyramidal paired with seesaw, t-shape, and linear shape

square pyramidal shape, square planar shape

-when 6 e- groups around central atom and some lone pairs, each even number lone pair will take a position opposite the previous lone pair. -when 6 e- groups around central atom and 1 lone pair, result=square pyramid shape -bond angles between axial and equatorial positions less than 90 -when 6 e- groups around central atom and 2 lone pairs, result=square planar shape -bond angles between equatorial positions 90 -octahedral paired with square pyramidal and square planar.

what are pyramidal and bent molecular geometries? what results in a pyramidal shape? what results in a tetrahedral-bent shape?

-when there are 4 electron groups around the central atom and one is a lone pair, the result is called a pyramidal shape (because it is a triangular-base pyramid with the central atom at the apex) -when there are 4 e- groups around the central atom and two lone pairs, the result is called a tetrahedral-bent shape) → planar, looks similar to the trigonal planar-bent shape except angles are smaller -for both shapes, bond angle < 109.5 -in general, electron group repulsions compare as follows: Lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair -goes from most repulsive to least repulsive

predicting hybridization and bonding scheme

1) start by drawing the lewis structure 2) use VSEPR theory to predict the electron group geometry around each central atom. 3) use table 10.3 to select the hybridization scheme that matches the electron group geometry 4) sketch the atomic and hybrid orbitals on the atoms in the molecule, showing overlap of the appropriate orbitals 5) label the bonds as sigma and pi

what are the 3 common ways of predicting how atoms combine to form molecules? (valence shell electron repulsion, valence bond theory, and molecular orbital theory) what do each of these theories entail?

3 common ways of predicting how atoms combine to form molecules. Approximations needed because solving Schrodinger's equation exactly is not possible (too complex). Computer techniques help but often mask the physical sense of what is happening: 1) Valence shell electron repulsion: qualitative approach covered last semester, treats all valence electrons the same, as belonging to the molecule as a whole without considering orbital shape 2) Valence bond theory: semi quantitative approach using quantum mechanics. Treats atoms as if they are described by quantum mechanical atomic orbitals. Predicts some properties better than VESPR. Takes into account shapes of the atomic orbitals -electrons reside in quantum-mechanical orbitals localized on individual atoms (in some cases, orbitals s, p, d, and f atomic orbitals. In others, hybridized orbitals-blend/cmbination of 2+ standrad atomic orbitals) 3) Molecular orbital theory: construct orbitals for the molecule as a whole (molecular orbitals). We construct trial molecular orbitals and select one that minimizes energy. Predicts some properties better than valence bond theory

which is an exception to the octet rule? a) CH3OH b) CCl4 c) PH3 d) BF3 E) BF4-

BF3

When evaluating resonance structures: better structures have.... (in regards to formal charges) better structures have (in regards to formal charge on more EN atom) what are exceptions to the octet rule? there are 3!

Better structures have fewer formal charges, better structures have smaller formal charges, better structures have the negative formal charge on the more electronegative atom Exceptions to the octet rule: -odd number electron species (molecules or ions with an odd number of electrons) -will have 1 unpaired e- -free-radical -very reactive -incomplete octets (BF3... molecules of ions with fewer than 8 electrons) -expanded octets → molecules or ions with more than 8 electrons around an atom. Ex: AsF5 -elements in third row and beyond have expanded octets of up to 12 electrons -will never occur in second period elements

what is a dipole moment? -what is it directly proportional to? equation? Generally, the more electrons 2 atoms share and the larger the atoms are, the.... what is percent ionic character? equation? If an electron was completely transferred from 1 atom to another, the bond would have ___% ionic character bonds with greater than 50% ionic character=

Bond dipole moments: Dipole moment=measure of bond polarity, occurs any time there is a separation of a bond by the size of its dipole moment. -dipole material with + and - end. Directly proportional to the size of the partial charges and directly proportional to the distance between them u=qr larger the dipole moment Percent ionic character: ratio of a bond's actual dipole moment to the dipole moment it would have if the electron were completely transferred from 1 atom to the other, multiplied by 100% Percent ionic character=(measured dipole moment of bond/dipole moment if e- completely transferred)100 -bond in which electron completely transferred from 1 atom to another would have 100% ionic character (but not possible) -bonds w greater than 50% ionic character=ionic bonds.

what is a bond length? why do we often use the average bond length? what does the average bond length represent? the more e-s two atoms share, the __ the covalent bond bond length periodic trends? As bonds get longer, they also get...

Bond length: The distance between the nuclei of bonded atoms -because the actual bond length depends on the other atoms around the bond, we often use the average bond length (averaged for similar bonds from many compounds) -average bond length represents the average length of a bond between 2 particular atoms in a large number of compounds. -depend not only on kind of atoms involved in the bond, but also on type of bond. Trends in bond lengths: -in general, the more e-s two atoms share, the shorter the covalent bond -must be comparing bonds between like atoms -Generally, bond length decreases from left to right across period ex: C-C (154pm)>C-N(147pm)>C-O(143pm) -Generally, bond length increases down column -in general, as bonds get longer, they also get weaker

bond rotation and reactivity: -where do the orbitals that form a sigma bond point? where do the orbitals that form the pi bond interact? sum of hybridized orbitals=sum of...

Bond rotation and reactivity: -because the orbitals that form a sigma bond point along the internuclear axis, rotation around that bond doesn't require breaking the interaction between the orbitals -orbitals that form the pi bond interact above and below the internuclear axis, so rotation around the axis requires the breaking of the interaction between the orbitals -the pi bond being weaker and more exposed is subject to chemical attack by reactants. Sum of hybridized orbitals=sum of unhybridized orbitals

what are bonding theories? what does lewis theory emphasize? what do lewis structures allow us to predict? -what is one limitation to lewis structures and lewis theory?

Bonding theories: explain how and why atoms attach together/bond to form molecules, explain why some combinations of atoms are stable and others are not, can be used to predict the shapes of molecules, can be used to predict the chemical and physical properties of compounds lewis theory: emphasizes valence electrons to explain bonding -lewis structures allow us to predict many properties of molecules (molecular stability, size, and polarity) → can predict whether particular set of atoms will form a stable molecule and what the molecule might look like -one limitation of representing electrons as dots and covalent bonds as two dots shared between two atoms is that the shared electrons always appear to be equally shared, which isn't the case.

according to the valence bond theory, bonding takes place between atoms when their atomic or hybrid orbitals interact. How can they interact? what is a sigma bond? what does it result from? what is a pi bond? what does it result from?

Bonding with valence bond theory: -according to valence bond theory, bonding takes place between atoms when their atomic or hybrid orbitals interact (overlap) → to interact, orbitals must either be aligned along the axis between atoms, called sigma bonds, or be parallel to each other and perpendicular to the interatomic axis (called pi bond) Types of bonds: -sigma bond- results when interacting atomic orbitals point along the axis connecting the two bonding nuclei. Either standard atomic orbitals or hybrids to s, p to p, hybrid to hybrid, s to hybrid, etc. -A pi bond results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei. Formed between unhybridized parallel p orbitals. The interaction between parallel orbitals is not as strong as between orbitals that point at each other, so sigma bonds stronger than pi bonds

determine the molecular geometry of CBr4 a) linear b) trigonal planar c) tetrahedral d) trigonal pyramidal

C

Why do chemical bonds form? when do they form? when you are calculating energy (or PE) what interactions do you need to consider? what kind of bonds to metal and nonmetal atoms form? are electrons transferred or shared? what about nonmetal and nonmetal atoms? metal and metal atoms?

Chemical bonds form because they lower the potential energy between the charged particles that compose atoms. Chemical bond forms when the potential energy of the bonded atoms is less than the potential energy of the separate atoms To calculate PE, you need to consider the following interactions: -nucleus-to-nucleus repulsions, electron-to-electron repulsions, nucleus-to-electron attractions -when two atoms approach each other, e-s of one attracted to nucleus of other according to coulomb's law, and e-s of each atom repel the e-s of the other and the nucleus of each atom repels nucleus of other → can lead to chemical bonding Metal and nonmetal atoms → ionic bonds (e- transferred) Nonmetal and nonmetal atoms → covalent bonds (e- shared) Metal and metal atoms → metallic bonds (e- pooled)

Covalent bonding: electrons that are shared by atoms are called.... electrons that are not shared by atoms are called.... what are single covalent bonds? double covalent bonds? triple covalent bond? how do they relate in terms of shortness and strongness?

Covalent bonding: bonding and lone pair electrons: -electrons that are shared by atoms are called bonding pairs -electrons that are not shared by atoms but belong to a particular atom are called lone pairs (nonbonding pairs) Single covalent bonds: when 2 atoms share 1 pair of electrons, called single covalent bond (2 e-s). Double covalent bond: when 2 atoms share 2 pairs of electrons the result is called a double covalent bond (4 electrons) Triple covalent bond: when 2 atoms share 3 pairs of electrons the result is called a triple covalent bond (6 electrons) -triple bonds even shorter and stronger than double bonds

determine the molecular geometry of SeF4 a) Tetrahedral b) trigonal bipyramidal c) t-shaped d) seesaw

D

which compound is likely to have an incomplete octet? a) NH3 b) SO3 c) N2O d) BH3

D

which pair of elements is most likely to form an atomic bond? a) nitrogen and oxygen b) carbon and oxygen c) sulfur and oxygen d) calcium and oxygen

D

what is electronegativity? periodic trends? Note: noble gas atoms are not assigned EN values How does electronegativity relate to polarity? if the difference in electronegativity between bonded atoms is 0, the bond is... if the difference in electronegativity between bonded atoms is 0.1-0.4, the bond is..... if the difference in electronegativity between bonded atoms is 0.4-1.9, the bond is.... if the difference in electronegativity between bonded atoms is larger than or equal to 2, the bond is... small EN difference= intermediate EN difference= Larger EN difference=

Electronegativity: the ability of an atom to attract electrons to itself in chemical bond Increases across period, decreases down group -the larger the difference in electronegativity, the more polar the bond (negative end toward more electronegative atom.) -larger the atom, less ability it has to attract electrons to itself in a chemical bond Electronegativity scale: electron affinity is an absolute energy. Electronegativity is a relative scale. Electronegativity difference and bond type: -if the difference in electronegativity between bonded atoms is 0, bond is pure covalent (= sharing) -if difference in electronegativity between bonded atoms 0.1-0.4, bond is nonpolar covalent -if difference in electronegativity between bonded atoms 0.4-1.9, bond polar covalent -if difference in electronegativity between bonded atoms larger than or = to 2, bond is "100% ionic". Small electronegativity difference, covalent Intermediate electronegativity difference, polar covalent Larger electronegativity difference, ionic

what does lewis theory predict in ionic bonding? What happens to energy when the formation of a crystal lattice occurs? what does the crystal lattice maximize?

Lewis theory predictions for ionic bonding: -lewis theory predicts the number of e-s a metal atom should lose or a nonmetal atom should gain in order to attain a stable electron arrangement (octet rule) -allows us to predict the formulas of ionic compounds that result. -also allows us to predict the relative strengths of the resulting ionic bonds from coulomb's law this extra energy that is released comes from the formation of a structure, called a crystal lattice, in which every cation is surrounded by anions, and vice versa. -the crystal lattice maximizes the attractions between cations and anions, leading to the most stable arrangement.

when there are multiple central atoms for molecules, what do we do to describe the shape?

Multiple central atoms: -many molecules have larger structures with many interior atoms- we can think of them as having multiple central atoms. When this occurs, we describe the shape around each central atom in a sequence. -shape around left C tetrahedral, shape around right C trigonal planar, shape around right O bent

what is polar covalent bonding? how does it result? where does it lay in comparison to pure covalent bonds and ionic bonds? what is bond polarity? what does it depend on? The greater the EN difference, the more... how to classify a bond as polar covalent or covalent?

Polar covalent bonding: -covalent bonding between unlike atoms results in unequal sharing of the electrons -1 atom pulls the electrons in the bond closer to its side -1 end of the bond has larger electron density than the other -the result is a polar covalent bond (bond polarity, the end with the larger electron density gets a partial negative charge, the end that is electron deficient gets a partial positive charge) -intermediate in nature between pure covalent bond and ionic bond (in between 2 extremes) Bond polarity: degree of polarity in chemical bond depends on EN difference between 2 bonding atoms. Greater EN difference, more polar the bond. -bonds classified as covalent if the amount of e- transfer is insufficient for the material to display the classic properties of ionic compounds -if the sharing is unequal enough to produce a dipole in the bond, bond classified as polar covalent.

For a molecule to be polar it must.... How do nonbonding pairs affect molecular polarity? if the bond in a diatomic molecule is nonpolar, then the whole molecule is..... -how to know that a molecule is nonpolar? polar? why can dipole moments cancel each other out?

Polarity of molecules: For a molecule to be polar it must: -Have polar bonds (electronegativity difference-theory and bond dipole moments-measured) -Have an un-symmetrical shape (vector addition) Polarity affects intermolecular forces of attraction (therefore, boiling points and solubilities. Like dissolves like!) -nonbonding pairs affect molecular polarity, strong pull in its direction. -if the bond in a diatomic molecule is nonpolar, the molecule as a whole is nonpolar -if molecular geometry is such that the dipole moments of individual polar bonds sum together to a net dipole moment, then the molecule is polar. If dipole moments of individual polar bonds cancel each other, molecule nonpolar (if two dipole moments sum of zero) -dipole moments can cancel each other because they are vector quantities (have magnitude and direction)

Steps for predicting the polarity of molecules? -if linear.... -if bent.... -if trigonal planar.... -if tetrahedral... -if trigonal pyramidal...

Predicting polarity of molecules: 1) Draw lewis structure and determine the molecular geometry 2) Determine whether the bonds in the molecule are polar -If no polar bonds, molecule nonpolar 3) Determine whether the polar bonds add together to give a net dipole moment -if linear.... nonpolar -if bent.... polar -if trigonal planar....nonpolar -if tetrahedral... nonpolar -if trigonal pyramidal...polar

how to predict the shapes around central atoms. How to represent 3D shapes on 2D surface?

Predicting shapes around central atoms: 1) Draw lewis structure 2) Determine number of e- groups around central atom 3) Classify each e- group as a bonding or lone pair, and count each type (remember, multiple bonds count as one group 4) Use table 10.1 to determine the shape and bond angles representing 3D shapes on 2D surfaces: -by convention, the central atom is put in the plane of the paper -other atoms that are in the same plane as the central atom are connected with a straight line -for atoms in front of the plane, use solid wedge -for atoms behind plane, used hashed wedge.

Sp atoms: how many electron groups, what shape, what bonded orbital? Sp3d using expanded octet: what are Sp3d2 hybrid orbitals?

Sp: -atom with 2 e- groups, linear shape, 180 bond angle -atom uses hybrid orbitals for sigma bonds or lone pairs, and uses unhybridized p orbitals for pi bonds -hybridization of one s and one p orbital results in 2 sp hybrid orbitals and two leftover unhybridized p orbitals Sp3d using expanded octet: Atoms with 5 e- groups around it: -trigonal bipyramid e- geometry -seesaw, t-shape, linear -120 and 90 bond angles -use empty d orbitals from valence shell -d orbitals used to make pi bonds -5 sp3d hybrid orbitals have a trigonal bipyramidal arrangement Sp3d2 hybrid orbitals: hybridization of one s orbital, 3 p orbitals, and 2 d orbitals. Octahedral geometry

what is the process to determine molecular shape and polarity

Summarizing the process to determine molecular shape and polarity: 1) Draw the lewis structure for the molecule and determine its molecular geometry 2) Determine whether the molecule contains polar bonds → polar if two bonding atoms have sufficiently different ENs. if molecule contains polar bonds, superimpose vector and point it toward more EN atom on each bond. Draw length of vector proportional to the EN difference between the bonding atoms 3) Determine whether the polar bonds add together to form a net dipole moment → sum the vectors corresponding to the polar bonds together. If vectors sum to 0, molecule nonpolar. If vectors sum to net vector, molecule is polar.

where do the valence electrons of the atoms in a molecule reside? what do chemical bonds result from? what determines the shape of the molecule?

Summarizing valence bond theory: 1) The valence electrons of the atoms in a molecule reside in quantum-mechanical atomic orbitals. The orbitals can be the standard s, p, d, f orbitals, or may be hybrid combination of these 2) Chemical bond results from the overlap of two half-filled orbitals with spin-pairing of the two valence electrons (or less commonly the overlap of a completely filled orbital with an empty orbital) 3) The geometry of the overlapping orbitals determines the shape of the molecule

two electron groups: linear electron geometry: -bond angle? three electron groups: trigonal planar electron geometry: -bond angle?

Two electron groups: linear electron geometry: -when 2 e- groups around the central atom, they will occupy positions on opposite sides of the central atom. This results in the e- groups taking a linear geometry. Bond angle=180 Three e- groups: trigonal planar electron geometry: -when there are 3 e- groups around the central atom, they will occupy positions in the shape of a triangle around the central atom. -this results in the e- groups taking a trigonal planar geometry. Bond angle=120 -different types of electron groups exert slightly different repulsions

how to write the lewis structure of a molecule

Writing Lewis structures of molecules: 1) Write the correct skeletal structure for the molecule (hydrogen atoms always termal, the more electronegative atoms are placed in terminal positions) 2) Calculate the total number of electrons for the lewis structure by summing the valence electrons of each atom in the molecule (if writing lewis structure for polyatomic ion, must consider the charge of the ion when calculating the total # of electrons. Add one for neg charge, subtract for +) 3) Distribute the electrons among the atoms, giving octets (or duets in the case of hydrogen) to as many atoms as possible. 1) begin w bonding electrons, placing 2 e-s between every two atoms 2) lone pairs of terminal atoms 3) lone pairs on central atom 4) If any atoms lack an octet, form double or triple bonds as necessary to give them octets

"overlap" between a hybrid orbital on one atom with a hybrid or nonhybridized orbital on another atom results in a .... "overlap" between unhybridized p orbitals on bonded atoms result in a... what does a double bond in the lewis model always correspond to? -are pi bonds or sigma bonds stronger? are pi bonds or sigma bonds generally easier to break in a double bond?

sigma bond pi bond -hybrid orbitals overlap to form sigma bond. Unhybridized p orbitals overlap to form pi bond -a double bond in the lewis model always corresponds to to one sigma and one pi bond in valence bond theory. -pi bonds weaker than sigma bonds because side-to-side orbital overlap tends to be less efficient than end-to-end orbital overlap -pi bond in double bond generally easier to break than sigma bond

PCl3 is an industrial chemical used in many herbicides and insecticides. What is the molecular shape of PCl3? a) bent b) tetrahedral c) tetrahedral trigonal pyramidal d) t-shaped e) trigonal planar

tetrahedral trigonal pyramidal