General Chemistry

electron delocalization

Distribution of electron density beyond a fixed place such as a single atom, lone pair, or covalent bond via resonance or inductive effects. resonance increases stability of molecule

What is a Polyatomic ion?

A polyatomic ion is a charged species consisting of multiple atoms bonded together. H2SO4 is not charged, so it is not categorized as polyatomic ion.

What are molecules?

Any structure composed of multiple atoms Example: H2 is a molecule, but not a compound

how many bonds is Ba(OH)2? and what kind?

2 ionic bonds

What are ion-dipole forces?

(attractive forces between an ion (+,-) and a polar molecule)-ions have a full charge -Occurs between ions and molecules with a dipole (be careful with ionic bonding, bc ionic bonding is an intramolecular force)

What are hydrogen bonds?

-(super strong version of dipole-dipole) -Occurs when a H attached to a N, O, or F is attracted to the lone pair on a N, O, F. - N,O, F are very electronegative and generate strong dipoles with H. -Strong stable dipoles (more polar) lead to strong intermolecular interaction; The stronger the stable dipole is within a molecule, the stronger interactions it will have with other molecules of the same substance (partial charges)

What are dipole-dipole forces?

-forces of attraction between polar molecules (stable dipoles) -stronger than london dispersion forces -attractive force occurs between the positive dipole of one polar molecule and the negative dipole of another molecule.

Rank the following molecules in order of increasing bond angle. NH3 Carbon in methanol (CH3OH) Oxygen in methanol (CH3OH)

-oxygen in methanol -NH3 -Carbon in methanol (CH3OH) All these molecules have the same electronic geometry (tetrahedral), they all have varied molecular geometry. At the oxygen in methanol, there are 2 lone pairs and two bond, given shape of bent of 104.5. NH3 is trigonal pyrimidal and has bond angle of 107. At the carbon in methanol, there are four bonds that give the tetrahedral shape, with a bond angle of 109.5

What are ionic bonds?

-transfer of valence electrons between atoms (from metal to the nonmetal) -When electronegativity exceeds 1.7 -Bonds between metal and nonmetal -stronger than covalent bonds metal becomes a positive cation, while the nonmetal becomes a negatively charged anion.

What is the formal charge of the central sulfur in sulfur trioxide?

0 Since sulfur "should" have 6 valence electrons (from the periodic table), and in this molecule it has 12 bonding electrons (or 6 bonds), its formal charge is 6-6=0

What are the rules to keep in mind whether 2 structures are resonance forms of each other?

1. All structures have the same number of electrons. (can differ whether they are bonds or lone pairs.) 2. Shift lone pair or pi electrons to adjacent atoms. 3. Atoms do not change position in resonance form.

What are three types of intramolecular forces?

1. Ionic bonds 2. Covalent bonds 3. Metallic bonds Fairly strong bc this is what keeps molecules together

What are the 5 main types of intermolecular forces in order of increasing strength?

1. London dispersion forces 2. Dipole-Dipole interactions 3. Hydrogen bonds 4. Ion-dipole forces 5. Ionic interactions

what is the bond angle of trigonal planar?

120 degrees (no lone pairs)

what is the bond angle in the linear shape?

180 degrees CO2

Octahedral

90, 180

trigonal bipyramidal

90-180

What are the different electronegativity number for bonds?

<0.5 correspond to nonpolar covalent bonds 0.5-1.7 electronegativity correspond to polar covalent bonds >1.7 electronegativity difference is an ionic bond C-H Nonpolar N-H Moderately polar O-H Highly polar F-H Highly polar C-N Slightly polar C-O meaningfully polar (but not as much as OH bonds)

Ozone

A form of oxygen that has three oxygen atoms in each molecule instead of the usual two.

Which of the following molecules are possible resonance structures for the carbonate anion (CO3^2-)

Central atom (carbon) must have a complete octet.

What is the correct lewis structure for Cl2?

Chlorine gas: 14 total valence electron, with two electrons shared in a covalent single bond.

Which of the following compounds can be considered a polyatomic ion that can engage in ion-dipole interactions?

ClO- The hypochlorite ion satisfies both requirements of a polyatomic ion: first, it must be charged to be considered an ion, and second, it contains two different atoms covalently bonded. The polar oxygen anion on hypochlorite can interact with a metal cation such as calcium through ion-dipole interactions.

Resonance

Compounds that have more than one possible valid lewis structure is said to have resonance. Differ in the distribution of electrons across a molecule; Resonance structures must have the same positioning and connectivity of atom, but they differ in the distribution of electrons. Example: Nitrate anion

What are Molecular compounds?

Contain 2 nonmetals Nitrogen dioxide, NO2

What are ionic compounds?

Contain a metal and nonmetal Example: Potassium Chloride KCl

True or false: π bonds have a small area of directly overlapping electron density, form double bonds, and are stronger than σ bonds.

False, In sigma bonds, there is a relatively large area of directly overlapping electron density compared to pi bonds, which occur between two parallel p orbitals and are weaker than sigma bonds. Single bonds between two atoms are made of sigma bonds, while double bonds are one sigma bond and one pi bond, and triple bonds are one sigma bond and two pi bonds. Therefore, double bonds are indeed stronger than single bonds, but that is because they have both a sigma bond component and a pi bond component. In a direct comparison, sigma bonds are stronger than pi bonds.

True or false: During an MCAT exam, the fastest way to determine an atom's formal charge is by counting up the relative number of electrons and protons it contains.

False, during a timed exam, formal charge should be calculated as the number of valence electrons an atom "should" have (according to the periodic table) and the number it actually has. Thus, formal charge can be quickly determined by counting the number of valence electrons and bonds made to other atoms.

True or false: Free radicals are highly reactive because they have more electrons than their valence shells can hold stably.

False: This statement is false. Free radicals are compounds that have an odd number of valence electrons and so have an unpaired electron in their structure. This unpaired electron makes these compounds highly unstable.

True or false: Formal charge values allow the actual charge on a given atom within a molecule to be determined.

False: Formal charges do not always apply to actual charge. Formal charge calculations assume that electrons are evenly shared between atoms that are covalently bonded with each other. In reality, due to differences in electronegativity, this is not the case. Many compounds without formal charges will have strong partial charges distributed through the molecules.

True or false: Ion-dipole interactions require a metal and a non-metal.

False: This statement is false. Ion-dipole interactions can take place between any ion and a dipole, not requiring a metal to be involved. Note that ion-dipole interactions are an intermolecular force; do not confuse them with ionic bonds, an intramolecular force that typically forms between a metal and non-metal.

Intramolecular forces

Forces that hold atoms together in molecules (Connect atoms within a molecule) (forces within molecules. Forces caused by the attraction and repulsion of charged particles)

How do you calculate formal charge?

Formal charge= valence electrons-lone pairs- 1/2 bonding electrons = should-actually

Which of the following elements has a completely-filled valence shell when it only has two valence electrons?

Helium

In DNA, A-T base pairs involve two hydrogen bonds, whereas G-C pairs have three hydrogen bonds. Based on this, which of the following sequences would be the most stable and could be isolated from a single-cell organism living in very hot anaerobic conditions?

Hydrogen bonds are strong non-covalent intermolecular attractions that raise the melting and boiling points of a substance. As such, the DNA sequence with the most GC pairs would be expected to be the most heat-stable - and therefore, the most suitable to this environment. Of the answer choices, CCGATCGCTACG has the most C and G nucleotides.

What are the octet rule exceptions?

Hydrogen: single valence electron subshell, 1s, so perfectly stable with 2 electrons Helium: (max 2 valence electrons) Lithium: (max 2 valence electrons) Beryllium: (max of 4 valence electrons) Boron: (max of 6 valence electrons) Hypervalent molecules Odd numbered Electrons: oxygen contains 6 valence electrons and Nitrogen contains 5 valence electrons with a total of 11 valence electrons, so a distribution of 8 valence electrons is impossible. Nitric acid has 1 paired electron, such compounds are known as free radicials.

In liquid chromatography, a mobile phase containing various solutes is run through a stationary phase containing crystals with amine (-NH2) groups. Arrange the following molecules in order from the weakest interaction with the -NH2 group to the strongest interaction.

N2 HI HF Nonpolar solutes such as N2 (london dispersion forces) would be eluted first due to their weak interactions with the amine groups in the stationary phase. The molecule HI (hydroioidic acid) is polar, but cannot hydrogen bond due to a lower electronegativity difference compared to HF. HF (hydrofluoric acid) would interact with the NH2 group through hydrogen bonding and would therefore have the strongest interaction.

Important Polyatomic ions to memorize?

Nitrate (NO3^-), Nitrite (NO2^-), Carbonate (CO3^2-), Bicarbonate (HCO3^-), Perchlorate (ClO4^-), Chlorate (ClO3^-), Sulfate (SO4^2-), Sulfite (SO3^2-), Hydroxide (OH-), Chromate (CrO4^2-), Cyanide (CN-), Permanganate (MnO4^-), Acetate (C2H3O2^-)

How to determine central atom?

One with the lowest electronegativity. Carbon is commonly the central atom Hydrogen is never a central atom.

How to name transition metals?

Oxidation number specified with Roman numerals (ex. Fe(III) vs. Fe(II) ->Tells us how many electrons that transition metal has lost Example: ZnO2 = Zinc (IV) oxide ZnO= Zinc (II) oxide

Which of the following atoms may be capable of having an expanded octet? Select all that apply.

Phosphorus :Phosphorus is capable of having an expanded octet, as in phosphorus pentafluoride, in which the central phosphorus has ten valence electrons. Sulfur: Sulfur is capable of having an expanded octet, as in sulfur hexafluoride, in which the central sulfur has twelve valence electrons.

Match each chemical formula to the type of intramolecular force that it is most likely to experience.

Potassium chloride (KCI) has ionic bonding as there is attractive force between the K+ cation and I- anion, and potassium has donated one electron of its outermost orbit to Iodine to complete its octet. Methane (CH4) contains nonpolar covalent bonds because the electronegativity difference between hydrogen (2.20) and carbon (2.55) is lower than 0.5. Metallic bonding occurs in sodium (Na) because when sodium atoms come together, the electron in the 3s atomic orbital of one sodium atom shares space with the corresponding electron on a neighboring atom to form a molecular orbital.

What is shell, subshell, and orbital?

Shell= [2s, 2pz, 2px,2py] Subshell= [2s] [2pz, 2px, 2py] orbital = [2s][2pz][2px][2py]

The following molecule is nitrogen triiodide, a highly explosive compound. NI3

Yes, there are eight electrons surrounding the nitrogen. Nitrogen has achieved its octet and there are eight valence electrons. There is a lone pair of electrons as well as three shared pairs (two electrons with each iodine).

octet rule

States that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons (first few electron in the first few periods all have valence shells that are filled when they contain eight electrons)

molecular geometry

The arrangement of atoms determined by the arrangement of bonding electron pairs and lone pairs around the central atom in a molecule. (only bonded atoms) (molecular shape) Ammonia: trigonal pyramidal : 107 degrees

What happens to melting and boiling point if compound has strong intermolecular forces?

The higher its melting and boiling points if compound has strong intermolecular forces.

What is the correct lewis structure for oxygen?

The image shows the correct lewis structure for oxygen, which has 6 valence electrons and should have 2 electrons occupying their own orbitals.

True or false: Hydrogen bonding can be intermolecular or intramolecular.

This statement is true. Hydrogen bonding can occur intramolecularly as well as intermolecularly. Perhaps the most familiar example of intramolecular hydrogen bonding would be hydrogen bonding between the backbone carbonyl oxygen and backbone nitrogen in proteins.

True or false: The strongest bond between two atoms in the solid phase is an ionic bond.

This statement is true. In solids, ionic bonds are stronger than covalent bonds because of the significant attraction between ions of opposite charges. Note, however, that this is not necessarily the case in aqueous solution, wherein ionic compounds may dissociate into their component ions.

VSEPR theory

Valence-shell electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible

What is a dipole?

When there is a large difference in electronegativity in a polar bond so there is a large difference in charge between the two atoms caused by a shift in electron density in the bond. -Partial charges, negative dipole on the more electronegative atom: an electron surplus and an electron deficiency on the more partial positive charge

Which of the following is the correct identification of ZnO2?

Zinc (IV) Oxide For transition metals, we must specify the oxidation number of the metal using Roman numerals. This tells us how many electrons the transition metal has lost. The oxidation number of oxygen is -2 and there are two of them, giving oxygen a -4 total oxidation state. Thus, zinc must have a +4 oxidation state or (IV) Roman numeral to balance the overall molecule to neutral.

What are metallic bonds?

a bond formed by the attraction between positively charged metal ions and the electrons around them the forces of attraction between the free-floating valence electrons and the positively charged metal ions

Binary Compound

a compound made up of two elements NaCl CaCl2

Define orbital

a region in an atom where there is a high probability of finding electrons Is the angular momentum quantum number (l) The pattern in which the electrons move.

What are London dispersion forces?

a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles arise by chance -Weakest intermolecular force - Can occur between any molecule -Larger structure= larger LDF

What are polar covalent bonds?

atoms with moderate differences in electronegativity bonded together

intermolecular forces

attractive forces between molecules Important bc we never encounter molecules in isolation. They are much weaker than intramolecular forces, but practically important Example two H2O : Intramolecular: polar covalent bonds

Why doesn't formal charge not always equal to actual charges

electronegativity Example: H2O The formal charges on all the atoms in water are zero, molecule as a whole has a net zero charge. However, oxygen is quite electronegative and pulls electrons towards itself. So oxygen has a partial negative charge and the hydrogens have a partial positive charge.

What are hypervalent molecules?

elements which have more than an octet

What are nonpolar covalent bonds?

elements with similar or same electronegativity bonded together ex: Cl2

How are covalent bonds formed?

formed between two nonmetals by sharing valence electrons bc nonmetals have relatively similar electronegativity values

What are the molecular shapes

linear= 180 trigonal planar: 120 tetrahedral: 109.5 Trigonal pyramidal : 107 degrees Bent: 104.5 Trigonal bipyramidal octahedral

What are free radicals?

molecules with an unpaired electron such as nitric oxide with 11 valence electrons and one unpaired. Free radicals are highly unstable, but nitric oxide is relatively stable.

hypervalent molecules examples

phosphorus pentafluoride, PF5 (pass the 3rd period.) -->phosphorus has 10 valence electrons Sulfur hexafluoride --> Sulfur atom contains 12 valence electrons

If a particular atom from the first two periods had 6 electrons in its valence shell, which orbital would these electrons be distributed in? Select all that apply.

s orbital : All atoms with valence electrons will have some electrons in the s orbital because this orbital fills first. p orbitals: The valence s orbital can hold two electrons, and the remaining four electrons would occupy p orbitals.

Sigma bond (σ bond)

sigma bond is created when a single bond is formed between two atoms. covalent bond formed by overlap of atomic orbitals along the internuclear axis

electronic geometry

spatial arrangement of all electron pairs (lone pairs and bonded atoms) Ammonia: tetrahedral: 107 degrees methane: tetrahedral: 109.5 degrees Water: bent: 104.5 degree

What is a resonance hybrid?

the actual structure of a molecule that is intermediate between two or more resonance structures

Hybridization

the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals Triple bond= sp (Two regions of electron density) double bond= sp2 (three regions of electron density) single bond= sp3 (four regions of electron density)

Place the following molecules in order of highest to lowest boiling point in an aqueous solution. Ethanol (C2H6O) water (H2O) Hexane (C6H14)

water ethanol Hexane Boiling point is largely determined by intermolecular forces such as hydrogen bonding and London-dispersion forces. Water contains two sites of hydrogen bond donation as well as acceptance, so it will have the highest boiling point of the options provided. Ethanol is smaller than hexane, but its ability to hydrogen bond will mean its boiling point is higher than hexane. Hexane is nonpolar and has the weakest intermolecular forces.

In organic chemistry lab, a student synthesizes the following molecule. Note that in the skeletal structure, each turn between the line represents a hidden carbon atom. Thus, the arrow represents a carbon atom double bonded to the oxygen atom. Has the indicated carbon (carbonyl carbon) achieved a complete octet?

yes, this carbon has achieved its octet, and it has eight electrons: two from each single bond and four from the double bond.

What are the Atomic Theory Postulates?

•All matter consists of indivisible atoms •Atoms of the same element are identical •Compounds consists of atoms of more than one element connected together (Ex: H2O) •Chemical reactions are the result of atoms recombining

Atoms

•Consists of Protons, Neutron, and electrons Protons+Neutrons=Nucleus Electrons= orbiting nucleus •Mostly composed of empty space •Protons and neutrons are larger than electrons (by factor of 2000) •Protons and electrons are equivalent in charge Protons= +1.6*10^-19 Electrons= -1.6*10^-19 •Atoms in their elemental state always have the same number of protons and electrons

how to name molecular compounds

•In order of electronegativity ---->Exceptions: Carbon first ---->Exceptions:Hydrogen is written after Nitrogen •Suffix "ide" is added to the end of the name of the second element •Prefixes are used to indicate how many atoms of each element are present. ---> 1 is mono-, 2 is di-, 3 is tri-, 4 is tetra, 5 is penta- (If first element just has one atom, mono can be left out) Ex: CO= Carbon monoxide

How to name ionic compounds

•Metal retains its normal name, is followed by the nonmetal with an -ide suffix. •No prefixes(Ex: CaF2 : Calcium Fluoride) -> bc of charge differences