Test 4 CH 131

How do you determine whether a molecule is polar? Why is polarity important?

-A molecule is said to be polar when it consists of a least one polar bond- To determine whether a molecule is polar, the structure should be drawn and determine its molecular geometry.- Molecule is polar if the polar bonds add together to form a net dipole movement- it is important because of various properties of molecules such as solubility, dipole movement, surface tensions, and melting and boiling points.

What is a chemical bond according to valence bond theory?

-Defined as the interaction of half-filled atomic or hybrid orbitals.-Sometimes the overlap between completely filled atomic or hybrid orbitals with empty orbitals is also considered a chemical bond

In valence bond theory what determines the geometry of a molecule?

-Determined by using the hybridization concept-Procedure in which standard atomic orbitals combine to form new atomic orbitals called hybrid orbitals

Name and sketch the five basic electron geometries, and state the number of electron groups corresponding to each. What constitutes an electron group?

-Linear geometry (2 electron groups, bond angle is 180)-Trigonal planar (three electron groups, bond angle is 120)-tetrahedral (4 electron groups, 109.5)-Trigonal Bipyramidal (5 electron groups, 120 equatorial, 90 axial)-Octahedral (6 electron groups, 90)

In valence bond theory the interaction energy between the electrons and nucleus of one atom with the electrons and nucleus of another atom is usually negative stabilizing when

-When a bond forms between the two atoms-When the interaction energy is negative or decreased, it means that the atoms are stabilized by the formation of the bond

What is hybridization? Why is hybridization necessary in valence bond theory?

-it is a mathematical procedure in which standard atomic orbitals are combined to form new atomic orbitals called hybrid orbitals.-necessary for valence bond theory to adequately explain bonding in some molecules

Which elements can have expanded octets? Which elements should not have expanded octets?

Elements in the third row of the periodic table and beyond often exhibit expanded octets. Elements in the first or second row of the periodic table never have expanded octets.

What are the exceptions to the periodic trends in first ionization energy? Why do they occur?

Exceptions occur with elements Be, Mg, and Ca in group 2A having a higher first ionization energy than elements B, Al, and Ga in group 3A. This exception is caused by the change in going from the s block to the p block. The result is that the electrons in the s orbital shield the electron in the p orbital from nuclear charge, making it easier to remove. Another exception occurs with N, P, and As in group 5A having a higher first ionization energy than O, S, and Se in group 6A. This exception is caused by the repulsion between electrons when they must occupy the same orbital. Group 5A has 3p electrons, whereas group 6A has 4p electrons. In the group 5A elements, the p orbitals are half-filled, which makes the configuration particularly stable. The fourth group 6A electron must pair with another electron, making it easier to remove.

How does the electron sea model explain the conductivity of metals? The malleability and ductility of metals?

However, the electrons are mobile, and no individual electron is confined to any particular metal ion. When a metal wire is connected to the terminals of a battery, electrons flow through the metal toward the positive terminal and into the metal from the battery at the negative terminal. The high heat conductivity of metals is also accounted for by the mobility of the electrons, which permits ready transfer of kinetic energy throughout the solid. The ability of metals to deform (their malleability and ductility) can be explained by the fact that metal atoms form bonds to many neighbors. Changes in the positions of the atoms brought about in reshaping the metal are partly redistributed

According to the Lewis model, what is a chemical bond?

In Lewis theory, a chemical bond is the sharing or transferring of electrons to attain stable electron configurations for the bonding atoms. If electrons are transferred, the bond is an ionic bond. If the electrons are shared, the bond is a covalent bond.

How do you draw an ionic lewis structure?

In Lewis theory, we represent ionic bonding by moving electron dots from the metal to the nonmetal and allowing resultant ions to form a crystalline lattice composed of alternating cations and anions. The cations lose its valence electrons and is left with an octet in the previous principal energy level ; the anion gains electrons to form an octet. The Lewis structure of the anion is usually written with brackets with charge in the upper right hand corner, outside the brackets. positive and negative charges attract one another, forming compounds.

How do you determine how many dots to put around Lewis symbol of an element?

In a Lewis structure, the valence electrons of main-group elements are represented as dots surrounding the symbol for the element. The valence electrons can be determined from the group they are in on the periodic table.

List all orbitals from 1s through 5s according to increasing energy for multielectron atoms.

In order of increasing energy the orbitals are 1s<2s<2p<3s<3p<4s<3d<4p<5s. The 4s orbital fills before the 3d and the 5s fills before the 4d. They are lower in energy because of greater penetration of the 4s and 5s orbitals.

Which of the transition elements in the first transition series have anomalous electron configurations?

In the first transition series of the d block, Cr and Cu have anomalous electron configurations. Cr is expected to be [Ar]4s^2 3d^4, but is found to be [Ar]4s^1 3d^5, and Cu is expected to be [Ar]4s^2 3d^9, but is found to be [Ar]4s^1 3d^10.

What is the general trend in first ionization energy as you move down a column in the periodic table? As you move across a row?

Ionization energy generally increases as you move to the right across a period in the periodic table because electrons in the outermost principal level become farther from the positively charged nucleus and are therefore held less tightly.

How do you apply VESPR theory to predict the shape of a molecule with more than one interior atom?

Larger molecules may have two or more interior atoms. When predicting the shapes of these molecules, determine the geometry about each interior atom and use these geometries to determine the entire three-dimensional shape of the molecules.

What is lattice energy?

Lattice energy is associated with forming a crystalline lattice of alternating cations and anions from the gaseous ions. Because the cations are positively charged and the anions are negatively charged, there is a lowering of potential—as described by Coulomb's law—when the ions come together to form a lattice. That energy is emitted as heat when the lattice forms.

What is metallic character? What are the observed periodic trends in metallic character?

Metals are good conductors of heat and electricity, they can be pounded into flat sheets (malleability), they can be drawn into wires (ductility), they are often shiny, and they tend to lose electrons in chemical reactions. As you move to the right across a period in the periodic table, metallic character decreases. As you move down a column in the periodic table, metallic character increases.

Explain the contributions of Meyer and Moseley to the periodic table.

Meyer proposed an organization of the known elements based on some periodic properties. Moseley listed elements according to the atomic number rather than the atomic mass. This resolved the problems in Mendeleev's table where an increase in atomic mass did not correlate with similar properties.

Why is molecular geometry important?

Molecular geometry is very important-it tells us about the shape of molecules-This helps us account for the properties of molecules as wel

Do resonance structures always contribute equally to the overall structure of a molecule?

No, the resonance structure with the overall lowest formal charge on the atoms and the most negative formal charge on the most electronegative atom in the structure will contribute most to the overall structure

Define atomic radius. For main-group elements, describe the observed trends in atomic radius as you move: a. across a period in the periodic table b. down a column in the periodic table

One way to define atomic radii is to consider the distance between nonbonding atoms in molecules or atoms that retouching each other but are not bonded together. An atomic radius determined this way is called the nonbonding atomic radius or the van Der Waals radius. The van Der Waals radius represents the radius of an atom when it is not bonded to another atom. Another way to define the size of an atoms, called bonding an atomic radius or covalent radius, is defined differently for nonmetals and metals as follows: Nonmetals: one-half the distance between two of the atoms bonded together. Metals: one-half the distance between two of the atoms next to each other in a crystal of the metal. A more general term, the atomic radius, refers to a set of average bonding radii determined from measurements on a large number of elements and compounds. The atomic radius represents the radius of an atom when it is bonded to another atom and is always smaller than the van Der Waals radius. a) as you move to the right across a period in the periodic table, atomic radius decreases b) as you move down a column in the periodic table, atomic radius increases

How is the electron configuration of an anion different from that of the corresponding neutral atom? How is the electron configuration of a cation different?

The electron configuration of a main-group monatomic ion can be deduced from the electron configuration of the neutral atom and the charge of the ion. For anions, we simply add the number of electrons required by the magnitude of the charge of the anion. The electron configuration of cations is obtained by subtracting the number of electrons required by the magnitude of the charge,

Explain the contributions of Johann Döbereiner and John Newlands to the organization of elements according to their properties.

The first attempt to organize the elements according to similarities in their properties was made by the German chemist Johann Dobereiner. He grouped elements into triads: three elements with similar properties. A more complex approach was attempted by the English chemist John Newlands. He organized elements into octaves, analogous to musical notes. When arranged this way, the properties of every eighth element were similar.

What is formal charge? How is formal charge calculated?

The formal charge of an atom in a Lewis structure is the charge it would have if all the electrons were shared equally bet. bonded atoms.

What is ionization energy? What is the difference between first ionization energy and second ionization energy?

The ionization energy (IE) of an atom or ion is the energy required to remove an electron from the atom or ion in the gaseous state. The ionization energy is always positive because removing an electron takes energy. The energy required to remove the first electron is called the first ionization energy. The energy required to remove the second electron is called the second ionization energy. The second IE is always greater than the first IE.

Describe the relationship between a main-group element's lettered group number (the number of the element's column) and its valence electrons.

The lettered group number of a main-group element is equal to the number of valence electrons for that element.

Who is credited with arranging the periodic table? How are the elements arranged in the modern periodic table?

The modern periodic table is credited primarily to Medeleev. His table is based on the periodic law, which states that when elements are arranged in order of increasing mass, their properties recur periodically. Mendeleev arranged the elements in a table in which mass increased from left to right and elements with similar properties fell in the same columns.

Explain why the s block in the periodic table has only two columns while the p block has six.

The number of columns in a block corresponds to the maximum number of electrons that can occupy the particular sub level of that block. The s block has two columns corresponding to one s orbital holding a max of two electrons. The p block has six columns corresponding to the three p orbitals with two electrons each.

The periodic table is a result of the periodic law. What observations led to the periodic law? What theory explains the underlying reasons for the periodic law?

The periodic law was based on the observations that the properties of elements recur and certain elements have similar properties. The theory that explains the existence of the periodic law is quantum-mechanical theory.

Which periodic property is particularly important to nerve signal transmission? Why?

The relative size of the sodium and potassium ions is important to nerve signal transmission. The pumps and channels within cell membranes are so sensitive that they can distinguish between the sizes of these two ions and selectively allow only one or the other to pass. The movement of ions is the basis for the transmission of nerve signals in the brain and throughout the body.

Describe the relationship between an element's row number in the periodic table and the highest principal quantum number in the element's electron configuration. How does this relationship differ for main-group elements, transition elements, and inner transition elements?

The row number of a main-group element is equal to the highest principal quantum number of that element. However, the principal quantum number of the d orbital being filled across each row in the transition series is equal to the row number minus one. For the inner transition elements, the principal quantum number of the f orbital begin filled across each row is the row number minus two.

Why do the rows in the periodic table get progressively longer as you move down the table? For example, the first row contains 2 elements, the second and third rows each contain 8 elements, and the fourth and fifth rows each contain 18 elements. Explain.

The rows in the periodic table grow progressively longer because you are adding sub levels as the n level increases.

Describe how to write the electron configuration for an element based on its position in the periodic table.

To use the periodic table to write the electron configuration, find the noble gas that precedes the element. The element has the inner electron configuration of that noble gas. Place the symbol for the noble gas in [ ]. Obtain the outer electron configuration by tracing the element across the period and assigning electrons in the appropriate orbitals.

What are valence electrons? Why are they important?

Valence electrons are important in chemical bonding. For main-group elements, the valence electrons are in the outermost principal energy level. For transition elements, we also count the outermost d electrons among the valence, even though they are not in the outermost principal energy level. The chemical properties of an element depend on its valence electrons, which are important in bonding because they are held most loosely. This is why the elements in a column of the periodic table have similar chemical properties: they have the same number of valence electrons.

How does the ionic bonding model explain the relatively high melting points of ionic compounds?

We modeled ionic solids as a lattice of individual ions held together by coulombic forces, which are equal in all directionsTo melt the solid, these forces must be overcome. This requires a significant amount of heat. The model accounts for high melting point of solids.

What is the electron sea model for bonding in metals?

When metal atoms bond together to form a solid, each metal atom donates one or more electrons to an electron sea.

How can Lewis structures be used to determine the formula of ionic compounds? Give an example.

With the Lewis structure, you can see how many of the cations or anions are needed for every ion to fulfill their octet. For example Na has one electron and Cl has seven electrons. Na+ and Cl- attract one another and fulfills their octet.

What is the magnitude of the dipole moment formed by seperating a proton and an electron by 100 om?

[(1.610^-19 C) (10010^-12 m)](1D/ 3.3410^-30 CM)=4.8 D

In a covalent Lewis structure, what is the difference between lone pair and bonding pair electrons?

bonding pair electrons are the electrons shared between two atomslone pair of electrons is associated with only one atoms and not involved in bonding

How does the Lewis model for covalent bonding account for why certain combinations of atoms are stable while others are not?

combinations of atoms that can satisfy the octet rule on each atom are stable while combinations that do not satisfy the octet rule are not stable

How does the Lewis model for covalent bonding account for the relatively low melting and boiling points of molecular compounds compared to ionic compounds?

covalent bond is not as strong as ionic compounds

In what ways are double and triple covalent bonds different from single covalent bonds?

double and triple are greater in strength than the single bondsdouble and triple are shorter than the single bonds

What is electronegativity? What are the periodic trends in electronegativity?

electronegativity is the ability of an atom to attract electrons to itself in a chemical bondthis results in a polar bondelectronegativity increases across a period from left to right and decreases down a column(group)most electronegative element-fluorine

Explain the difference between endothermic and exothermic reactions with respect to bond energies of the bonds broken and formed.

endothermic: bonds brokenexothermic: bonds forming

What is bond energy? How can you use average bond energies to calculate enthalpies of reaction?

energy required to break one mole of the bond in the gas phasebreaking bond is endothermicforming bond is exothermicsum of enthalpy changes associated with the bond breaking the required bonds in the reactants and forming the required bonds in the productsadd bond energies of product with bond energies of reactant

How does the ionic bonding model explain the non-conductivity of ionic solids, and and the same time the conductivity of ionic solutions?

in solutions the ionic solids breaks into cations and anions and electricity flows between them when the electrons are transferredionic solids do not conduct electricity b/c the ions are locked into a rigid lattice or arraythe ions cannot move out of the lattice so solid cannot conduct electricity.

What are resonance structures? What is a resonance hybrid?

resonance hybrid is the average of all the resonance structureresonance structure occur when bonds are equivalent are intermediate in strength and length of a double and single bondresonance hybrid: actual structure of the molecule, intermediate of the resonance structures

Copy this blank periodic table onto a sheet of paper and label each of the blocks within the table: s block, p block, d block, and f block.

see table

What is a dipole movement?

separation of positive and negative charge

Why is electron spin important when writing electron configurations? Explain in terms of the Pauli exclusion principle.

the Pauli exclusion principle states the following: no two electrons in an atom can have the same four quantum numbers. Because two electrons occupying the same orbital have three identical quantum numbers (n, l, ml), they must have different spin quantum numbers. The Pauli exclusion principle implies that each orbital can have a maximum of only two electrons, with opposing spins.

Why is the formation of solid sodium chloride from solid sodium and gaseous chlorine exothermic, even though it takes more energy to form the Na+ ion than the amount of energy released upon formation of Cl-?

the formation of ionic compounds is not exothermic because sodium "wants" to lose electrons and chlorine "wants" to gain them; rather, it is exothermic because of the large amount of heat released when sodium and chlorine ions coalesce to form a crystal lattice.

Why does the octet rule have exceptions? List the three major categories of exceptions and an example of each.

1) odd octets-electron species, molecules, ions with an odd number of electron ( NO)2) incomplete octets-molecules/ions with fewer than 8 electrons around an atom ( BF3)3) expanded octets - molecules or ions with more than eight electrons around an atom ( AsF5)

Explain percent ionic character of a bond. Do any bonds have 100% ionic character?

A percent ionic character is the actual dipole moment of the atom divided by the dipole moment if the electron was completely transferred. A bond in which an electron is completely transferred form one atom to another would have 100% ionic character. No bond is 100% ionic. Percent ionic character increases with electronegativity differences increase. bonds with greater than 50% ionic character are referred as ionic bonds

What are periodic properties?

A periodic property is predictable based on the element's position within the periodic table.

According to VESPR theory what determines the geometry of a molecule?

According to VSEPR theory, the repulsion between electron groups on interior atoms of a molecule determines the geometry of the molecule.

Write a general equation for the reaction of a halogen with each substance. a. a metal b. hydrogen c. another halogen

All of the halogens are powerful oxidizing agents a) the halogens react with metals to form metal halides 2M(s) + nX2-->2MXn(s) b) the halogens react with hydrogen to form hydrogen halides H2(g) + X2 --> 2HX (g) c) The halogens react with each other to form inter halogen compounds. for example, BR2(l) + F2(g) --> 2BrF (g)

What is an electron configuration? Give an example.

An electron configuration shows the particular orbitals that are occupied by electrons in an atom. Some examples are H=1s^1, He=1s^2, and Li=1s^2 2s^1

Describe how to write an electron configuration for a transition metal cation. Is the order of electron removal upon ionization simply the reverse of electron addition upon filling? Why or why not?

An important exception of simply subtracting the number of electrons occurs for transition metal cations. When writing the electron configuration of a transition metal cation, remove the electrons in the highest n-value orbitals first, even this does not correspond to the reverse order of filling. Normally, even though the d orbital electrons add after the s orbital electrons, the s orbital electrons are lost first. This is because (1) the ns and (n-1)d orbitals are extremely close in energy and, depending on the exact configuration, can vary in relative energy ordering and (2) as the (n-1)d orbitals begin to fill in the first transition series, the increasing nuclear charge stabilizes the (n-1)d orbitals relative to the ns orbitals. This happens because the (n-1)d orbitals are not outermost orbitals and therefore are not effectively shielded from the increasing nuclear charge by the ns orbitals.

What is an orbital diagram? Provide an example.

An orbital diagram is a different is a different way to show the electron configuration of an atom. It symbolizes the electron as an arrow in a box that represents the orbital. see orbital diagram of a hydrogen atom

How does lattice energy relate to ionic radii? To ion charge?

As the ionic radii increase as you move down a group, the ions cannot get as close to each other and therefore do not release as much energy when the lattice forms. Thus, the lattice energy decreases (becomes less negative) as the radius increases. b. Because the magnitude of the potential energy of two interacting charges depends not only on the distance between the charges but also on the product of the charges, the lattice energies become more exothermic with increasing magnitude of ionic charge.

Use the concepts of effective nuclear charge, shielding, and n value of the valence orbital to explain the trend in atomic radius as you move across a period in the periodic table.

As you move to the right across a row in the periodic table, the n level stays the same. However, the nuclear charge increases and the amount of shielding stays about the same because the number of inner electrons stays the same. So the effective nuclear charge experienced by the electrons in the outermost principal energy level increases, resulting is a stronger attraction between the outermost electrons and the nucleus and, therefore, smaller atomic radii.

Why are bonding theories important? Provide some examples of what bonding theories can predict.

Bonding theories are central to chemistry because they explain how atoms bond together to form molecules. Bonding theories explain why some combinations of atoms are stable and others are not.

Describe the octet rule in the Lewis model.

Bonds are formed when atoms attain a stable electron configuration. Because the stable configuration usually has eight electrons in the outermost shell, this is known as the octet rule.

What is the Born-Haber cycle? List each step in the cycle and show how the cycle is used to calculate lattice energy?

Born Haber cycle is a hypothetical series of steps that represent the formation of an ionic compound from its constituent elements. The steps are chosen so that change in enthalpy of each step is known excel for the last one, which is lattice energy.For formation of NaClstep 1: formation of gaseous Na from solid Na (heat of sublimation of Na)step 2: formation of Cl atom from Cl molecule (bond energy of Cl)step 3: Na becomes Na+ (first ionization energy)step 4: Cl becomes Cl- ( electron affinity)step 5: formation of crystalline solid from gaseous ions (lattice energy)The overall reaction is the formation of NaCl(s), so we can use Hess's Law to determine the lattice energy.heat of sublimation+ 1/2 bond energy+ first IE+ EA+Lattice EnergyAll the terms are known except for the lattice energyis starting with the reactants in its elemental form and undergoing multiple steps that change the enthalpy and end up with the solid ionic compound

Why do chemical bonds form? What basic forces are involved in bonding?

Chemical bonds form because they lower the potential energy between the charged particles that compose the atom. Bonds involve the attraction and repulsion of charged particles.

What is Coulomb's law? Explain how the potential energy of two charged particles depends on the distance between the charged particles and on the magnitude and sign of their charges.

Coulomb's law states that the potential energy (E) of two charged particles depends on their charges (q1 and q2) and on their separation, (r). E=1/4piE0 * q1q2/r. The potential energy is positive for charges of the same sign and negative for charges of opposite sign. The magnitude of the potential energy depends inversely on the separation between the charged particles.

What are degenerate orbitals? According to Hund's rule, how are degenerate orbitals occupied?

Degenerate orbitals are orbitals of the same energy. In a multi electron atom, the orbitals in a sub level are degenerate. Hund's rule states that when filling degenerate orbitals, electrons fill them singly first, with parallel spins. This is a result of an atoms tendency to find the lowest energy state possible.

How does hybridization of the atomic orbitals in the central atom of a molecule help lower the overall energy of the molecule?

During hybridization, atomic orbitals combine to form hybrid orbitals which have different shapes and energies from those of standard atomic orbitals-in these hybrid orbitals, the electron probability density is more concentrated in a single directional lobe-This allows greater overlap with the orbitals of other atoms-Hence hybrid orbitals lower the energy of the molecule by maximizing the orbital overlap in a bond

What is penetration? How does the penetration of an orbital into the region occupied by core electrons affect the energy of an electron in that orbital?

Penetration occurs when an electron penetrates the electron cloud of the 1s orbital and experiences the charge of the nucleus more fully because it is less shielded by the intervening electrons. As the outer electron undergoes penetration into the region occupied by the inner electrons, it experiences a greater nuclear charge and therefore, according to Coulomb's law, a lower energy.

What is shielding? In an atom, which electrons tend to do the most shielding (core electrons or valence electrons)?

Shielding or screening occurs when one electron is blocked from the full-effects of the nuclear charge so that the electron experiences only a part of the nuclear charge. It is the inner (core) electrons that shield the outer electrons from the full nuclear charge.

Describe the relationship between the properties of an element and the number of valence electrons that it contains.

The chemical properties of elements are largely determined by the number of valence electrons they contain. Their properties are periodic because the number of valence electrons is periodic. Because elements within a column in the periodic table have the same number of valence electrons, they also have similar chemical properties.

What is effective nuclear charge? What is shielding?

The effective nuclear charge (Zeff) is the average or net charge from the nucleus experienced by the electrons in the outermost levels. Shielding is the blocking of nuclear charge from the outermost electrons. The shielding is primarily due to inner (core) electrons, although there is some interaction and shielding from the electron repulsions of the outer electrons with each other.

What is electron affinity? What are the observed periodic trends in electron affinity?

The electron affinity (EA) of an atom or ion is the energy change associated with the gaining of an electron by the atom in the gaseous state. The electron affinity is usually--though not always--negative because an atom or ion usually releases energy when it gains an electron. The trends in electron affinity are not as regular as trends in other properties. For main-group elements, electron affinity generally becomes more negative as you move to the right across a row in the periodic table. There is no corresponding trend in electron affinity going down a column, with the exception of group 1A which becomes more positive as you go down the column.

Examination of the first few successive ionization energies for a given element usually reveals a large jump between two ionization energies. For example, the successive ionization energies of magnesium show a large jump between IE2 and IE3. The successive ionization energies of aluminum show a large jump between IE3 and IE4. Explain why these jumps occur and how you might predict them.

The second ionization energy of Mg involves removing the second outermost electron leading to an ion with a noble gas configuration for the core electrons. The third ionization energy requires removing a core electron from an ion with a noble gas configuration. This requires a tremendous amount of energy, making IE3 very high. For Al, IE3 involves removing the third outermost electron for Al, leaving the ion with a noble gas configuration of the core electrons. IE4 then requires removing a core electron from an ion with a noble gas configuration. This requires a tremendous amount of energy and makes IE4 very high. You can predict whether the IE energy is going to be very high by looking for the ionization that requires removing a core electron.

Why are the sublevels within a principal level split into different energies for multielectron atoms but not for the hydrogen atom?

The sublevels within a principal level split in multi electron atoms because of penetration of the outer electrons into the region of the core electrons. The sub levels in hydrogen are not split because they are empty in the ground state.

What are the three basic types of chemical bonds? What happens to electrons in the bonding atoms in each type?

The three types of bonds are ionic bonds, which occur between metals and nonmetals and are characterized by the transfer of electrons; covalent bonds, which occur between nonmetals and are characterized by the sharing of electons; and metallic bonds, which occur between metals and are characterized by electrons being pooled.

Describe the relationship between a. the radius of a cation and that of the atom from which forms b. the radius of an anion and that of the atom from which it forms

a) in general, cations are much smaller than their corresponding parent. This is because the outermost electrons are shielded from the nuclear charge in the atom and contribute greatly to the size of the atom. When these electrons are removed to form the cation, the same nuclear charge is now acting only on the core electrons. b) In general, anions are much larger than their corresponding atoms. This is because the extra electrons are added to the outermost electrons but no additional protons are added to increase the nuclear charge. The extra electrons increase the repulsions among the outermost electrons, resulting in an anion that is larger than the atom.

List the number of valence electrons for each family, and explain the relationship between the number of valence electrons and the resulting chemistry of the elements in the family. a. alkali metals b. alkaline earth metals c. halogens d. oxygen family

a) the alkali metals (group 1A) have one valence electron and are among the most reactive metals because their outer electrons configuration (ns^1) is one electron beyond a noble gas configuration. They react to lose the ns^1 electron, obtaining a noble gas configuration. this is why the group 1A metals tend to form 1+ cations. b) the alkaline earth metals (group 2A) have two valence electrons, have an outer electron configuration of ns^2, and also tend to be reactive metals. They lose their ns^2 electrons to form 2+ cations. c) The halogens (group 7A) have seven valence electrons and an outer electron configuration of ns^2np^5. They are among the most reactive nonmetals. They are only one electron short of a noble gas configuration and tend to react to gain that one electron, forming 1- anions. d) The oxygen family (group 6A) has six valence electrons and has an outer electron configuration of ns^2np^4. They are two electrons short of a noble has configuration and tend to react to gain those two electrons, forming 2- anions.

For transition elements, describe and explain the observed trends in atomic radius as you move: a. across a period in the periodic table b. down a column in the periodic table

a) the radii of transition elements stay roughly constant across each row instead of decreasing in size as in the main-group elements. The difference is that across a row of transition elements, the number of electrons in the outermost principal energy level is nearly constant. As another proton is added to the nucleus with each successive element, another electron is added as well, but the electron goes into an n highest -1 orbital. The number of outermost electrons stays constant, and they experience a roughly constant effective nuclear charge, keeping the radius approximately constant. b) As you go down the first two rows of a column within the transition metals, the elements follow the same general trend in atomic radii and the main-group elements; that is, the radii get larger because you are adding outermost electrons into higher n levels.

Write a general equation for the reaction of an alkali metal with each substance. a. a halogen b. water

a) the reactions the alkali metals with halogens result in the formation of metal halides. 2M(s) + X2 --> 2MX(s) b) Alkali metals react with water to form the dissolved alkali metal ion, the hydroxide ion, and hydrogen gas. 2M(s) + 2H2O(l) -->2M+(aq) +2OH-(aq) + H2(g)

how do a pure covalent bond, a polar covalent bond, and an ionic bond differ?

a. If two elements with identical electronegativities form a covalent bond, they share the electrons equally, and the bond is purely covalent or non polar. b. If there is an intermediate electronegativity difference between the two elements, such as between two different non-metals, the bond is polar covalent. c. If there is a large electronegativity difference between the two elements in a bond, such as normally occurs between a metal and a nonmetal, the electron from the metal is almost completely transferred to the nonmetal, and the bond is ionic.

explain the difference between electron geometry and molecular geometry. Under what circumstances are they not the same?

a. The electron geometry is the geometrical arrangement of the electron groups around the central atom.b. The molecular geometry is the geometrical arrangement of the atoms around the central atom.c. The electron geometry and the molecular geometry are the same when every electron group bonds two atoms together. The presence of unbounded lone pair electrons gives a different molecular geometry and electron geometry.

How do you determine the number of electrons in the Lewis structure of a molecule? A polyatomic ion?

a. The total number of electrons for a Lewis structure of a molecule is the sum of the valence electrons of each atom in the molecule. b. The total number of electrons for the Lewis structure of an ion is found by summing the number of valence electrons for each atom and then subtracting one electron for each positive charge or adding one electron for each negative charge.