Chapter 3 Bonding and Chemical Interactions

Question 1

What are the three types of octet exceptions?

Answer 1

There are three types of octet exceptions: incomplete octet, expanded octet, and odd numbers of electrons

Question 2

What are the elements that have an incomplete octet? How many electrons do they need to be stable?

Answer 2

These elements are stable with fewer than 8 electrons in the valence shell.

The elements are:

hydrogen (stable with 2 electrons)

helium (stable with 2 electrons)

lithium (stable with 2 electrons)

beryllium (stable with 4 electrons)

boron (stable with 6 electrons)

Question 3

What elements have an expanded octet?

Answer 3

Any element in period 3 and greater can hold more than 8 electrons.

Examples include:

phosphorous (10 electrons)

sulfur (12 electrons)

chlorine (14 electrons)

Question 4

Explain the following octet exception:

odd number of electrons? Give an example.

Answer 4

Any molecule with an odd number of valence electrons cannot distribute those electrons to give eight to each atom.

Nitric oxide (NO) has 11 valence electrons.

Question 5

What are the type distinct types of chemical bonds?

Answer 5

Ionic and covalent bonds

Question 6

Explain ionic bonding. Give an example.

Answer 6

In ionic bonding, one of more electrons from an atom with low ionization energy (typically a metal), are transferred to an atom with a high electron affinity (typically a nonmetal)

Example: NaCl

Sodium has a low ionization energy (because it has a smaller Z_eff so the valence electrons are not as tightly bound to the nucleus), thus it easily releases an electron. Chlorine has a high electron affinity (because it has a stronger Z_eff thus the energy release will be greater when an electron is gained), thus it easily absorbs the electron.

Question 7

1. Explain how ionization energy and electron affinity play a role in NaCl.
2. What type of bonding is present in NaCl?
3. What holds the ions together?

Answer 7

1. Sodium has a low ionization energy (because it has a smaller Z_eff so the valence electrons are not as tightly bound to the nucleus), thus it easily releases an electron. Chlorine has a high electron affinity (because it has a stronger Z_eff thus the energy release will be greater when an electron is gained), thus it easily absorbs the electron.
2. Ionic bonding
3. The resulting electrostatic attraction between the opposite charges is what holds the ions together. The positively charged sodium cation is electrostatically attracted to the negatively charged chloride anion.

Question 8

What type of structure does sodium chloride have?

Answer 8

The electrostatic attraction between the sodium cation and chloride anion creates lattice structures consisting of repeating rows of cations and anions, rather than individual molecular bonds.

Question 9

Explain covalent bonding.

Provide an example.

What is the structure like?

Answer 9

In covalent bonding, an electron pair is shared between two atoms (typically nonmetals that have relatively similar values of electronegativity).

Example: F₂

Unlike ionic crystal lattices, covalent compounds consist of individually bonded molecules.

Question 10

Explain nonpolar and polar.

Answer 10

Nonpolar: the electron pair is shared equally

Polar: the electron pair is shared unequally

Question 11

What does coordinate covalent mean?

Answer 11

Both of the shared electrons are contributed by only one of the two atoms

Question 12

Describe the melting and boiling points of ionic compounds and explain the reasoning.

Answer 12

Ionic compounds have very high melting and boiling points due to the strength of the electrostatic force between the cation (loses electron, positive) and anion (gains electron, negative).

Question 13

List the characteristics of ionic compounds (hint: there’s …)

Answer 13

1. high melting and boiling points due to strength of electrostatic force between anion and cation
2. readily dissolve in water and other polar solvents
3. in molten or aqueous states, ionic compounds are good conductors of electricity
4. in solid form, components of ionic compound form a crystalline lattice, consisting of repeating positive and negative ions

Question 14

What is maximized and minimized with the crystalline lattice structure within ionic compounds?

Answer 14

With crystalline lattice, the attractive forces between oppositely charged ions are maximized, thus the repulsive forces between ions of like charge are minimized.

Question 15

Why do ionic bonds tend to form between metals and nonmetals?

Answer 15

Metals have low ionization energy (meaning they give up electrons easily), and nonmetals have high electron affinities (meaning they gain electrons easily). These processes are complementary, leading to the formation of an ionic bond

Question 16

How are the electronegativities of the atoms within a covalent bond and an ionic bond?

Answer 16

Covalent bond: similar electronegativities

Ionic bond: one low electronegativity, one high; electronegativities are significantly different

Question 17

Why do atoms with similar electronegativities share electrons rather than transfer them?

Answer 17

When atoms with similar electronegativities interact, the energy required to form ions through the complete transfer of electrons is greater than the energy that would be released upon the formation of an ionic bond; thus, it is energetically unfavorable to create ions.

Question 18

Why do covalent compounds tend to have lower melting and boiling points?

Answer 18

Covalent compounds contain weak intermolecular interactions

Question 19

Are covalent compounds good conductors of electricity?

Answer 19

No, covalent compounds are poor conductors of electricity because they do not break down into constituent ions.

Question 20

What is bond order?

Answer 20

Bond order refers to the umber of shared electron pairs between two atoms

Question 21

What is bond length?

Answer 21

Bond length is the average distance between the two nuclei of atoms in a bond. As the number of shared electron pairs increases, the two atoms are pulled closer, resulting in a shorter bond length.

Question 22

What is bond energy?

Answer 22

Bond energy is the energy required to break a bond by separating its components into isolated, gaseous atomic states. The greater number of electron pairs shared between the atomic nuclei, the more energy is required to break the bonds holding the atoms together (triple bonds have the greatest bond energy).

Question 23

When does polarity occur?

Answer 23

Polarity occurs when two atoms have a relative difference in electronegativities. When atoms come together in covalent bonds, they must negotiate the degree to which the electron pairs will be shared. The atom with the higher electronegativity will get the larger share of electron density.

Question 24

What does a polar bond create?

Answer 24

A polar bond creates a dipole, with the positive end of the dipole at the less electronegative atom, and the negative end at the more electronegative atom.

Question 25

What does a nonpolar covalent bond occur?

Answer 25

A nonpolar covalent bond occurs when atoms that have identical or nearly identical electronegativities share electron pairs. They do so with equal distribution of the electrons. Only bonds between atoms of the same element will have exactly the same electronegativity and therefore exhibit a purely equal distribution of electrons.

Question 26

What are the seven common diatomic molecules.

Answer 26

1. H₂
2. N₂
3. O₂
4. F₂
5. Cl₂
6. Br₂
7. I₂

Question 27

What difference in electronegativity is generally considered nonpolar?

Answer 27

Any bond between atoms with a difference in electronegativity less than 0.5 is generally considered nonpolar.

Question 28

When do polar covalent bonds occur?

Answer 28

Polar covalent bonds occur when there is a moderate difference in electronegativities. This difference is between 0.5 and 1.7, and it is not enough to result in the formation of an ionic bond.

However, this difference is sufficient to cause a separation of charge across the bond. The more electronegative element acquires a greater portion of the electron density, taking on a partial negative charge, and the less electronegative element takes on a partial positive charges and acquires less of the electron density.

Question 29

What is a dipole moment?

Answer 29

A molecule, such as HCl, that has a separation of positive and negative charges is called a polar molecule, and it has a dipole moment.

Question 30

What are bonding and nonbonding electrons? What are lone pairs?

Answer 30

Bonding electrons: electrons that are in the valence shell and are involved in covalent bonds

Nonbonding electrons: electrons that are in the valence shell and are not involved in covalent bonds

Lone pairs are the unshared electron pairs

Question 31

The most stable Lewis Structure will have the …

Answer 31

smallest Formal charge (formal charge will be minimized)

Question 32

How do you calculate formal charge?

Answer 32

FC= V - N_nonbonding - ½N_bonding

where:

V is the normal number of electrons in the atom’s valence shell

N_nonbonding is the number of nonbonding electrons

N_bonding is the number of bonding electrons (this is double the number of bonds because each bond has two electrons)

Question 33

What is the difference between electronic geometry and molecular geometry?

Answer 33

Electronic geometry describes the spatial arrangement of all pairs of electrons around the central atom

Molecular geometry describes the spatial arrangement of only the bonding pairs of electrons

Question 34

What is a coordination number?

Answer 34

The coordination number is the number of atoms that surround and are bonded to a central atom

Question 35

Rank the three intermolecular forces from weakest to strongest

Answer 35

Weakest: dispersion forces (London forces)

Intermediate: Dipole-dipole interactions

Strongest: Hydrogen bond

Question 36

London Dispersion Forces

Answer 36

1. they do not extend over long distances, thus they are only significant when molecules are in close proximity
2. large molecules are more easily polarizable (electrons can be shifted around more) than smaller molecules, thus they have greater dispersion forces

Question 37

Dipole-Dipole interactions

Question 38

Hydrogen bonds

Answer 38

1. may be intra or inter molecular
2. hydrogen bonds are not actually bonds- there is no sharing or transferring of electrons between two atoms
3. when hydrogen is bonded to one of three highly electronegative atoms (Fluorine, Nitrogen, Oxygen), the hydrogen atom carries only a small amount of the electron density in the covalent bond