E. Principles of Chemical Bonding

Question 1

Ionic, covalent, vs metallic bond

Answer 1

Ionic - transfer of electron pair

Covalent - sharing of electron pair

Metallic - attraction between positively charged ions and a sea of delocalized electrons within a metal lattice

Question 2

Differentiate types of covalent bond

Answer 2

1. Nonpolar covalent - equal sharing of e-
2. Polar covalent - unequal sharing of e-
3. Covalent network - usually occurs at solids

Question 3

Electronegativity difference and its corresponding type of bond

Answer 3

EN → Type of Bond
<0.4 → nonpolar covalent
0.4 - 1.7 → polar covalent
> 1.7 → ionic

Question 4

Differentiate covalent bond and coordinate covalent bond

Answer 4

Coordinate covalent bond - 1 atom donates both electrons in electron pair to form bonds
Covalent bond - both atoms contribute 1 electron (sharing) to form the bond

Question 5

The energy of a resonance hybrid structure is ____ than that of any single contributing structure.

Answer 5

lower = more stable

Question 6

The ____ resonance structure contribute more to the resonance hybrid

Answer 6

lower energy = more stable

Question 7

How to compute for formal charges?

Answer 7

FC = valence - nonbonding - (bonding/2)

Question 8

The presence of unpaired electrons causes odd-electron species to be _____ while molecules with even number of electrons (all are paired) are called ____

Answer 8

paramagnetic - unpaired, odd
diamagnetic - paired, even

NOTE: O2 is paramagnetic (12 e-)

Question 9

Atoms that exhibit exemption to octet rule

Answer 9

H, B, Be, Al (incomplete)
P, S, Cl (expanded)

Question 10

What is VSEPR?

Answer 10

Valence Shell Electron Pair Repulsion
- simple model used to predict the shape (geometry) of molecules based on the idea that electron pairs repel each other.

Question 11

Lone pair has ___ repelling effect than bonds

Answer 11

greater repelling effect → lower angle than tetrahedral (e.g., HOH = 104.5)

Question 12

A Valence Bond wavefunction is formed by ____ of the electrons in the two contributing atomic orbitals.

Answer 12

spin pairing (Pauli principle)

Question 13

In a molecular potential energy curve, the deeper the minimum of the curve, the _____ the atoms are bonded together.

Answer 13

more strongly

Question 14

Differentiate homonuclear diatomic molecules and polyatomic molecules

Answer 14

homonuclear diatomic molecules - diatomic molecules in which both atoms belong to the same element

Question 15

Give the electron-group/pair geometries (AXn) and bond angle for n = 1 to 6:

Answer 15

AX2 = linear (180°)
AX3 = trigonal planar (120°)
AX4 = tetrahedral (109.5°)
AX5 = trigonal bipyramidal (120° and 90°)
AX6 = octahedral (90°)

Question 16

Molecular geometry and bond angle for AX2E

Answer 16

bent
120°

Question 17

Molecular geometry for AX3E and AX2E2

Answer 17

AX3E = trigonal pyramidal (<109.5°)

AX2E2 = bent (<109.5°)

Question 18

Molecular geometry for AX4E, AX3E2 and AX2E3

Answer 18

AX4E - seesaw (<120° and <90°)

AX3E2 - T-shaped (<90°)

AX2E3 - linear (180°)

Question 19

Molecular geometry for AX5E, AX4E2, AX3E3, and AX2E4

Answer 19

AX5E - square pyramidal (<90°)

AX4E2 - square planar (90°)

AX3E3 - T-shaped (<90°)

AX2E4 - linear (180°)

Question 20

All of AXn molecules are nonpolar if (1) ____ and (2) ____

Answer 20

1. all terminal atoms are identical
2. all bonding groups have the same bond order

Question 21

Order of repulsive forces

Answer 21

lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

Question 22

How to know the molecular geometry of molecules with more than one central atom?

Answer 22

Apply VSEPR theory on each of the central atom

Question 23

Formula for dipole moment

Answer 23

μ = δ x d

δ - partial charge
d - distance

Question 24

The higher the bond order, the ____ the bond strength, ____ the bond length, and the ___ the bond energy

Answer 24

↑ bond order = ↑ bond strength = ↓ bond length (same atom) = ↑ bond energy

Question 25

Energy is _____ when isolated atoms join to form a covalent bond, and energy must be ____ to break apart covalently bonded atoms.

Answer 25

released - bonds form absorbed - bonds break

Question 26

Enthalpy change using bond dissociation energies

Answer 26

ΔH = ΔH (bonds broken) + ΔH (bonds formed) ΔH = ΣBE (reactants) - ΣBE (products)

Question 27

weak bonds → strong bonds The reaction is _____ process and ΔH __ 0

Answer 27

The reaction is exothermic process ΔH < 0

Question 28

strong bonds → weak bonds The reaction is _____ process and ΔH __ 0

Answer 28

The reaction is endothermic process ΔH > 0

Question 29

Why the overlap of orbitals leads to a chemical bond?

Answer 29

→ two atomic wave function in the same phase will lead to constructive interference → will increase electron density between two nuclei → electron density (negative) will attract the positive charge of nuclei → lower energy → bond formed

Question 30

Why hybridization of atomic orbitals is needed?

Answer 30

to explain the number of bonds that an atom can make by combining individual atomic orbitals e.g., C in CH4 makes four bonds even if in its ground state, only 2 of its valence electrons are unpaired

Question 31

Geometric orientation based on the hybrid orbitals

Answer 31

sp = linear sp2 = trigonal planar sp3 = tetrahedral sp3d = trigonal bipyramidal sp3d2 = octahedral

Question 32

Differentiate bonding and nonbonding MO

Answer 32

bonding MO (lower energy) - resulted from constructive interference (addition of wavefunction), places high electron density between nuclei → reduces repulsion between nuclei → promotes strong bond antibonding MO (higher energy) - resulted from destructive interference (subtraction of wavefunction), places very low electron density between nuclei → repulsion between nuclei → weak bond

Question 33

The number of molecular orbitals (MOs) formed is equal to ______

Answer 33

the number of atomic orbitals combined

Question 34

A stable molecular species has more electrons in _____ than _____

Answer 34

bonding orbitals than in antibonding orbitals

Question 35

Bond order (single, double, triple bond) formula for diatomic molecules

Answer 35

BO = (no of e- in bonding MO − no of e- in antibonding MO) / 2

Question 36

Bond order formula using Lewis structure for polyatomic molecules. What can be deduced in this formula?

Answer 36

BO = no. of bonds / no. of bonding groups ↑ no. of covalent bonds (diatomic) = ↑ BO = ↑ Bond Energy = ↓ Bond Length

Question 37

A fractional bond order means ___

Answer 37

Partial bonding as in resonance structures

Question 38

The strength of a bond is _____ to its bond order.

Answer 38

directly proportional

Question 39

What is the order of π energy levels when constructing energy diagrams in lighter atoms (Z<7)? Why?

Answer 39

π 2p (x,y) > σ 2p (z) > π* 2p (x,y) > σ* 2p (z) Because of s-p orbital mixing due to close energy of two orbitals

Question 40

What is the order of π energy levels when constructing energy diagrams in heavier atoms (Z>8)? Why?

Answer 40

σ 2p (z) > π 2p (x,y) > π* 2p (x,y) > σ* 2p (z) Because less s-p mixing happens due to large difference in s and p energy levels

Question 41

Differentiate intermolecular and intramolecular forces of attraction

Answer 41

INTERmolecular forces → between separate molecules of liquids or solids → London dispersion forces, dipole-dipole interactions, hydrogen bonds, ion-dipole interactions INTRAmolecular forces → forces that hold atoms together in a single molecule or ionic unit → ionic, covalent, metallic

Question 42

Type of IMFA that forms a temporary dipole that can induce a similar dipole in nearby atoms

Answer 42

London dispersion forces

Question 43

Forces that occur between polar molecules with permanent dipoles

Answer 43

dipole-dipole interactions

Question 44

Hydron bonds occurs when ____

Answer 44

→ H-atoms bonds with N, O, or F (electronegative) → forms a partial positive charge on H atom → the partial positive charge on H atom is attracted to nearby lone pair (negative) on another electronegative atom

Question 45

Occurs when an ion and a polar molecule interact with each other

Answer 45

ion-dipole interactions

Question 46

Boiling point/melting point relationship with IMFA strength and molecular weight

Answer 46

stronger IMFA = higher BP and MP → strong IMFA, molecules are harder to separate ↑ MW = ↑ BP and MP → ↑ MW, ↑ polarizability (distortion of electron cloud) → forms temporary dipole → induces dipoles in neighboring molecules → stronger dispersion forces

Question 47

Molar mass and IMFA relationship

Answer 47

↑ MM ↑ LDF ↓ MM w/ polar molecules ↑dipole-dipole forces

Question 48

Differentiate solubility of a metal, ionic solid. covalent molecular solid, and covalent network solid

Answer 48

1. Metal - insoluble in solvents but forms alloys with other molten metals 2. Ionic solids - soluble in H2O and polar solvents 3. Covalent molecular - soluble in nonpolar or polar solvents 4. Covalent network - insoluble in any solvent

Question 49

Electrical conductivity of *metal* in (1) solid, (2) molten, and (3) aqueous forms

Answer 49

1. positive 2. positive 3. N/A

Question 50

Electrical conductivity of *ionic compound* in (1) solid, (2) molten, and (3) aqueous forms

Answer 50

1. negative 2. positive 3. positive

Question 51

Electrical conductivity of *covalent molecular compound* in (1) solid, (2) molten, and (3) aqueous forms

Answer 51

1. negative 2. negative 3. negative

Question 52

Electrical conductivity of *covalent network solid* in (1) solid, (2) molten, and (3) aqueous forms

Answer 52

1. negative 2. N/A 3. N/A