Ionic Molecular Bonding

Question 1

What is the Aufbau Principle?

Answer 1

That each electron in ground states occupy orbitals in order of increasing energy level

Question 2

Explain the Pauli Exclusion Principle:

Answer 2

An orbital cannot hold more than two electrons and electrons occupying orbital must have opposite spins

Question 3

Explain Hund’s rule:

Answer 3

Orbitals in a subshell must be occupied signly with parallel spins before they can be occupied in pairs

Question 4

Why does atomic radii increase down the group?

Answer 4

As number of protons increase, effective nuclear charge increases. Down the group, increases by one electron shell, thus shielding effect increases. Shielding effect increases more than effective nuclear charge, resulting in nucleus exerting weaker pull on valence electrons

Question 5

Why does atomic radii decrease across a period?

Answer 5

Nuclear charge increases due to increase in number of protons, resulting in stronger electrostatic forces of attraction between nucleus and valence electrons, while shielding effect remains relatively constant. Outermost electrons pulled closer to the nucleus

Question 6

What are physical properties of ionic compounds?

Answer 6

High melting and boiling points, soluble in water, conducts electricity in molten and aqueous state and is hard, rigid and brittle

Question 7

What is the formula for lattice energy?

Answer 7

Product of charges / Sum of ionic radii

Question 8

Explain why ionic molecules are soluble in water:

Answer 8

Each ion on the crystal’s surface attract oppositely charged poles of polar water molecules. Ion dipole interactions result in the ions being hydrated, which releases energy, and results in ionic crystal structure breaking down and solid dissolving

Question 9

Why do ionic compounds not conduct electricity in their solid states?

Answer 9

The ions are fixed in positions and aren’t free to move in molten and aqueous solutions. In molten and aqueous solutions, ions are mobile acting as charge carriers

Question 10

Why are ionic compounds brittle?

Answer 10

When sufficient pressure is applied, ions of like charge are brought next to each other, and the repulsive forces crack the salt suddenly

Question 11

Describe metallic bonding:

Answer 11

Has a giant metallic lattice containing array of ions, with sea of delocalised electrons that are bonded to the cation.

Question 12

Why do metals conduct electricity?

Answer 12

Delocalised electrons in the metallic lattice act as charge carriers to conduct electricity

Question 13

Why are metals good conductors of heat?

Answer 13

The delocalised electrons in metal disperse the heat quickly from region of higher temperature to lower. More energetic electrons collide and speed up the slower less energetic molecules

Question 14

Why are metals malleable and ductile?

Answer 14

When external force applied, layers of metal ions slide past one another. Although shape changes, metal does not break because sea of electrons prevents repulsions among cations

Question 15

Why are alloys harder?

Answer 15

Alloying makes metals harder as atoms of added metal have different size, which will disrupt the orderly arrangement of metal atoms that can no longer slide over each other.

Question 16

What is band length?

Answer 16

Distance between 2 nuclei when the covalent bond is formed

Question 17

What are the different types of bonds in covalent bonds and their shapes?

Answer 17

Sigma and Pi bonds. Sigma bonds (only p or d orbitals) is round and head on overlap, whereas bonds are shaped like a hourglass and have side on overlap

Question 18

Define Electronegativity.

Answer 18

Relative ability of atom to attract the shared electrons in a covalent bond

Question 19

What are the criteria for electron-deficient molecules or expansion of octet?

Answer 19

Only central atom is allowed to have fewer or more than 8 electrons (ie. peripheral atoms must have full octet). Only atoms with period 3 onwards can have expansion of octet, as they have vacant d-orbitals.

Question 20

What are radicals/odd electron species and their characteristics?

Answer 20

They are molecules that contain an odd number of valence electrons, and extremely reactive. Usually have group 5 or 7 as the central atom. Examples: ClO2, NO2

Question 21

What are dative/coordinate bonds?

Answer 21

They are bonds formed when one atom donates a lone pair to another atom with a vacant orbital. Denoted by arrow in Lewis Structure. Usually formed between electron deficient species and molecule with lone pair

Question 22

What are the names for bonds between 2, 3 and 4 electron groups without lone pair?

Answer 22

2 electron groups: Linear (eg. CO2)
3 electron groups: Trigonal Planar (eg. CO3)
4 electron groups: Tetrahedral (eg. CH4)

Question 23

What are the names for bonds between 2, 3 and 4 electron groups with lone pair?

Answer 23

2 bonds/1-2 lone pair: Bent/V shaped (eg. SO2, H2O)

3 bonds/1-2 lone pair: Trigonal Pyramidal (eg. NH3)

Question 24

What is delta minus and delta plus?

Answer 24

Delta minus denotes a partial negative charge due to the build up of electron density around the more electronegative atom, whereas delta plus acquires a partial positive charge.

Question 25

What are non-polar and polar bonds?

Answer 25

In non-polar bonds, electrons are shared equally (eg. Cl2), with net-dipole charge of 0. Whereas in polar bond, there is unequal sharing of bonding electrons due to differences in electronegativity of atoms (eg. HCl)

Question 26

Which covalent molecules have partial ionic character?

Answer 26

A polar covalent bond is said to have partial ionic character.

Question 27

What are ionic bonds with covalent character?

Answer 27

These molecules are ones with have large different in polarising power. The attraction on the anion’s electron cloud may be strong enough to distort it such that there is partial sharing of electrons from the covalent bond

Question 28

What is polarity?

Answer 28

Polarity is the separation of positive and negative charge

Question 29

What is Fajan’s Rules?

Answer 29

1. Bonding tends to be covalent if the charges on both cation and anion are large.
2. Bonding tends to be covalent if the cation is small and the anion is large.

Question 30

What intermolecular forces exist between polar molecules?

Answer 30

Hydrogen Bonds (strongest, 5% covalent bond), permanent dipole permanent dipole (pdpd) interactions (1% covalent bond)

Question 31

What intermolecular forces exist between non-polar molecules?

Answer 31

Dispersion Forces

Question 32

What factor affects PDPD interactions?

Answer 32

1. Dipole moment (greater the dipole moment, stronger the pdpd interactions)

Question 33

What are the criteria for hydrogen bonding?

Answer 33

1. Hydrogen atom bonded to either N, O or F molecules

2. Lone pair present

Question 34

Describe the formation of dispersion forces:

Answer 34

In an atom, since the electrons are constantly moving, it sometimes results in an instantaneous (temporary) dipole as electron cloud becomes distorted. This can induce a dipole in neighboring molecule, and the electrostatic forces of attraction between the fluctuating dipoles are called dispersion forces

Question 35

What are the factors affecting dispersion forces?

Answer 35

1. Size of electron cloud (measure of the ease which electron cloud can be polarized, thus the greater electron cloud size, stronger the dispersion forces)
2. Molecular Shape (when a molecule has higher surface area, it allows for more points of contact for polarizability, allowing for stronger forces)

Question 36

What are covalent molecules soluble in?

Answer 36

Covalent molecules are soluble in organic solvents such as propanone, benzene. Only some are soluble in water.

Question 37

Describe the covalent bonding in Diamond:

Answer 37

1. Giant molecular structure, 3D covalent network

2. Each C atom tetrahedrally bonded to 4 other C atoms

Question 38

Describe the covalent bonding in Graphite:

Answer 38

1. Giant molecular structure, 3D covalent network
2. Made of individual flat layers of carbon atoms arranged hexagonally
3. Each carbon atom is bonded to 3 other carbon atoms
4. Fourth valence electron delocalised throughout the layer, overlapping with each other sideways to form pi bonding throughout sheet of atoms
5. Dispersion forces between the layers