CHEM BONDING

Question 1

Describe the structure of an ionic compound

Answer 1

A giant lattice structure consisting of oppositely-charged ions arranged in a regular pattern

Question 2

Describe an ionic bond ITO (In terms of) EFOA (Electrostatic forces of attraction)

Answer 2

The electrostatic force of attraction between oppositely-charged ions

Question 3

Factors affecting strength of ionic bond

Answer 3

(i) Magnitude of charge > (ii) interionic distance

Question 4

Why are ionic compounds hard but brittle

Answer 4

A strong force is needed to overcome EFOA between oppositely-charged ions.
As oppositely-charged ions are arranged in regular pattern, displacing a layer of ions relative to another causes ions of similar charge to come together, losing EFOA.

Question 5

Why are ionic compounds soluble in polar solvent but insoluble in non-polar solvents.

Answer 5

Ion-dipole interactions formed in polar solvents release sufficient energy to overcome forces of attraction between polar solvent molecules and ionic bonds.
Opposite is true in non-polar solvents.

Question 6

What classes of covalent substances are there

Answer 6

(i) Giant molecular substancr

(ii) Simple molecular substance

Question 7

Describe covalent bond ITO EFOA

Answer 7

A covalent bond is the strong EFOA between 2 positive nuclei and a shared pair of electrons

Question 8

Describe structure of a giant molecular substance

Answer 8

It consists of atoms held by strong EFOA between their positively-charged nuclei and shared pair of electrons arranged in a 3-dimensional network

Question 9

Why are simple molecules soluble in non polar solvents

Answer 9

IMF formed with molecules of non-polar solvents release enough energy to overcome IMF of solvent molecules and the molecules

Question 10

What does bond length refer to

Answer 10

Distance between the 2 positive nuclei in a covalent bond

Question 11

What is a sigma bond

Answer 11

A sigma bond refers to a covalent bond formed due to head-on orbital overlap

Question 12

What is a pie bond

Answer 12

A pie bond refers to a covalent bond formed due to sideways-orbital overlap, which can only be formed after the atoms involved have formed a sigma bond

Question 13

What is a dative bond

Answer 13

A dative bond is a covalent bond formed when an atom donates an available lone pair of electrons to an atom with an accessible empty orbital

Question 14

What is a dimer

Answer 14

A dimer refers to a molecule consisting of a molecule bonded to an identical molecule

Question 15

What is a transition metal complex ion

Answer 15

A transition metal complex ion is a transition metal ion able to be bonded to ligands due to the vacant low-lying d-orbitals in the transition metal ions

Question 16

What are the factors determining covalent bond strength

Answer 16

(i) number of bonds

(ii) effectiveness of orbital overlap

Question 17

Why do longer bond lengths lead to weaker covalent bonds

Answer 17

Longer bond length leads to more diffuse orbitals, which leads to less effective orbital overlap, and thus a weaker EFOA between positive nuclei

Question 18

What are the 5 steps in making a ‘dot-and-cross’ diagram

Answer 18

1. Find central atom
2. Find out number of valence electrons present in the atoms involved
3. Find out number of bonds needed for each atom to achieve stable conf.
4. Draw out the lone pairs of electrons in central and surrounding atoms
5. Ensure all atoms achieve octet configuration (or duet for hydrogen)

Question 19

How do you find out which atom is the central atom in a ‘d-n-c’ diagram

Answer 19

The least electronegative atom

Question 20

What are the exceptions of the octet configuration (aside from hydrogen)

Answer 20

(i) electron-deficient
(ii) radicals
(iii) expanded shells

Question 21

What is the first postulate of VESPR theory

Answer 21

The first postulate states that the electron pairs arround the central atom are arranged as far apart as possible, in space to minimise repulsive forces between electron pairs

Question 22

What is the second postulate of the VESPR theory

Answer 22

The second postulate states that the repulsion between lone-pair - lone-pair electrons are greater than in lone-pair - bond-pair electrons which is in turn greater than in bond-pair - bond-pair electrons.

Question 23

What is the third postulate of the VESPR theory

Answer 23

The third postulate is that repulsion between bond-pair of electrons increases with an increase in the electronegativity of the central atom

Question 24

What does the first postulate tell us about the basic shape of a molecule or ion

Answer 24

The first postulate tells us that the number of electron-pairs surrounding the central atom determines the basic shape of the molecule or ion. Additionally, the electrons in a multiple bonds are regarded as a single region of electron cloud as the electrons are localised between the atoms involved in the covalent bond.

Question 25

What does the second postulate of VESPR tell us about the bond angles

Answer 25

The second postulate tells us that when a lone pair is present, the greater repulsive force exerted on adjacent bond-pairs would in turn cause a compression of bond angle

Question 26

What does third postulate of VESPR theory tell us about bond angles

Answer 26

The third postulate tells us that when a more electronegative central atom is present, the electron cloud would be pulled in towards the atom to a greater extent, and hence result in a greater repulsive force experienced between bond-pairs as they are closer to each other. Hence bond angle is higher.