Chapter 5: Chemical Bonding

Question 1

1st Exception to the Octet rule

Answer 1

Transition metals do not usually obey the octet rule. In many of their compounds transition metals can have more or fewer than eight electrons in their outermost energy level.

Question 2

2nd Exception to the Octet Rule

Answer 2

The elements near helium (hydrogen, lithium and beryllium) tend to achieve the electron arrangement of helium with two electrons in the outer energy level rather than the eight electrons of the other noble gases.

Question 3

Characteristics of transition metals

Answer 3

1) Transition metals have variable valency.
2) Transition metals usually form coloured compounds.
3) Transition metals are widely used as catalysts.

Question 4

Characteristics of Ionic compounds

Answer 4

1) Contain a network of ions in the crystal.
2) Usually hard and brittle.
3) Have high melting points and boiling points.
4) Usually solid at room temp.
5) Conduct electricity in a molten state or when dissolved in water.

Question 5

Characteristics of covalent compounds

Answer 5

1) Contain individual molecules.
2) Usually soft.
3) Have low melting points and boiling points.
4) Usually liquids, gases or soft solids at room temp.
5) Do not conduct electricity.

Question 6

Compound

Answer 6

A compound is a substance that is made up of two or more different elements combined together chemically.

Question 7

The Octet rule

Answer 7

The octet rule states that when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost energy level.

Question 8

Ion

Answer 8

An ion in a charged atom or group of atoms.

Question 9

Ionic Bond

Answer 9

An ionic bond is the force of attraction between oppositely charged ions in a compound. Ionic bonds are always formed by the complete transfer of electrons from one atom to another.

Question 10

Crystal lattice

Answer 10

A crystal lattice is a three dimensional arrangement of ions.

Question 11

Transition metal

Answer 11

A transition metal is one that forms at least one ion with a partially filled d sublevel.

Question 12

Molecule

Answer 12

A molecule is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently.

Question 13

Valency

Answer 13

The valency of an element is defined as the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines.

Question 14

Sigma bond

Answer 14

A sigma bond is formed by the head- on overlap of two orbitals.

Question 15

Pi bond

Answer 15

A pi bond is formed by the sideways overlap of p orbitals.

Question 16

Electronegativity

Answer 16

is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.

Question 17

Polar covalent bond

Answer 17

A polar covalent bond is a bond in which there is unequal sharing of the pair(or pairs) of electrons. This causes one end of the bond to be slightly positive (δ +) and the other end slightly negative (δ -).

Question 18

Pure covalent bond

Answer 18

There is equal sharing of the two electrons in the covalent bond.

Question 19

Uses of electronegativity values

Answer 19

1. To predict the polarity of covalent bonds.
2. To predict which compounds are ionic and which are covalent.

Question 20

How to predict which compounds are ionic and which are covalent.

Answer 20

> 1.7 = Ionic bonding
≤ 1.7 = Covalent bonding
0.4 < Polar covalent bonding < 1.7
≤ 0.4 = Pure covalent bonding

Question 21

Intramolecular bonding

Answer 21

Intramolecular bonding is bonding that takes place within a molecule. Covalent bonding and polar covalent bonding are examples of intramolecular bonding.

Question 22

Intermolecular forces

Answer 22

Intermolecular forces are the forces of attraction that exist between molecules. Van der waals forces, dipole- dipole forces and hydrogen bonding are examples of intermolecular forces

Question 23

Van der Waals forces

Answer 23

Van der Waals forces are weak attractive forces between molecules resulting from the formation of temporary dipoles. They are the only forces of attraction between non - polar molecules.

Question 24

Boiling points of hydrogen and oxygen are 20.0 k and 90.2 k respectively. Account for the higher boiling point of oxygen:

Answer 24

Since both of these molecules are non- polar, the intermolecular forces are Van der Waals forces. The strength of Van der Waals forces increases as the molecules get bigger. Oxygen is a bigger molecule than hydrogen. Therefore, the Van der Waals forces are stronger between oxygen molecules than between hydrogen molecules. Therefore, it takes more energy to break the Van der Waals forces in oxygen than in hydrogen.