Covalent bonding + properties

Valency

The number of electrons that must be lost, gained or shared in order for the atom to attain a noble gas electronic configuration

Covalent bond

The strong electrostatic forces of attraction between the positive nuclei and negative shared pair of electrons

3 covalent structures

1. Simple (covalent) molecules

2. Giant (covalent) molecules

3. Macromolecules

Simple (covalent) molecular structure

• Particles: molecules

• Bonding: weak intermolecular forces between molecules

• Have a countable number of atoms in a fixed ratio.

• Each molecule have a fixed no. of atoms

Giant (covalent) molecular structure

• Particles: atoms

• Bonding: strong covalent bonds between atoms

• Has practically uncountable number of atoms

• Eg diamond and sand (silicon dioxide)

Macromolecular structure

• Particles: molecules

• Bonding: weak intermolecular forces between polymers

Polymers

consists of many covalent molecules (called monomers) joined together into chains of much larger molecules

Examples of macromolecules

Silk, wool, starch, rubber, cellulose, polyester, nylon

Properties of simple covalent molecules

• Soft

• Does not conductivity in any state

• Low melting & boiling points

• Soluble in organic solvents but not in aqueous solvents

Hardness of simple covalent molecules?

Soft (only for those in solid state at r.t.p.)

Only a small amount of force is needed to overcome the weak intermolecular forces of attraction between molecules

Simple covalent molecules _______ ________ upon dissolving in organic solvent.

remain intact

Electrical conductivity of simple covalent molecules?

Unable to conduct electricity in any state.

There are no mobile ions and electrons (mobile charge carriers) to conduct electricity.

Which solutions (with simple covalent molecules) can conduct electricity?

HCl, NH3, CO2 can dissolve in water to form aqueous solutions with mobile ions. Hence, these solutions can conduct electricity.

Melting & boiling points of simple covalent molecules?

Low.

Small amount of energy is required to overcome the weak intermolecular forces of attraction between molecules.

Properties of giant covalent molecules

• Hard

• Insoluble in aqueous & organic solvents

• Does not conduct electricity in any state

• High melting and boiling points

Hardness of giant covalent molecules?

Hard.

Large amount of force is needed to break the numerous strong covalent bonds between the atoms present throughout the giant covalent molecular structure.

Hardness of graphite (giant covalent molecule)?

Soft and slippery

The layers of carbon atoms are held loosely by weak intermolecular forces of attraction. These layers of carbon atoms can slide each over each other when a force is applied.

Electrical conductivity of giant covalent molecules?

Does not conduct electricity in any state (exception: graphite).

There are no mobile ions and electrons to conduct electricity.

Why can graphite conduct electricity?

Each carbon bonds to 3 other atoms, leaving one unbonded valence electron per carbon atom that is mobile within the layer to conduct electricity.

Cannot conduct electricity between 2 layers.

Melting & boiling points of giant covalent molecules?

:rage amount of energy is required to break the (many strong covalent bonds between atoms)

Properties of macromolecules

• Hardness varies greatly

• Insoluble in aqueous solvent, depends for organic solvents

• Does not conduct electricity in any state High

• Low melting & boiling points (> simple covalent), over a range

Hardness of macromolecules?

Their hardness varies greatly because they exist in so many different combinations of atoms.

The longer/denser the chain of polymers, the harder the macromolecules.

Electrical conductivity of macromolecules?

Do not conduct electricity in any state.

There are no mobile ions and electrons (mobile charge carriers) to conduct electricity.

Melting & boiling points of macromolecules?

Low (but higher than simple molecules), over a range

Small amount of energy is required to overcome the weak intermolecular forces of attraction between polymer molecules.

Melting & boiling points: macromolecules VS simple molecules

Melting & boiling points of macromolecule are higher than that of simple molecules because of the larger polymer chain molecular size, leading to more extensive intermolecular forces of attraction