3.1.3.4 - Bonding and physical properties

Are ionic compound boiling + melting points high/low?

High

What is the state of ionic compounds at room temp + pressure?

Solid

Do ionic compounds conduct electricity when solid?

No (ions held in place)

Do ionic compounds conduct electricity when liquid?

Yes (ions free to move)

Are ionic compounds soluble in water?

Yes

Are simple covalent compound boiling + melting points high/low?

Low (involves breaking intermolecular forces but not covalent bonds)

What is the state of simple covalent compounds at room temp + pressure?

Usually liquid/gas (may be solid like I₂)

Do simple covalent compounds conduct electricity when solid?

No

Do simple covalent compounds conduct electricity when liquid?

No

Are simple covalent compounds soluble in water?

Depends on how polarised molecule is

Are giant covalent compound boiling + melting points high/low?

High

What is the state of giant covalent compounds at room temp + pressure?

Solid

Do giant covalent compounds conduct electricity when solid?

No (except graphite)

Do giant covalent compounds conduct electricity when liquid?

N/A (sublimes rather than melting)

Are giant covalent compounds soluble in water?

No

Are metallic compound boiling + melting points high/low?

High

What is the state of metallic compounds at room temp + pressure?

Solid

Do metallic compounds conduct electricity when solid?

Yes (delocalised electrons)

Do metallic compounds conduct electricity when liquid?

Yes (delocalised electrons)

Are metallic compounds soluble in water?

No

Diamond structure

GIANT COVALENT (macromolecular)

Each C atom covalently bonded to 4 other C atoms, in tetrahedral shape

Diamond properties

Because of strong covalent bonds:

• Very high melting point

• Extremely hard

• Good thermal conductor - vibrations travel easily through stiff lattice

• Can’t conduct electricity - all outer electrons held in localised bonds

• Insoluble in any solvent

Graphite structure

GIANT COVALENT (macromolecular)

C atoms covalently bonded with 3 other C atoms, arranged in sheets of flat hexagons
4th outer electron of each C atom is delocalised

Hexagon sheets bonded together by weak VdW forces

Graphite slipperiness

Slippery (used as dry lubricant; in pencils)

• Weak bonds between layers are easily broken, so sheets slide over each other

Graphite electrical conductivity

Good electrical conductor

• Delocalised electrons free to move along sheets, carrying charge

Graphite density

Low density (used for strong, lightweight sports equipment)

• Layers far apart compared to length of covalent bonds

Graphite melting point

High melting point

• Strong covalent bonds

Graphite solubility

Insoluble in any solvent

• Covalent bonds too strong to break

Ice

SIMPLE MOLECULAR

As liquid water cools to form ice, molecules make more H bonds and arrange themselves into regular lattice structure

In regular structure, H₂O molecules are further apart than molecules in liquid water

→ ice less dense than water

Iodine

SIMPLE MOLECULAR

Solid at room temp.

VdW forces between iodine molecules hold them together in lattice

• Iodine atoms held together in pairs by strong covalent bonds to form I₂ molecules

• Molecules held in molecular lattice by weak VdW attractions

Magnesium structure

METALLIC

• Outer shell is delocalised - electrons free to move around metal
  → leaves +ve metal ion, e.g. Mg²⁺

• +ve metal ions attracted to delocalised sea of electrons, forming lattice

Metal melting points

High melting points

• Strong electrostatic attraction between +ve metal ions + delocalised sea of electrons

  • More delocalised electrons per atom → stronger bonding → higher melting point

Metal thermal conductivity

Good thermal conductors

• Delocalised electrons can pass KE to each other

Metal solubility

Insoluble

• Metallic bonds are strong

NaCl ionic lattice

Na⁺ + Cl⁻ ions packed together in cube shape

Ionic compound solubility in water

Dissolve in water

• Water molecules are polar - one part has slight -ve charge, one part has slight +ve charge

  • Charged parts pull ions away from lattice, causing it to dissolve