4. Models of Bonding and Structure // S2.1, S2.2

Ionic compounds

Formed when electrons are transferred from one atom to another

Forms ions with complete valence shells

The cations and anions are attracted to each other by strong electrostatic forces

Have high melting opints

Naming binary ionic compounds

Cation first, Anion second, add -ide suffix

Covalent bonds

Sharing one or more pairs of electrons so each atoms achieves a noble gas configuration

Coordinate bonds

Both shared electrons come from the same atom

2 Electron domains

Linear, 180°

3 electron doains

Trigonal planar, 120°'

bent or V-shaped (smaller than 120°)

4 electron domains

Tetrahedral, 109.5°

Trigonal pyramidal, 107°

Bent, or V-shaped 105°

Differences in single, double. triple bonds

The more bonds in one, the shorter and stronger

Boiling point

Liquid to gas

All attractive forces between particles are broken

Good indication of the strength of intermolecular forces

Melting point

Crystal structure is broken down, but attractive forces between particles exist

Impurities impact

Impact structure and result in lower melting points

Diamond properties

Each carbon covalently bonded to four others

Giant tetrahedral diamond structure'

109°

1.54/10¹⁰ m long lengths.

All electrons are localized = Doesn’t conduct electricity

All bonds equally strong, so hard to break and high melting point

Graphite

Each Carbon is bonded to three other carbons

Layers of hexagonal rings

120°

1.42/10¹⁰ m

Weak attractive forces between layers = layers slide over each other = lubricant and waxy feeling

Between layers, electrons are delocalized = Good conducter of electricity

Graphene

One atom thick layer of Graphite

Extremely light

Semiconductor

200 times stronger than steel

Fullerenes

Large spheroidal molecules = hollow cage of sixty or more carbon atoms.

E.g. Buckminsterfullerene C₆₀

Hexagons and pentagons → geodesic spherical structure similar to a football

Silicon

1. Giant tetrahedral covalent structure like diamond.

2. Si-Si bond length is 2.32x10-10 m

3. hard brittle solid

4. high melting point

5. metalloid

6. semiconductor.

Silicon dioxide (silica)

SiO₂, quartz

Giant tetrahedral covalent structure similar to diamond and silicon.

Very hard and has a high melting point.

No delocalized electrons = does not conduct electricity.

unipositive cation

positively charged ion with a charge +1

Bond polarity

More electronegative atoms exert greater attraction for electron pair(s)

One end of the bond will be more electron rich, resulting in bond dipole (polar bond)

Put number behind the atom with positive pole for how many bonds its pulling electrons with. E.g. NH₃ would have Nitrogen with 3§+

Shape can also cause polarity.

Allotropes

Element can exist in different crystalline forms.

Different bonding and structural patterns, thus different chemical and physical properties

Intermolecular forces

Van Der Waals Forces

London Dispersion Forces

Dipole-Dipole Forces

Hydrogen Bonds

Van Der Waals Forces

More inclusive term for intermolecular forces where a temporary dipole occurs between both polar and non-polar molecules

London Dispersion Forces (LDP)

Temporary instantaneous dipole, which can induce another dipole in a neighbouring particle, resulting in a weak attraction between the two particles.

Increase with increasing mass.

Dipole-Dipole Forces

Polar molecules are attracted to each other by electrostatic forces.

Relatively weak, but the attraction is stronger than London dispersion forces.