5. Structures

Question 1

What is NaCl and CsCl coordinate number and Ionic Structure?

Answer 1

NaCl - 6:6
CsCl - 8:8

Ionic solids are giant lattices of positive and negative ions. Cs+ ion is larger than Na+ and therefore more Cl- ions can fit around it

Ionic -
High m.p and b.p - takes a lot of energy to overcome strong electrostatic forces of attraction between oppositely charged ions.

Often soluble in water: The oxygen end of the water molecules is attracted to the positive ions and vice versa for negative ions.

Hard but brittle - When force is applied, layers of ions slide over each other cauing ions of the same charge to be aside each other. Ions repel and the crystal shatters

Poor electrical conductivity when solid but good when molten/dissolved - In solid state ions are fixed in position by strong ionic bonds, however when molten/dissolved the ions are free to move and carry charge.

Question 2

Giant Covalent Solids

Answer 2

Diamond - Each cabron atom is joined to each other with strong covalent bonds

Atoms arrange themselves in a tetrahedral shape making it very hard

Very high melting point - a lot of energy required to break numerous, strong covalent bonds

Does not conduct electricity - no free electrons

Graphite - consists of hexagonal layer. Each carbon is joined to three other by strong covalent bonds.

High m.p - strong covalent bonds

soft and slippery - layers can slider other each others due to the weak forces between them

Good conductor of electricity - delocalised electrons are free to move along the layers

Low Solubility - Composed of atoms which have no charge for water to attract too.

Question 3

Simple Molecular Solids

Answer 3

Atoms are covalently bonded with weak intermolecular forces

Low m.p and b.p - although the covalent bonds within the molecules are strong, the intermolecular forces holding the molecules together are weak

Poor conductors of electricity - No delocalised electrons/ions

Soluble in polar/non polar solvents. Polar substances able to break H bonds between molecules and form new ones.

Question 4

Why is ice less dense than water?

Answer 4

In ice, molecules of water are arranged in rings of six held together by h bonds. In this structure, the water molecules are further apart than they are in the liquid state. Due to the large areas of open space ice is less dense than water (at 0C)

Question 5

Metallic Structure

Answer 5

High m.p and b.p - A lot of energy is needed to overcome forces of attractions is high

Hard - metallic bond is very strong

Good conductors of electricity and heat - delocalised electrons can carry charge/kinetic energy

Malleable and Ductile - When force is applied to a metal, the layers of cations can slider other each other and the delocalised electrons prevents repulsion

Not soluble in water -delocalised elctrons repel water from getting in and accessing metal cations.