(U1) Structure

Question 1

How are ionic compounds structured?

Answer 1

• Arranged in a Giant ionic lattice,
• where the electrostatic forces of attraction hold the ions in rows
• on every side of each ion there is an oppositely charged ion

Question 2

What are the physical properties of ionic compounds? (3)

Answer 2

• high m.p. And b.p.
• only conduct electricity when molten or in solution
• physically hard

Question 3

What is the co-ordination of the lattice of NaCl?

Answer 3

6-6 co-ordination

Question 4

What are allotropes? (3)

Answer 4

• different forms
• of the same element
• in the same physical state

Question 5

Name 3 allotropes of carbon.

Answer 5

• diamond
• graphite
• graphene

Question 6

What are the physical properties of Ionic compounds? (5)

Explain each in detail

Answer 6

1. High m.p and b.p:

• The bonds within the ions are extremely strong
• need a substantial amount of energy to break the strong bonds

2. Soluble in water:

• Ionic solids are dipolar
• attracted by polar water molecules

3. Good conductors of electricity and heat when molten or in solution:

• the ions are free to move and carry charge.
• When dissolved, ionic compounds such as sodium chloride can cause aqueous solutions to boil faster

4. Physically brittle:

• pressure causes a layer to shift

5. Insoluble in organic solvents

• attraction between solvent molecules and ions weaker than ionic bonds

Question 7

Describe the structure and bonding in diamond

What are the physical properties of diamond? (4)

Explain each

Answer 7

1. • Each carbon atom makes 4 strong covalent bonds
   • Tetrahedral structure (3d giant covalent)
2. • high m.p and b.p - substantial amount of energy required to break covalent bonds
   • No electrical conductivity - all electrons involved in bonds
   • physically hard - substantial amount of force required to overcome covalent bonds
   • insoluble in water and organic solvents - no attractions can be stronger than the covalent bonds

Question 8

Describe the structure and bonding in graphite

What are the physical properties of graphite? (5)

Explain each

Answer 8

• giant covalent structure
• hexagonal layers separated by Van der Waals forces
• each carbon bonds 3x - 1 free electron per each carbon

• good conductor of electricity - delocalised electrons free to move and carry a charge
• high m.p and b.p - substantial amount of energy required to break covalent bonds
• physically brittle - small amount of force required to overcome Van der Waals
• lower density than diamond - ‘wasted space’ between sheets
• insoluble in water and organic solvents - covalent bonds stronger than any other possible attraction

Question 9

What are the physical properties of molecular covalent structures? (5)

Explain.

Answer 9

1. low m.p and b.p:

• non-substantial amount of thermal energy required to overcome Van der Waals

2. Usually soft and brittle:

• Van der Waals easily overcome by force

3. Insoluble in water:

• hydrogen bonds are stronger than bonds formed with molecular covalent structures

4. Soluble in organic liquids:

• non-polar organic liquids have weak intermolecular forces
• iodine crystals can penetrate the liquid and dissolve

5. Never conduct electricity:

• all electrons used in covalent bonds
• no ions
• therefore can’t carry a charge

Question 10

What are metallic, ionic, covlent and dative covalent bonds examples of?

Answer 10

Intra-molecular forces

Question 11

What are the physical properties of metallic compounds? (4)

Answer 11

• malleable and ductile - pressure can cause layers of cations move over each other, bonds reform
• physically hard - strong force of attraction between cations and electrons requires a substantial amount of force to overcome
• high m.p. and b.p. - attraction requires a substantial amount of thermal energy to overcome
• electrical conductivity - delocalised electrons free to move and carry a charge