Unit 9

Question 1

Giant ionic structure

Answer 1

Sodium chloride (ionic compound) —> sodium ions and chloride ions packed together in a regular arrangement called a lattice

Question 2

Ionic compounds (properties + explanation)

Answer 2

1. Hard but brittle
   Hard: relative motion of the ions is restricted by the strong ionic bonds between the ions
   Brittle: an ionic compound is a lattice of alternating positive and negative ions. When an external force is applied, the layers of ions may move relative to each other. This can bring ions of the same charge close to each other and result in repulsion between the ions. Thus, the lattice splits.
2. High melting points and boiling points
   They have giant ionic structure. They have strong ionic bonds between the ions with opposite charges. In order to melt and boil ionic compounds, lots of front ionic bonds Beeren the ions have to be overcome. It takes a lot of heat, so ionic compounds have high melting point and boiling point.
   all ionic compounds are crystalline solids at room temperature and pressure
   melting point increases with strength of attraction between particles
3. Usually soluble in water
   calcium carbonate is insoluble in water because the ionic bonding within the lattice is stronger than the attraction between the ions and the water molecules
   - Water molecule: the oxygen atom has a greater attraction for electrons in bonds than the hydrogen atoms, this makes one end of the molecule slightly negative and the other end slightly positive
   NaCl —> the partial negative charge of oxygen atoms attract the negative chloride ions sufficiently to remove them from the lattice. The sodium ions then become surrounded by water molecules. The partial positive charge on hydrogen of the water molecules attractive the negative chloride ions sufficiently to r of them from the lattice. The chloride ions then become surrounded by water molecules as well.

usually insoluble in non-aqueous solution: any solvent other than water, eg. Cyclohexane
—> ionic bonding within the lattice is stronger than the attraction between the ions and the solvent molecules. The solvent molecules cannot pull the ions out of the lattice.

4. Conduct electricity when molten or dissolved in water
   Do not conduct electricity in solid Tate —> ions are fixed in position and are not free to move around
   —> when it is melted , ions can move freely throughout the liquid. When electricity is passed through the molten compound, cations move towards a positive electrode, so allowing the conduction of electricity.
   molten/aqueous —> ions are free to move and mobile, allowing the conduction of electricity

Question 3

Solubility

Answer 3

In order for a substance to dissolve in a solvent, the following two conditions must be met:
- the attractive forces between its particles and the solvent particles are strong enough to overcome the attraction forces between particles in the pure substance
- particles in the substance must separate from each other and become surrounded by the solvent particles

Question 4

Electrical conductivity (2 requirements)

Answer 4

It must contain charged particles and these particles must be mobile, free to move.

Question 5

ONLY these giant covalent structure would be tested

Answer 5

Diamond, graphite , quartz (silicon dioxide)

Question 6

Allotropes (DEFINITION)

Answer 6

different forms of the same element (like graphite and diamond)

Question 7

DIAMOND (giant covalent structure)

Answer 7

Each carbon atom is covalently bonded to four neighbouring carbon atoms.
All the carbon atoms are arranged tetrahedrally. The strong covalent bonds extend in all directions throughout the structure.

Question 8

GRAPHITE (Giant covalent structure)

Answer 8

-carbon atoms are arranged in flare layers.
-there are billions of carbon toms arranged in hexagons.
-each carbon atom is covalently bonded to three neighbouring carbon atoms, so very layer has a giant covalent structure.
-only weak Van Der Waals’ force exist between the layers of carbon atoms.
one layer of carbon atoms —> graphene
-with 3 covalent bonds formed between carbon atoms

Question 9

SILICON DIOXIDE (quartz) GIANT COVALENT STRUCTURE

Answer 9

Quartz: a mineral that contains mainly silicon dioxide
Each silicon ago is bonded to four oxygen atoms while each oxygen atom is bonded to only two silicon atoms. Silicon atoms and oxygen atoms in the whole structure are held together by strong covalent bonds.

Question 10

Giant Covalent Structure (properties + explanation)

Answer 10

1.They are very hard (except graphite)
- Hard: strong covalent bonds extend throughout the structure. Relative motion of the atoms is restricted.
**makes the substances very hard and useful as abrasives

2. Very high melting points
   - it has a giant covalent structure.
   - There are a lot of strong covalent bonds between the atoms and need a lot of heat to break.
3. Insoluble in water or non-aqueous solvents
   - attraction between the atoms and solvent molecules is not strong enough to overcome the strong covalent bonds to hold the atoms together.
4. Do not conduct electricity (except graphite)
   - no mobile electrons or ions as all of the outermost shell electrons are either held by bindividual atoms or used to form covalent bonds.

Question 11

Simple molecular structure (examples)

Answer 11

Nitrogen, hydrogen, oxygen halogens in group VII, ammonia, water and carbon dioxide

Question 12

Simple molecular substances (general infromation)

Answer 12

They have strong covalent bonds joining their atoms within each molecule. However, only weak attraction forces exist among the molecules

Question 13

IODINE (SIMPLE MOLECULAR STRUCTURE)

Answer 13

It is a black crystalline solid. It contains a regular arrangement of iodine molecules held closely together by weak van der Waals’ force.

Question 14

DRY ICE (Simple molecular structure)

Answer 14

• for carbon dioxide molecule, strong covalent bonds hold the carbon atom and oxygen atoms together. Dry ice contains a regular arrangement of carbon dioxide molecules held closely together by weak can der Waals’ forces.

Question 15

Simple molecular substances (properties + explanation)

Answer 15

1. Soft if they are solids
   - due to weak attractive forces (van der Waals’ forces) among the molecules
   - it is easy to break the solid
2. Low melting points and boiling points
   -It has simple molecular structure.
   - only weak attractive forces moon molecules are needed overcome when simple molecular substances are melted or boiled
3. Are often slightly soluble or even insoluble in water but soluble in non-aqueous solvent
4. Do not conduct electricity