C5thebicesterschool.org.uk/wp-content/uploads/2015/...C5 . Overview • Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent

C5

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

The Earth is the source of all our materials.

We get things from:

the atmosphere

the lithosphere

the hydrosphere

Chemicals from the Earth’s spheres

Some of the useful materials we extract from the lithosphere are:

• coal, oil and gas

• aluminium

• zinc

• iron

• copper

• diamond and graphite

• building materials (clay, stone, gravel)

Chemicals from the Earth’s spheres

Chemicals of the atmosphere

Air is a mixture of gases including: • non-metal elements (e.g. N2, O2 and Ar) • compounds between non-metal elements (e.g. CO2). These chemicals are molecular. They have low melting and boiling points, so are gases at normal temperatures.

nitrogen (N2) oxygen (O2) argon (Ar) carbon dioxide (CO2)

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

• Attractive forces between molecules are weak.

• Small molecules are gases or liquids at room temperature.

oxygen (gas)

carbon dioxide

(gas)

attraction between molecules

water (liquid)

• The bonds inside molecules are strong.

• Water molecules do not fall apart when the liquid boils and turns to steam.

water molecule

water molecule

How are the atoms in an H2 molecule held together?

• To picture this you need to look at the structure of a hydrogen atom.

• The positively charged nucleus and the negatively charged electron attract each other.

When two hydrogen atoms approach each other . . .

. . . the electron of one atom and the nucleus of the other atom start to attract each other.

When the atoms are close, the attractions are so strong that a molecule of hydrogen (H2) is formed.

The atoms are held together by the attractions between the two nuclei and the shared pair of electrons. This is a single covalent bond.

Chemists draw a line between element symbols to show a covalent bond.

H—H

hydrogen, H2

O O

oxygen, O2

N N

nitrogen, N2

O C O

carbon dioxide, CO2

H

H—C—H

H

methane, CH4

H H

H—C—C—O—H

H H

ethanol, C2H5OH

O H H

water, H2O

Molecules have a definite shape.

methanol

water ethene

methane

Chemists have different ways of describing molecules.

molecular formula

displayed formula with lines for covalent bonds

ball-and-stick model

space-filling model

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

Sun

evaporation

condensation

rain

rivers

weathering of rocks followed by dissolving of soluble salts

solutions of soluble salts and sediment end up in the sea

+

When NaCl is added to water, the ions are pulled off the crystal structure and they become free to move in the water.

The ions can move independently, so a solution of NaCl in water conducts electricity.

• A sodium chloride crystal is made up of millions of Na+ and Cl– ions arranged in a regular pattern called a crystal lattice.

• The lattice is responsible for the cubic shape of all sodium chloride crystals.

Crystals of sodium chloride

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

Salts are ionic compounds containing positive and negative ions.

Overall the compound has no charge.

The positive and negative charges of the ions in the formula balance.

sodium ion Na+

chloride ion Cl-

+

sodium chloride NaCl

- + -

What is the formula for copper(II) hydroxide?

Cu(OH)2

Copper(II) hydroxide

copper ion Cu2+

hydroxide ion OH-

2+

- 2+ - -

What is the formula for magnesium chloride?

MgCl2

magnesium chloride

magnesium ion Mg2+

chloride ion Cl-

2+

- 2+ - -

What is the formula for calcium sulfate?

CaSO4

calcium sulfate

calcium ion Ca2+

sulfate ion SO4

2-

2-

2+

2+ 2-

What is the formula for calcium carbonate?

CaCO3

calcium carbonate

calcium ion Ca2+

carbonate ion CO3

2-

2-

2+

2+ 2-

What is the formula for iron(III) oxide?

Fe2O3

iron(III) oxide

iron ion Fe3+

oxide ion O2-

3+

2- 3+ 3+ 2- 2- 2-

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

Other giant covalent structures include diamond and graphite.

Diamond has carbon arranged so that each atom is attached to its neighbours by four covalent bonds. This is incredibly tough.

Graphite has carbon atoms arranged in layers. These can easily slip over each other and detach, such as when a pencil line is drawn.

Covalent bonds between carbon atoms in the same layer are strong. Bonds between layers are weak.

Overview

• Spheres of the earth • Covalent Bonding • Dissolving • Precipitation • Ionic formulae • Giant covalent structures

• Now a Quiz!

A B

C D

Which of these four diagrams shows the best picture of the type of structure in . . . nitrogen gas?

A B

C D

Which of these four diagrams shows the best picture of the type of structure in . . . gold?

A B

C D

Which of these four diagrams shows the best picture of the type of structure in . . . silicon dioxide?

A B

C D

Which of these four diagrams shows the best picture of the type of structure in . . . potassium chloride?

A B

C D

Which of these four diagrams shows the best picture of the type of structure in . . . water?