Atoms combining. Plan.

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N Topic Source

1 4.1. Compounds, mixtures and chemical change

pp. 46-48, Complete Chemistry for Cambridge IGCSE.

2 Separating a mixture. Paper chromatography.

http://www.youtube.com/watch?v=J8r8hN05xXk

3 Paper chromatography question http://www.scienceprojectlab.com/science-methods-and-techniques-chromatography.html

4 4.2. Why do atoms form bonds? pp. 48-50

5 4.3. The ionic bond pp. 50-52

6 4.4. More about ions pp. 52-54

N Topic Source

7 4.5. The covalent bond pp. 54-56

8 4.6. Covalent compounds pp. 56-58

9 4.7. Comparing ionic and covalent compounds

pp. 58-60

10 4.8. Giant covalent structures pp. 60-62

11 4.9. The bond In metals pp. 62-64

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4. Atoms combining.Introduction.

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In this presentation you will learn:

1) The difference between compounds and mixtures.

2) Why atoms combine.

3) How atoms form compounds.

4.1. Compounds, mixtures and chemical change

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Element Compound Formula

One type of atom Atoms of different elements bonded together

Symbols that describe the compound

Compound vs mixture

Separating mixtures. Paper Chromatography.

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Paper chromatography question

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4.1. Compounds, mixtures and chemical change

The signs of chemical change (=chemical reaction) :

1) New substances are formed.

2) Energy is taken in or given out.

3) Change is difficult to reverse.

Chemical vs physical change

4.2. Why do atoms form bonds?

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Why does it happen?

Atoms bond with each other in order to gain a stable arrangement of outer-shell electrons, like the atoms of Group 0.

Reminder: Draw half-reactions for Na and Cl

4.3. The ionic bond.

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The bond between two oppositely charged atoms is called ionic bond.

Here is a bonding diagram for sodium and chlorine:

4.4. More about ions.

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4.4. More about ions.

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Some metals form more than one type of ion.

There are also ions that contain more than one atom – compound ions.

4.5. The covalent bond.

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Covalent bond is formed by non-metals when they share outer-shell electrons to gain stable outer shells.

H-H

Cl-Cl

O=O

Molecule

4.6. Covalent compounds.

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The shapes of the molecules.

Water Methane

4.7. Comparing ionic and covalent compounds.

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4.7. Comparing ionic and covalent compounds.

Ionic compounds Covalent compounds

High melting and boiling points Low melting and boiling points

Usually soluble in water Tend to be insoluble in water

Conduct electricity when melted or dissolved in water

Do not conduct electricity

4.8. Giant covalent structures.

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The hardest substance on earth.Doesn’t conduct electricity.

4.8. Giant covalent structures.

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Unlike diamond it is soft. Conducts electricity. Diamond and graphite are allotropes of carbon.

4.9. The bonding in metals.

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Metals must be giant structures too.

4.9. The bonding in metals.

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Some key properties of metals:

1) Usually have high melting points (but there are exceptions).

2) Metals are malleable and ductile.

3) Metals are good conductors of heat.

3) Metals are good conductors of electricity.