# Additional Science C2 Topic 6

Topic 6

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• Created by: Victoria
• Created on: 14-05-12 19:44

## Atoms

Nucleus
-Middle of the atom
-Protons and Neutrons
-Positive charge

Electrons
-Move around the Nucleus
-Negatively charged

PARTICLE      RELATIVE MASS      RELATIVE CHARGE
Proton                    1                                    +1
Neutron                  1                                      0
Electron                  1/2000                           -1

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## Atomic Number and Mass Number

The mass number is the total number of Neutrons and Protons- Larger number
The atomic number is the number of protons- Smaller number

23
Na
11

To get the number of neutrons you just subtract the atomic number from the mass number. The Mass number is usually roughly double the atomic number.

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## Isotopes and Relative Atomic Mass

Isotopes are different atomic forms of the same element. These have the same number of protons but different numbers of neutrons.

Isotopes must have the same proton number but different mass number. If they had different proton numbers they would be a different element all together.
An Example of isotopes would be:

Carbon 12        Carbon 14
12                     14
C                      C
6                       8

6 Protons          6 Protons
6 Electrons        6 Electrons
6 Neutrons        8 Neutrons

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## The Periodic Table

Vertical Columns- Groups
The group that an element fits in corrosponds to the number of electrons it has in its outer shell. This is why the elements in the same group have similar properties.

Some groups have special names, for example Group 1 are the alkali metals, Group 7 are the halogens and Group 0 are the noble gasses.

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## Electron shells

Electrons always occupy shells.
The shells closser to the nucleus are always filled first. Only a certain amount of electrons are allowed in each shell.
1st Shell :2      2nd Shell :8      3rd Shell :8

Atoms are happier when they have full electron shells. Such as the noble gasses in group 0.
In most atoms the outer shell is not full this is what makes them want to react.

Electron configurations:
The periodic table tells us nitrogen has 7 protons so it must have 7 electrons. the first shell can only take 2 electrons and the second shell can take 8.
The electron configuration of nitrogen must be 2,5.

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## Ionic Bonding

Ionic bonding is when atoms lose or gain electrons to form charged particles these are called ions. These are strongly attracted to each other (because of the attraction between charges + - )

If atoms have a small amount of electrons on their outer shell they will want to get rid of them to make have a full outer shell. Once they have got rid of these electrons they become an ion. They tend to find another ion with the opposite charge and stick together like glue.

A nearly full shell is keen to get an extra electron. This is Group 6 and 7 for example. When they gain these electrons to fill their outer shell they becom an ion. they then stick to each other.

Group 1 & 2 and 6 & 7 are the most likely to form ions.

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## Ionic Compounds

Ionic compounds
'Dot and cross' diagrams show what happens in ionic bonds.

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## Giant Ionic Structures

Ionic bonds always produce giant ionic structures. The ions form a closely packed lattice arrangement. There are always very strong bonds between all the ions.

Giant ionic structures have high melting and boiling points.This is beacuse they have strong bonds between them.

They dissolve to form solutions that conduct electricity. When dissolved the ions seperate and carry an electric current. This is the same when the ions are melted.

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## Metals

Like ionic compounds metals are made of Giant Structures.
Metallic bonds involve 'free electrons' which produce the properties of metals.
These 'free electrons' come from the outer shell of every metal atom in the structure.

The 'free electrons' carry both heat and electrical current. Metals are good conductors of heat and electricity.

Most metals are malleable. The layers of atoms in metal can slide over eachother making them malleable. They can be hammered or rolled into flat sheets.

They usually have high melting and boiling points. Metallic bonds are very strong.

Some metals are hard. Others are soft for example alkali metals.

Metals can be mixed together to make alloys. Alloys changes the properties of metals usually making the metals harder.

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## Electrolysis

Electrolysis means 'splitting up with electricity'
Electolysis is the breaking down of a substance using electricity. It needs a liquid to conduct electricity called the electrolyte.
Electrolytes are usually ionic compunds  that are dissolved in water or melted.
Its the free electrons that conduct this electricity.

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