Atomic Structure

Atomic StructureAtoms are made out of:

Protons

Neutrons &

Electrons

These are known as subatomic particles

Atomic StructureSubatomic particles have charge

Protons are positive (+)

Neutrons are neutral (0)

Electrons are negative (-)

Atomic StructureA neutral atom must have the same number of protons and electrons so the +ve and –ve cancel each other out

Lithium has 3 electrons and 3 protons

Atomic StructureNote the number of neutrons in the nucleus does not have to be the same. In fact the same atom can have different number of neutrons in the nucleus.

Different numbers of neutrons in the same type of atom are called isotopes of that atom

Atomic StructureThe electrons have particular orbits called shells.

Only a maximum of two electrons can ever exist in the first shell

Atomic StructureOnly a maximum of eight electrons can ever exist in the second shell.

The outside shell is special and is called the Valence shell

Atomic StructureAs the numbers of protons (and thus electrons) increase the third shell fills, it can have a maximum of 18 and the fourth, 32. This follows a pattern:

Shell number Number of electrons

Shell Name

1234..n

28

1832..

2n2

KLMN

But there is a catch..the valence shell (outside shell) can only ever have a maximum of eight electrons.

Atomic StructureExample: Oxygen has eight protons (and so eight electrons)

The first shell can only have two electrons so oxygen has two electrons in the first shell and six in the second and we would write this electron configuration as 2,6

Atomic Structure

Because the second shell can not have more than eight the 11th electron goes into the 3rd shell.

Example: Sodium has 11 protons (and so 11 electrons)

Electron configuration: 2,8,1

Atomic Structure

Because the outer (valence) shell can not have more than eight, the 19th and 20th electron go into the 4th shell even though the 3rd is not full

Example: Calcium has 20 protons (and so 20 electrons)

Electron configuration: 2,8,8,2

What is the electron configuration of this atom?

Count the number of electrons in each shell. Do they follow the pattern? What element is it?