Atomic Structure

Atoms are made out of: Protons Neutrons & Electrons These are known as subatomic particles

Atomic Structure Subatomic particles have charge Protons are positive (+) Neutrons are neutral (0) Electrons are negative (-)

Atomic Structure A 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 Structure Note 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 atomisotopes

Atomic Structure The electrons have particular orbits called shells. Only a maximum of two electrons can ever exist in the first shell

Atomic Structure Only a maximum of eight electrons can ever exist in the second shell. The outside shell is special and is called the Valence shell

Atomic Structure As 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 numberNumber of electrons Shell Name n1234..n n 2 KLMNKLMN But there is a catch..the valence shell (outside shell) can only ever have a maximum of eight electrons.

Atomic Structure Example: 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 11 th electron goes into the 3 rd 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 19 th and 20 th electron go into the 4 th shell even though the 3 rd 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?