3.1 atomic structure and the periodic table.

All mater are made from atoms. Atoms are made from:

• protons(nucleus)
• neutrons(nucleus)
• electrons(shells)

Relative charge and mass of particles in an atom

In an atom, the number of the electrons and protons are the same.

electrons fill shells around the nucleus.

The electrons start filling the inner electron shell closest to the nucleus first. only once this shell is full can the electrons start filling the next, further away shell from the nucleus.

1st shell holds 2 electrons.

2nd and 3rd shell hold upto 8

symbols of elements

all elements are denoted by a symbol which is one or two letters. The first letter is always upper case, and the second if there is one is lower case.

example : hydrogen = H, sodium = Na, chlorine+Cl

proton and nucleon Number

two numbers are associated with the elements in the periodic table.

The larger one is usually at the top and is nucleon/ mass number.
The smaller one is usually at the botom and is called a proton/ atomic number.

These work out the number of protons, neutrons, and electrons in an atom.

Proton number

This is how many protons are in the nucleus of…