Atomic Structures

• The centre is called the nucleus. Protons and neutons are here. Electrons orbit the nucleus in groups called shells. 
• Protons as positivly charged 
• Electons are negativly charged
• Neutons have no charge 

    Particle    Charge   Mass   

• Proton      +1            1
• Neutron      0            1
• Electron    -1            0

• Electrons orbit the nucleus 
• The first shell only holds 2 electrons then the rest hold 8 

• This shows the number of electrons in each shell, working outwards from the nucleus. 

• Groups are vertical colums of elements 
• The group number is the number of electrons in the last shell. 

• Periods are the horizontal lrows across the periodic table. 
• The period number is the number of shells used. 

Isotope - atoms of the same elements that have the same number of protons but different numbers of neutrons. 

Heavy isotopes like carbon 14 can be unstable and radioactive. 

The mass of an atom is measured on a scale by comparing it with the mass of the other atoms. This scale is known as the relative atomic mass. 

The number at the top of the symbol is the Mass number.