Modern development of atomic structure

1st shell= 2 electrons

2nd shell = 8 electrons

3rd shell= 18 electrons

• Atoms are the smallest part of an element that can exist chemically.
• Protons and neutrons are found in the nucleus and the electrons are found in the shells around it. 

Particles

Proton:

Location: Nucleus 

Relative mass: +1

Relative charge: +1

Neutron:

Location: Nucleus

Relative mass: +1

Relative charge: 0

Electron: 

Location: Electron shells

Relative Mass: 0/1000 

Relative charge: -1 

Atomic number: no. of protons in the nucleus of an atom. 

The number of protons in an atom, this is equal to the number of electrons in a neutral atom. 

Mass number:

The number of protons and neutrons in the nucleus of an atom. 

Neutral atom:

The number of electrons= The number of protons.

The number of electrons=(mass-protons)

Examples:

A lithium atom has an atomic number of 3, therfore a mass number of 7. A lithium atom contains 3 protons, 3 neutrons and 4 neutrons. (composition)

A flourine atom has a mass number of 19. A flourine atom has a proton number of 9 protons, 9 electrons and 10 neutrons. (composition)