Atomic Structure

Atoms are very small, with the radius of about 1 x 10 (power of -10) metres.

They contain a positively charged nucleus made up of protons and neutrons, which are surrounded by negitavely charged electrons.

Electrical charge : Protons = +1 Electrons = -1  Neutrons = 0. 

Atoms have equal numbers of electrons and protons, so they overall have no electrical charge.

The nucleus is most of the mass in an atom even though its redius is less than 1/10000 of the radius of the atom.

The electrons are arranged at different distances away from the nucleus (shells).

Electromagnetic radiation is emitted when an electron drops to a lower energy level.

LIPGIN = Loss Is Positive, Gain Is Negative. This means that is an atom loses an electron it becomes a positive ion, and when it gains one it becomes a negative ion. 

All atoms of a particular element have the same number of protons.

The number of protons or neutrons in an atom of an element is called its atomic number (bottom, smaller number).

The total number of protons and neutrons in an atom is called its  mass number (top, larger number).

Atoms of the same element can have different numbers of neutrons, these are called isotopes, e.g. carbon-12 has 6 protons and 6 neutrons. carbon-14 has 6 protons and 8 neutrons. In both of these examples the atomic number is 6 but the mass number is different. 

               Mass Number  >         4

                                                       He          < Element Symbol

             Atomic Number  >         2