Atoms, Ions and Isotopes

What is an atom?

An atom is the smallest particle of an element.

What are atoms made up of?

The atom is made up of 3 subatomic particles - Protons (heavy and positively charged), Neutrons (heavy and neutral) and Electrons (hardly any mass and negatively charged).

Describe the structure of the atom

The nucleus is the centre of the atom, and contains the protons and neutrons. It has a positive charge due to the protons. The nucleus is surrounded by electrons which orbit it on shells which are negatively charged.

Charge of an atom

The charge of the atom is neutral - no charge. This is because in an atom the number of protons and electrons is always equal - these two cancel each others charge out leaving it neutral.

Atomic and Mass number

The atomic number tells you how many protons the atom has - every atom of an element has the same. The mass number tells you the number of protons and neutrons in the atom. To work out the number of neutrons you would do = mass number - atomic number.

What is an Ion?

Ions are when atoms (or groups of atoms) gain or lose electrons. They can be negative or positive ions depending on whether they have lost or gained.

Example of an ion

F- = single negative charge, so there must be one more electron than proton. F has an atomic number of 9 so has 9 protons = 10 electrons.

What is an Isotope?

Atoms of the same element that have the same number of protons but a different numbers of neutrons.

Example of an isotope

Carbon-12 = 12 C 6 ---> 6 protons, 6 electrons, 6 neutrons.

What is Relative Atomic Mass? (Ar)

When speaking about an element as a whole, the bigger number next to the nuclear symbol is the RAM. It is the average mass number of all the isotopes of that element.