Atoms

• The smallest unit of an element that has the chemical properties of that element
• An atom consists of
• a nucleus
• composed of protons and neutrons.

– electrons that

• occupy space about the nucleus.
• In a neutral atom the number of protons is the same as the number of electrons.

Elements

• They are composed of atoms that have the same number of protons.
• The element carbon (C) is made up of atoms having six protons.
• They are pure substances.
• The individual atoms of an element may differ in mass due to varying numbers of neutrons present in the nucleus.
• These atoms are referred to as isotopes.