C1.1

C1.1

1. atoms and elements

   • all substances are made of ATOMS. an individual atom is too small for you to see, so everything around us contains lots of atoms
   • an ELEMENT is a substance that is made of only one sort of atom. oxygen is an element because it only contains oxygen atoms

2. particles in atoms

   • protons, neutrons and electrons are called SUBATOMIC PARTICLES. you can work out how many of each type of subatomic particle an atom has from its atomic number and mass number.
   • the number of protons in an atom of an element is called its ATOMIC NUMBER. the atoms of different elements have different numbers of protons.
   • no 2 elements can have the same atomic number

3. electronic structure

   • the electrons in an atom occupy different ENERGY LEVELS around the nucleus. each electron in an atom in an atom is at a particular energy level. electrons occupy the lowest available energy levels.
   • energy levels are also known as SHELLS.

4. making compounds

   • metals and non-metals react together to make compounds. compounds are made of IONS
   • an ion is a charged particle formed when an atom , or group of atoms, loses or gains electrons
   • compounds formed from reactions between non-metals consist of MOLECULES. in a molecule, electrons are shared between atoms. the shared electrons make COVALENT BONDS, which hold the atoms in the molecule together.