* Key Concepts

• chemical changes are shown using chemical equations.
• Symbol equations show the atoms on both sides.
• there must always be the same number of atoms of each element on both sides of a symbol equation.
• ionic equations only show the useful parts of the reaction. Only the reacting particles are included.
• oxidising provides oxygen which allows other materials to burn more fiercely. e.g. liquid oxygen.
• Atoms are tiny particles of matter which make up everything in the universe.
• at the start of the 19th century, John Dalton described atoms as solid spheres and said that different spheres made up different elements.
• In 1897, J J Thompson concluded from his experiments that atoms were even smaller than originally thought and were negatively charged particles - electrons.
• The solid sphere idea is now known as ‘the plum pudding’ model.
• In 1909, Ernest Rutherford and his students fired positively charged alpha particles at an extremely thin sheet of gold.
• Rutherford and his students expected the particles to pass straight through the sheet or be slightly defected. Whilst most of the particles did go straight through the sheet, more were deflected than expected and a smaller number were deflected backwards. So the plum pudding model couldn‘t have been right.
• the theory of the nuclear atom is when there is a tiny, positively charged nucleus in the centre, surrounded by lots of negative electrons in majority of the atoms empty space.
• Bohr suggested that electrons can only exist in fixed orbits or shells and not anywhere in between.
• The atom is made up of 3 subatomic particles - protons, neutrons and electrons.
• protons are heavy and positively charged.
• Neutrons are heavy and neutral.
• Electrons have little mass and are negatively charged.
• The nucleus:

  • in the middle of the atom
  • contains protons and neutrons
  • has a positive charge
  • almost the whole mass is in the nucleus
  • compared to the whole atom the nucleus is tiny.
• Electrons: move around nucleus in electron shells, negatively charged, tiny but their shells have a lot of space, size of shells determines size of atom, have a tiny mass.
• Atoms have a radius of 10 -10 m
• The relative atomic mass of an element is the average mass of one atom of the element.
• Isotopes are different forms of the same element which have the same number of protons but a different number of neutrons (same atomic number + different mass number).
• ions are charged particles -they can be single atoms or groups of atoms.
• negative ions (anions) from when atoms gain electrons.

  positive ions (cations) forms when atoms lose electrons.
• oppositely charge ions are strongly attracted to one another by electrostatic forces. this attraction is called an ionic bond.
• Ionic compounds always have giant ionic lattice structures.
• A covalent bond is a strong bond that forms when a pair of electrons is shared between two atoms.
• polymers are molecules made up of long chains of covalently bonded carbon atoms.
• Fullerenes are molecules of carbon shaped like closed tubes or hollow balls.
• During a chemical reaction no atoms are destroyed and no atoms are created.
• One mole of atoms or molecules of any substance will have a mass in grams equal to the relative particle mass (Ar or Mr) for that substance.
• Number of moles = mass (g) / Mr or Ar
• Concentration = mass of solute / volume of solution