Chemistry (Edexcel GCSE)

• Atom


  The smallest particle that has the properties of a chemical element
• Structure of an atom

  • A nucleus containing protons and neutrons, surrounded by electrons in shells
• Relative charges and masses of protons, neutrons and electrons

  • Protons: mass 1, charge +1
  • Neutrons: mass 1, charge 0
  • Electrons: mass almost zero, charge -1
• Atoms are neutrally charged so they must have the same number of positive particles (protons) as negative particles (electrons)
• Size of the nucleus relative to the rest of the atom

  Very small
• Most of the mass of the atom is found in the nucleus
• Mass number of an element

  The total number of protons and neutrons
• Atomic number of an element

  The number of protons
• The number of protons is unique to an element and gives it its identity
• An atom with 12 protons will have 12 electrons
• An atom with a mass number of 23 and atomic number of 11


  • 11 protons
  • 11 electrons
  • 12 neutrons
• Isotope


  Two or more atoms of the same element (the same number of protons) but with a different number of neutrons
• Relative atomic mass


  The average mass of atoms that make up an element compared to the one twelfth mass of an atom of carbon-12
• The relative atomic mass is an average mass of all the isotopes that make up the element
• Formula for calculating relative atomic mass

  Relative atomic mass = (% abundance x relative mass) / 100
• How Mendeleev arranged the elements

  By using the mass number and the properties of the elements and the properties of their compounds of the elements
• How Mendeleev used his table

  To predict the existence and properties of some elements that were still to be discovered
• Ordering elements by atomic mass doesn't always work as Mendeleev noticed some elements' properties best fitted the neighbouring group and vice versa
• How the modern periodic table is arranged

  • In order of increasing atomic number, in rows called periods and elements with similar properties are placed in the same vertical columns called groups
• Non-metals are found at the top on the right hand side of the periodic table
• What elements in the same row of the periodic table have in common

  • They have the same number of shells of electrons
• What elements in the same column of the periodic table have in common

  • They have the same number of electrons in their outer shell (and therefore have similar chemical properties)
• Ion


  A charged atom or group of atoms
• How an ionic bond is formed

  A metal loses electron(s) to a non-metal, resulting in the metal becoming a positively charged ion (cation) and the non-metal a negatively charged ion (anion), which are held in place by electrostatic forces of attraction
• Cations are positively charged
• Anions are negatively charged
• Charges of ions formed from elements in group:

  • +1
  • 2+
  • 2-
  • -
• Compound endings


  • ide: a compound of only the named substances
  • ate: a compound of the named substances and oxygen
• Formulas of compounds formed from:

  • Mg and Cl: MgCl

  b. Na+ and O: Na2O
• Structure of ionic substances

  • A regular arrangement of oppositely charged ions held together in a lattice structure by strong electrostatic forces
• Magnesium has 12 electrons
• What happens in covalent bonding


  Two non-metals overlap their outer electron shells and share at least one pair of electrons
• Covalent bonding results in the formation of molecules
• Physical properties of ionic compounds

  • High melting and boiling points because there are strong electrostatic forces holding the oppositely charged ions in place, therefore a lot of energy is needed to separate the ions

  2. Can conduct electricity when molten or in aqueous solution (dissolved in water) because the ions are free to move and carry their charge
• Physical properties of covalent, simple molecular compounds

  • Low melting and boiling points because there are weak intermolecular forces of attraction between molecules, little energy is needed to separate molecules

  2. Poor conductors of electricity in all states because there are no delocalised electrons or ions to carry charge
• Structure of diamond


  • Each carbon atom is held in place by 4 strong covalent bonds to other carbon atoms, this arrangement is replicated throughout the whole structure creating a giant structure
• Structure of graphite


  • Each carbon forms 3 bonds, leaving one electron left over from each carbon atom. These delocalised electrons sit between the graphite layers and are free to move
• Diamond is used in cutting tools because it is very hard due to the strong covalent bonds
• Diamond has a high melting point because it takes a lot of energy to break the strong covalent bonds
• Graphite conducts electricity because the delocalised electrons between the layers are free to move and carry charge