C1 - Atomic Structure and the Periodic Table

• Atom


  The smallest part of an element that can exist
• Element


  A substance made of only one type of atom
• Compound


  A substance containing atoms of two or more elements, which are chemically combined in fixed proportions
• Reactants


  The substances that react together in a chemical reaction
• Products


  The substances produced in a chemical reaction
• Mixture


  A combination of elements or compounds not chemically combined
• Filtration


  Used to separate insoluble solids from soluble solids
• Crystallisation


  Used to obtain a soluble solid from a solution
• Simple distillation


  Used to separate a substance from a mixture due to a difference in the boiling points of the components in the mixture
• Fractional distillation


  Used to separate mixtures which contain components with similar boiling points
• Chromatography


  Used to separate the coloured components of mixtures
• Scientists use chemical formulae to show the different elements in a compound and how many atoms of each element one molecule of the compound contains
• Filtration is used to separate soluble solids from insoluble solids
• Crystallisation is used to obtain a soluble solid from a solution
• Obtaining salt crystals from a solution of salty water


  1. The mixture is gently warmed

  2. The water evaporates, leaving crystals of pure salt
• Simple distillation


  Used to obtain a solvent from a solution
• Fractional distillation


  Used to separate mixtures in which the components have different boiling points
• Chromatography


  Used to separate the different soluble, coloured components of a mixture
• Plum-pudding model (Thompson): •Tiny negative electrons •Sea of positive charge
• Nuclear model (Rutherford): •Alpha scattering experiment proved that positive mass was concentrated in the centre, in the nucleus
• Nuclear model (Bohr): •Electrons are contained in shells
• Chadwick then provided evidence of neutrons within the nucleus
• Later experiments led to the idea that the positive charge of a nucleus could be explained by particles called protons
• Group 1 (alkali metals)


  • Have one electron in their outermost shell
  • Have low melting and boiling points that decrease down the group
  • Become more reactive down the group because there are more shells so the outermost electron is far away from the nucleus so it can be lost easily
• Alkali metals are stored under oil because they react very vigorously with oxygen and water, including moisture in the air
• Reaction of alkali metals with water


  1. A metal hydroxide is formed

  2. Hydrogen gas is given off
• Alkali metals react with non-metals to form ionic compounds
• Group 7 (halogens)


  • Have seven electrons in their outermost shell
  • Exist as molecules made of pairs of atoms
  • Reactivity decreases down the group because the outer shell gets further away from the nucleus, so it is less easy to gain an electron
• Halogens reacting with metals


  The halogen atom gains one electron to form a halide ion with a negative charge (-1)
• Group 0 (noble gases)


  Have a full outer shell of electrons, making them very unreactive non-metals
• Subatomic Particles

  • Proton
  • Neutron
  • Electron
• Proton


  Subatomic particle with relative mass 1 and relative charge +1
• Neutron


  Subatomic particle with relative mass 1 and no charge
• Electron


  Subatomic particle with very small relative mass and relative charge -1
• Almost all of the mass of an atom is in the nucleus
• The radius of the nucleus is less than 1/10000 of the atomic radius, so most of an atom is empty space
• Atoms have no overall charge because they contain an equal number of protons and electrons
• Atomic Number


  The number of protons in an atom
• Mass Number


  The total number of protons and neutrons in the nucleus of an atom
• Number of neutrons


  mass number - atomic number