Atomic structure and the periodic table

• Atom


  The smallest particle of an element that can exist
• Element


  A substance made up of atoms with the same atomic number
• Compound


  A substance formed from two or more elements chemically bonded together in fixed proportions
• Nuclear symbol


  Used to describe atoms
• Nucleus


  • Contains protons and neutrons
• Proton


  Positively charged particle in the nucleus
• Neutron


  Neutral particle in the nucleus
• Electron


  Negatively charged particle orbiting the nucleus
• Mass number


  Total number of protons and neutrons in an atom
• Atomic number


  Number of protons in an atom
• Atoms have no overall charge
• There are about 100 elements
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Relative atomic mass (A)

  The average mass number for an element, calculated from the sum of (isotope abundance x isotope mass number) divided by the total abundance of all isotopes
• Molecule


  A particle containing two or more non-metal atoms bonded covalently
• Molecules can be elements if they only have one type of atom, or compounds
• At least one new substance is made in a chemical reaction
• You can usually measure an energy change in a chemical reaction
• Chemical formula

  Shows the proportion of atoms of each element in a compound
• Chemical equation

  Shows the overall change in a reaction
• Chemical equations


  • Word equation: methane + oxygen
  • Symbol equation: CH + 20,-
• There must be the same number of each atom on each side so the equation is balanced
• Products of a chemical reaction

  • carbon dioxide + water
• The large numbers in front of the formulas tell you how many units of that element or compound there are
• Mixture


  Substances made up of different elements or compounds that aren't chemically bonded to each other
• Mixtures


  • The chemical properties of a substance aren't affected by being part of a mixture
  • Mixtures can be separated by physical methods-these don't involve chemical reactions or form new substances
• Paper chromatography


  1. Spot of mixture (eg ink)

  2. Pencil line

  3. Paper removed when solvent is nearly at the top

  4. Components separate as they move up the paper

  5. Insoluble components stay on the baseline
• Topic C1-Atomic Structure and the Periodic Table
• Filtration


  Separates insoluble solids from liquids and solutions. Can be used to separate out a solid product, or purify a liquid by removing insoluble impurities.
• Evaporation


  Separates soluble salts from solution. Slowly heat solution, as solvent evaporates, crystals form and dry out.
• Crystallisation


  Also separates soluble salts from solution. Heat solution, but cool it when crystals start to form. Large crystals form as solution cools. Filter out crystals and leave to dry.
• Evaporation is quick, but can't be used if the solid decomposes when heated
• Use crystallisation for salts that decompose when heated, or if you want big crystals
• Simple distillation


  The part with the lowest boiling point evaporates first. Vapour is cooled and condenses.
• Simple distillation can't separate liquids with similar boiling points, but fractional distillation can
• Fractional distillation


  Liquids reach the top of the column when the temperature at the top matches their boiling point. Mixture of liquids is heated, and fractions are collected separately.
• Topic C1-Atomic Structure and the Periodic Table
• 1800s


  Atoms described as solid spheres that can’t be divided
• 1897


  Plum pudding model- ball of positive charge contains small negative electrons
• 1909 nuclear model


  Mass is concentrated in a positive nucleus with a cloud of electrons (and mostly empty space)