Atomic structure and the Periodic Table

• All substances are made of atoms
• An atom is the smallest part of an element that can exist
• Atoms of each element are represented by a chemical symbol
• There are about 100 different elements
• Elements are shown in the periodic table
• Compounds are formed from elements by chemical reactions
• Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change
• Compounds contain two or more elements chemically combined in fixed proportions
• Compounds can only be separated into elements by chemical reactions
• A mixture consists of two or more elements or compounds not chemically combined together
• The chemical properties of each substance in a mixture are unchanged
• Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography
• Processes used to separate mixtures don't involve chemical reactions and no new substances are made
• Filtration is used to separate an insoluble solid from a liquid
• Crystallisation is used to separate a soluble solid from a liquid
• Explain the process of filtration

  1. A piece of filter paper is placed in a filter funnel above a beaker
  2. A mixture of insoluble solid and liquid is poured into the filter funnel
  3. The filter paper will only allow small liquid particles to pass through as filtrate
  4. Solid particles are too large to pass through the filter paper so will stay behind as a residue
• Explain the process of crystallisation?

  1. The solution is heated which allows the solvent to evaporate and leaves a saturated solution 
  2. The saturated solution is then allowed to cool slowly
  3. Crystals begin to grow as solids come out of solution due to decreasing solubility
  4. The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
• Simple distillation is used to separate a soluble solid from a liquid when you want to keep the liquid
• Explain the process of simple distillation

  1. The solution is heated and a liquid evaporates producing a vapour which rises through the neck of the round-bottomed flask
  2. The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
  3. After all the liquid is evaporated from the solution, only the solid solute will be left behind
• Explain the process of fractional distillation

  1. The solution is heated to the temperature of the substance with the lowest boiling point
  2. This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
  3. All of the substance is evaporated and collected, leaving behind the other components of the mixture
• Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided
• The discovery of the electron led to the plum pudding model of the atom
• The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it
• The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
• Describe the alpha scattering experiment

  Scientists fired alpha particles at thin gold foil
• What were the results of the alpha scattering experiment?

  • Most alpha particles passed straight through the gold foil
  • Some deflected
  • Some bounced back off the gold foil
• The nuclear model replaced the plum pudding model
• Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances
• The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus
• What is the relative charge of a proton?

  +1
• What is the relative charge of a neutron?

  0
• What is the relative charge of an electron?

  -1
• The number of protons in an atom of an element is its atomic number
• What is the size of an atom?

  0.1nm
• What is the size of a nucleus?

  1 x 10^-14 m
• What is the relative mass of a proton?

  1
• What is the relative mass of a neutron?

  1
• What is the relative mass of an electron?

  Very small
• What is mass number?

  Sum of protons and neutrons
• What is an isotope?

  Atoms of the same element with different numbers of neutrons