Chemistry 1.1 Model of the Atom

• Atoms

  The building blocks of matter
• All substances are made of particles of matter called atoms which are the building blocks of all matter
• what are atoms made up of

  • Made of subatomic particles called protons, neutrons, and electrons
  • Protons and neutrons are located at the centre of the atom, which is called the nucleus
  • Electrons move very fast around the nucleus in orbital paths called shells
  • The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located
• The atom is the smallest part of an element that exists even though it can be divided into smaller particles. The atom is the smallest part as it retains the properties of the element while the subatomic particles do not.
• Element

  A substance made of atoms that all contain the same number of protons and cannot be split into anything simpler
• There is a limited number of elements, and all elements are found on the Periodic Table
• Chemical symbol

  A unique symbol representing each element on the Periodic Table
• Where a symbol contains two letters, the first one is always written in uppercase letters and the other in lowercase
• Elements that exist in nature as two atoms joined together

  • H2
  • N2
  • O2
  • F2
  • Cl2
  • Br2
  • I2
• Atomic number

  The number of protons in the nucleus of an atom
• Mass number

  The total number of protons and neutrons in the nucleus of an atom
• The Periodic Table is the chemists' best friend
• You will be provided with a periodic table in your Chemistry exams
• You need to be able to use the names and symbols for the first 20 elements in the table, as well as the name and symbols of the elements in group 1, group 7 and any other elements specified in these notes
• Compound

  A pure substance made up of two or more elements chemically combined and which cannot be separated by physical means
• The properties of compounds are usually quite different from the elements that form them
• Chemical formula

  Tells you the ratio of atoms in a compound
• Chemical formulas

  • H2O
  • NH3
• A common error is to say elements are pure while compounds are impure. Pure substances contain only one element or compound and are not mixed with anything else
• Ionic compound

  Contains metal and non-metal elements joined together as particles called ions
• Covalent compound


  Contains only non-metals
• Naming conventions for compounds

  • Metals and non-metals: Metal element symbol written first, non-metal element name ends in -ide unless oxygen is present then ends in -ate
  • Non-metal only compounds: Use prefixes (mono, di, tri, tetra, penta) to show how many of each element is present in the formula
• Word equation

  Shows the reactants and products of a chemical reaction using their full chemical names
• Symbol equation

  Uses the formulae of the reactants and products to show what happens in a chemical reaction
• Nothing is created or destroyed in a chemical reaction, the same atoms are always present before and after the reaction, they have just joined up in different ways
• The total mass of reactants is always equal to the total mass of products, this is known as the Law of Conservation of Mass
• Balancing chemical equations


  Use the Law of Conservation of Mass to ensure the same number of atoms of each element are present on both sides of the equation
• Chemical equations are written with an arrow instead of an equals sign, the arrow means the reactants have reacted together and formed the product(s)
• Half equation

  Shows what happens to the electrons in reactions where atoms, molecules or ions are gaining or losing electrons
• Ionic equation

  Indicates what happens to ions during reactions, helps to simplify complicated processes where many substances are present, but only certain ions are actually reacting with each other
• Spectator ions

  Ions which are present but do not take part in reactions
• Mixture

  Contains elements and/or compounds where each constituent retains its chemical properties, the parts are not chemically bonded together and can be separated by physical means
• Filtration

  Used to separate an undissolved solid from a mixture of the solid and a liquid / solution
• Crystallisation

  Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold
• Ratio

  Mixture of sand and water
• Crystallisation

  Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water)
• Crystallisation

  1. The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind

  2. Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution

  3. If the solution is saturated, crystals will form on the glass rod

  4. The saturated solution is allowed to cool slowly

  5. Crystals begin to grow as solids will come out of solution due to decreasing solubility

  6. 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

  Used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
• Simple Distillation

  1. The solution is heated, and pure water 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 water is evaporated from the solution, only the solid solute will be left behind
• If asked to draw or label a diagram of simple distillation, make sure that the water goes in at the bottom or the condenser near the collecting beaker and comes out at the top near the column.