Atomic Structure and the Periodic Table

• Atom

  The smallest part of an element that can exist
• Element

  A substance made of one type of atom only
• Chemical symbols

  • O (oxygen)
  • Na (sodium)
• Elements are arranged into groups with similar properties in the periodic table
• In the periodic table, metals are on the left of the stepped line, and non-metals are on the right
• Compound

  A substance formed by the chemical union of two or more elements
• Examples of chemical symbols for elements

  • helium, He
  • lithium, Li
  • beryllium, Be
  • boron, B
  • carbon, C
  • neon, Ne
  • sodium, Na
  • magnesium, Mg
• Molecule

  A collection of two or more atoms held together by chemical bonds
• Some non-metal elements exist as molecules that are made up of two atoms joined together
• Examples of molecular elements

  • iodine, I2
  • bromine, Br2
  • chlorine, Cl2
  • fluorine, F2
  • oxygen, O2
  • nitrogen, N2
  • hydrogen, H2
• In compounds made up of non-metal elements only, the second word of the compound's name starts with mon-, di-, or tri-, eg carbon dioxide. This shows the number of atoms of this element for every one atom of the first element in the name.
• Ion

  Electrically charged particle, formed when an atom or molecule gains or loses electrons
• Ionic compound

  An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron)
• Simple formulae of ionic compounds

  • Sodium chloride (NaCl)
  • Sodium oxide (Na2O)
  • Magnesium oxide (MgO)
  • Magnesium chloride (MgCl2)
• Conservation of mass

  The total mass of reactants before a reaction is equal to the total mass of products after a reaction, because no atoms can be created or destroyed so the mass must remain unchanged
• Mass

  The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g)
• A pure substance consists of only one element or one compound
• Filtration is used to separate an insoluble solid from a liquid. It is useful for separating excess reactant from a reaction mixture.
• Crystallisation is used to produce solid crystals from a solution.
• Simple distillation is used to separate a solvent from a solution. It works because the dissolved solute has a much higher boiling point than the solvent.
• Fractional distillation is used to separate different liquids from a mixture of liquids. It is useful for separating different fractions from crude oil.