1. Atomic structure and the periodic table

• Atoms contain protons, neutrons and electrons.
• Protons are positively charged particles found in the nucleus.
• Neutrons have no charge and are located in the nucleus.
• Electrons are negatively charged particles that orbit around the nucleus in different shells.
• The Nucleus

  • Is in the middle of an atom
  • Contains protons and neutrons
  • Has a radius of 1 x10^14m
  • Has a positive charge (because of the protons).
  • Contains most of the mass in the atom.
• • Atoms are neutral- they have no overall charge (unlike ions).
  • They have the same number of protons and electrons.
  • The charges of protons cancel out the charges of electrons.
  • In an ion, the number of protons doesn't equal the number of electrons.
• Electrons


  They orbit the nucleus in shells.

  • Are negatively charged and tiny.
  • The volume of their orbits determines the size of the atom.
  • They have virtually no mass.
• The atomic and mass numbers

  • Mass number tells us the total number of protons and neutrons.
  • The atomic number tells us the number of protons or electrons.

  
• Element


  A substance made up of atoms that all have the same number of protons in their nucleus
• Elements


  • Consist of atoms with the same atomic number
  • Atoms can have different numbers of protons, neutrons and electrons
  • It's the number of protons in the nucleus that decides what type of atom it is
  • If a substance only contains atoms with the same number of protons it's called an element
  • There are about 100 different elements
• Atom


  The basic unit of an element, consisting of a nucleus containing protons and usually neutrons, and an outer shell of electrons
• Atomic symbol


  A one or two letter symbol used to represent an element
• Isotopes


  Different forms of the same element, which have the same number of protons but a different number of neutrons
• Relative atomic mass


  The average mass of all the isotopes of an element, taking into account their different masses and abundances
• Calculating relative atomic mass

  Sum of (isotope abundance X isotope mass number) / Sum of abundances of all the isotopes
• Compounds


  Substances formed from the mixing and matching of elements
• Atoms

  1. Atoms bond with other atoms

  2. Atoms form chemical bonds.

  3. Atoms joining together to make compounds
• Compounds


  • Atoms of each element are dispersed throughout the compound
  • Atoms are held together by chemical bonds
• Chemical bonding


  • Involves atoms giving, taking or sharing electrons
  • The nuclei of the atoms are not affected
• It is difficult to separate the original elements of a compound
• Ionic bonding


  • Metal atoms lose electrons to form positive ions
  • Non-metal atoms gain electrons to form negative ions
  • The oppositely charged ions are strongly attracted to each other
• Covalent bonding


  • Atoms share electrons
  • Forms molecules
• Compounds with covalent bonding

  • Hydrogen chloride gas
  • Carbon monoxide
  • Water
• The properties of a compound are usually totally different from the properties of the original elements
• Chemical equation


  Represents a chemical reaction using symbols and formulas
• Chemical formula


  Represents the composition of a compound using element symbols and subscripts
• Word equation


  One way to show a chemical reaction, not as quick as using chemical symbols and can't tell straight away what's happened to each of the atoms
• Symbol equation


  Shows the symbols or formulas of the reactants and products
• Balancing a symbol equation

  1. There must always be the same number of atoms on both sides

  2. Balance the equation by putting numbers in front of the formulas where needed
• Steps to balance a symbol equation

  1. Find an element that doesn't balance and pencil in a number to try and sort it out

  2. See where it gets you, it may create another imbalance, but if so, pencil in another number and see where that gets you

  3. Carry on chasing unbalanced elements and it'll sort itself out pretty quickly
• Mixture


  A combination of two or more substances that are not chemically bonded
• Compound


  A substance made up of two or more different elements chemically bonded together
• Separating mixtures


  1. Filtration

  2. Crystallisation

  3. Distillation

  4. Chromatography
• Mixtures are easily separated, unlike compounds
• The properties of a mixture are just a combination of the properties of the separate parts
• Paper chromatography can be used to separate different dyes in an ink
• Paper chromatography


  1. Draw line on filter paper

  2. Add ink spot

  3. Place in solvent

  4. Solvent seeps up paper

  5. Dyes separate out

  6. Dry paper to get chromatogram
• You shouldn't use a pen to draw the line on the filter paper as pen marks are soluble
• Filtration


  1. Separate insoluble solids from liquids

  2. Separate soluble solids from solutions
• Evaporation


  1. Pour solution into evaporating dish

  2. Slowly heat to evaporate solvent

  3. Crystals form as solution becomes more concentrated