Chemistry

• Molecule


  A group of two or more atoms that are held together by chemical bonds
• Compound


  A substance that contains two or more different elements, with the atoms held together by chemical bonds
• Molecules


  Can contain multiple different elements
• Compounds always contain two or more different elements
• Compounds have the elements in the same proportions
• Chemical formula


  Uses chemical symbols and numbers to represent the composition of a compound
• Mixture


  Two or more substances that are not chemically combined, just physically mixed together
• Mixtures can be separated using physical methods like filtration, crystallization or distillation
• Everything whether it's living, non-living or even a cell itself is made up of lots of tiny particles which we call atoms
• Atom


  Basic structure is a central nucleus surrounded by electrons which orbit around the nucleus in rings that we call shells
• Particles that make up the nucleus


  • Protons
  • Neutrons
• Protons and neutrons


  • Have the same mass, with a relative mass of 1
  • Protons have a positive charge of 1+
  • Neutrons have no charge (are neutral)
• Electrons


  • Have a mass 2000 times smaller than protons and neutrons
  • Have a negative charge of 1-
• The size of an atom depends on which element it is
• Atoms have a radius of around 0.1 nanometers
• Electrons are even smaller than the nucleus and would be too small to see in the atom diagram
• Ion


  An atom that has lost or gained electrons, so the positive and negative charges no longer balance
• Ions

  • One minus negative ion (one extra electron)
  • Two minus negative ion (two extra electrons)
  • One plus positive ion (one electron lost)
• The periodic table represents different types of atoms, which we call elements
• Atomic number


  Tells us how many protons the atoms of that element have
• Mass number


  Tells us the total number of neutrons and protons in that atom
• The number of protons and electrons in an atom is always the same
• Atom


  Central nucleus comprising protons and neutrons, with electrons orbiting the nucleus
• Protons


  Determine which element the atom is
• Hydrogen


  • Smallest element, with 1 proton and 1 electron
• Atomic number


  Unique number representing the number of protons in the element
• Atoms with the same number of protons are the same element
• Isotopes


  Different forms of the same element that have the same number of protons but different number of neutrons
• Isotopes chemically react in the same way
• Chemical equation


  A way to show what's happening in a chemical reaction
• Word equation


  1. Reactants

  2. Reaction arrow

  3. Products
• Reactants


  The molecules that react together
• Products


  The molecules that are produced
• Symbol equation


  1. Chemical symbols of each molecule

  2. Reaction arrow
• Oxygen exists as a molecule made up of two atoms, so it is written as O2
• Balanced chemical equation


  • Has the same total number of each type of atom on either side of the reaction arrow
• Balancing a chemical equation


  1. Can't change the little numbers (subscripts)

  2. Change the big numbers (coefficients) in front of elements/compounds

  3. Keep whole numbers
• When balancing, it's recommended to balance the least common elements first
• AtomsIncomplete outer shell of electrons

  • Need a full outer shell to be stable
  • Can gain or lose electrons to achieve a full outer shell
• Arranging electrons in atoms

  1. Draw nucleus

  2. Add electrons to shells in order of increasing energy level

  3. Fill shells clockwise until full or run out of electrons