More chem

• Atom


  The building block of matter
• Element


  Only 1 type of atom
• Molecule


  Two single atoms (same or different) bonded together
• Compound


  Two or more different types of atoms bonded together
• Mixture


  Two or more different atoms together but not joined
• Sub-atomic particles


  • Protons
  • Neutrons
  • Electrons
• Protons & Neutrons


  • Make up the nucleus, number of protons determines what element it is
  • Protons and neutrons have approximately the same mass
• Protons


  Positively charged (+1)
• Neutrons


  Neutrally charged (0)
• Electrons


  • Orbit the nucleus in electron shells or orbitals
  • 1st shell (closest to nucleus) can hold up to 2 electrons
  • 2nd & 3rd shell can hold up to 8 electrons each
  • 4th shell can hold up to 18
  • Very little mass, do not contribute to atoms mass
  • Negatively charged (-1), number of electrons in atom determines atoms overall charge
• Atomic number


  Number of protons in atom, unique to each element
• Atomic mass/ mass number


  Average mass of the atom (number of protons + neutrons)
• Bohr diagram


  1. Number of protons = number of electrons

  2. Neutrons = atomic number - atomic mass
• Ions (cations & anions)

  • Neutral atoms have the same number of electrons and protons
  • If an atom loses or gains electrons it will have a net electric charge; meaning it becomes positively or negatively charged
  • Cations are the positive ions formed by the loss of one or more electrons
  • Anions are the negative ions formed from the gain of one or more electrons
  • More protons than electrons = positively charged = cation
  • Less protons than electrons = negatively charged = anion
• Isotope


  Atoms of the same element, that have the same number of protons, but different numbers of neutrons
• Average atomic mass (how to calculate)

  (mass)(%) + (mass)(%) / 100
• Stable atom


  Forces among the particles that makeup the nucleus are balanced
• Unstable (radioactive) atom


  Forces among the particles that makeup the nucleus are unbalanced; if the nucleus has an excess internal energy
• Radioisotope


  An isotope that has unstable nuclei making it radioactive
• Nuclear decay/ radioactive decay

  1. A nucleus can be unstable or radioactive, because of its combination or arrangement of protons and neutrons

  2. To reduce the energy within the nucleus, it may decay; emitting electromagnetic radiation and possibly ejecting a particle

  3. The original, parent, nucleus may change from one element to another, the new nucleus is referred to as the daughter, and this change is called transmutation

  4. There are 3 processes of natural radioactive decay: Alpha decay, Beta decay, Gamma decay
• Half-life


  • The time it takes for half the nuclei to decay (change into a more stable form by emitting particles and/or energy)
  • The shorter the half life the more unstable (quicker decay rate)
• Finding half-life


  Can be worked out using the table method
• Law of conservation of mass
• Physical change


  Makes substances appear differently, however no new substances is actually formed
• Chemical change


  • Actually makes the final substance chemically different to the starting substance (colour change, one or more substances disappears, new substances appearing, temperature change, sound and light, bubbling and gas)
  • Compounds can be formed by chemical reactions
• Chemical reaction


  • A process in which one or more substances are converted to one or more different substances
  • Starting substance (used in a reaction) - called the reactants
  • New substance (formed in a reaction) - called the products
• Exothermic reaction


  Heat is given off during reaction, creates warm feeling, makes the surroundings increase in temperature
• Endothermic reaction


  Absorbs heat during the reaction, creates cold feeling, makes the surroundings drop in temperature
• Acid


  • A substance that donates hydrogen ions
  • Properties: corrosive, have a sour taste, turn blue litmus paper red, neutralised by bases
  • pH values below 7
  • All acidic solutions contain more hydrogen ions than hydroxide
• Base


  • A substance that accepts hydrogen ions
  • Properties: caustic, have a soapy slimy feeling, turn red litmus paper blue, neutralised by acids
  • pH value above 7
  • All basic solutions contain more hydroxide ions than hydrogen ions
• Neutral


  • pH value of 7
  • In water and neutral solutions, the concentrations of hydrogen ions and hydroxide ions are equal
• Combustion


  Happens when something burns or explodes (react with oxygen)
• Corrosion


  Happens when a metal such as copper or an alloy such as steel changes into something else (reacts with oxygen)
• Oxidation reactions


  A type of chemical reaction
• Hydrocarbons


  A group of chemicals we mostly know through fossil fuels such as natural gas and oil
• General equation of combustion of hydrocarbons

  Hydrogen + oxygen --> carbon dioxide + water
• Complete combustion


  Products are carbon dioxide and water
• Incomplete combustion


  Products are carbon dioxide, water, carbon monoxide and carbon
• Worded equations


  Anything with oxygen becomes oxide

  Anything with water becomes hydroxide + hydrogen gas
• Acid reactions


  Acid reacts with reactive metal to produce salt + hydrogen

  Acid reacts with carbonate to produce salt + water + carbon dioxide

  Acid reacts with base (neutralisation) to produce salt + water