Chemistry

• 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
• Atoms are made up of three sub-atomic particles
• 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, becoming positively or negatively charged
• Cations


  The positive ions formed by the loss of one or more electrons
• Anions


  The negative ions formed from the gain of one or more electrons
• Isotope


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

  Avg. atomic mass = (mass)(%) + (mass)(%) / 100
• Stable atom


  If forces among the particles that make up the nucleus are balanced

  
• Unstable (radioactive) atom


  If the nucleus has an excess internal energy
• Radioisotope


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

  1. 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

  2. There are 3 processes of natural radioactive decay: alpha decay, beta decay, gamma decay
• Alpha decay


  A helium particle is ejected from the nucleus, the parent nucleus changes to a different element (daughter nucleus) because the atomic number changes
• Beta decay


  A negatively charged electron is emitted from the nucleus, this changes the charge within the nucleus, making it more positive such that a neutron becomes a proton
• Gamma decay


  Electromagnetic radiation is emitted, reducing the energy allows the excited (unstable) to become more stable
• 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
• The law of conservation of mass states that in a chemical reaction, atoms are neither created or destroyed, and instead are just rearranged
• 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)
• Chemical reaction


  A process in which one or more substances are converted to one or more different substances
• Reactants


  Starting substances used in a reaction
• Products


  New substances formed in a reaction
• Exothermic reaction


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


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


  A substance that donates hydrogen ions, properties: corrosive, sour taste, turn blue litmus paper red, neutralised by bases, pH values below 7
• Base


  A substance that accepts hydrogen ions, properties: caustic, soapy slimy feeling, turn red litmus paper blue, neutralised by acids, pH values above 7
• 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
• Corrosion


  Happens when a metal such as copper or an alloy such as steel changes into something else