Chemistry

• Substances are made of atoms, which are represented in the periodic table by a symbol
• Compound


  A substance that contains two or more different types of atoms chemically bonded together
• Atoms change what they're bonded to and how they're bonded through chemical reactions
• Word equation


  A representation of a chemical reaction using words
• Chemical equation


  A representation of a chemical reaction using symbols
• Balancing a chemical equation

  1. Start with atoms that are only in compounds

  2. Balance carbons first

  3. Balance hydrogens

  4. Balance oxygens

  5. Balance any remaining elements
• Plum pudding model


  A model of the atom proposed by JJ Thompson, with a positive charge and electrons dotted around it
• Rutherford's model


  A model of the atom with a small, positive nucleus and electrons orbiting relatively far away, discovered by Rutherford
• Bohr's model


  A model of the atom with electrons existing in shells or orbitals, discovered by Niels Bohr
• Protons


  Positive charges in the nucleus of an atom
• Neutrons


  Neutral charges in the nucleus of an atom, discovered by James Chadwick
• Electrons


  Negative charges that orbit the nucleus of an atom
• Atomic number

  The number of protons in the nucleus of an atom, which determines the element
• Mass number


  The total number of protons and neutrons in the nucleus of an atom
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Relative abundance


  The percentage of each isotope of an element found in nature
• Periodic table


  A table that organises elements based on their properties
• Mendeleev's periodic table


  An early version of the periodic table that grouped elements based on their properties, even if it didn't follow atomic weight order
• Electron configuration


  The arrangement of electrons in an atom's shells or orbitals
• Metals


  Elements to the left of the staircase on the periodic table, which donate electrons when bonding
• Non-metals


  Elements to the right of the staircase on the periodic table, which accept electrons when bonding
• Group


  The column an element is in on the periodic table, which indicates the number of electrons in its outer shell
• Alkali metals


  Group 1 elements, which have one electron in their outer shell and readily donate it
• Halogens


  Group 7 elements, which have seven electrons in their outer shell and readily accept one more to fill it
• Noble gases


  Group 0 elements, which have a full outer shell and are very unreactive
• Ionic bonding


  Bonding between a metal and a non-metal, where the metal donates electrons to the non-metal
• Ionic compound


  A compound made up of positive and negative ions in a lattice structure
• Covalent bonding


  Bonding between non-metals, where they share electrons to fill their outer shells
• Simple molecular/covalent structure


  Individual molecules made up of covalently bonded atoms
• Giant covalent structure


  A continuous network of covalently bonded atoms, as seen in diamond and graphite
• Metallic bonding


  Bonding in metals, where a lattice of positive ions is surrounded by delocalized electrons
• Metals are generally harder and less reactive than alkali metals, and form coloured compounds
• Ionic compounds have high melting and boiling points, and can conduct electricity when molten or dissolved
• Simple molecular/covalent structures have relatively low melting and boiling points, and cannot conduct electricity
• Giant covalent structures like diamond and graphite have very high melting and boiling points due to their strong covalent bonds
• Covalent bonds


  Bonds atoms form to other atoms which form bonds to other atoms and so on until what we have in effect is one giant molecule
• Diamond


  • It's so hard and has such a high melting point
  • You would have to break the covalent bonds in order to do that and they're incredibly strong
• Graphite


  An allotrope of carbon made out of the same atoms bonded together in a different way
• Graphite


  • Consists of layers of carbons with three bonds each in a hexagonal structure
  • The spare delocalised electrons form special weak bonds between the layers
  • This means it can conduct electricity because the electrons can move between the layers
  • It also means the layers can slide over each other easily which is why it's used in pencils
• Metal alloys


  • Stronger than pure metals
  • Having mixtures of metals means that we have different size atoms and that disrupts the regular lattice so layers can't slide over each other as easily