Chemistry 2A

Chemistry 2A

1. Bonding and Structure

   • Ionic Bonding - metal atoms lose electrons and become positively charged. Non-metal atoms gain electrons and become negative.
   • Covalent bond is between non-metals, which share electrons. They are very strong, with low melting and boiling points.
   • Macromolecules have giant covalent structures. Arranged in giant lattices, they have very high melting and boiling points.
   • Thermosoftening polymers soften and can be shaped when hot, but harden when cooled, because they have no cross links to hold the shape together.
   • Thermosetting polymers cannot be reshaped or softened once moulded, because they have cross links.
   • Metals are good conductors of electricity because of their free electron.
   • Ionic compounds don't conduct electricity when in solid form because their lattice form means ions cannot move around.
   • Graphite conducts well because of its delocalised electrons.

2. Atoms

   • The mass number is total number of protons and neutrons
   • Atomic number is number of protons
   • Compounds are chemically bonded
   • Isotopes are different atomic forms of the same element, which have the same number of protons but a different number of neutrons
     • Carbon-12 and Carbon-14 are a pair of isotopes
   • Ions are atoms that have lost or gained at least one electron
   • In ionic bonding metals lose electrons to form positive ions, non-metals gain electrons to form negative ions

3. Relative Mass and Percentage Yield

   • Relative Atomic Mass is the same as the mass number of an element, they are added together when there is more than one atom
   • Number of moles = mass in g/ relative formula mass
   • Percentage mass of an element in a compound = relative atomic mass of that element/relative formula mass of the whole compound X100
   • Empirical formula is an element in its simplest form, so list all the elements in a compound and write their experimental masses. Divide each mass by the relative atomic mass for that element. Turn the answers into a ratio, then simplify the ratio as much as possible
   • Calculating masses in reactions - write out the balanced equation, work out the relative formula mass for the parts you need, divide to get one part then multiply to get all
   • Percentage yield compares the actual outcome with the predicted outcome. Percentage yield = actual yield/predicted yield X100
     • Will always be under 100%