Chemistry Paper 1

• Atoms are the smallest part of an element that can exist. They make up all substances.
• An element is a substance made up of only one type of atom.
• Compounds are two or more elements chemically bonded. They are formed from chemical reactions.
• Chemical symbols represent an atom of an element.

  E.g. Na represents an atom of sodium.
• Chemical reactions always involve the formation of new substance(s) and often involve a energy change.
• Compounds can be represented using the symbols of the atoms from which they were formed.

  E.g. HCl is a compound containing 1 atom of hydrogen and 1 of chlorine per molecule
• A mixture contains two or more elements or compounds that are not chemically bonded together.

  Therefore, the chemical properties of each substance in the mixture have not been changed (unlike a compound).
• Mixtures can be separated by filtration, crystallisation, simple distillation, fractional distillation and chromatography.

  These are physical processes that do not involve any chemical reactions.
• Atoms contain protons and neutrons in the nucleus.
• Electrons orbit the nucleus in shells.
• What mass and charge do the subatomic particles have?

  • Proton: 1, +1
  • Neutron: 1, 0
  • Electron: less than 0, -1
• Atoms have no overall charge as they have the same number of protons and electrons.#
• An ion doesn't have the same number of protons and electrons, meaning it has an overall charge.
• Atomic number tells you how many protons (and electrons) an atom has. This is the bottom number.
• Mass number tells you how many protons and neutrons an atom has. This is the top number. To find out how many neutrons an atom has, we subtract the atomic number from the mass number.
• Isotopes are different forms of the same element with the same number of protons but different number of neutrons. They have the same atomic number but different mass numbers.
• Making bonds only includes taking, giving or sharing electrons. Only the electrons are involved, not the nuclei of the atoms.
• A compound formed from a metal and a non-metal has ions. Ions are atoms that have lost or gained electrons.
• A compound formed with non-metals has molecules. Molecules are groups of atoms that are held together by covalent bonds.
• The properties of a compound are usually different from the properties of original elements.
• Ammonia - NH3

  Hydrochloric acid - HCl

  Calcium chloride - CaCl2

  Sodium carbonate - Na2CO3

  Sulfuric acid - H2SO4

  Nitric acid -HNO3
• Mixtures can be separated fairly easily
• The chemical properties of a substance are not affected from being part of a mixture.
• Electrons always occupy shells (energy levels)
• Atoms want full shells. If the outer shell is not complete, the atoms will react to gain a full shell.
• Two ways to catagorise elements on the periodic table were:

  1. Physical + chemical properties
  2. Atomic weight
• Elements on the periodic table are laid out in order of increasing atomic number.
• The properties of the period table are said to occur periodically
• Metals are found on the left and non-metals on the right of the periodic table
• Metals form positive ions when they react (lose an electron)
• Non metals form negative ions when they react (gain electrons)
• Metals

  • Strong
  • Malleable
  • Conductors of heat + electricity
  • High melting and boiling points
• Non-metals

  • Brittle
  • Aren't always solids at room temp
  • Don't conduct electricity
  • Lower density
• The most reactive are the group 1 metals, followed by the group 2 metals, then transition metals.
• metal + acid ---> metal salt + hydrogen
• Reduction + oxidation at same time = redox reaction
• metal oxides + acid ---> salt + water

  metal hydroxides + acid ---> salt + water
• metal carbonate + acid ---> salt + water + carbon dioxide