C1 - Atomic Structure & the Periodic Table

• The nucleus is in the middle of the atom and contains protons and neutrons. It has a positive charge because of the protons. Almost all of the mass of the atom is concentrated in the nucleus.
• Electrons move around the nucleus in shells. They're negatively charged and tiny (they have virtually no mass).
• Atoms are neutral. They have the same number of protons as electrons.
• In an ion, the number of protons doesn't equal the number of electrons. This means that they have an overal charge.
• The nuclear symbol of an atoms tells you the atomic (proton number) and mass number. The atomic number tells you how many protons. The mass number tells you the total number of protons and neutrons. To get the number of neutrons, subtract the atomic number from the mass number.

  
• An element is a substance made up of atoms that have all the same number of protons in their nucleus.
• Atoms can have different numbers of protons, neutrons, and electrons. It's the number of protos in the nucleus that decide what type of atom it is.
• Isotopes: different forms of the same element, which have the same number of protons but a different number of neutrons.
• Isotopes have the same atomic number but different mass numbers.
• Relative atomic mass is an average mass taking into account the different masses and abundances of all the isotopes that make up the element.
• relative atomic mass (Ar) = sum of (isotope amount x isotope mass number) / sum of amount of all the isotopes
• Elements are mixed to make compounds.
• Compounds: substances formed from two or more elements held together by chemical bonds.
• Mixtures: two or more elements mixed together (can be easily separated).
• Chromatography: draw a line near the bottom of a sheet of filter paper. Add a spot of ink to the link and place in a beaker of solvent, make sure the ink isn't touching the solvent as you don't want it to dissolve. Solvent seeps up the paper, carrying the ink, dyes will separate at different rates.
• Filtration and crystalisation(1): Pour the solution into an evaporating dish. Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated, eventually crystals form. Keep heating until all is left is dry crystals.
• Filtration and crystalisation (2): Pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate and the solution becomes more concentrated. Once some of the solvent has evaporated or you see crystals begin to form remove the dish from the heat to allow it to cool. Filter the crystals out of the solution and leave in a warm place to dry (or use a drying oven).
• Distillation: simple distillation is used for separating out a liquid from a solution. The solution is heated and the part with the lowest boiling point evaporates first. Vapour is the cooled and condenses and is collected. The rest of the solution is left in the flask.

  
• Fractional distillation: Place the mixture in the flask and stick a fractionating column on top. The apply heat. Different liquids will have different boiling points so will evaporate at different temperatures. Liquids with higher boiling points may also begin to evaporate but the column s cooler at the top so will only get part way before condensing. When the first liwuid is collected, raise the temperature until the next one reaches the top.

  
• • 19th century: John Dalton described the atom as a solid sphere made up of different elements.
  • 1897: JJ Thompson concluded they weren't solid spheres, and instead made up of electrons.
  • The 'solid sphere' idea changed to become the 'plum pudding model'.

  
• Rutherford conducted the alpha particle scattering experiment whereby atoms were fired at a thin gold sheet, expecting them to pass straight through but instead some deflected, which is how he decided that there was a nucleus with a small amount of positive charge.

  
• Niels Bohr suggested that electrons are arranged in shells.
• 1st shell: 2 electrons

  2nd shell: 8 electrons

  3rd shell: 8 electrons
• • Elements are laid out in order of atomic weight.
  • Arranged in increasing atomic (proton) number.
  • Metals are on the left and non-metals are on the right.
  • Group number tells you how many electrons are on the outer shell.
  • All elements in the same group typically react in the same way.

  
• METALS

  • They form positive ions when they react.
  • Towards the bottom and to the left of the periodic table.
• NON-METALS

  • Found on the far right and near the top of the periodic table.
  • Generally don't form positive ions when they react.