Chemistry paper 1

• • The atom has a positive nucleus because of the protons.
  • Inside the nucleus there are protons and neutrons.
  • Electrons are in the shells.
  • Atoms are neutral unlike ions, this is because protons and electrons are the same in an atom.
  • Ions are atoms that lose or gain electrons.
  • Atomic number (bottom number) tell you how many protons there are.
  • mass number (top number) tells you the total number of protons and neutrons.
  • To work out the number of neutrons you subtract the atomic number from the mass number.
• Protons = positive, charge is +1, mass is 1

  Neutrons = neutral, charge is 0, mass is 1

  Electrons = negative, charge is -1, mass is very small
• Elements are substance that have the same atoms with them all having the same amount of protons.

  Isotopes have the same number of protons but different number of neutrons. Meaning they have the same atomic number but different mass number.

  relative atomic mass is used instead of mass number when talking about elements.
• Relative atomic mass = sum of isotope abundance x isotope mass number / sum of abundance of all the isotopes
• compounds are when elements mix together. Compounds are founded when electrons are shared or taken away.

  Ionic bonding - compound formed between metal and non metal consists of ions. The metal loses electrons to make positive ions and the non metal gains electrons to make negative ions.

  covalent bonding - compound formed between two non metals consist of molecules.

  Some compounds are H2O, NaCl, CO2.
• Mixtures are easily separated as they aren’t chemically bonded.

  Crude oil is a mixture of hydrocarbons.
• Ways to separate mixtures :

  • Chromatography
  • evaporation
  • crystallisation
  • filtration
• Evaporation :

  Pour the solution into an evaporating dish.

  Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated and crystals will form.

  Keep heating until dry crystals are left.

  Crystallisation :

  Pour the solution into an evaporating dish.

  Slowly heat the solution. Some of the solvent will evaporate, and the solution will get more concentrated.

  once crystals are there stop heating and leave the solution to cool.

  Filtration :

  use filtration paper and beaker, the solids will be left in the paper but the liquid will go through to the beaker.
• Distillation :

  Simple distillation is used for separating out a liquid from a solution. The solution is heated the point of the solution with the lowest boiling point will evaporate first. The vapour is cooled, condensed and collected. The rest of the solution is left in the beaker.

  You can use distillation for separating salt water, it can only work with substance that contain different boiling points if they have similar boiling points you need to use fractional distillation.
• Fractional distillation :

  Fractional distillation is used for separating mixtures with similar boiling points.

  Put your mixture in a flask and stick a fractional column at the top and heat it.

  The liquid with the lowest boiling point will evaporate first and go to the top of the column. Liquids with higher boiling points will start evaporating but the column is cooler at the top so they will condense and run back to the flask. When the first liquid is collected you raise the temperature until the next one does.
• John dalton - atoms are solid spheres.

  JJ Thomson - atoms aren’t solid spheres, discovered electrons, plum pudding model (a positive charge ball containing electrons).

  Rutherford - proved the plum pudding model is wrong. Used gold leaf and fired positive alpha particles through it, some particles were reflected backwards and defected so the model couldn’t be true. Came up with the idea of nuclear model where the nucleus is positively charged and is where the mass is concentrated. Found protons.

  Bohr - electrons are in the shells and rotate the nucleus.

  Chadwick - discovered neutrons.
• atoms react with each other to get full outer shells.

  2,8,8.
• history of periodic table :

  Elements used to be arranged in relative mass meaning they were placed in the wrong places. Gaps were left in the periodic table for elements which werent discovered yet.
• Group 1 - all metals, more reactive as you go down the group because the further down the more shells, alkali metal, have one electron in the outer shell, lower melting and boiling points, high reactive mass, when it reacts with water it produced hydrogen, can react with oxygen to form metal oxide, react vigorously when heated in chlorine gas to form metal chloride.

  Group 8/0 - non metals, not reactive, full outer shells, noble gases, colourless gases at room temperature, higher boiling point as you go down the group.
• Group 7 - non metals, more reactive as you go up the group because it is easier to gain electrons closer to the nucleus, halogens, have seven outer electrons, high melting and boiling points, high relative mass, halogens replace less reactive halogens in a displacement reaction, compounds that form with halogens reacting with non metals have simple molecular structures, compounds that form with halogens reacting with metals are called halides and have ionic structures.
• Metals - malleable, strong, good conductors of electricity, high boiling and melting points.

  Non metals - brittle, low density, don’t conduct electricit.
• Group 1 make 1+ ions

  Group 2 make 2+ ions

  Group 6 make 2- ions

  Group 7 make 1- ions

  positive = cations

  Negative = anions
• Ionic bonding - transfer electrons, between a metal and non metal, form a positive and negative ion, uses electrostatic force, metal looses, non metal gains.