Chemistry

• An atom is the smallest part of an element.
• A compound is a substance that is made up of 2 (or more) elements, that are chemically bonded together.
• A molecule is a substance that is made up of the same elements chemically bonded together.
• Separation techniques is a method used to separate mixtures. It includes; fractional distillation, distillation, chromatography, crystallisation and filtration.
• A mixture is a group of different elements and / or compounds that are not chemically bonded together.
• Filtration is a process used to separate insoluble solids from liquids using a filter medium that allows the fluid to pass through but not the solid. It is also used for purification.
• Evaporation is a very quick way of separating a soluble solid from a liquid, but you can only use this method if the solid does not decompose (break down when heated)
• Distillation separates a liquid from a mixture. It involves evaporation and condensation. It can be used to separate mixtures with different boiling points.
• Fractional distillation is used for separating a mixture of different liquids and is especially useful when the boilings point of the liquids are close to eachother.
• Chromatography separates small amounts of dissolved substances by running a solvent along absorbent paper. It is used to separate different substances dissolved in a liquid.
• An element is a substance that is made up of only 1 type of atom
• The top number is the mass number. The mass number tells us the sum of protons and neutrons in the nucleus.

  The bottom number is the atomic number. The atomic number tells us the number of protons.

  The number of protons is equal to the number of electrons.

  
• Protons have a +1 charge. They have a mass of 1
• Neutrons have a charge of 0. It has a mass of 1
• Electrons have a charge of -1. They have a very small mass.
• Shell 1: maximum of 2 electrons

  Shell 2: maximum of 8 electrons

  Shell 3 : maximum of 8 electrons
• Isotopes are elements with the same atomic number (same number of protons) but different mass number (number of neutrons)
• Ions

  Atoms tend to loose or gain electrons to form charged particles called ions.

  Metals loose electrons to form positive ions
• In the early 1800s, John Dalton proposed that all matter is made up of tiny particles called atoms. He described atoms as tiny solid shapes that could not be broken down.
• During 1897, JJ Thompson described the atom as a ball of positive charge with negative electrons embedded into it. (The Plum Pudding Model). He discovered the electron.
• In 1909, Ernest Rutherford described the atom as having a positively charged nucleus at the centre with electrons surrounding it. (The Nuclear Model) He discovered the nucleus.
• In 1913, Neil Bohr described the electrons to be in specific shells / energy levels, orbiting the nucleus.
• Prefixes:

  • '-ate' means that the element is embedded with oxygen
  • '-ide' means that the element is singular
• state symbols;

  • solid (s)
  • liquid (l)
  • gas (g)
  • aqueous (aq)
• Describe the method used for filtration:

  1. Add water to the mixture
  2. A filter paper is placed in a filter funnel above a beaker.
  3. The mixture of the insoluble solid and salt solution is poured into the filter funnel
  4. The filter paper will only allow the small solution particles to pass through as filtrate.
  5. Solid sand particles are too large to pass through the filter paper so it will stay behind as residue
• Describe the method used for crystallisation:

  1. The solution is poured into an evaporating dish and it is heated, either using a Bunsen Burner or by leaving it in a warm sunny place.
  2. The solvent evaporates/boils and crystals of the solute are left.
• Describe the method of crystallisation:

  1. The solution is heated and the liquid evaporates/boils which produces a gas which rises through the flask
  2. The vapour passes through a condenser, where it cools and condenses, turning back into a liquid
  3. A thermometer monitors the temperature of the gas to check to see if it is only one substance because different substances have different boiling points.
• Describe the method of chromatography:

  1. A starting line is drawn in pencil.
  2. Place drops of ink on the paper
  3. The paper is lowered into the solvent container (making sure that the pencil line sits above the level of the solvent)
  4. Wait for the results
• neutrons = mass number - atomic number
• The group of an element in the period table will tell you the number of electrons in the outer shell.
• The period of an element in the periodic table shows how many shells the element has
• Relative Atomic Mass = (abundance of isotope 1 * mass of isotope 1) + (abundance of isotope 2 * mass of isotope 2) / 100
• Group 1 (Alkali Metal) properties:

  • very reactive
  • stored in oil to stop them from reacting with oxygen
  • reactivity increases as you go down the group
  • very low density
  • they float on water
  • soft
  • softness increases as you go down the group
• Alkali metals loose one electron to form..?

  a positive ion with a +1 charge
• Why are group 1 electrons so reactive?

  they only have to loose one electron
• the melting / boiling point .... as you go down group 1?

  decreases
• All alkali metals react vigorously with chlorine and other group 7 elements to produce white solids (metal chloride)
• When Lithium, Sodium and Potassium are added to water, the metal floats and fizzes.
• When potassium is added to water, the hydrogen that is produced ignites to produce a lilac flame.
• The word equation for group 1 reactions with water?

  Alkali Metal + Water --> Alkali Metal Hydroxide + Hydrogen