Chemistry topic 1

• Atom


  Smallest particle of an element
• Element


  A pure substance made of only one kind of atom
• Molecule


  two or more atoms held together by covalent bonds
• Compound


  compound contains two or more elements chemically combined in fixed proportions
• First 20 elements


  Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulfur, Chlorine, Argon, Potassium, Calcium
• Mixture


  A combination of two or more substances that are not chemically combined
• How can mixtures be separated? (5)

  Filtration, crystallisation, simple distillation, fractional distillation and chromatography
• Chromotography


  a process which separates the parts of a solution with special paper and a solvent.
• How to carry out chromatography (4)

  1. Use a pencil line as a reference line(pencil doesn't move)

  2. Add dots of ink

  3. Dip filter paper in water

  4. Furthest dot has the greatest solubility
• Solvent


  the substance in which the solute dissolves
• Solute


  the substance that is dissolved
• if chemicals are strongly attracted will it move up or down the papering chromatography


  will not move
• Simple distillation


  Used to separate solute from solvent

  Separates 2 liquids with different boiling points
• How to carry out fractional distillation(4)

  -mixture in a flask and stick a fractionating column on top, then heat it

  -liquid with lowest boiling point evaporates first.

  - vapour then condenses

  -raise temperature until next liquid reaches the top.
• Crystallization


  Separate solutions into their different parts: solids (solutes) and liquids (solvents)
• How is crystallisation carried out?

  1. A solution is placed in an evaporating basin and heated with a Bunsen burner.

  2. The volume of the solution has decreased because some of the water has evaporated. Solid particles begin to form in the basin.
• Filtaration


  Separates mixtures that contain insoluble (can't dissolve) solids and liquids (which are soluble)
• How is filtration carried out

  Mixture is poured through filter paper

  Insoluble solid is trapped by the filter paper and the liquid runs through and is collected below
• Mixture


  A combination of two or more substances that are not chemically combined
• An example of a mixture is

  air
• Evaporation


  Separates soluble salts from solutions
• Crysallization


  Separates solvable salts from solutions
• Crystallisation process


  1) Pour the solution into anevaporating dishand gentlyheatthe solution. Thewaterwill evaporate and the solution will be moreconcentrated.

  2) The solution will start tocrystallise.

  3) Leave the solution tocool.

  4) Leave the crystals todry.
• History of atom


  1800s: solids that can't be divided

  1897: plum pudding model- ball of + charge with -electrons embedded

  1909:Nuclear model is concentrated in the middle (nucleus) with cloud of electrons

  1913: Bohr model- electrons orbit nucleus

  Alpha particle experiment- nucleus contains protons (+charge)

  James Chadwick provides evidence for neutrons
• What were atoms thought to be before the discovery of the electron? and who came up with this?

  tiny spheres that couldn't be divided. John Dalton
• Which sub particle led to the plum pudding model?


  electron
• Who discovered the electron?

  JJ Thomson
• What was just Thompson model called

  Plum pudding model
• what did the plum pudding suggest?

  the atomism ball of positive charge with negative electrons embedded in them.
• Who discovered that alpha particles could bounce off atoms

  Rutherford
• What was the alpha scattering experiment?

  At experiment in which alpha particles were fired at thin gold foil. The results from the experiment were recorded
• what was concluded from the alpha particle scattering expierment?

  that the mass of a atom was concentrated at the centre (nucleus) and that iy was charged.
• Who discovered that electrons orbit the nucleus at fixed distances

  Neils Bohr
• How were protons discovered?

  Rutherford showed that the nucleus can be divided into smaller particles which each have the same charge as a hydrogen nucleus
• What did James Chadwick discover?

  He discovered the neutron
• what's the difference between nuclear model and plum pudding model (2)

  -in plum pudding, nucleus is a positive sphere with negative electrons embed in it

  -in nuclear model nucleus has no charge with electrons orbiting it from a specific distances
• what's the charge of a proton

  +1 (positive)
• what's the charge of a neutron

  0 (neutral)
• what's the charge of an electron

  -1 (negative)
• Why do atoms have overall no charge

  The total number of negative electrons are equal to the number of positive electrons= 1-1=0