C2

• When Democritus first conceived of atomic theory, around 500 BC, how did he describe atoms?


  Separated from each other by empty space

  Small spheres

  The smallest possible unit of matter 
• In the 1800's, John Dalton described atoms as solid spheres, and suggested that different types of spheres make up the different elements. 
• Plum pudding model

  In 1897 J. J. Thomson theorised that an atom consisted of a ball of positive charge, with negative electrons mixed throughout it.
• How Rutherford developed the nuclear model

  1. In Rutherford's experiments, alpha particles were fired at a thin sheet of gold foil.
  2. Most particles passed through, but some were deflected off course. 
  3. This caused him to hypothesise that there was a dense region of positive charge at the centre of the atom that repelled the alpha particles.
  4. As a result he developed the nuclear model of the atom, in which there was a central positive nucleus, surround by negative electrons. 
• One issue with Rutherford's nuclear model was that the atom should collapse as the negative electrons would be attracted to the positive nucleus, causing them to rush inwards.

  In response to this, in 1913 Bohr suggested that electrons orbit the nucleus in shells which prevents the atom from collapsing. 
• molecule

  made from 2 or more of the same atom, and those atoms are not chemically combined
• Compound


  A substance made from more than one type of element chemically bonded together.
• When metal atoms react, they lose electrons from their outer shell. 

  This creates ions with a positive charge. 
• three general properties of metals

  Sonorous (produce a ringing sound when struck)

  Good conductors of heat 

  Malleable
• two properties of the Group 1 metals (alkali)

  soft

  reactive
• As you go down group 1, the metals become more reactive. Their melting and boiling points decrease.
• The reactivity of group 1 elements increases as you go down the group because the atoms become larger, which means that the outer electron becomes further from the nucleus.

  This in turn means that the electrostatic attraction between the positive nucleus and the outer negative electron decreases in strength. 

  As a result the outer electron will be lost more easily, and so the element will be more reactive
• Alkali metal + water ➔ metal hydroxide + hydrogen
• Halogen displacement reactions


  • Halide salts (e.g. KCl, KBr, KI) are colourless
  • Bromine water is orange
  • Chlorine water is colourless
  • Iodine water is brown
• Halide salts + halide waters

  A) bromine, orange solution

  B) no reaction, colourless

  C) no reaction, colourless

  D) iodine, brown solution

  E) no reaction, colourless

  
• Colours and physical states of the halogens at room temperature

  1. Fluorine is a poisonous yellow coloured gas and is the most reactive halogen
  2. Chlorine is a green coloured gas.
  3. Bromine is a red-brown volatile liquid which is also poisonous. 
  4. Iodine is a grey coloured solid with purple vapours. 
• properties seen in group 7 elements

  They can form covalent bonds with other non-metals

  Their ions usually have a 1- charge
• Melting and boiling points of the halogens increase as you go down the group
• The halogens exist as diatomic molecules, meaning each molecule consists of two atoms.

  The two atoms are joined by a covalent bond, which allows each atom to share an electron, giving each atom a full outer shell.
• Atoms need a full outer shell of electrons in order to be stable. One way they can achieve this is by gaining or losing electrons. 

  Those that gain electrons become ions with a negative charge, whilst those that lose electrons become ions with a positive charge. 
• Ions with opposite charges will attract each other. 

  This force of attraction between oppositely charged ions forms an ionic bond. 
• three properties that ionic compounds have:

  High melting and boiling points

  High strength bonds

  Conduct electricity when liquid
• 1. Hydroxide:  OH-
  2. Sulphate:  SO42-
  3. Nitrate:  NO3-
  4. Carbonate:  CO32-
  5. Ammonium:  NH4+