chemistry

• element- only made up of one type of atom

  Compound- two or more different elements chemically joined together

  Mixture- two or more different elements that are not chemically joined together
• John Dalton-

  published about atoms in 1803

  atoms cannot be divided
• JJ Thompson-

  1904 discovered electron

  plum pudding model

  ball of positive charge, negative electrons
• Ernest Rutherford-

  1909 tested plum pudding model

  fired alpha particles at thin gold sheet

  nuclear model

  mass of atom is concentrated in nucleus

  nucleus positive

  atoms are mostly empty space
• Niels Bohr-

  1913 discovered Planetary model

  positive charge nucleus

  electrons orbit in shells
• James Chadwick-

  1932 discovered neutrons (with mass/ no charge)
• nobel gases (group 0) were not in Mendeleev's table
• John Newlands elements were ordered in atomic weight
• Mendeleev's ideas:

  • The elements are arranged in order of increasing atomic mass.
  • The horizontal rows are called periods.
  • The vertical columns are called groups.
  • Elements in the same group are like each other.
• Mendeleev's table:

  gaps

  ordered atomic weight

  In common:

  groups (with similar properties)

  Modern table:

  ordered atomic number

  has every element
• modern table-

  • elements are arranged in order of increasing atomic number.
  • horizontal rows are periods.
  • vertical columns are groups.
  • Elements in the same group are similar to each other
• group 1-

  reactivity increases (atoms gets larger, outer electron futther from nucleus)

  alkali metals

  soft, low melting points, low densities
• Lithium-

  reacts with water:

  floats, fizzes, becomes smaller until disappeared

  lithium + water → lithium hydroxide + hydrogen

  2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
• Sodium-

  reacts with water:

  melts forming a ball, moves on surface, fizzes until gone

  sodium + water → sodium hydroxide + hydrogen

  2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
• Potassium-

  reacts with water:

  melts and floats, moves fast on surface

  potassium + water → potassium hydroxide + hydrogen

  2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
• test for hydrogen gas-

  1.     Collect the gas in a test tube.

  2.    Put the flame from a burning splint into the top of the test tube.

  3.    The gas will burn quickly and give off a squeaky ‘pop’.

  lilac flame- hydrogen present
• tarnish-

  metals are cut, appear shiny and grey

  changes into dull and white when reacting with oxygen.
• Lithium-

  reacts with O2:

  tarnish slowly- relatively low reaction with O2

  lithium + oxygen → lithium oxide

  4Li(s) + O2(g) → 2Li2O(s)
• Sodium-

  reacts with O2:

  tarnishes faster- greater reactivity.

  sodium + oxygen → sodium oxide

  4Na(s) + O2(g) → 2Na2O(s)
• Potassium-

  reacts with O2:

  tarnishes quickly, more reactive than K and Li

  potassium + oxygen → potassium oxide

  4K(s) + O2(g) → 2K2O(s)
• Group 7-

  halogens

  non- metals

  each molecule has 2 halogen atoms joined by 1 covalent bond

  all have 7 electrons on outer shell

  go down G7, forces of attractions increases between molecules

  melting/ boiling point increases going down:

  ·        molecules become larger.

  ·        The intermolecular forces become stronger.

  ·        More energy is needed to overcome these forces.
• Chlorine- pale green- gas

  Bromine- brown- liquid

  Iodine- purple/ black- solid
• chemical test for Chlorine

  Damp litmus paper is bleached turns white when placed in chlorine

  If blue litmus paper turns red then white, chlorine is present
• displacement reaction- a more reactive halogen displaces a less reactive halogen from its solution/ ore.
• G7 trends-

  its atom's outer shells gain an electron, forming negatively charged ions, called anions. (gains 1 electron- -1 charge)
• Group 0:

  nobel gases

  full outer shell

  unreactive

  atomic mass increases going down

  boiling/ melting/ density increases
• G0-

  non- metals

  low boiling points

  helium lowest boiling point

  atoms get larger going down

  forces get stronger
• chemical properties-

  When elements react, their atoms complete their outer shells by losing, gaining, or sharing electrons. not G0 (full outershell)
• ionic bonding-

  metal atoms lose electrons to become positive charge ions

  non- metal atoms gain electrons to become negative ions
• covalent bonding-

  forms when 2 non-metal atoms share a pare of electrons.

  things with covalent bonds within molecules often have low melting/ boiling points (hydrogen and water)
• metallic bonding-

  outer shell electrons (metal atoms) are delocalised- free to move

  resulting in electrons forming a strong metallic bond
• properties of Ionic substances-

  giant ionic structure structure

  ^ - strong electrostatic forces of attraction acting in all directions between opposite charge ions

  high melting/ boiling points- solid at room temp

  energy must be transferred to a substance to make it melt/ boil
• ionic compound conducts electricity when:

  melted- liquid

  dissolved in water to form a aqueous solution
• covalent-

  multiple bonds

  properties of simple structure:

  low melting/ boiling points

  do not conduct electricity

  giant properties:

  high melting points

  electrical conductor
• Graphite-

  3 carbon atoms

  used for lubricant

  softer than diamond

  conducts electricity (free electrons)

  high melting/ boiling points
• Diamond-

  form of carbon (each carbon atom is joined to 4 other carbon atoms creating a giant covalent structure)

  hard

  high melting points

  used in cutting tools

  does not conduct electricity
• properties of metals-

  strong

  hard

  can be beaten or pressed into shape

  made into wires

  good conductors of heat and electricity
• fullerenes-

  60 carbon atoms joined together by string covalent bonds

  examples: nanotubes and buckminsterfullerene (low melting point and slippery)
• Graphene-

  single layer of graphite

  high melting point

  strong

  conducts electricity

  useful in electronics and for making composites
• atoms cannot be created or destroys-can recharge to create new substances