periodic table

• group 1 elements (alkali metals)

  physical characteristic :

  • soft
  • silver metals
  • malleable
  • have low densities and can float on water

  chemical characteristics :

  • low ionisation energy, so they have low melting points
  • extremely reactive
  • they have one valance electron which they readily lose in chemical reactions - ionic/covalent bonding
• halogens (noble gases)

  physical characteristics :

  • low density - weigh very little
  • become darker as you go down the group - fluorine = pale, chlorine = yellow/green and bromine = red/brown
  • non - metals

  chemical characteristics :

  • not soluble in water
  • low melting/boiling point
  • all have 7 electrons in the outer shell
  • diatomic - each molecule contains 2 atoms joined by a single covalent bond
• elements are organised by :

  • increasing atomic number
  • elements in same group (column) have same amount of outer electron shells
  • elements in same period (row) have the same amount of electron shells
• elements in the same group have the same chemical properties because they have the same number of electrons in the outer shell
• alkali metals = group 1
• list properties of alkali metals

  • soft
  • relatively low melting point
  • high thermal and electrical conductivity
  • malleable
  • ductile
• alkali metals got the name because they react with water to make alkaline solutions (pH greater than)
• alkali metals should be stored in oil so they don't react with water vapour and oxygen in the air
• lithium reacts with water :

  • very slow reaction
  • bubbles of hydrogen form
  • doesn't melt (has highest melting points out of all the alkali metals)
• sodium reacting with water :

  • faster than lithium
  • floats on surface of water as its denser than water
  • bubbles of hydrogen form causing sodium to whizz on the surface of the water
  • melts as enough energy is given out to meet its melting point
• potassium reacts with water :

  • more violent reaction that sodium
  • bubbles of hydrogen cause whizzing on the surface of water
  • melts into shiny ball
  • burns with a lilac flame
• reactivity increase as you go down the group 1, lithium least reactive and francium is the most
• there is more electron shielding as you go down group 1 elements, there's weaker attraction between positive nucleus and outer shell electron - easier to remove outer shell electron to form a positive ion (complete outer shell)
• halogens are in group 7 - they have 7 outer shell electrons
• density increases down the group

  • helium is the lease dense and radon is the most dense
• chlorine at room temperature is pale green and is a gas
• bromine at room temperature is red-brown and is liquid
• iodine is black and solid at room temperature