CIE IGCSE Chemistry

Revision Notes

9.2.1 Group Properties

Group I Properties & Trends: Basics

The Group I metals

  • The Group I metals are also called the alkali metals as they form alkaline solutions with high pH values when reacted with water
  • Group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium
  • They all contain just one electron in their outer shell

Physical properties of the Group I metals

  • The Group I metals:
    • Are soft and easy to cut, getting softer and denser as you move down the Group (sodium and potassium do not follow the trend in density)
    • Have shiny silvery surfaces when freshly cut
    • Conduct heat and electricity
    • They all have low melting points and low densities and the melting point decreases as you move down the Group

 

Group 1 metals in Periodic Table, IGCSE & GCSE Chemistry revision notesThe alkali metals lie on the far left-hand side of the Periodic table


Chemical properties of the Group I metals

  • They react readily with oxygen and water vapour in air so they are usually kept under oil to stop them from reacting
  • Group 1 metals will react similarly with water, reacting vigorously to produce an alkaline metal hydroxide solution and hydrogen gas

Reactions of the Group I metals and water

Reactions of the Group I metals and water table, IGCSE & GCSE Chemistry revision notes

Extended Only

Group I Properties & Trends

Electronic configuration and reactivity in Group I

Electronic configuration of Li, Na and K, IGCSE & GCSE Chemistry revision notesDot and cross diagram showing the electronic configuration of the first three elements in Group I

 

Explaining the trend in reactivity in Group I

  • The reactivity of the Group 1 metals increases as you go down the group
  • Each outer shell contains only one electron so when they react, they lose the outer electron which empties the outermost shell
  • The next shell down automatically becomes the outermost shell and is already full, hence the atom obtains an electronic configuration which has a full outer shell of electrons
  • As you go down Group 1, the number of shells of electrons increases by 1 (Period number increases down the Periodic table)
  • This means that the outer electron is further away from the nucleus so there are weaker electrostatic forces of attraction
  • This requires less energy to overcome the electrostatic forces of attraction between the negatively charged electron and the positively charged nucleus
  • This allows the electron to be lost easily, making it more reactive as you go down the Group

Properties of other Alkali Metals (Rubidium, Caesium and Francium)

  • As the reactivity of alkali metals increases down the Group, rubidium, caesium and francium will react more vigorously with air and water
  • Lithium will be the least reactive at the top and francium will be the most reactive at the bottom
  • Francium is rare and radioactive so is difficult to confirm predictions

Predicted reaction with Water

Predicted Reaction with Water table, IGCSE & GCSE Chemistry revision notes

Group VII Properties & Trends

The halogens

  • These are the Group 7 non-metals that are poisonous and include fluorine, chlorine, bromine, iodine and astatine
  • Halogens are diatomic, meaning they form molecules of two atoms
  • All halogens have seven electrons in their outer shell
  • They form halide ions by gaining one more electron to complete their outer shells

Colours and states at room temperature

Colours and States at Room Temperature table, IGCSE & GCSE Chemistry revision notes

 

Trends in physical properties of the halogens

Melting point

  • The density and melting and boiling points of the halogens increase as you go down the Group

 

Melting & boiling points of the Halogens, IGCSE & GCSE Chemistry revision notesGraph showing the melting and boiling points of halogens

 

State at room temperature

  • At room temperature (20 °C), the physical state of the halogens changes as you go down the Group
  • Chlorine is a gas, bromine is a liquid and iodine is a solid

 

States of the Halogens, IGCE & GCSE Chemistry revision notesThe physical state of the halogens at room temperature

 

Colour

  • The halogens become darker as you go down the group
  • Chlorine is pale green, bromine is red-brown and iodine is black

Colours of the Halogens, IGCSE & GCSE Chemistry revision notesThe colours of the halogens

 

Electronic configuration and reactivity in Group VII

Group 7 element electronic configurations, IGCSE & GCSE Chemistry revision notesDot and cross diagram showing the electronic configuration of the first three elements in Group VII

 

Explaining the trend in reactivity in Group VII

  • Reactivity of Group 7 non-metals increases as you go up the Group
  • Each outer shell contains seven electrons and when they react, they will need to gain one outer electron to get a full outer shell of electrons
  • As you go up Group 7, the number of shells of electrons decreases (Period number decreases moving up the Periodic Table)
  • This means that the outer electrons are closer to the nucleus so there are stronger electrostatic forces of attraction that attract the extra electron needed
  • This allows an electron to be attracted more readily, so the higher up the element is in Group 7 then the more reactive it is

Reaction of the halogens with halide ions in displacement reactions

  • A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
  • The reactivity of Group 7 non-metals increases as you move up the Group
  • Out of the 3 halogens, chlorine, bromine and iodine, chlorine is the most reactive and iodine is the least reactive

Aqueous solution colour of halogens

Aqueous Solution Colour of Halogens table, IGCSE & GCSE Chemistry revision notes

 

Halogen displacement reactions

Chlorine and bromine

  • If you add chlorine solution to colourless potassium bromide solution, the solution becomes orange as bromine is formed
  • Chlorine is above bromine in Group 7 so is more reactive
  • Chlorine will therefore displace bromine from an aqueous solution of metal bromide
Potassium Bromide + Chlorine → Potassium Chloride + Bromine
2KBr (aq) + Cl2 (aq) → 2KCl (aq) + Br2(aq)

Bromine and iodine

  • Bromine is above iodine in Group 7 so is more reactive
  • Bromine will therefore displace iodine from an aqueous solution of metal iodide
Bromine + Magnesium Iodide → Magnesium Bromide + Iodine
 Br2 (l) + 2MgI (aq) → 2MgBr (aq) + I2 (aq or s)

Exam Tip

Iodine solid, solution and vapour are different colours. Solid iodine is dark grey-black, iodine vapour is purple and aqueous iodine is brown.

Properties of the other Halogens (Fluorine & Astatine)

Melting and boiling point

  • The melting and boiling point of the halogens increases as you go down the Group
  • Fluorine is at the top of Group 7 so will have the lowest melting and boiling point
  • Astatine is at the bottom of Group 7 so will have the highest melting and boiling point

Physical states

  • The halogens become harder as you go down the Group
  • Fluorine is at the top of Group 7 so will be a gas
  • Astatine is at the bottom of Group 7 so will be a solid

Colour

  • The colour of the halogens becomes darker as you go down the Group
  • Fluorine is at the top of Group 7 so the colour will be lighter, so fluorine is yellow
  • Astatine is at the bottom of Group 7 so the colour will be darker, so astatine is black

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.
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