group 2 and 7 Flashcards
What is a common name given to group 2 metals
Alkaline earth metals
What is the most reactive metal of group 2
Barium
List 3 physical properties of group 2 metals
- High melting and boiling points
- Low-density metals
- Form colourless (white) compounds
What ions does group 2 form in redox reactions?
Group 2 lose their two outer electrons to form 2+ ions
The highest energy electrons of group 2 metals are in which subshell?
S-subshell
What are the relative reactivities of Group 2 elements in redox reactions with oxygen
When group 2 metals are burnt in oxygen, they form solid white oxides.
What are the relative reactivities of Group 2 elements in redox reactions with water
The group 2 metals react with water to give metal hydroxide and a hydrogen gas
What are the relative reactivities of Group 2 elements in redox reactions with dilute acids
When group 2 metals react with dilute hydrochloric acid, you get a metal chloride and hydrogen gas
What is the trend of reactivity down group 2 metals
- Reactivity increases
- Electrons are lost more easily because larger atomic radius and more shielding
What is the trend in first ionisation energy down group 2
- Decreases
- Because electron number increases so shielding increases
- Increases atomic radius so there are weaker nuclear forces
- So less energy is needed to remove the electron
Which group 2 element reacts very slowly with water?
Magnesium
What type of reaction is the reaction between group 2 elements and oxygen?
Redox reaction
What type of reaction is the reaction between group 2 metals and water?
Redox reaction
What is oxidised and what is reduced in a reaction between group 2 metal and water?
- Metal is oxidised
- One hydrogen atom from each water is reduced
What group 2 metal oxide is insoluble in water?
Beryllium oxide
What is the trend in hydroxide solubility down group 2?
- Increases down the group
What is the use of Ca(OH)2
Used to neutralise soil
What is the use of Mg(OH)2
- Antacid to treat indigestion
What is calcium carbonate used for
- Present in limestone and marble
- Used in building construction
List 2 properties of halogens
- Low melting and boiling point
2. Exist as diatomic molecules
Explain the trend in the boiling group down group 7
- Increases down the group
- Because size of the atom increases as more occupied shells
- Stronger London forces of attraction between molecules, take more energy to overcome
Explain the trend in reactivity down group 7
- Reactivity decreases
- Because atomic radius increases
- Electron shielding increases
- Ability to gain an electron and form -1 ions decreases
Explain the trend in oxidising ability down the group
- Decreases down the group
- Cl has the fewest occupied electron shells, and greatest nuclear attraction so it is easiest to gain electrons and be reduced
Explain the trend in reducing the ability of the halides down the group
- Increases down the group
- Iodine has the most occupied electron shells so outer electrons are further from the nucleus, and is the easiest to be oxidised and lose electrons
What is the colour of chlorine in water
Pale green
What is the colour of bromine in water
Orange
What is the colour of iodine in water
Brown
What is the colour of chlorine in cyclohexane
Pale green
What is the colour of bromine in cyclohexane
Orange
What is the colour of iodine in cyclohexane
Violet
Define disproportionation
When an element is oxidised and reduced at the same time in a redox reaction
What type of reaction is the reaction of chlorine with water
Disproportionation
Why is chlorine added to drinking water
It kills the bacteria in the water and makes it safer to drink
What is the equation for forming bleach?
Cl2 + 2NAOH -> NaCl + NaClO + H2O
What is the formula of bleach
NaClO
What kind of molecules do halogens exist as?
Diatomic molecules
How can you see the colour change in a displacement reaction with halogens?
By adding an organic solvent like hexane, it settles out a distinct layer above the aqueous solution
Describe the test for halides
- Add dilute nitric acid
- Add silver nitrate solution
- A precipitate of the silver halide is formed
- Test results by adding ammonia solution
What is observed in the silver test for halides if a chloride ion is present?
- Precipitate colour: white
- Solubility in ammonia: dissolved in dilute NH3
What is observed in the silver test for halides if a bromide ion is present?
- Precipitate colour: Cream
- Solubility in ammonia: dissolves in concentration
What is observed in the silver test for halides if an iodide ion is present?
- Precipitate colour: Yellow
- Solubility in ammonia: insoluble in concentration
What are the alternatives to using chlorine in water and explain them?
- Ozone
- A strong oxidising agent which makes it good for killing microorganisms, its expensive to produce and has a short-half life so it’s treatment isn’t permanent - Ultraviolet light
- It kills microorganisms by damaging their DNA, it is ineffective in cloudy water and it won’t stop the water from being contaminated further down
