Chemistry Group 2 and 7

Reactivity down group 2

Increases

Reactivity down group 2 increases. Why?

Increased shielding

increased atomic radius

therefore easier to remove e-

Melting point down group 2

decreases

Melting point down group 2 decreases. Why?

e- get further from the nucleus so there is weaker attraction between them and +ve metal ions

Metal oxide into hydroxides ionic eq

O2- + H2O → 2OH-

Solubility of metal hydroxides down group 2

increases

Alkalinity down group 2

increases

Solubility of Metal sulphates down group 2

Decreases

Reaction of Mg in oxygen

Easy to ignite

Bright white flame

forms white powder of MgO

Reaction of Ca in oxygen

Difficult to ignite

Red flame

Reaction of Sr in oxygen

Difficult to ignite

Red flame

Reaction of Ba in oxygen

Difficult to ignite

Apple green flame

Mg react with water/steam

NO REACTION with water

vigorous with steam (Mg+ H2O → MgO + H2)

Ca react with water

Moderate

Sr react with water

Rapid

Ba react with water

Rapid

Metal + Water

Metal hydroxide + hydrogen

Metal oxides pH

Basic

Metal + acid

Salt + Hydrogen

Group 2 metals in HCl

Vigorous reaction

Magnesium + H2SO4

Reacts vigorously

Ca + H2SO4

Reaction slows as slightly soluble CaSO4 layer forms

Sr + H2SO4

Reaction quickly stopped as insoluble SrSO4 layer forms

Ba + H2SO4

Reaction quickly stopped as insoluble BaSO4 layer forms

Metal Hydroxide + acid

Salt + Water

All but BeCo3 carbonates are soluble/insoluble?

Insoluble

Metal carbonate + acid

Salt + water + CO2

Main use of calcium compounds

raise soil pH

Calcium in removing sulfur dioxide from flue gases

sulfur scrubbing

Limestone

Impure calcium carbonate

Quicklime

Calcium oxide (made from thermal decomposition of calcium carbonate)

Slaked lime

Calcium hydroxide (water added to quicklime)

Use of barium in medicine

Intestinal X-Ray, it absorbs X-Rays so shows up white on the scan.

Which form is barium in in medicine and why?

Barium sulphate because it is insoluble and so not absorbed into blood

Use of Magnesium in the body

used to neutralise stomach acid

Use of Magnesium in extraction of Titanium

Displacement (reduction) reaction. First TiO2 heated in stream of chlorine in presence of coke forming TiCl4. Then reduce this with magnesium.

Colour and State: Fluorine

Pale yellow gas

Colour and State: Chlorine

Green-Yellow gas

Colour and State: Bromine

Orange-Brown liquid

Colour and State: Iodine

Grey Black solid (purple vapour)

Melting point down group 7

Increase, more e- means stronger van der walls

Bond strength down the group

Decreases, bonding pair gets further from the nucleus, weaker attraction.

Why is fluorine the exception to bond strength down the group

It is so small its lone pairs are close together so repel and push the 2 atoms apart

What are Van der Walls

Instantaneous dipole in one MOLECULE induces an induced dipole in a neighbouring MOLECULE

Oxidising power down group 7

Decreases, atomic radius and shielding increases, weaker attraction to e-

Reducing power of HALIDES down group 7

Increases, ions are larger outer e- further from nucleus, weaker attraction, easier to remove

Test for Halide ions

Dissolve in nitric acid, add silver nitrate

Chlorine PPT

White

Bromine PPT

Cream

Iodine PPT

Yellow

Why add nitric acid first when testing

Remove CO3²- ions as they would cause a false +ve

Why do we sometimes add ammonia to confirm test

PPT is unclear

Add dilute NH3, if it dissolves it is…

Chloride

Add concentrated NH3, if it dissolves it is…

Bromide

Testing for halides with concentrated sulphuric acid. Chloride

𝐶𝑙− produces misty white 𝐻𝐶𝑙 fumes. Bad reducing agent so no redox

Testing for halides with concentrated sulphuric acid. Bromine, 1st step

Acid - base reaction, produces reddish brown gas

Bromine, 2nd step

HBr reduces sulphuric acid into SO2 and Br2 gas

Iodine

Acid-Base forms Iodine (purple) gas, it reduces the acid to hydrogen sulphide which has a bag egg smell.

Chlorine(gas) + XOH

XCl + XClO + H2O

Use of chlorine in water

Purify

Cl2 + H2O

HCl + HClO* *this kills bacteria

HClO disassociates into

ClO- + H+

-Ve of using Chlorine in swimming pools

• could form chlorinated hydrocarbons

• has to be topped up regularly in shallow pound because sunlight causes reaction (Cl2 + 2H2O → 4HCl +O2)