🧪 Group 2 & Group 7 Elements

What happens to atomic radius as go you down a group?

The atomic radius increases as there are more electrons

What is the trend of first ionisation energy down group 2?

First ionisation energy decreases down group 2

Why does ionisation energy decrease down group 2?

1. There are more electron shells so there is more shielding so less energy is needed

2. As more shells the atomic radius increases so attraction between electron and proton decreases (distance increases)

Although positive charge and electrons increase down group this effect is negated due to extra shells

What is reactivity trend of group 2?

They get more reactive down a group, because when they react they lose electrons (e,g. The lower the first ionisation energy they more reactive they are)

What do group 2 elements do when they react? (Electrons)

They loose electrons

What happens to melting point down group 2?

As group 2 metals have a normal metallic structure, the melting point decreases down group 2

why does melting point decrease down group 2?

In a metallic structure-

The metal ions are surrounded by delocalised electrons. Down the grow the metal ions get bigger but the number of delocalised electrons per ion doesn’t change and neither does the charge (2+)

So as ionic radius increases the distance between the ions and positive nucleus increases so attraction decreases so the bonds are broken more easily and the melting point decreases.

How does ionic radius increasing affect melting point in metals?

• As ionic radius of ions increases the distance between the delocalised electrons and positive nucleus increases therefore the attraction between them decreases.

• This means the metallic bonds can be broken more easily which lowers the melting point

What is the exception to the decreasing trend of melting points in group 2?

Magnesium (lowest of the group although second down)

• This is because the crystal structure (arrangement of metal ions changes)

What happens when group 2 metals react?

They get oxidised from 0 to +2

$$M\rightarrow M^{+2}+2e^{-}$$

What happens when group 2 react with water?

They form a metal hydroxide and hydrogen.

• if steam they form metal oxide and hydrogen

What happens to reactivity with water down group 2?

It becomes more reactive as ionisation energy decreases (loose electrons more easily)

What is solubility of group 2 compounds?

• Generally compounds that have single negative charge$\left(OH^{-}\right)$get more soluble down group

• While generally compounds that have double negative charge $\left(SO^{2-}_4\right)$get less soluble down group.

What is solubility of hydroxides in group 2?

They get more soluble down group

What is solubility of sulphates in group 2?

They get less soluble down group

Which sulfate is not soluble in water?

Barium sulfate $\left(BaSO_4\right)$

How to test for sulfate ions?

Add acidified barium chloride $\left(BaCl_2\right)$ to unknown ions.

If sulfate ions = white precipitate $\left(BaSO_4\right)$

Why do we acidify the barium chloride with HCL when testing for sulfate ions?

To get rid of any sulfites or carbonates which also produce a white precipitate

Uses of Barium sulphate do to insolubility?

1. Test for sulphate ions with acidified barium chloride (if sulphate forms white barium sulphate precipitate)

2. Barium meal - X-ray pictures

What is a barium meal?

Chalky white liquid containing barium sulfate

What is barium meal used for?

For X-rays as it covers the tissue inside the body (intestine, stomach, esophagus) which then comes up on X-rays.

Why is barium meal (barium sulfate) used?

• It is insoluble so forms a suspension rather than solution inside the body (not poisonous)

• As barium sulphate is opaque in X-rays so when coats inside of digestive track it can be seen on scan (normally can’t as soft tissue)

What is use of magnesium?

To extract titanium ore

What are the steps for extraction of titanium?

1. Main titanium ore is converted to titanium chloride by being heated in carbon with chlorine gas

2. The titanium chloride is then purified with fractional distillation

3. Then it is reduced by magnesium in a 1000c furnace

$$TiCl_{4\left(g\right)}+2Mg_{\left(l\right)}\rightarrow Ti_{\left(s\right)}+2MgCl_{2\left(\right)}$$

How is Calcium used in Flue gas desulfurisation?

The acidic sulfur dioxide can be removed from flue gas by reacting with an alkali

E,g Calcium Oxide, Calcium Carbonate

A slurry is made with these and sprayed onto the flue gas

$CaO_{\left(s\right)}+2H_2O_{\left(l\right)}+SO_{2\left(g\right)}\rightarrow CaSO_{3\left(s\right)}+2H_2O_{\left(l\right)}$ If Calcium Carbonate it is $CaCO_{3\left(s\right)}$ Instead and $CO_{2\left(g\right)}$

What are Group 2 alkali metals common used for?

To neutralise acids due to be alkali

How and why does boiling point change down group 7?

They increase down the group as Van der Waals forces become stronger due to there bigger side and increase of molecules mass (more electrons more frequent temporary dipoles).

How and why does electronegativity change down group 7?

It decreases down the group as the outer shell is further from nucleus and there is more shielding due to more shells so attraction and ability to attract electrons decreases.

Are halogen oxidising agents?

Yes

Do halogens become more or less oxidising?

The get less oxidising as for them to get a full outer shell/oxidise something they need to gain an electron and this gets harder down the group (further from nucleus)

When will halogen displace a halide?

If they are below them in the periodic table

How is bleach made?

If chlorine gas is mixed with cold sodium hydroxide a disproportionation of chlorine takes place (both oxidised and reduced)

What happens when chlorine and water is mixed?

A disproportionation reaction as chlorine form both chloride and chlorate ions

What is chlorine added to water?

Chlorate ions kill bacteria so chlorine/compound contains chlorate ions are added to kill bacteria

What are some of the dangerous of adding chlorine to water?

• Chlorine gas is really dangerous as it can damage eyes

• Also chlorine reacts with organic material and form Chlorinated hydrocarbons which carcinogens

What is the reducing power of halides down group?

The reducing power increase as when you go down the group it easier for the ions to lose an electron

Which halides reduce sulfuric acid?

• Bromide

• Iodide

What is overall equation between halides and sulfuric acid?

$$NaX+H_2SO_4\rightarrow NaHSO_4+HX$$

(+6)

What is reaction of halide with sulfuric when reducing enough to reduce sulfuric acid?

$$NaX+H_2SO_4\rightarrow X_2+SO_2+2H_2O$$

What does bromide reduce sulfuric acid to?

$$Br_2+SO_2+2H_2O$$

(+4)

• When formed see grey solid/purple gas

What does iodine reduce sulfuric acid to?

$$3I_2+H_2S+2H_2O$$

As most iodide is strongest reducing agent it reduces it even more the bromine and forms fumes $H_2S$ and solid iodine

(-2)

• Produces Bad egg smell

How to test for halides?

1. Nitric acid (get rid of other ions that could interfere)

2. Silver nitrate

3. Precipitate formed

Chloride- White

Bromide- Cream

Iodine- Yellow

How can you be extra sure after halide test forms precipitate?

Using ammonia solution have different solubilities

How to test with group 2 ions flame test?

1. Dip nichrome wire into concentrated HCL to clean

2. Then dip in unknown compound

3. Observe colour flame

Calcium - brick red

Strontium - red

Barium - pale green

How to test for carbonate ions?

How to test for Halide ions?

How to test for sulphate ions?

How to test for group 2 ions?

How to test for hydroxide ions?

How to test for ammonia ions?