Trends In Properties For S Block Elements And Group 7

Question 0

What can potassium form when burnt in oxygen under the right conditions?

Answer 0

Potassium peroxide (K₂O₂) and potassium super oxide (KO₂)

Question 1

What happens when the alkali metals and alkali earth metals burn in oxygen?

Answer 1

They form oxides.

Question 2

Describe the trend in violence for the reaction of group one metals with water.

Answer 2

The reaction becomes more violent as you go down the group.

Question 3

Give the equation for the reaction of Sodium with water (same for all alkali metals).

Answer 3

2Na + 2H₂O → 2NaOH + H₂

Question 4

Describe the reaction of magnesium and water.

Answer 4

Magnesium reacts very slowly with liquid water but burns in steam:

Mg + 2H₂O → MgO + H₂

Question 5

Describe the reaction of other alkali earth metals with water.

Answer 5

They form hydroxides. E.g Ca + 2H₂O → Ca(OH)₂ + H₂

The solubility of hydroxides increases down the group. Hence Calcium hydroxide is not very soluble and may form a white solid.

The reaction rate of the alkali earth metals and water increases down the group.

Question 6

Describe the reaction between acids and group one elements.

Answer 6

They react very violently with acids and as such they are not allowed to be performed in the school laboratory.

Question 7

Outline the reaction between group two metals and acids.

Answer 7

They react to produce Hydrogen gas. E.g:

Mg + H₂SO₄ → MgSO₄ + H₂

Or as an ionic equation: Mg + 2H⁺ → Mg²⁺ + H₂

Question 8

State the flame colors of relevant Metals.

Answer 8

Lithium - Red
Sodium - Yellow/orange
Potassium - Lilac
Calcium - Brick red
Strontium - Crimson 
Barium - Apple green
Magnesium - No colour.

Question 9

Outline the functions of calcium and phosphorus in skeletal systems.

Answer 9

Calcium is the most abundant mineral in the body with around 99% of that found in teeth and bones. Phosphorus sis the other element needed in bone formation. Calcium hydroxyapatite, Ca₅(OH)(PO₄)₃ and calcium carbonate are the main minerals in bone.

Question 10

In what form do the halogens exist?

Answer 10

They exist as diatomic molecules.

Question 11

Describe the physical appearance of the halogens.

Answer 11

Fluorine is a poisonous yellow gas.
Chlorine is a poisonous yellow/green gas.
Bromine is a heavy brown liquid which is very volatile.
Iodine is a shiny, dark grey solid which sublimes to give a purple vapour on gentle heating

Question 12

Describe the trend in changing van der waals forces as you go down the group.

Answer 12

The strength of the van der waals forces increases as you go down the group due to increasing numbers of electrons.

Question 13

How do halogens react with metals?

Answer 13

They form ionic bonds with metals by gaining one electron to form an octet of valance electrons and forming “X”⁻ ions.

Question 14

What is the trend in reactivity of the halogens?

Answer 14

The reactivity decreases as you go down the group.

Question 15

Why does the reactivity of the halogens decrease?

Answer 15

Because of its small size and high electronegativity, Flourine Is able to form ions most easily. As the electron cloud gets bigger it is less able to form ions and so reactivity decreases.

Question 16

How do the halogens react with non-metals.

Answer 16

They react by forming covalent bonds. Empty “D” orbitals are used in bonding by promoting electrons from “P” orbitals. In this manner chlorine can form three covalent bonds. However Flourine does not have access to “D” orbitals so can only form one covalent bond.

Question 17

Describe the displacement reactions seen in halogens.

Answer 17

When Chlorine is added to a solution of bromide e.g Sodium bromide, the bromine is displaced and Sodium chloride is formed:

Cl₂ + 2NaBr → 2NaCl + Br₂

Or as an ionic equation: Cl₂ + 2Br⁻ → 2Cl⁻ +Br₂

This happens because Chlorine is a stronger oxidizing agent than bromine. A similar reaction happens between chlorine and iodine compounds. And Bromine will displace iodine in a similar way.

Question 18

Outline a method by which Halogens can be identified.

Answer 18

They can be identified by their reactions with silver nitrate solution. Silver Nitrate diluted with Nitric acid is added to the halide compound in solution.

However all Halide precipitates are sensitive to light and the colour darkens if they are left in the test tube.

Question 19

What happens to a chlorides in the halide test?

Answer 19

A white precipitate of silver chloride is produced which is soluble in dilute ammonia solution.

KCl + AgNO₃ → AgCl + KNO₃

Or Ionically: Cl⁻

Question 20

What happens to bromides in the halide test?

Answer 20

A cream precipitate of Silver Bromide is formed which is soluble in concentrated ammonia solution.

KBr + AgNO₃ → AgCl + KNO₃

Ionically: Ag⁺ + Br⁻ = AgBr

Question 21

What happens to iodides in the halide test?

Answer 21

A pale aye low precipitate is formed of Silver Iodide. Insoluble even in concentrated ammonia solution.

KI + AgNO₃ → AgI + KNO₃

Or ionically: Ag⁺ + I⁻ → AgI