Group 2 elements

Question 1

The first and second ionisation energies..

Answer 1

DECREASE down the group.

• The electron being removed is FURTHER AWAY from the nucleus
• MORE SHIELDED from the nuclear charge as a result of more electron SHELLS.
• The outermost electron is LESS strongly attracted to the nucleus and requires LESS energy to be removed.

Question 2

Metallic bond in Group 2 elements

Answer 2

They form GIANT METALLIC STRUCTURES.

METALLIC BONDING ~ the electrostatic attraction between the positive metal ions and the delocalised electrons.

• Atoms in metals lose their outer shell electrons to form positively charge ions.
• The electrons lost from each metal atom are shared between ALL THE IONS in the metallic structure.
• A single electron is attracted to LL THE CATIONS surrounding it.

Question 3

ATOMIC RADII …

Answer 3

INCREASES down the group.

• The number of electron shells increases down the group.

Question 4

DENSITY …

Answer 4

INCREASES down the group.

• The ATOMIC MASS increases MORE than the atomic radii down the group and hence the SIZE of the atom.

Question 5

MP & BP …

Answer 5

DECREASES down the group.

• The strength of the METALLIC BONDING decreases .
• the metal ions become LARGER and so the distance between the delocalised electrons and nuclei INCREASES.
• The metallic bonding becomes WEAKER

Question 6

Group 2 elements with OXYGEN

Observation with MAGNESIUM

Answer 6

metal + oxygen ——— metal oxide

• Metal is OXIDISED from 0 to +2
  (reducing agent)
• Oxygen is REDUCED from 0 to -2
  (oxidising agent)
• A REDOX reaction

OBSERVATION WITH MAGNESIUM:
- Glowing
- White solid is produced

Question 7

Group 2 elements with WATER

Observation with Mg and Ca

Answer 7

metal + water — metal hydroxide + hydrogen

• Metal is OXIDISED from 0 to +2
  ( reducing agent)
• TWO of the four HYDROGEN atoms are REDUCED from +1 to 0.
• TWO H atoms remain UNCHANGED
• The water is the oxidising agent
• A REDOX reaction

MAGNESIUM:
- slight effervescence

CALCIUM:
- vigorous effervescence
- white solid suspension forms

Question 8

Group 2 elements with DILUTE ACIDS

Observation with MAGNESIUM & HNO3

Answer 8

metal + acid ——— salt + hydrogen

• Metal is OXIDISED from 0 to +2
  ( reducing agent)
• H+ is REDUCED as its oxidation number decreases from +1 to 0. ( oxidising agent)
• A REDOX reaction

MAGNESIUM & HNO3:
- gets hot
- effervescence
- solid dissolves
- with lighted splint the gas makes a squeaky pop sound

Question 9

The REACTIVITY…

Answer 9

INCREASES down the group.

Due to the DECREASE in first and second ionisation energies down the group.

Question 10

Group 2 OXIDES with WATER

Answer 10

Release aqueous OH- ions , and form alkaline solutions.

CaO (s) + aq ——– Ca2+(aq) + 2OH-(aq)

                       OR CaO (s)  +  H2O (l)   -----  Ca2+(aq) + 2OH-(aq)

Question 11

Group 2 HYDROXIDES solubility in water

Answer 11

• Only SLIGHTLY soluble in water.
• Once the solution is SATURATED, any further metal ions reacts with the hydroxide ions to form SOLID PRECIPITATE.

Ca2+ (aq) + 2OH- (aq) ———– Ca(OH)2 (s)

Question 12

TRENDS in solubility of group 2 hydroxides

Answer 12

INCREASES down the group.

• More OH-(aq) ions are released
• This means the ALKALINITY of the solution INCREASES down the group.

BERYLLIUM OXIDE is INSOLUBLE in water.

Mg(OH)2 (s) :
- SLIGHTLY soluble in water
- the solution has a LOW concentration of hydroxide ions.
- pH is about 10

Ba(OH)2 (s) :
- MUCH MORE soluble in water
- the solution has a GREATER concentration of hydroxide ions.
- pH is about 13.

Question 13

USES 1

Answer 13

• Used in purposes where NEUTRALISING is important.

AGRICULTURE:

• Solid calcium hydroxide is added to fields as LIME to increase the pH of soil.
• It NEUTRALISES the acid in the soil to form NEUTRAL WATER.
• IONIC equation:
  Ca(OH)2(s) + 2H+(aq) — Ca2+(aq) + 2H2O(l)

Question 14

USES 2

Answer 14

TREATING INDIGESTION:

• Magnesium and calcium carbonate are used in indigestion tablets.
• MILK OF MAGNESIA is a suspension of white magnesium hydroxide .
• They all NEUTRALISE the excess acid in the stomach.

Question 15

USES 3

Answer 15

BUILDING MATERIALS:

• Calcium carbonate as LIMESTONE &
  MARBLE.
• They can ERODE in ACID RAIN