Group 2 elements Flashcards
The first and second ionisation energies..
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.
Metallic bond in Group 2 elements
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.
ATOMIC RADII …
INCREASES down the group.
- The number of electron shells increases down the group.
DENSITY …
INCREASES down the group.
- The ATOMIC MASS increases MORE than the atomic radii down the group and hence the SIZE of the atom.
MP & BP …
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
Group 2 elements with OXYGEN
Observation with MAGNESIUM
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
Group 2 elements with WATER
Observation with Mg and Ca
metal + water ——— metal + hydrogen
hydroxide
- 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
Group 2 elements with DILUTE ACIDS
Observation with MAGNESIUM & HNO3
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
The REACTIVITY…
INCREASES down the group.
Due to the DECREASE in first and second ionisation energies down the group.
Group 2 OXIDES with WATER
Release aqueous OH- ions , and form alkaline solutions.
CaO (s) + aq ——– Ca2+(aq) + 2OH-(aq)
OR CaO (s) + H2O (l) ----- Ca2+(aq) + 2OH-(aq)
Group 2 HYDROXIDES solubility in water
- 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)
TRENDS in solubility of group 2 hydroxides
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.
USES of group 2 elements
- 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)
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.
BUILDING MATERIALS:
- Calcium carbonate as LIMESTONE &
MARBLE.
- They can ERODE in ACID RAIN
