2.11 Group II Metals and their compounds Flashcards
(31 cards)
S-block element
An element which has an atom with highest energy/outer electron in an s-subshell (orbital).
Where are Group II elements found
• Group II metals are isolated from ores (mostly carbonates) found in the Earth’s crust.
What is the other term for Group II metals
Alkaline Earth Metals
Why do they have similar chemical properties
Each have full s-subshell (2 electrons in outer shell)
Reactivity increases down the group
Why does Atomic/ionic radius increases down the group
o Complete electron shell is added as the group descends
Why is Ionic radius smaller than atomic radius
Greater proton:electron ratio
Greater electrostatic attraction between positive nucleus and the negatively charged outer electrons causing outer electrons to be pulled closer to the nucleus.
Why does First Ionisation energy decrease down the group i.e why do they become more reactive down the group?
Complete electron shell added as the group descends
This causes an increase in atomic radius
This causes an increase in the shielding effect
Both cause the electrostatic attraction between the positively charged nucleus and the negatively charged outer electrons to decrease therefore less energy is required to remove an electron
Why is second ionisation energy significantly lower than first
Proves that Alkaline Earth Metals readily lose 2 electrons (from outer shell)to form M2+
Method for the Combustion of Group II Metals
- Measure the mass of a crucible and lid using a balance
- Add some metal and measure the mass of the crucible, lid and metal
- Place the crucible on a pipeclay triangle and heat strongly (for 5mins), raising the lid at intervals to allow air into the crucible
- Allow the crucible to cool and weigh
- Repeat the heating, cooling and weighing until there is “constant mass”
Equation for the combustion of metal in oxygen
Group II metal + Oxygen => Metal Oxide
2M + O2 =>2MO
Heating heavy metal (e.g. Barium) in O2 rich environment can produce a Metal peroxide (MO2)
Observations for Group II metals burned in Oxygen
Mg - Burns with a bright white light to produce white solid
Ca - Burns with a red flame to produce white solid
Sr - Burns with a crimson flame to produce white solid
Ba- Burns with an apple green flame to produce white solid
Always exothermic
Always white solid
Group II metal and Water
Metal Hydroxide (M(OH)2) formed oWhite solid
Produces an alkaline solution (because of the hydroxide produced
Reaction increases with vigour as group descends
N.B- Mg(OH)2 insoluble
N.B- Ca(OH)2 slightly soluble
•Solubility of Hydroxides increases down the group
Equation for reaction of Group II with water
Group II Metal + Water => Metal Hydroxide + Hydrogen gas
M + 2H2O =>M(OH)2 + H2
Observations with Mg and Water
- Few bubbles produced slowly
* Metal dulls
Observations with Calcium and Water
• Fizzing (gas released)
• mixture warms up
• metal rises and falls (Heat from the
reaction warms the water causing it to
rise)
• metal disappears
• white solid producedObservations with Mg and Steam
- Burns with a bright white light
- Heat released
- White solid produced
Reaction of Group II metal and acid
• Reaction increases with vigour as group descends
• Metal atoms are reducing agents
• H+ ion is reduced
• If reacted with a strong acid, resulting aqueous solution formed has pH
approx. 7
Equation for reaction of Group II metal and acid
Group II Metal + Acid => Metal salt + Hydrogen
Observations with Group II metal and HCL
- metal disappears
- fizzing
- mixture warms up
Observations with H2SO4 and Magnesium
- metal disappears
- fizzing
- mixture warms up
Observation with H2SO4 and Calcium
• fizzing initially but reaction stops
Due to formation of insoluble calcium sulfate
forms an unreactive layer over the surface of the Calcium (prevents H+ ions reaching metal surface)
Properties of Group II compounds
• When Group II metal atom (M) reacts, it loses electrons to form the M2+ ion
Therefore, product formed is an ionic compound as a crystalline solid
• M2+ ions in a Group II compound do not absorb visible light
Therefore, product formed is a white crystalline solid
Group II oxides and water
Metal oxide + Water => Metal Hydroxide
MO + H2O => M(OH)2
N.B- Mg(OH)2 insoluble
N.B- Ca(OH)2 slightly soluble
•Solubility of Hydroxides increases down the group
Reaction of limewater and CO2
CaO + H2O => Ca(OH)2 (Limewater)
Ca(OH)2 + CO2 => CaCO3 + H2O
CaCO3 + H2O + CO2 => Ca(HCO3)2
