Group 2 Trends
Specification:
-Charge density of an ion and its relation to the thermal stability of the Group 2 carbonates
-A description and comparison of the following properties of the elements and compounds of Mg, Ca, Sr, and Ba in Group 2: reactions of the elements with water and oxygen, thermal stability of the carbonates, solubility of hydroxides and carbonates.
Group 2 Elements are called Alkali Earth Metals. They are called s-block elements because their highest energy electrons appear in the s sub-shell.
As you go down the Group:
1.Reactivity increases:
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As you go down the Group, the number of energy shells surrounding the nucleus increases.
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This means the distance between the positive nucleus and outer electron increases.
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This means there is less nuclear attraction between the outer electron and positive nucleus.
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This means it requires less energy to lose an electron = more reactive
2. First ionisation energy decreases:
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As you go down the Group, the number of orbitals increases.
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This increases the distance between the outer electrons and the positive nucleus.
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This decreases the nuclear attraction to the outer electron, which makes it easier for other elements to lose an electron.
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Another reason the first ionization energy decreases is because, of the shielding effect. All orbitals are filled up with electrons that constantly repel each other.
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The further out an orbital, the greater the shielding effect, therefore, it's easier to remove an electron
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3.Electronegativity decreases:
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As you go down the Group, the tendency of electrons to be attracted by other elements decreases because the orbitals are further from the nucleus and are shielded by the inner shells.
4.Thermal stability of Group 2 carbonates increases:
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As you go down Group 2, charge density decreases.
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Smaller ions with the same charge have higher charge density and thus distort the carbonate ion more.
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This means that the compound decomposes at lower temperatures.
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For example: Calcium decomposes more quickly than Barium. This is because Calcium is more charge-dense than Barium. This means that Calcium distorts/ polarizes the carbonate ion more hence forming a precipitate at a faster rate compared to Barium. This is because Barium is more thermally stable than Calcium.
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5. Melting/Boiling point increases down the group:
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As you go down the group, the number of Instantaneous dipoles – Dipole-induced dipole interactions increases. ( Or London Forces)
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This means that it requires more energy to break the bonds and hence has a high melting and boiling point.
6. Solubility Trends down Group 2:
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N.B: All Group 2 hydroxides, carbonates, and sulphates are Sparingly soluble.
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G2 Hydroxides:
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As you do down group 2, the solubility increases.
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G2 Carbonates:
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As you go down Group 2, the solubility with G2 carbonates decreases.
Authors: Poppy Seager and Bansari Sanghvi