C8 - Reactivity Trends Flashcards
Why are group 2 elements called reducing agents?
Because it is able to reduce other species as it loses 2 electrons / is oxidised during reactions and another species is reduced.
How do group 2 elements react with oxygen?
They all react with oxygen to form a metal oxide with the general formula MO.
E.g.
2Mg + O2 -> 2MgO
Mg is oxidised from 0 to +2
O is reduced from 0 to -2
How do group 2 elements react with water?
They react to form an alkaline hydroxide with the general formula M(OH)2 and hydrogen gas.
(Reactivity increases down the group.)
E.g.
Sr + 2H20 -> Sr(OH)2 + H2
Sr is oxidised from 0 to +2
H is reduced from +1 to 0
How do group 2 elements react with dilute acids?
They react to form a salt and hydrogen.
(Reactivity increases down the group)
E.g.
Mg + 2HCl -> MgCl2 + H2
Mg is oxidised from 0 to +2
H is reduced from +1 to 0
Why does the reactivity of group 2 elements increase down the group?
The atoms of group 2 elements react by losing electrons to form +2 ions which requires the input of 2 ionisation energies.
The first and second ionisation energies decrease going down the group because the attraction between the nucleus and outer electrons decreases due to increasing atomic radius and increased shielding.
How do group 2 oxides react with water?
They release hydroxide ions and form alkaline solutions of the metal hydroxide.
E.g.
CaO + H2O -> Ca2+ + 2OH-
How do group 2 hydroxides react with water?
They’re only slightly soluble in water and, when the solution becomes saturated,many further metal and hydroxide ions form a solid precipitate.
E.g.
Ca 2+ + 2OH- -> Ca(OH)2
How does the solubility of group 2 hydroxides in water vary down the group?
It increases down the group so solutions become more alkaline.
What are group 2 compounds used for?
Neutralising acids e.g. For neutralising acids in soils and antacids for treating indigestion.
How reactive are halogens?
They’re the most reactive non-metallic group.
They occur on Earth as stable ions dissolved in sea water or combined with Na or K as solid deposits.
What are the trends in boiling temperature of the halogens (at RTP)?
Boiling points of halogens increases going down the group. This is because there are more electrons meaning there are stronger London forces so more energy is required to break the intermolecular forces.
What states do the halogens exist as at RTP?
At RTP, all halogens exist as diatomic (X2) molecules.
The group contains elements in all 3 physical states from gas to liquid to solid down the group (Cl gas, I is solid).
In their solid states the halogens form lattices with simple molecular structures.
What occurs during the redox reactions of halogens?
(These are the most common type of reaction for halogens)
Each halogen requires just 1 electron for a full outer shell.
Therefore, each halogen atom gains an electron and is reduced to form a 1- halide ion with the electron configuration of the nearest noble gas.
Another species loses electrons to halogen atoms and is oxidised so the halogen is known as an oxidising agent.
Why are halogens also known as oxidising agents?
They gain an electron from another species and becoming reduced, causing the other species to lose an electron and become oxidised.
What occurs during halogen-halide displacement reactions?
A halogen solution is added to aqueous solutions of other halides e.g. Cl solution (Cl2) is added to bromine ion and iodine ion solutions.
If the halogen added is more reactive than the halide present, a reaction occurs and the halogen displaces the halide from the solution.
This causes the solution to change colour.
