reactivity trends
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where are the two electron of the outer shell in a group 2 element found?
outer s sub shell
what is the most common reaction in group 2 elements?
redox reactions, each metal ion is oxidised forming a 2+ ion. Another species will gain 2 electrons and become reduced therefore group 2 elements are also known as a reducing element.
describe the redox reaction between group 2 elements and oxygen
metal oxide is formed e.g MgO is formed when using magnesium, made up go Mg2+ and O2- ions.
what can you see when magnesium reacts with oxygen?
brilliant white light which forms white magnesium oxide
describe the change in oxidation number when magnesium reacts with oxygen
as two magnesiums are needed to react with oxygen and each magnesium increases by +2, the total increase is +4. As two oxygen are in O2 (diatomic) and each oxygen decreases by 2 the total decrease is -2.
Describe the redox reaction between group 2 elements and water
an alkaline hydroxide is formed with the general formula M(OH)2 and hydrogen gas.
Describe the redox reaction between group 2 elements and dilute acids.
salt and hydrogen gas in formed
why does reactivity increase going down the group 2 elements?
ionisation energies decrease down the group because the attraction between the nucleus and outer electron decreases as a result of its increasing atomic radius and shielding
In group 2 elements what takes up most of the energy input?
first and second ionisation energy.
Describe how group 2 oxides react with water?
hydroxide ions(OH-) are released therefore solution becomes more alkaline and filled with group 2 hydroxides. Group 2 hydroxides are only slightly soluble in water, they form a solid precipitate.
Describe the trend in solubility of group 2 hydroxides
group 2 hydroxides become more soluble going down the group so the solutions more hydroxide ions (OH-) and are more alkaline.
How are group 2 compounds used in agriculture?
Calcium hydroxide, Ca(OH)2 is added to fields to increase the pH of acidic soil. The calcium hydroxide neutralises the acid forming neutral water
How are group 2 compounds used in medicine?
they are used as antacids to neutralise stomach acid to relieve indigestion.
why does boiling point increase going down group 7 (halogens)?
• higher electron density • stronger London forces • more energy required to break the intermolecular forces • boiling point increases
where are the outer electrons found in halogens?
two electrons are in the outer s-sub shell and 5 in the outer p sub shell.
what is the most common reaction in halogens?
redox reactions, each halogen atom gains one electron to form a 1- halogen ion. I becomes reduced however the other species becomes oxidised therefore halogens are known as a oxidising agent
how can you test the trend in reactivity of halogens?
do a displacement reaction, a colour change indicates a displacement.
what colour is chlorine and bromine?
chlorine is a pale green and bromine is orange
what is the colour of iodine?
brown but for a positive result of iodine from a displacement reaction it is the colour, violet
what is the colour of fluorine?
pale yellow gas that reacts with almost any substance
what is the colour of astatine?
rare decays rapidly, has never been seen. Least reactive halogen
why do halogens become less reactive going down the group?
• atomic radius increases • sheilding increases • less nuclear attraction to capture an electron • reactivity decreases
what is disproportionation?
a redox reaction where the same element is oxidised and reduced.
how is the reaction of chlorine and water a disproportionate reaction?
in the chlorine molecule, one atom is oxidised and the other is reduced. Chloric (I) acid, HClO, and hydrochloric acid are made.