group 2 Flashcards
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alkaline earth metals
all group 2 have hydroxides that are alkaline
physical properties- group 2
high mp/bp
light metals with low densities
form colourless (white compounds)
stable electronic structure
the atoms of the elements have a tendency to lose 2 electrons in their outer shells to form a stable electronic structure
ionisation energy as you go down the group-2
the ionisation energy decreases due to the increasing atomic radius and shielding effect , so there is a weaker positive attraction from the nucleus
highest energy electron in … shell
s sub - shell (in the s block )
ionisation of the elements - {m= any group2}
M –> M+ + e- {oxidation first state }
M + –> M2+ + e- {+2 oxidation state }
reactive metals are oxidised to produce
2+ ions
are ….. reducing agents
strong
reactivity …. down a group
increases - easier to lose electrons
group 2 elements form … ions
positive (cation)
group 2 elements
Be, Mg, Ca, Sr, Ba, Ra
reactions with oxygen - redox- g2
- react vigorously
- ionic oxide MO eg. calcium oxide = CaO
2Ca(g) + O2(g) –> 2CaO(s)
reactions with water - g2
- all group 2 elements except beryllium, react with water to form hydroxides
- general formula M(OH)2
- and H (gas)
- mg reacts with water very slowly
- going down the group each metal reacts more vigorously with water
- redox reaction - metal is oxidised and hydrogen is reduced
reactions with dilute acid- g2
all group 2 elements except Be react with dilute acids to form a salt and hydrogen gas
- more vigorous down the group
reaction with oxides and water- g2
group 2 oxides react with water to form metal hydroxides and the general reaction for this (m )
MO(s) + H2O –> M(OH)2 (aq)
- metal hydroxides are soluble in water and form alkaline solutions with water because they release OH- ions and the typical PH is 10-12
solubility- g2
the solubility of hydroxides in water increases down the group, meaning if a hydroxide is more soluble it will release more oh- ions forming an alkaline solution with a higher ph.
beryllium is at the top of the group and is insoluble in water
Magnesium forms Mg(OH) 2 (s) which is only slightly soluble in water – the resulting
solution is dilute with a comparatively low OH - (aq) concentration
Ba(OH) 2 (s) is much more soluble in water than Mg(OH) 2 (s) and so has a higher OH -
concentration therefore, the resulting solution is more alkaline than a solution of Mg(OH) 2
thermal decomposition - g2
- Carbonates decompose at higher temperatures down the group
- Thermal decomposition gets harder as you go down the group
- MgCO 3 (s) MgO(s) + CO 2 (g)
uses - compounds - g2
The oxides, carbonates and hydroxides of group 2 metals are basic – this means they will react with acids to form a salt and water
- As these reactions with hydrochloric acid take place, you will see a solid oxide or hydroxide ‘dissolve’
- The alkalinity of group 2 metal compounds has resulted in them being used for a number of purposes, where neutralising acids is important and they are also important substances in the construction industry
neutralising acidic soils
Calcium hydroxide is used by farmers and gardeners as
‘lime’ and it is used to reduce the acidity levels of soil
g2- indigestion remedies
Human stomachs contain a small amount of
hydrochloric acid so when we suffer from indigestion, there is a build-up of too much of this acid
- Many indigestion remedies are available, for example ‘milk of magnesia’ which contains magnesium hydroxide which neutralises the excess acid producing a salt and water
- This is a weak alkali so
doesn’t damage stomach
tissues
building and construction uses
- One of the group 2 metal carbonates, calcium carbonate, is an extremely useful building material – it is present in both limestone and marble
- It is by far the most important calcium compound industrially – it is used in the building trade and in the manufacture of glass and steel
- However, calcium carbonate reacts readily with acids for example rainwater has an acidic pH which leads to gradual erosion of objects made using limestone or marble
