group 2 and 7 Flashcards
What is the electron configuration of group 2 elements?
2e- in outer shell
What is the trend in atomic radius of group 2?
Increases down the group, as there are more energy levels being filled with electrons and the outermost electrons are further from the nucleus
What is the trend in first ionisation energy in group 2?
Decreases down the group as the electron being removed is from successively higher energy levels and is increasingly shielded from the nucleus- and so less attracted
What is the trend in melting point in group 2?
Decreases going down the group. Attraction of the positive ions to the delocalised electrons decreases as the size of the positive ions increases and hence the charge density decreases.
Magnesium doesn’t fit, as this metal has a different crystal structure
Why do group 2 metals sink?
All are more dense than water
How does magnesium react with cold water?
Mg(s) + 2H2O(l) –> Mg(OH)2(aq) + H2(g)
reacts slowly, slow bubbling
How does magnesium react with steam?
Mg (s) + H2O (g) –> MgO (s) + H2 (g)
Burns with bright white light , gas produced very quickly
What is the trend in the reactivity of group 2 metals with water?
React with increasing vigour as group is descended, as easier to lose electrons further away from the nucleus
What is the trend in the solubility of the group 2 metal hydroxides?
Solubility increases down the group
Mg(OH)2 is sparingly soluble, whilst Ba(OH)2 is very soluble
What is the trend in the strength of the group 2 metal hydroxides as bases?
Strength increases down the group, as [OH-] increases
What is magnesium hydroxide used for?
Milk of magensia is a tablet used as an antacid- weak base and therefore won’t harm stomach as it neutralises excess acid
Also used as a laxative
What is calcium hydroxide used for?
Reduces the acidity of soils so that a wider range of crops can be grown as they are able to extract nutrients from the soil
Also provides calcium ions which are essential for plant growth
What is lime?
a mixture of calcium hydroxide and calcium carbonate
What is the trend in solubility of the group 2 sulfates?
Decreases going down the group
MgSO4 is soluble, whilst BaSO4 is very insoluble
What is barium sulfate used for?
Used as a test for sulfate ions in solution- solution acidified first with HCl or HNO3 to remove BaCO3, then solution of barium chloride added, and the formation of a white ppt confirms presence of sulfate
Barium sulfate can also be used in x-rays as its opaque to x-rays and not toxic
How can magnesium be used in the extraction of titanium?
Titanium oxide first converted to titanium chloride at around 900ºC
TiO2 + C + 2Cl2 –> TiCl4 + CO2
Titanium chloride then reduced by a more reactive metal
TiCl4 + 2Mg –> Ti + 2MgCl2
Why is the reaction of TiCl4 with Mg carried out in an atmosphere of argon?
Argon is inert, and orevents any reaction or contamination with oxygen or nitrogen
What is calcium carbonate and calcium oxide used for?
To remove sulfur dioxide from flue gas, which could cause acid rain
CaO + 2H2O + SO2 –> CaSO3 + 2H2O
CaCO3 + 2H2O + SO2 –> CaSO3 + 2H2O + CO2
What does acid rain do?
Causes acidification of lakes, damages plant and can lead to the death of aquatic plants and fish
What are the halogens at room temp?
all covalently bonded diatomic molecules
What are the colours of each of the halogens vapours?
F2 pale yellow
Cl2 green/yellow
Br2 amber (red/brown)
I2 purple
What is the trend in boiling point in group 7?
As the group is descended, the boiling group increases. This is because the size of the molecules increases so increases the number of Van de Waals forces and thus the energy required to overcome these
What is the trend in electronegativity in group 7?
As the group is descended, the electronegativity decreases
What are the three factors that affect electronegativity?
Nuclear charge- as the group is descended, this increases and leads to an increases in the attraction of the nucleus for the bonding electrons
Atomic radius- this increases down the group and causes the outermost electrons to be further away, reducing the attraction for the bonding electrons
Shielding- increase in the number of filled energy levels down the group so decreases attraction for bonding electrons
