Trends in Group 2: The Alkaline Earth Metals

Question 1

All elements in Group 2 (also called alkali earth metals) have two electrons in their ……………

All Group 2 metals can form ……..compounds in which they donate these two outermost electrons (so they act as …………agents) to become an ion with +2 charge (so they themselves become ……….)

Answer 1

outermost principal quantum shell

ionic

outermost principal quantum shell

oxidised

Question 2

Going down the group, the metals become more

Answer 2

reactive

Question 3

Going down the group 2, why do the metals become more reactive

and how is this shown in HCl and water reactions

Answer 3

The first ionisation energy is the energy needed to remove the first outer electron of an atom

The second ionisation energy is the energy needed to remove the second outer electron of an atom

The graph above shows that going down the group, it becomes easier to remove the outer two electrons of the metals

Though the nuclear charge increases going down the group (because there are more protons), factors such as an increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge

As a result of this, the elements become more reactive going down the group as it gets easier for the atoms to lose two electrons and become 2+ ions
This trend is shown by looking at reactions of the Group 2 metals:

With dilute hydrochloric acid: bubbles of hydrogen gas are given off much faster indicating that the reactions become more vigorous

With oxygen: the metals get more reactive with oxygen down the group (Ba is so reactive, that it must be stored in oil to prevent it from reacting with oxygen in air)

Question 4

Going down the group 2, the elements become larger/ atomic radius as

Answer 4

the outer two electrons occupy a new principal quantum shell which is further away from the nucleus

Question 5

What is the trend of melting point

Answer 5

The melting point of the elements decreases going down the group as the outer electrons get further away from the nucleus

This means that the attraction between the nucleus and the bonding electrons decreases causing a decrease in melting point

The graph shows a general decrease in melting point going down the group with a slight anomaly in magnesium

Question 6

As you go down the group, the density of the alkali earth metals

Answer 6

drops and then increases

Density is also affected by the packing structure of the metals, not just the atomic radius - no trend is perfect!

Be-Ca decreases

Sr - Ba increases