Figure 22 Along the horizontal axis of the graph are two sets of labels. The first set, labelled 'Group 2', are Be, Mg, Ca, Sr and Ba. The second set, labelled 'Group 13' and positioned under the first, are B, Al, Ga, In and Tl.
The left-hand vertical axis is labelled 'Group 2 (italic uppercase I subscript 1 + italic uppercase I subscript 2) in kJ mol superscript -1'. The values 1500, 2000 and 2500 have been marked along the axis.
The right-hand vertical axis is labelled 'Group 13 (italic uppercase I subscript 1 + italic uppercase I subscript 2) in kJ mol superscript -1'. The values 4000, 5000, 6000 and 7000 have been marked along the axis.
Two curves have been drawn, one labelled 'Group 2', the other 'Group 13'.
The Group 2 curve starts at the left at about 2700 above Be, drops to about 2200 above Mg, 1700 above Ca, 1600 above Sr, and 1400 above Ba.
The group 13 curve starts at the left at about 7000 above B, drops to about 4800 above Al, goes up slightly to 5000 above Ga, drops slightly to 4800 above In, and rises slightly to 5000 above Tl.