Question

One way of determining the valance electron of a number is by looking at what it last shell holds .For example Aluminum(Al) has 13 atomic number and its electronic configuration is (2,8,3)looking at what its last shell holds it has valance electron of 3 .but when we take Calcium(Ca) it has 20 atomic number and its electronic configuration is (2,8,10) looking at the last digit it should have had 10 valance electron , but its 2 .How did that come? pleases answer

Answer 1

Answer:

that is because in electronic configuration we only consider 8 electrons in each shell so here the configuration wil be2,8,8,2