Question

Consider the two electron arrangements for neutral atoms A and B. What is the atomic number of A?

A - 1s2, 2s2, 2p6, 3s1

B - 1s2, 2s2, 2p6, 5s1

Answer 1

They gave you A and B but only want A? Strange but okay..

Just look at the last electron that was added to the atom (3s1)

The 3 indicates the energy level, the s indicates that the electron is in the "s" sub-level, and the 1 indicates that there is 1 electron in the s sub-level (column 1)

So, row 3 column 1 is element 11 - Na (Sodium).

You can also add the electrons together to find the atomic number.

A - 1s2, 2s2, 2p6, 3s1

1s2 = 2
2s2 = 2
2p6 = 6
3s1= 1

2+2+6+1 = 11, element # 11 (Sodium)

Answer 2

thank u