1.4 Electronic configuration

Question 1

Electronic configurations

Answer 1

In an atom:
Electrons occupy electron shells
Shells are filled, starting with the innermost shell
Different shells hold different maximum numbers of electrons

1st shell holds 2 electrons
2nd shell holds 8 electrons
3rd shell holds 8 electrons (if needed)
4th shell (if needed) holds 8 electrons

Question 2

Electronic configurations for first 20 elements

Answer 2

The electronic configuration of hydrogen is 1.
In general for the first 20 elements:
Metal atoms have up to two electrons in their outer shell (the exception is aluminium which has three)
Non-metal atoms (except for group 0) have four or more electrons in their outer shell.

Question 3

Electronic configurations and the periodic table

Answer 3

The number of occupied shells is the same as the period number and the number of electrons in the outer shell is the same as the group number (except for elements in group 0, which have full outer shells)

Elements in a group have the same number of electrons in their outer shell, except for helium in group 0