Periodic Table and Electron Configuration

Question 1

How many periods and groups are there in the modern periodic table?

Accepted Answer

There are 7 periods (horizontal rows) and 18 groups (vertical columns).

Question 2

What decides the period number of an element?

Accepted Answer

The number of the outermost (highest) principal energy level / shell in which electrons are present equals the period number.

Question 3

What is the maximum number of electrons a shell can hold, given by the 2n² rule?

Accepted Answer

A shell with principal quantum number n holds a maximum of 2n² electrons: 1st shell 2, 2nd shell 8, 3rd shell 18, 4th shell 32.

Question 4

What are the four types of subshells and the maximum number of electrons each can hold?

Accepted Answer

s – 2, p – 6, d – 10, f – 14 electrons, i.e. 2(2l + 1). s has 1 orbital, p has 3, d has 5 and f has 7.

Question 5

In what order are electrons filled into subshells?

Accepted Answer

In increasing order of subshell energy, i.e. increasing (n + l). When (n + l) is equal, the subshell with lower n fills first (e.g. 2p before 3s, 3d before 4p).

Sample questions