# Formulae on Classification Of Elements And Periodicity In Properties

**Memorizing Periodic Table**

Have a way to reconstruct an element's position after a little thought. For example, the first row has 2 elements, the second and third have 8, the fourth and fifth have 18 and the last two have 32. The place at which the table divides is after 1 element in the first row, after 2 elements in next two rows and after 3 elements in the last two rows (rows 4 and 5 don't divide). The metals/nonmetals division is a predictable zig-zag (except for #85). To expedite things, you can memorize a few additional bits of information.

2

*Van der Waals radius*- It is half of the shortest internuclear distance between two adjacent non-bonded atoms.

*Covalent bond radius*- It is half the internuclear distance between two identical atoms joined by a single covalent bond.

3

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The total number of electron shells an atom has determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order.

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**Preparation Tip for You!**

Read the Tips? Now why don't you try solving a few questions in the Practice Lounge