State the important salient features of the modern periodic table. State how separation of elements and periodicity of elements forms an important feature of the modern periodic table.

Salient Features of the Modern Periodic Table are:

(a) Classification — Physical and chemical properties of elements are periodic function of their atomic number.

(b) Position — Correlates position of elements with it’s electronic configuration.

(c) Methodical Arrangement — Arrangement of elements is in increasing order of atomic numbers in:

1. Seven horizontal rows called called periods and
2. Eighteen vertical columns called groups.

(d) Periods — Completion of each period is logical since each period:

1. begins with an element having one electron in the outermost shell
2. ends with zero group element having completely filled outer shell.
3. A transition from metallic to non-metallic is seen across a period.

(e) Groups — Each vertical column accommodates elements with the same outer electronic configuration hence having similar properties.

1. 18 vertical columns consists of groups 1 to 17 and 18 [zero group]
2. Group 1, 2 and 13 to 17 [IA to VII A] are called Normal elements.
3. Group 3 to 12 [IB to VII B and VIII] are called Transition elements.
4. Group 18 [zero] at extreme right contains Noble or Inert gases.

(f) Separation of elements — The modern periodic table provides the separation of elements with similar properties in the following ways:

1. Reactive metals are placed in group 1 [IA] and 2 [IIA]
2. Transition elements (i.e., metals) are placed in the middle.
3. Non-metals are placed in the upper right corner of the periodic table.

(g) Periodicity of Elements — Gradual change in properties is seen with increase in atomic number in the periodic table. Recurrence of properties is observed with elements belonging to the same subgroup in the periodic table after a difference of 2, 8, 18 or 32 in the atomic numbers due to recurrence of similar valence shell electronic configuration.