Modern periodic Law

Day 3
20.5.20

Good Morning Boys,
I hope you have done your paper well , now we continue with classification of elements.

Learning Objective
student will be able to 

• state the modern periodic law
• Describe the modern periodic table

Modern Periodic Law :

Moseley modified Mendeleefs periodic law. He stated 

 “Physical and chemical properties of elements are the periodic function of their atomic numbers.” It is known as modern periodic law and considered as the basis of Modern Periodic Table.

Structural Features of Long Form of Periodic Table

1. Long form of Periodic Table has 18 groups and seven periods .

2. The horizontal rows are called periods.

• First period (₁H – ₂He) contains 2 elements. It is the shortest period
• Second period (₃Li – ₁₀Ne) and third period (₁₁ Na – ₁₈Ar) contain  8 elements each. These are short periods.
• Fourth period (₁₉K – ₃₆Kr) and fifth period (₃₇Rb – ₅₄Xe) contain 18 elements each. These are long periods.
• Sixth period (₅₅Cs – ₈₆ Rn) consists of 32 elements and is the longest period.
• Seventh period starting with ₈₇Fr is incomplete and consists of 19 elements.

3. The 18 vertical columns are known as groups.

• Elements of group 1are called alkali metals.
• Elements of group 2 are called alkaline earth metals.
• Elements of group 16 are called chalcogens [ore forming elements].
• Elements of group 17 are called halogens. [sea salt forming]
• Elements of group 18 are called noble gases.

Thats All  for the day.

stay safe

Take Care