Page 3 - 3. Lesson Note Ch-5 MODERN PERIODIC TABLE

• Periods in the Modern Periodic Table-

At present there are seven periods in the Modern Periodic Table.

• 1 period: This is known as very short period as there are only two elements,
st
i.e. hydrogen and helium.
• 2 and 3 period: There are total 8 elements in each of the 2nd and 3rd
rd
nd
periods. These periods are known as short periods.
th
th
• 4 and 5 period: There are total 18 elements in each of the 4th and 5th
periods. These periods are known as long periods.
th
• 6 period: There are total 32 elements in 6th period. This period is known as
very long period.
th
• 7 period This period is also a very long period with newly discovered
elements.
Elements having same number of shells are placed in the same period.

So, we can identify the period to which an element belongs from the number of
shells it has-

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