Question

The modern Periodic Table has been divided into

• A. seven periods: three short and four long
• B. nine periods: six short and three long
• C. eighteen periods: ten short and eight long
• D. nine periods from zero to VIII

Answer 1

Answer: (A)

The long form of periodic table consists of seven periods. The number of elements in a period and the type of orbitals being filled up is given in the table.
Period
No. of the energy level being filled
Orbitals being filled
No. of electrons or elements in the period
1.
$n=1$
$1s$
2 (very short period)
2.
$n=2$
$2s,2p$
8 (short period)
3.
$n=3$
$3s,3p$
8 (short period)
4.
$n=4$
$4s,3d,4p$
18 (long period)
5.
$n=5$
$5s,4d,5p$
18 (long period)
6.
$n=6$
$6s,4f,5d,6p$
32 (very long period)
7.
$n=7$
$7s,5f,6d,7p$
29 (incomplete period)