Finding Location of Elements in Periodic Table with Examples

Finding Location of Elements in Periodic Table with Examples

a) Finding Period of Elements:

Period of the element is equal to highest energy level of electrons or principal quantum number. Look at following examples for better understanding;

₁₆S: 1s²2s²2p⁶3 s²3 p⁴ 3 is the highest energy level of electrons or principal quantum number. Thus period of S is 3.

₂₃Cr: 1s²2s²2p⁶3s²3p⁶4 s²3d⁴ 4 is the highest energy level of electrons or principal quantum number. Thus period of Cr is 4.

b) Finding Group of Elements:

Group of element is equal to number of valence electrons of element or number of electrons in the highest energy level of elements. Another way of finding group of element is looking at sub shells. If last sub shell of electron configuration is “s” or “p”, then group becomes A.

₁₉K : 1s²2s²2p⁶3s²3p⁶4s ¹ Since last sub shell is “s” group of K is A.

₃₅Br : 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p ⁵ Since last sub shell is “p” group of Br is A.

Elements in group B have electron configuration ns and (n-1)d , total number of electrons in these orbitals gives us group of element. Look at following examples.

₂₆Fe : 1s²2s²2p⁶3s²3p⁶4s²3d⁶ Group of Fe is; 6 + 2 = 8 B Group

Here are some clues for you to find group number of elements.

Last Orbital Group

ns¹ 1A

ns² 2A

ns²np¹ 3A

ns²np² 4A

ns²np³ 5A

ns²np⁴ 6A

ns²np⁵ 7A

ns²np⁶ 8A

Last Orbital Group

ns²(n-1)d¹ 3B

ns²(n-1)d² 4B

ns²(n-1)d³ 5B

ns²(n-1)d⁴ or ns¹(n-1)d⁵ 6B

ns²(n-1)d⁵ 7B

ns²(n-1)d⁶8B

ns²(n-1)d⁷ 8B

ns²(n-1)d⁸ 8B

ns²(n-1)d⁹ or ns¹(n-1)d¹⁰ 1B

ns²(n-1)d¹⁰2B

Example: Find period and group of ₁₆X.

₁₆X: 1s²2s²2p⁶3s²3p⁴

3. period and 2+4=6 A group

Example: Find period and group of ₂₄X.

₂₄X:1s²2s²2p⁶3s²3p⁶4s²3d⁴

4. period and 4+2=6 B group

Groups and Periods of elements are found according to their neutral states. Ions and isotopes of elements are not shown in periodic table.

Example: If X⁺² ion has 10 electrons, find its group and period number.

Number of protons=10 + 2=12

In neutral element, number of proton is equal to number of electrons. Thus, X has 12 electrons in neutral state. We write electron configuration according to neutral state of element.

₁₂X=1s²2s²2p⁶3s²

Period number is 3

Group number is 2 and group is A(last orbital is “s”)

Example: If electron configuration of X⁺⁵ is 1s²2s²2p⁶3s²3p⁶, which one of the following statements are true for X element.

I. Period number of X is 4 and it is transition element

II. X is metal

III. Valence electrons of X are in “s” and “d”

Neutral X element has electron configuration;

X: 1s²2s²2p⁶3s²3p⁶4s²3d³

X is in 4. period and 3+2=5 B group.

Thus, it is metal and all the statements  I. II. and III. are true.

Example: Locations of elements X, Y, Z, T and U are given in the picture below. Which one of the following statement are false for these elements.

I. X is alkaline metal

II. Y is in p block

III. Z is halogens

IV. U is lanthanide

V. T is noble gas

Since X is in 1A group, it is alkaline metal, I is true.

Y is in III A group an it is in p block. II is true.

Z is in VII A group and we know it is halogens. III is true

U is in d block and it is transition element not lanthanide, IV. is false

T ,s in VIII A group an it is noble gas, V is also true.

Periodic Table Exams and Problem Solutions