Classification of Elements

Prepared By: Md. Imran Nur Manik; B.Pharm; M.Pharm Page 1

manikrupharmacy@gmail.com; Lecturer; Department of Pharmacy; Northern University Bangladesh.

Position of hydrogen in the periodic table

Placing hydrogen in group IA:

1. Electronic configuration: Hydrogen has the same electronic configuration as the alkali metals (group IA).

2. Valence: Hydrogen has the valence of “1” like the alkali metals. 3. Electropositive: Hydrogen is an electropositive element like the alkali metals. 4. Reducing agent: Like the alkali metals it also acts as a reducing agent. 5. Forms stable compound: Hydrogen forms stable compounds with oxygen and halogen

like H2O, HX similar to the compounds Na2O and NaX. 6. Formation of M+ ions: Like alkali metals Hydrogen is a strong electropositive element

and has the tendency to loose its electron to form a unipositive cation. H-e-

H+ Li-e-

Li+ 7. Affinity for non metals: Both hydrogen and alkali metals have a strong affinity for non-

metals and little affinity for mortals.

Placing hydrogen in group VIIA:

1. Hydrogen should be placed just before Helium. Therefore it should be placed in group VIIA.

2. Valence: Hydrogen has the valence of similar to the halogens. 3. Non Metals: Hydrogen is a non-metal like halogens. 4. Atomic state: Like the halogens hydrogen is a diatomic gas. 5. Combination with non metals: Hydrogen forms compounds like CH4 and SiH4 with non-

metals similar to Chlorine forming CCl4 and SiCl4. 6. Formation of Negative ions: Like halogens, Hydrogen also gain one electron to form

negative ion. H+e-

H- F+e-

F- 7. Formation of hydride: Hydrogen forms hydride with some metals NaH, CaH2, like

halogens form the halides e.g. NaCl, KBr.

Thus, there is a debate whether hydrogen should placed group IA or VIIA. But since it is an s-block element it is placed with the alkali metals.

Md. Imran Nur Manik