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what is octet arrangement? How can we find valency of this element? 1S2 2S2 2P6 3S2 3P6 4S2 3D5.?
The octet rule is the principle that describes the bonding in atoms. Individual atoms are unstable unless they have an octet of electrons in their highest energy level. The electrons in this level are called valence electrons. When atoms gain, lose, or share electrons with other atoms, they satisfy the octet rule and form chemical compounds.

Consult the molecular formula and sum up all the valence electrons from the separate atoms. The Group number in the Periodic Table = the number of valence electrons for an atom.
Add one for each (-) charge (extra electron);
Subtract one for each (+) charge (missing electron).
For example:
CH3NH2 = 5(1) + 4 + 5 = 14 e-
POCl3 = 5 + 6 + 3(7) = 32 e-
NO3- = 5 + 3(6) + 1 = 24 e-
Name of Element : Aluminum [Al]
Atomic Weight : 27.0
Atomic Number : 13
Group : Transition Elements
Electron Configuration: 1s2 2s2 2p6 3s2 3p1


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