The combining capacity of an atom is known as its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.
Method to find Valency
There are different ways to determine the valency of a given atom and they are:
- Octet rule: According to the octet rule, a compound is said to be stable when the outermost shell of the compound is having eight electrons. If the number of electrons in the outer shell is between one and four, the compound is said to have positive valency. For compounds with electrons four, five, six, or seven, the valency is determined by subtracting the electron from eight. All noble gases except for Helium have eight electrons.
- Periodic table: Periodic table consists of elements that are arranged in such a way that, the valency of a given element can be determined. Metals in column 1 have a valency of +1 while the noble gases in column 18 have a valency of 0 and are inert.
- Valency from the chemical formula: This rule is based on the octet rule and by observing the combining of an element, the valency can be determined.
Valency of silicon
Atomic number of silicon is 14.
- The electronic configuration of the element is – K=2, L=8,m=4.
- According to the electronic configuration the valency is +4 or -4 because silicon can either gain 4 electrons or lose 4 electrons because it is a noble gas.
- Hence, valency of silicon is 4.
Valency of oxygen
Atomic number of Oxygen is8.
- Electronic configuration – K=2, L=6.
- According to the electronic configuration the valency is 6, but it is easy for oxygen to gain 2 electrons instead of loosing 6 electrons.
- Hence, the valency of oxygen is 2.