The noble gases, or group 18 elements, have oxidation states of zero. However, their chemistries are not as barren as one might expect. Please see the link for the Periodic Table and individual articles for these elements.
All 2A elements show the valency of two.
helium's valency is zero as id does not combine with other elements
The valency of elements can vary depending on the conditions and compounds they are in. Generally, for hydrogen, it is +1, for elements in groups 1 and 2, it is +1 and +2 respectively, for elements in groups 13-18, it corresponds to their group number. Zinc typically has a valency of +2.
The number of electrons in the outermost energy shell is usually used in finding the valency of a given element. For instance elements that have two electrons in the outermost energy shell have valency 2.
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The valency of SO2 is 4, while the valency of SO3 is 6. The valency of an atom is the combining power of an element, which indicates the number of bonds it can form with other elements.
Oxygen has a valency of 2. This means that it can form up to two bonds with other elements in chemical compounds.
The valency of an element measures its ability to combine with other elements. This valency is determined by the number of electrons in the outer shell of each atom of an element.
The valency of elements tends to remain constant or increase by one going down a group on the periodic table. This is because elements in the same group have the same number of valence electrons, which determines their valency. As you move down a group, the number of electron shells increases, allowing elements to either maintain their valency or increase it by gaining electrons to achieve a full outer shell.
Nitrogen typically has a valency of three or five, depending on the compound it is in. Nitrogen forms compounds with a wide range of elements due to its versatile valency.
I guess, the most fundamental is their valency. This dictates how many times it can bond to other elements. Elements with the same valency often share similar properties with other elements with the same valency. The Periodic Table is divided into 8 rows (and a D block). Each of these 8 rows have elements with similar properties, related to their valencies.