Why the element in periodic table which have more than three electron valens must plus ten in order to know the group in periodic table ?

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If an element has 3 or more valence electrons then the element belongs to p block of the periodic table. For p block elements the group number is found out by adding the number of electrons in valence shell + 10.

The reason for this is because in the middle of the periodic table there are the d block elements ranging from group 3 to group 12 a total of 10 groups in between elements having 2 valence electrons and 3 valence electrons

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

it would be d. henry moseley

hope this !

and sorry if i'm late. have a good rest of your day! : d