Question

The elements $Na$ , $Mg$ , $Al$ , $Si$ , $P$ , $S$ , $Cl$ and $Ar$ are arranged in the periodic table in the increasing order of their atomic numbers. Which element is the most electronegative?

Answer 1

All these elements $Na$ , $Mg$ , $Al$ , $Si$ , $P$ , $S$ , $Cl$ and $Ar$ belongs to Period 3.As we move from left to right the atomic number increases and atomic number defines the increase in electronegativity of elements. As the atomic number increases the electronegativity of the number increases.
Complete step by step solution:
So if we see the definition of electronegativity it suggests that when two elements are joined in a chemical bond, the element that attracts the shared electrons strongly. The metallic elements are known as electropositive.
As we move from $Na$ to $Ar$ we will see below points:
1. Nuclear charge will increase
2. Atomic radius will decrease
3. More electrons will be there but shielding is negligible as extra electron entered into same shell
4. Hence the electrons will have a stronger attraction to the nucleus.
So when we move from left to right electronegativity increases. That means Argon has the most electronegativity because it is the last element in Period 3. But there is contrast here and below we see how:
Chlorine needs only one electron to fill its valence shell and then it will be stable. So it has more tendency to attract the shared electrons strongly if it is joined in a chemical bond.
And now if we see for Argon, it is noble gas. It already has full valence shells that are already stable and it does not have to bond with another element. So its electronegativity is almost negligible.
So if we consider all the above facts, we will conclude that Chlorine has a higher tendency to make bonds and higher tendency to attract the electrons strongly towards itself.

Additional Information: Electronegativity decreases in classes from bottom to top. However it increases from left to right. The most electronegative element present in the periodic table is: fluorine.
So the answer is Chlorine is the most electronegative rather than $Na$, $Mg$, $Al$ , $Si$, $P$, $S$ and $Ar$.

Note: The main point is that electronegativity depends on atomic number. Also the electronegativity of the elements depends on the tendency of how strongly it can attract the electrons from another element to complete its valence shells. For Example Chlorine attracts electrons fastly because it just needs 1 electron to complete its shell.