Question

cl⁻: which neutral atom is isoelectronic with cl⁻? how many valence electrons does neutral cl have?

Explanation:

First sub - question: Which neutral atom is isoelectronic with $\boldsymbol{Cl^-}$?

Step 1: Determine the number of electrons in $\boldsymbol{Cl^-}$

A neutral chlorine ($Cl$) atom has an atomic number of 17, so it has 17 electrons. When $Cl$ gains an electron to form $Cl^-$, the number of electrons becomes $17 + 1=18$.

Step 2: Find the neutral atom with 18 electrons

The atomic number of an atom is equal to the number of electrons in a neutral atom. The element with atomic number 18 is argon (Ar). So, the neutral atom isoelectronic with $Cl^-$ is Ar.

Second sub - question: How many valence electrons does neutral $\boldsymbol{Cl}$ have?

Step 1: Recall the electron configuration of Cl

Chlorine has an atomic number of 17. Its electron configuration is $1s^22s^22p^63s^23p^5$.

Step 2: Identify valence electrons

Valence electrons are the electrons in the outermost shell. For Cl, the outermost shell is the third shell, and the number of electrons in the third shell is $2 + 5 = 7$. So, a neutral Cl atom has 7 valence electrons.

Answer:

• The neutral atom isoelectronic with $Cl^-$ is Ar.
• A neutral Cl atom has 7 valence electrons.