# If an element's electron configuration ends in ns^2 np^5, what is the element?

The element is member of the halogen group.

#### Explanation:

The halogens are group 17 on the periodic table and include F, Cl, Br, I

If an electron configuration ends in...

$2 {s}^{2} 2 {p}^{6}$ the element is F
$3 {s}^{2} 3 {p}^{6}$ the element is Cl
$4 {s}^{2} 3 {d}^{10} 4 {p}^{6}$ the element is Br
und so weiter...

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Nov 4, 2016

Any element in Group 7A (or Group 17).

#### Explanation:

The most important piece of information provided here is that you have 5 electrons in your $p$ orbital. Now let's identify the $p$ bloc on the periodic table:

As you can see, the $p$ bloc is to the far right. Quantum mechanical calculations tell us that there are $3$ $p$ orbitals per energy level (or row of the periodic table), and each orbital can carry 2 electrons. This means that as we move across the 6 elements of the $p$ bloc, we add one electron to the electron configuration.

So, if you were to find what elements have 5 electrons in the $p$ orbitals, you'd discover that any element in Group 7A (Florine, Chlorine, Iodine, etc.) satisfies this requirement. Note that it is not possible to specify one element without knowing an energy level (or value of $n$).

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