Question

A certain atom consists of 16 protons, 18 neutrons, and 16 electrons. What is its atomic number, mass number, and electron configuration?

Answer 1

Here's what I got.

Explanation:

So, you know that your atom contains

• `16` protons
• `18` neutrons
• `16` electrons

Right from the start, you know that you're indeed dealing with a neutral atom, since the number of protons it has in its nucleus is equal to the number of electrons it has surrounding its nucleus.

Now, an atom's atomic number, `Z`, tells you how many protons it has in its nucleus. Nothing more, nothing less.

In your case, you are told that the atom contains `16` protons in its nucleus, which means that `Z` will be equal to

`Z = 16`

A quick look in the periodic table will reveal that you're dealing with an atom of sulfur, `"S"`.

An atom's mass number, `A`, tells you how many protons and neutrons it contains in its nucleus. Since the number of protons is given by `Z`, you can say that

`A = Z + "no. of neutrons"`

In your case, the atom contains `18` neutrons in its nucleus. This means that `A` will be equal to

`A = 16 + 18 = 34`

Finally, focus on the atom's electron configuration, which you know that must account for a total of `16` electrons.

`"S: " 1s^2 2s^2 2p^6 3s^2 3p^4`

Its noble gas shorthand notation, which uses the electron configuration of neon, `"Ne"`, the noble gas that comes before sulfur in the periodic table, will look like this

`"S: " ["Ne"] 3s^2 3p^4`