# An atom has 25 protons, 30 neutrons, and 25 electrons. What ls the charge of the atom's nucleus?

Jan 14, 2016

Interesting question.

#### Explanation:

Unless you mistyped the question, the answer should be $25 +$.

Basic atomic structure has protons and neutrons located in the nucleus and electrons surrounding the nucleus. Your atom is said to contain $25$ protons and $30$ neutrons in its nucleus. As you know, protons are positively charged particles. On the other hand, neutrons are neutral particles.

This means that regardless of what atom we're talking about, its nucleus will always carry a positive charge.

The net charge of the atom is given by the ratio of protons to electrons, which as you know are negatively charged particles.

You can thus say that if an atom has

• more electrons surrounding its nucleus than protons located in its nucleus $\to$ it will carry a negative charge
• more protons located in its nucleus than electrons surrounding its nucleus $\to$ it will carry a positive charge
• equal numbers of protons and electrons $\to$ it will be neutral

Now, if you're interested in the charge of the atom's nucleus, all you have to do is imagine that you're taking away all the electrons that it has surrounding its nucleus.

In this case, the starting atom is neutral, since you have $25$ protons and $25$ electrons. If you start taking away electrons, you'll end up with

• $\text{25 protons / 24 electrons} \to 1 +$ charge
• $\text{25 protons / 23 electrons} \to 2 +$ charge
• $\text{25 protons / 22 electrons} \to 3 +$ charge
• $\text{25 protons / 21 electrons} \to 4 +$ charge
$\vdots$

and so on. By the time you take away the last electron, you'll be left with a $25 +$ charge that corresponds to the $25$ protons located in the nucleus.

If the question actually asks for the charge of the atom, then the equal number of protons and electrons tells you that you're dealing with a neutral atom.