Question Video: Identifying What Changes When an Atom Forms a Positive Ion | Nagwa Question Video: Identifying What Changes When an Atom Forms a Positive Ion | Nagwa

# Question Video: Identifying What Changes When an Atom Forms a Positive Ion Science • First Year of Preparatory School

Which of the following changes when a neutral atom forms a positive ion? [A] Number of protons [B] Number of neutrons [C] Number of electrons [D] Atomic number [E] Mass number

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### Video Transcript

Which of the following changes when a neutral atom forms a positive ion? (A) Number of protons, (B) number of neutrons, (C) number of electrons, (D) atomic number, or (E) mass number.

To answer this question, we need to be able to define a positive ion. A positive ion is an atom that has lost one or more electrons during a chemical reaction.

Let’s look at an example using magnesium, which has the chemical symbol Mg. You will often see the symbol for a magnesium atom written like this. The number on the bottom left of the symbol represents the atomic number. The atomic number of an element tells us the number of protons its atoms contain. Protons are positively charged particles. They are found in the center of the atom, called the nucleus. The number in the top left of the symbol is called the mass number. It tells us the total number of protons and neutrons. Neutral particles, called neutrons, are also found in the nucleus.

In energy levels ordinarily found outside of the nucleus, there is the third type of particle. This diagram represents the energy levels containing electrons, with the blue numbers representing the electrons. The electrons are negatively charged. We can see that the total number of electrons is the sum of the electrons from each energy level. And a magnesium atom has 12 electrons.

In a neutral atom, the number of protons and electrons are the same. We can see that this is true for magnesium, as it contains 12 protons and 12 electrons. Often, in a chemical reaction, magnesium will lose its two outermost electrons. This forms a positively charged magnesium ion. This ion now only has 10 electrons. This ion is a positive ion, because there are now more protons than electrons.

We can see that the only thing about the magnesium atom that has changed is the number of electrons. Therefore, answer choice (C) is correct. So, when a neutral atom forms a positive ion, the factor that changes is the number of electrons.

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