1. Ions are formed by loss or gain of electrons.
QUESTION:
How many protons and electrons are in a magnesium ion (Mg2+)? A. 10, 12, B. 12, 10, C. 24, 22, D. 22, 24
Ions are formed by loss or gain of electrons.
A positive ion is formed by losing electrons.
A charge of +2 means a loss of two electrons.
Mg atom has 12 protons, 12 electrons.
Mg2+ ion has 12 protons, 10 electrons
Charge = (#protons) – (#electrons)
= 12 – 10 = +2
SCRIPT:
How many protons and electrons are in a magnesium ion (Mg2+)? A. 10, 12, B. 12, 10, C. 2, 0 PAUSE
Ions are formed by loss or gain of electrons.
The number you see written on the upper right hand corner
HIGHLIGHT 2+
Is the charge of the charge of the ion.
CALLOUT “charge”
A positive charge is obtained by by losing electrons.
Therefore, a positive ion must have more protons than electrons.
This means that choices A and D are wrong. In choice A, there are fewer protons …ten… than electrons.. 12.
CROSS OUT B and D
So how do we determine the number of protons and electrons in the ion? CLICK We refer to the periodic table. From the periodic table, we find that the atomic number of magnesium is 12.
CLICK
The number of protons in a magnesium atom is, therefore, 12.
Therefore, choice C, which is wrong.
CROSS OUT 24 in choice C.
Since an atom is neutral, a magnesium atom also has 12 electrons.
CLICK A magnesium ion is formed by the loss of two electrons.
12 minus 2 equals 10.
Therefore… a magnesium ion has only 10 electrons.
HIGHLIGHT 10.
But it still has twelve protons.
The correct answer is B.
Note that the charge of an ion is just equal to the number of protons minus the number of protons.
In the case of magnesium ion, 12 minus 10, equals +2.
PAUSE CLICK END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08