1. A. Mg(s) + N2(g)  MgN2(s), B. Mg(s) + O2(g)  MgO2(s)
QUESTION:
Which of the following is a correct chemical equation for a combination reaction between a metallic element and nonmetallic element?
A. Mg(s) + N2(g)  MgN2(s), B. Mg(s) + O2(g)  MgO2(s)
C. Mg(s) + N(g)  MgN
D. none of these
Metal + nonmetal  ionic compound
Naturally occurring ions: Mg2+, N3-, O2- (group VIA)
magnesium nitride is Mg3N2, not MgN2
magnesium oxide is MgO, not MgO2
Correct chemical equations:
3 Mg(s) + N2(g)  Mg3N2(s)
2 Mg(s) + O2(g)  2 MgO(s)
Which of the following is a correct chemical equation for a combination reaction between a metallic element and nonmetallic element?
A. Mg(s) + N2(g)  MgN2(s) B. Mg(s) + O2(g)  MgO2(s)
C. neither
D. both
PAUSE
First of all, you should know that naturally occurring forms of nitrogen and oxygen are diatomic. So, we can eliminate choices C right away.
CROSS OUT N(g) in choice C
CLICK
Whenever a metallic element reacts with a nometallic element, we can expect the product formed to be an ionic compound.
To predict the formulas of the compound formed, we look at the monatomic ions that we’re likely to get from the elements involved.
You should know by now that the only magnesium ion with you’ll find in nature has a charge of +2. We can use the periodic table to help us make this prediction.
Magnesium is an alkaline earth metal; it belongs to group IIA and monatomic ions derived of elements belonging to this group are always found in nature to have a +2 charge.
Similarly, based on their location in the periodic table, you should know that the monatomic ions derived from nitrogen and oxygen have charges of –3 and –2, respectively
Therefore,
CLICK the ionic compound formed between magnesium and nitrogen should have a formula of of Mg3N2, not MgN2.
CROSS OUT MgN2 in choice A
CLICK and the ionic compound formed between magnesium and oxygen should have a formula of of MgO, not MgO2.
CROSS OUT MgO2 in choice B
Therefore, the correct answer is D. None of these.
The correct equations are...
3 Mg solid, plus N2 gas, yields Mg3N2 solid
and
2 Mg solid plus O2 gas, yields 2 MgO solid.
These are the reactions that occur when a piece of magnesium is ignited in air. The nitrogen and oxygen molecules from air
react with magnesium to form magnesium nitride and magnesium oxide.
In the process, heat and light are produced as well.
PAUSE 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