## Determining the equation of written formulas

Annie Chantasirivisal_4G
Posts: 114
Joined: Wed Sep 18, 2019 12:21 am

### Determining the equation of written formulas

Does anyone understand how exactly to determine a formula from its written form? Like for example, exercise M.7 states "Solid boron can be extracted from solid boron oxide by reaction with magnesium metal at a high temperature. A second product is solid magnesium oxide." Solid boron oxide is B2O3, but how would I be able to determine that if it wasn't originally stated as "trioxide" in order to assume there are three oxygens?

Posts: 87
Joined: Sat Aug 24, 2019 12:15 am

### Re: Determining the equation of written formulas

To calculate this, you would have to look at the net charges of each molecule. This is a comprehensive topic but let me try to shorten it:\
All molecules must be neutral in charge
Different atoms have different charges
Group 1 elements have a charge of +1
Group 2 elements have a charge of +2
Group 13 elements have a charge of +3
Group 15 elements have a charge of -3
Group 16 elements have a charge of -2
Group 17 elements have a charge of -1
Therefore, something such as lithium oxide would be Li2O because we need two lithium two get a +2 charge and oxygen has a -2 charge therefore making the molecule neutral in charge.
For non group 1, 2, 13-17 elements, the charge should be given such as Sn(IV) this would mean that the tin has a +4 charge. Therefore something such as tin (IV) oxide would be SnO2, the +4 charge of tin and two -2 charges of oxygen cancel. Hope this helps!

christabellej 1F
Posts: 109
Joined: Sat Aug 17, 2019 12:17 am

### Re: Determining the equation of written formulas

With B2O3 specifically, you could use the rules listed above can be used to. Oxygen, because it is in group 16, has a -2 charge. Boron has a +3 charge. Because this is a neutrally charged molecule, you know that somehow, the -2 and +3 charge have to cancel out. This is why there are 2 boron atoms and 3 oxygen atoms. Since each boron atom has a +3 charge, 2 borons will give a +6 charge. Since each oxygen has a -2 charge, 3 oxygens will have -6 charge. The +6 and -6 therefore make this molecule neutral, and so you would know to write boron oxide as B2O3.