Chemistry can be a daunting subject for a lot of students. Since it’s possible for high school students to take chemistry in Grade 11 (in Canada at least), this guide will go over what you need to know.
Firstly, there’s the two different, basic types of compounds, ionic and covalent compounds. These compounds are created when the electrons of two atoms interact with each other, sometimes they are shared, other times they are transferred. Ionic compounds are compounds that are created from a metal and non-metal. The electronegative difference between a metal and non-metal is almost always higher than 1.7 (and you can check this on a periodic table), which means that the electrons are being shared very unevenly. So unevenly in fact, that the electrons are just transferred off to the non-metal. This gives the metal a very positive charge since it would rather lose a couple of electrons to gain a stable octet, rather than gain several more. This also gives the non-metal a very negative charge since it would rather gain a couple of electrons to gain a stable octet rather than lose several more.
The second type of compounds, covalent compounds, are when two non-metals bond and share electrons with each other. There are polar covalent compounds, where the electrons aren’t shared equally, similar to the ionic compound but to a lesser degree, which gives it a positive and negative dipole. There are also non-polar covalent compounds, ones which don’t have a dipole, and thus lack a positive and negative charge. All covalent compounds have an electronegative difference between their atoms by, at most, 1.7.
There’s also the scientific nomenclature that a student must be familiar with. This helps in identifying what compound or acid is asked of them when asked. There’s nomenclature for acids, salts, and metals.
For the acid nomenclature, phosphoric acid (H3PO4) will be used as an example.
This acid contains 4 oxygens. The acid is able to have 5 oxygens, but its name will change to perphosphoric acid. It gains the per- prefix. The acid is also able to have 3 oxygens. It’s name changes to phosphorous acid, and gains an -ous suffix. It’s also able to have 2 oxygens, where it’s name changes to hypophosphorous acid, with a hypo- prefix along with the previous -ous suffix.
The acid when it’s in a salt is also spelled differently. Similar to when phosphoric acid is by itself, it can have 5, 3 or 2 oxygens. if it has 5, it’s spelled as perphosphate. With 3, it’s phosphite. With 2, it’s hypophosphite.
Metals are different from the acids nomenclature because they aren’t spelled differently, but because an indicator has to be added to tell what charge the metal has, since it is multivalent. The charge is always in roman numerals, and as an example, is shown as: Copper (III) Oxide. The roman numeral is only shown when writing the compound out, and not in the molecular form as in Cu2O3.
