Binary compounds are compounds consisting of two different kinds of atoms or two kinds of monoatomic atoms.
Binary Ionic Compounds
Binary ionic compounds are compounds consisting of a metal and a non metal. There are only two atoms in this compound.
The rules for naming them are as follows:
- The metal atom is always written first.
- The name of the metal is written in full.(i.e Aluminum)
- The name of the non metal, written after the metal, is written with an -ide suffix.(i.e Sulfide or Oxide)
Predicting the Formula for an Ionic Compound
- Write the symbols in the order that they appear in the name.(i.e. Li2O)
- Write the number in which the atom wants to achieve for its valence.( For example, Oxygen has a valence of 6 electrons.
In order for Oxygen to obtain a stable octet, oxidation state, it needs 2 more electrons, to bring it to 8 electrons in its
valence. Therefore, the number written above the Oxygen atom is 2.)
- Criss cross the numbers above the atoms to get the formula. LiO, Li has 1 to lose, Oxygen has 2 to gain. Therefore, the
formula will be Li2O. This means that there are two Lithium atoms for every Oxygen atom.
NOTE: Check the ChemoLab in the Web Links section for balancing and chemical nomenclature.
Multivalent Metal Ions
Multivalent Ions are compounds that have a metal with more than one valence. Refer to a periodic table
to help see if the metal atom is multivalent. Here are the steps to write the formula:
- Write out the atoms in the order they appear, with the metal atom first, and the non metal second.
- Find the "oxidation state"(the amount of electrons it wants to become stable) and criss cross upwards.
- You will find that when you criss cross, the metal will get a new number above it. An example is CuCl2. When you criss cross, you get a 2 over the Copper and a 1 over the Chlorine. Since Copper is a multivalent atom, you
would write the Roman Numeral 2(II) after Copper, and put Chloride after it. It will look like this, Copper (II) Chloride.
- Don't forget to state the charge on the atom in a superscript. So, Copper will be 2+, and Chlorine will be 2-. This gives
the overall compound's charge of 0.
There you have it. That is how you write formulas and name the compounds in IUPAC form for Multivalent Ions.
First off, there are different types of compounds with polyatomic ions in them. These are:
- Tertiary: A compound composed of three different elements.
- Tertiary Ionic: A compound composed of a metal ion and a polyatomic ion.
- Oxyanion: A polyatomic ions that includes an Oxygen in it.
There is no easy way to remember polyatomic ions but to memorize them by continuously using them. Polyatomic Ions like
NaOH, Sodium Hydroxide, becomes easy to remember as you deal with the same polyatomic ions quite often. The steps to determine
the formula are as follows:
- Write out the atoms in the order they appear.
- Criss cross down and determine the numbers to be placed in a subscript to the right of the atom. If the metal has a valence
that is greater than 1, and criss crosses down to give the polyatomic ion a number greater than 2, you must put a bracket
around the polyatomic ion and write the number outside of the bracket. Here is an example: FeBrO3 --> Fe(BrO3)2.
- As you can see, Iron(Fe) has an oxidation state of 2. It needs to gain 2 electrons in order to become stable. When you
criss cross downwards, the polyatomic ion must be bracketed and you must put the number on the outside, to the right, of the
bracket, as shown above.
That is basically the gist of things. With enough practise and studying, you will have all of the most common polyatomic
ions memorized. This will help a lot too when writing the formulas.