S2-2-03: Write formulas and names of binary ionic compounds. 

Include: IUPAC guidelines and rationales

• Review of element vs. compound
  • practice page on elements and compounds (answer sheet)
• Rules for naming and writing ionic compounds, more on nomenclature
• Help with writing & naming compounds
• Check out the online quizzes:
  • Writing 30 Binary Chemical Formulas
  • Writing 30 Polyatomic Formulas
  • Naming chemical formulas
  • Assignment sheets for practice

• When writing an ionic formula between a metal and a nonmetal follow these 5 steps:
  1. Write the symbols for the metal and the nonmetal.
  2. Write the valences as superscripts above each symbol.
  3. Drop the + and - sign.
  4. Crisscross the valences so they become the subscript for the other element.
  5. Reduce subscripts whenever possible. Only when both are divisible by a number greater than one.

  Let's use these rules to figure out the chemical formula for our compound between aluminum and oxygen.

  

  Here are two examples where you must reduce:

  

  That's all there is to writing a formula for a binary (only two elements) ionic compound between an A-Group metal and a nonmetal.

  Using a periodic table try these then check your answers.

  1. sodium and phosphorus
  2. magnesium and fluorine
  3. aluminum and sulfur
  4. calcium and nitrogen
  5. barium and iodine
  6. potassium and bromine
  7. aluminum and phosphorus
  8. strontium and oxygen
  9. magnesium and nitrogen
  10. cesium and phosphorus

  Check answers

   

  • Rules for the Stock System
  • Naming Ionic formulas

The transition metals are located between 2-A and 3-A on periodic table. They are called transition metals because their valences change - there is no orderly arrangement of valences in this group. Also some of these metals can lose inner energy level electrons as well as valence electrons which means they can have multiple valences. Iron can lose 2 e- in some reactions and take on a +2 charge while in other reactions it can lose 3 e- and take on a +3 charge. So how can you tell the valence when the periodic table doesn't help? By looking at the roman numeral in their name.

Iron with a +2 valence is called Iron(II)) while iron with a +3 valence is called iron(III). Here are some other transition metals cations:

Using a periodic table try these then check your answers.

1. iron(III) and phosphorus
2. copper(II) and fluorine
3. silver(I) and sulfur
4. manganese(II) and nitrogen
5. lead(IV) and iodine
6. copper(II) and bromine
7. gold(II) and phosphorus
8. lead(IV) and oxygen
9. silver(I) and nitrogen
10. copper(II) chloride

Check Answers

Some compounds contain a polyatomic ion (many atom ion - a molecule with a charge). Here is a list of some common polyatomic ions.

When you write formulas for compounds containing a polyatomic ion:

1. Write the symbols for the metal and the polyatomic ion.*
2. Write the valences as superscripts above each.
3. Drop the + and - sign.
4. Crisscross the valences so they become the subscript for the other element.
5. If you have more than one of the polyatomic ion, you must encase it in parenthesis and place the subscript outside.
6. You can only reduce a subscript outside the parenthesis of a polyatomic ion - you cannot change the formula the polyatomic ion.

*In the case of ammonium (the only polyatomic cation) you would write it first and then the anion.

Here are some examples of writing formulas with polyatomic ions:

Try these using a periodic table an a list of polyatomic ions.

1. aluminum and sulfate
2. ammonium and sulfur
3. barium and hydroxide
4. magnesium and phosphate
5. lead(IV) and sulfite
6. strontium and carbonate
7. zinc(II) and phosphate
8. ammonium and oxygen
9. calcium and nitrate
10. tungsten(II) and sulfate

Check answers

When naming binary ionic compounds simply name the metal then the nonmetal changing it's name to end in -ide. Here is a list of nonmetal anions:

Never use prefixes when naming ionic compounds. Unlike covalent formulas, ionic compounds do not have more than one formula between two elements. So prefixes are not used when naming ionic compounds (compounds containing a metal or a polyatomic ion).

Examples of ionic compound names:

NaCl = sodium chloride

BaF2 = barium fluoride

Al2(SO4)3 = aluminum sulfate

Li2S = lithium sulfide

IMPORTANT: You must remember to look for transition metals when naming ionic compounds. Be sure to include a roman numeral in the cation name so that it shows its valence of the transition metal. Examples: iron(III) = Fe⁺³, manganese(IV) = Mn⁺⁴, gold(II) = Au⁺², copper(I) = Cu⁺¹...

To do this you must figure out the valence of the transition metal by looking at the compound formula and crisscrossing the subscripts so they become valences again. If the formula was Fe2O3, iron would have a +3 valence and the name of the compound would be iron(III) oxide. In the case of MnO2, manganese would have to have a valence of +4 for the valence of oxygen (-2) to reduce out. So MnO2 is named manganese(IV) oxide.

• Choose a game to play on Binary Ionic Compounds

Use the Ion Cut outs to make binary compounds

A-Group Metal Answers

1. sodium and phosphorus = Na3P
2. magnesium and fluorine = MgF2
3. aluminum and sulfur = Al2S3
4. calcium and nitrogen = Ca3N2
5. barium and iodine = BaI2
6. potassium and bromine = KBr
7. aluminum and phosphorus = AlP
8. strontium and oxygen = SrO
9. magnesium and nitrogen = Mg3N2
10. cesium and phosphorus = Cs3P

Transition Metal Answers

1. iron(III) and phosphorus = FeP
2. copper(II) and fluorine = CuF2
3. silver(I) and sulfur = Ag2S
4. manganese(II) and nitrogen = Mn3N2
5. lead(IV) and iodine = PbI2
6. copper(II) and bromine = CuBr2
7. gold(II) and phosphorus = Au3P2
8. lead(IV) and oxygen = PbO2
9. silver(I) and nitrogen = Ag3N
10. copper(II) chloride = CuCl2

Compounds with Polyatomic Ions Answers

1. aluminum and sulfate = AlPO4
2. ammonium and sulfur = (NH4)2S
3. barium and hydroxide = Ba(OH)2
4. magnesium and phosphate = Mg3(PO4)2
5. lead(IV) and sulfite = Pb(SO3)2
6. strontium and carbonate = SrCO3
7. zinc(II) and phosphate = Zn3(PO4)2
8. ammonium and oxygen = (NH4)2O
9. calcium and nitrate = Ca(NO3)2
10. tungsten(II) and sulfate = WSO4

Writing & Naming Chemicla Formulas help:

There are two basic things you must be able to do if you ever want to be successful in Chemistry: write a chemical formula and name a chemical formula. But before you do that let's see why and how elements combine to form compounds.

In a chemical reaction, two or more elements combine to form a compound. Right now as you sit in front of your computer, billions of atoms of carbon in the food you eat are combining with the oxygen you breathe producing energy and carbon dioxide. The chemical formula for carbon dioxide is CO2 - a colorless, odorless gas.

The first thing you need to know about compounds is something about the elements that combine to make them. There are three types of elements: Metals, Nonmetals and Metalloids. Metals are on the left side and center of the periodic table, metalloids along the zigzag line that begins at 3A, and nonmetals (except for hydrogen) are on the right side of the table.

In a chemical reaction between a metal and nonmetal, metal atoms lose their valence electrons, while nonmetal atoms gain valence electrons. These actions allow the atoms to have eight valence electrons and become chemically stable.

Metals generally have between 1 and 3 valence electrons (the Group number at the top of each family). Lets see what happens to magnesium (an Alkaline Earth Metal) in a chemical reaction.

If magnesium can lose 2 electrons to a nonmetal (such as oxygen), it will be stable since now has eight valence electrons. But when it loses 2 electrons it now has 12 protons and only 10 electrons and becomes a cation (+ charged particle) with a +2 valence.

Nonmetals generally have between 5 and 7 valence electrons (Noble Gases have filled valence energy levels so we aren't concerned with them). Let's see what happens to phosphorus, a member of the Nitrogen Family.

If a phosphorus atom can gain 3 electrons from one or more metallic atoms it will be stable. When phosphorus gains 3 electrons in a chemical reaction, it now has 15 protons and 18 electrons and becomes a phosphide anion (- charged particle) with a -3 valence.

Important: When a nonmetal gains electrons and becomes an anion, the last few letters of its name is replaced with the suffix -ide. Here is a list of anions: nitride, oxide, phosphide, sulfide, fluoride, chloride, bromide, and iodide.

So why do ions stay together in a compound if both the elements are stable with 8 valence electrons? Two words: electromagnetic force. The positive charge on the metallic cation and the negative charge on the nonmetal anion attract each other and form a repeating pattern of ions called a crystalline lattice. In the reaction between sodium and chlorine, sodium loses an electron to become a +1 sodium cation while chlorine gains the electron to become a -1 chloride anion. They form a crystalline lattice - a salt crystal.

To sum it up:

Metals lose all their valence electrons in a chemical reaction and become cations (+ ions) with a +1, +2 or +3 oxidation number.

Nonmetals gain enough electrons to fill their outer energy level and therefore become anions (- ions) with a -1, -2, or -3 oxidation number.

The attraction between these two opposite charged ions hold the crystalline lattice together.

Two nonmetals have a tight hold on their valence electrons and neither is willing to give up any electrons. So when two nonmetals react, they share electrons to become chemically stable with eight valence electrons. Here is an example.

When you burn hydrogen gas (as we did the first day of school when Mr. G ignited the hydrogen balloon) it combines with oxygen (in the air) to produce H2O (water). Since both hydrogen and oxygen are nonmetals they share valence electrons. Hydrogen only needs 2 electrons to become stable (H, Li, Be and B only need 2 valence e- since the first energy level fills with 2 e-) while oxygen needs 8 valence electrons. So when they combine each hydrogen atom shares one electron with oxygen and oxygen shares one electron with each hydrogen atom - covalent bonds between the atoms hold the water molecule together.

Unlike a metal and nonmetal, when two nonmetals combine neither takes on a charge since neither lost or gained electrons. They remain atoms and do not become ions. Unlike ionic compounds which form crystals, covalent compounds form molecules. The shared pair of electrons orbit both nuclei giving each atom a filled outer electron energy level. The attraction for these shared pair of electrons produce a covalent bond which holds the molecule together.

Now that you understand why compounds form, lets move on to seeing how we can write their chemical formulas.