1. -Molecules -Compounds -predicting ion charges -Writing chemical formulas of molecules -naming molecules and compounds (IUPAC Rules)

2. Write out the Chemical Formulas for the following molecules
Practise
Write out the Chemical Formulas for the following molecules
Sodium hydroxide
Barium sulfate
Aluminum bromide
Iron (II) Chlorate
Dihydrogen carbonate
Hydrogen Chloride
Barium dichromate
Zinc hydroxide
Bismuth trifluoride
Carbon tetrachloride

3. Molecules and compounds
A molecule is a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compounds.
Molecular Hydrogen(H2), molecular Oxygen (O2) and molecular Nitrogen (N2) are not compounds because each is composed of a single element.
Water (H2O), carbon dioxide (CO2) and methane (CH4) are compounds because each is made from more than one element.
So a molecule of H2 is composed of 2 Hydrogen atoms but a molecule of H20 is composed of 2 atoms of Hydrogen combined with 1 atom of Oxygen.

4. Properties of compounds
In general, the properties of compounds are different than elements. As an example, sugar (C12 H22 O11) is a sweet tasting solid that dissolves easily in water. Elemental Carbon is a black, tasteless solid, while both Hydrogen and Oxygen are colorless gases.
They combine chemically to form sugar. Sugar can be broken down into Carbon and Water by heating it up.
Because this heating is a chemical reaction – it breaks bonds – it cannot be reversed easily. Think of frying an egg – once fried (a chemical change) it cannot be ‘unfried’.
Compounds are formed by three common types of chemical bonds:
Covalent (the different elements share electrons. Ex. CH4 (aka Methane))
Ionic (one element ‘donates’ an electron. Ex. NaCl ( aka Sodium Chloride)
Metallic (Metallic bonds are formed from the attraction between mobile electrons and fixed, positively charged metallic atoms. Ex. Cu (Copper)

5. The combination of elements in a compound will determine the compound’s physical characteristics ( smell, taste, melting point, boiling point, etc.) as will the type of bond.
Ionic materials, like NaCl, have very high melting points and boiling points.
Covalent materials, like CH4, have lower melting points and conduct electricity poorly.
Metallic materials have varying melting points, conduct electricity very nicely, and are ductile and malleable.
Images of the different bonds:
Covalent Ionic

6. Metallic

7. Predicting Ion Charges
How do we predict if element is going to produce a positive cation or a negative anion?
A very easy way to tell if an element’s ion is positive or negative is to look at the group number. We will look at Cations first
Group 1 – Alkali metals 1+ (aka Group 1a
Group 2 – Alkali Earth Metals 2+ (aka Group 2a)
We jump over the transition metals and just look at (Group 3a)Ag (Silver) 1+ , then (Group 4a) Zn (Zinc) and Cd (Cadmium) both are 2+, and finally (Group 5a) Al (Aluminum) and Ga (Gallium) with 3+ each.
NOTE: The transition metals have varying charges – as an example Cu (Copper) can either be a 2+ or 3+ - and we will look at these on a case by case basis.

8. Anions
You will notice that Groups 15 and 16 also appear on the anion list.
Groups 15, 16, and 17 are also called 5a, 6a, and 7a respectively.
To find the negative charge of each group simply subtract 8 from the ‘new’ group numbers.
Example : Group 5a (or 15) – 8 = 3 –
Group 6a (or 16) – 8 = 2 –
Group 7a (or 17) – 8 = 1 –
NOTE: Most polyatomic ions carry a negative charge. The common exceptions are H30+, NH4+ , and Hg22+

9. Writing chemical formulas
Chemical formulas represent the composition of a compound (what makes up a compound) using the symbols for the elements in the compound. * The periodic table is like the “alphabet” of chemistry – the elements are used to build compounds *
There are some rules for writing formulas:
1)  Represent each element in a compound with the correct symbol for that element.
2)  Use subscripts to indicate the number of atoms of each element in the compound. The subscript follows the element. If there is only one atom of a particular element, no subscript is used.
3)  Write the symbol for the more metallic element first.

10. NOTE: The net charge on this molecule is zero 0
NOTE: The net charge on this molecule is zero 0. This is because the Sulfur cation has a 4+ charge and each Oxygen anion has a 2- charge.

11. Polyatomic ions
There are certain ions that contain several types of ions. (Ex: SO42- is an example of a polyatomic ion.)
For the most part, these polyatomic ions are negative. The exception to this rule is the ammonium ion (NH4+).
The formula for compounds containing polyatomic ions is written the same as the formula for binary compounds.
o Positive ion is always written first – negative ion is always written second. o Once again, the algebraic sum of the changes must be ZERO. o Since the charge on the polyatomic ion pertains to the ion as a whole, parentheses must be placed around the ion before a subscript can be used.
Ex. Ca NO3 - = Ca(NO3)2 Calcium Nitrate
There are a couple of problems using this method: 1) we can create compounds that don’t exist in Nature and 2) There are many compounds that exist that we can write the formulas for.

12. A quick and dirty way of writing formulas
A fast way of determining the final molecule when combining ions is to firstly look at the cation and anion charges
Ca Cl - Calcium is a 2+ and the Chloride ion is a 1- .
Write the molecule with the most metallic element first (in this case the winner is Calcium), followed by the non-metal (Chlorine aka Chloride ion).
Ca2+Cl-
We then take the 2 from the Calcium ion and move it down behind the Chloride ion. The 1 from the Chloride ion moves down behind the Calcium ion. This shows us that we need 2 Chloride ions to balance out the 1 Calcium ion in order to create a neutral charge molecule.
NOTE: We write brackets around the Chloride ion and place a 2 subscript behind the bracket. We don’t write a 1 behind the Calcium ion.
We end up with: Ca(Cl)2

13. Naming molecules and compounds
The naming of molecules and compounds has to follow the standards developed by IUPAC (International Union of Pure and Applied Chemistry).
Naming Binary Ionic Compounds - f the metal ion has a specific charge, you name the positive ion first, and change the ending of the negative ion to “ide”. LiCl = lithium chloride or NaBr = sodium bromide
Sometimes the charges on certain metal ions varies from one compound to another. The charge on the metal ion is indicated with a Roman numeral in parenthesis.
Fe(Cl)2 = iron(II)chloride or Fe(Cl)3 = iron(III)chloride

14. Naming Binary Compounds of Nonmetals (Covalent compounds)
These compounds involve the bonding of only nonmetals
The rules are:
Write the names of the elements in the same order that they appear in the formula. (The more metallic element is named first.)
Add prefixes to the name of the elements in each molecule of the compound. (In practice, the mono (which means 1) prefix is often omitted for the more metallic element. If no prefix is given, one atom of the element is understood.) Use the following Greek prefixes:
mono=1
di = 2 tri = 3 tetra = 4
penta = 5
hexa=6
hepta = 7
octa=8
Drop the last syllable in the name of the final element and add “ide”.

15. Examples:
o CO = carbon monoxide o CO2 = carbon dioxide o N2O3 = dinitrogen trioxide
When naming compounds with elements and polyatomic ions, simply name the positive ion first (followed by a Roman numeral if necessary) and add the name of the polyatomic ion.