Molecular Nomenclature Lesson 9

Molecular Nomenclature Most compounds that you find everyday are molecular compounds, not ionic. Sugar (molecular) for example has similar physical properties as salt (ionic) but they are very different in reality.

For example if you were to dissolve salt in water it would make the water conductive to electricity were the sugar would not. This is due to the fact that ionic compounds are made of ions which can conduct electricity. Molecular compounds on the other hand are not made of ions. They do not lose or gain electrons, they share electrons.

Ionic compounds can only bond to non metals in so many ways. Ex for every Ca we can only bond 2 F to it. Molecular compounds do not work that way. Molecular compounds can have various numbers of atoms bonded together to create various molecules. Ex. NO, NO2, N2O2, etc. Due to this method of bonding there are thousands more molecular compounds than there are ionic compounds.

Molecular Compounds are made of two or more Non-metals which share pairs of electrons to form bonds. Each pair of shared electrons is called a Covalent Bond.

The names of molecular compounds often contain prefixes The names of molecular compounds often contain prefixes. The prefixes are used to count the number of atoms in the molecule. This is important as molecular compounds containing 2 elements can have different combinations of atoms which have different properties.

# of atoms 1 2 3 4 5 6 7 8 9 10 Prefix Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca

Naming Binary Molecular Compounds: IUPAC Write down the name of the first element. If there is more than one atom of this element attach a Greek prefix. (if there is only one atom do not attach the prefix) Attach a Greek prefix (relating to the number of atoms) to the second elements name and add -ide. Example: CO = Carbon monoxide CO2 = Carbon dioxide

Word Equations (p90-91)

A word equation is a way of representing a chemical reaction: it tells you what reacts and what is produced. Word equations are an efficient way to describe chemical changes, to help chemists recognise patterns, and to predict the products of a chemical reaction.

Writing word equations They are written in a particular order. Reactants (what you start with) are always on the left side of the arrow and products (what you make) are always on the right side of the arrow. Multiple reactants or products are separated by a + sign.

Word Equations examples. Reactants Products Silver nitrate + copper  silver + copper (II) nitrate  Reactants Products Hydrogen + Oxygen  water vapour Reactants Products

The Conservation of Mass In a chemical reaction, the total mass of the reactants is always equal to the total mass of the products. This tells us a few things. Atoms do not change in a reaction. The molecules that they form can be changed but the atoms themselves are not. Mass cannot be destroyed. If it could we could use E = MC2 to create energy

Example Methane + oxygen  water + carbon dioxide

Skeleton equations + Balancing Equations A representation of a chemical reaction where the formulas of the reactants are connected to the formulas of the products by an arrow. CH4 + O2  H2O + CO2 This however does not demonstrate the Law of Conservation of Mass. The law states that the mass of the products will equal the mass of the reactants.

Combustion of methane (the above reaction) Type of atom Reactants Products C 1 H 4 2 O 2 + 1 = 3

We can’t change the formulas of the products or reactants so the only thing we can do is change the number of molecules instead of their formulas.

CH4 + O2 + O2  H2O +H2O + CO2 = CH4 + 2O2  2H2O + CO2 Now the chemical equation is balanced and the mass of the reactants will equal the mass of the products. Type of atom Reactants Products C 1 H 4 O 2 + 1 + 1= 4

Steps to balancing an equation Write the word equation of the reaction Aluminum + bromine  aluminum bromide Step 2 Write the skeleton equation by replacing each name with a correct formula. Al +Br2  AlBr3

Steps to balancing an equation Count the number of atoms on each side of the equation Type of atom Reactants Products Al 1 Br 2 3

Steps to balancing an equation Multiply each of the formulas by the appropriate coefficients to balance the number of atoms.

Start out by picking the element with the most number of atoms and try to balance it first. We will start with Bromine. The 2 and 3 will be balanced if we multiply the reactant side by 3 which would give it 6 Br, and multiply the product side by 2 to give us 6 Br. Now we have 2 Al products which need to be balanced so we add a 2 to the Al on the reactant side. 2Al + 3Br2  2AlBr3

More examples on the board Hydrogen gas + Chlorine gas  hydrogen chloride   Sodium + chlorine  sodium chloride Nitrogen + hydrogen  ammonia (hydrogen nitride) N2 + H2  NH3 = N2 + H2  NH3