Molecular Compounds

September 15th, 2011

is called "hydroxyl acid", the substance is the major component of acid rain.

contributes to the "greenhouse effect". may cause severe burns. is fatal if inhaled. contributes to the erosion of our natural landscape. accelerates corrosion and rusting of many metals. may cause electrical failures and decreased

effectiveness of automobile brakes. has been found in excised tumors of terminal 

cancer patients.

Dihydrogen Monoxide

Despite the danger, dihydrogen monoxide is often used:

as an industrial solvent and coolant. in nuclear power plants. in the production of Styrofoam. as a fire retardant. in many forms of cruel animal research. in the distribution of pesticides. Even after

washing, produce remains contaminated by this chemical.

as an additive in certain "junk-foods" and other food products.

Dihydrogen Monoxide cont’d

http://en.wikipedia.org/wiki/Dihydrogen_monoxide_hoax

Just kidding – it’s water.

Usually composed of two or more different non-metals

Atoms share a pair of electrons The shared electrons are attracted to the

nuclei of both atoms Since they’re sharing and not transferring,

the atoms remain uncharged Let’s look at a Lewis Dot of water to see

what’s going on...

Molecular or Covalent Compounds

Molecular compounds are made of individual molecules with a fixed ratio

Molecules are neutral particles composed of two or more atoms joined together by covalent bonds

Molecules

Each group will be assigned a different molecular/covalent compound

You will have 10 minutes to figure out how this molecule bonds covalently!

On chart paper, draw what’s going on Your group will explain the

molecular/covalent compound to the class!

Let’s look at some molecular/ covalent compounds...

Naming Binary Molecular Compounds *Remember! Binary means 2* Let’s name CO2

How do we name these?

Prefix Number Prefix Number

Mono- 1 Penta- 5

Di- 2 Hexa- 6

Tri- 3 Hepta- 7

Tetra- 4 Octa- 8

NO2 is nitrogen dioxide What about N2O4? Is it the same as NO2? Answer – NO!

More naming practice

We don’t simplify the subscripts for molecular/covalent because since molecules are separate particles, (not a solid crystalline structure like ionic bonds), different formulas represent different molecules!

Step Example – N2O4

1. Count the number of atoms of the first element in the chemical formula.

Number of nitrogen atoms: 2

2. Write the appropriate prefix followed by the name of the element. Note that the prefix mono- is never used for the first element.

First part of the name:dinitrogen

3. Count the number of atoms of the second element in the chemical formula.

Number of oxygen atoms: 4

4. Write the appropriate prefix followed by the name of the element using the suffix –ide. If the prefix ends with a or o, this letter is dropped before the oxide.

Second part of the name:tetroxide

Full name: dinitrogen tetroxide

Naming a Binary Molecular Compound

Name your compounds!

Back in your groups!

Steps Phosphorus Trichloride (used to make insecticide)

1. Write the chemical symbol of the first element.

First element in formula : P

2. Figure out how many atoms you need based on the prefix (mono-, di-, etc.) If there is no prefix, there is just one!

Number of phosphorus atoms: 1

3. Write the chemical symbol of the second element.

Second element in formula: Cl

4. Figure out how many atoms you need, based on prefix.

Number of chlorine atoms: 3

5. Write the formula using the subscripts

Formula: PCl3

Writing Chemical Formulas for Binary Molecular Compounds

Write the chemical formula for dinitrogen pentoxide

Name the following molecular compounds CO PCl5

Practice!