What is a Molecular

Compound?• A molecular compound is when two elements, usually non-metals, combine. Non-metal + non-metal = molecular compound

Writing the Names• Step 1: The first element is usually the

element the furthest to the left in the periodic table of elements.

• Step 2: For the second element add the suffix “ide.”

• Step 3: Use prefixes (table on next slide) to indicate how many atoms of each element there are.

Prefix Number of Atoms

Mono 1

Di 2

Tri 3

Tetra 4

Penta 5

Hexa 6

Hepta 7

Octa 8

Nona 9

Deca 10

Mono is only used for the second element because it is assumed that if there is no prefix for the first element that there is one.

Drop the “o” in mono if the element begins in “o.”

Exceptions• Many molecular compounds are known by

there “trivial” names.

• Ex: water H2O

Naming Example #1

• CO2

• Carbon is the element the furthest to the left in the periodic table of elements so it comes first.

• Next you add “ide” to the second element which is oxygen. Oxygen becomes oxide.

• For the final step add the appropriate prefix for how many atoms of each element there are. Carbon stays the same and oxide becomes dioxide.

• The name of CO2 is carbon dioxide.

Naming Example #2

• N2O5

• Nitrogen comes first. There are two atoms of it so it becomes dinitrogen.

• Oxygen becomes oxide.

• There are five atoms of oxygen so it becomes pentoxide.

• The name of N2O5 is dinitrogen pentoxide.

Naming Example #3

• CF4

• Carbon is first and there is a single atom of it so it remains the same.

• Fluorine becomes fluoride.

• There are four atoms of fluorine so it becomes tetrafluoride.

• The name of CF4 is carbon tetrafluoride.

Writing the Formula

• Step #1: The first element in the name is the first in the formula so you write it’s symbol first. The prefix (table on next slide) indicates the number of atoms of each element. This number goes in the subscript on the bottom right of the symbol.

• Step #2: The second element’s symbol comes next with its appropriate amount of atoms determined by the prefix.

Prefix Number of Atoms

Mono 1

Di 2

Tri 3

Tetra 4

Penta 5

Hexa 6

Hepta 7

Octa 8

Nona 9

Deca 10

If there is no prefix in the first element’s name the it is assumed there is one atom of that element.

Also if there is no number in the subscript it is assumed that there is one atom of that element.

Formula Example #1

• Dinitrogen monoxide

• The symbol for nitrogen is N and the prefix is “di” which means two. So it becomes N2.

• The symbol for oxygen is O and the prefix is “mono” which means one which isn’t written in a subscript.

• The formula for dinitrogen monoxide is N2O.

Formula Example #2• Silicon tetrachloride

• The symbol for silicon is S and there is no prefix so it remains S.

• The symbol for chlorine is Cl and the prefix is “tetra” so there are four atoms of chlorine. Cl4

• The formula for silicon tetrachloride is SCl4.

Formula Example #3

• Dihydrogen monosulfide

• The symbol for hydrogen is H and the prefix is “di” so in the formula it becomes H2.

• The symbol for sulfur is S and the prefix is “mono” so there is one atom of sulfur, S.

• The formula for dihydrogen monosulfide is H2S.

Questions• Change these molecular formulas to their

name forms.

1.CO2->

2.N203->

3.Ar2S3->

4.PH3->

5.S2F10->

Questions1. selenium trichloride 2. Oxygen difluoride

3. Dinitrate tetraoxide

4. Phosphorus pentachloride

5. Sulfur hexafloride