Molecular Names & Formulas Covalent bonds happen when two atoms share one or more pairs of electrons, causing a molecule to be formed. Because covalent bonds are less strong than ionic bonds, covalent (or molecular – same thing) compounds tend to be less hard. They also have lower melting and boiling points than ionic compounds. How will you know when a compound is molecular?

Molecular Names & Formulas A covalent bond is formed by two atoms whose electronegativities are not vastly different. Because neither is strong enough to “take” an electron from the other, the two atoms will share a pair of electrons. Below is a diatomic molecule – a molecule made when two of the same atom join together to share a pair of electrons – one from each atom, so each can have a full outer energy level. (Note: for hydrogen, a full outer energy level only has 2 electrons.

Molecular Names & Formulas Molecular formulas look just like ionic formulas; They have chemical symbols for each element with subscripts to tell how many of each element. The molecule on the previous slide was H 2, because it had two hydrogen atoms. What is the formula for the chlorine gas molecule below? It is Cl 2. Notice how the Lewis dot diagrams help you to visualize the sharing of electrons.

Molecular Names and Formulas You may remember from biology class that glucose has the formula C 6 H 12 O 6. From that formula, you can tell what kinds of atoms are in glucose, and how many of each. See if you can find all of the atoms that make up the glucose molecule on the illustration below.

Molecular Names and Formulas Many chemicals have common names, like water. All compounds also have chemical names. Review how to name ionic compounds. Naming covalent compounds is similar, but with prefixes to tell how many of each type of atom. Water, for instance, is also known as dihydrogen monoxide. Why?

Molecular Names & Formulas Prefixes on names of atoms in molecular names (chemical names of molecular compounds) tell how many of each kind of atom. Dihydrogen means two hydrogens are in the molecule. Monoxide means there is one oxygen. The prefixes are: Mono=one Di=two Tri=three Tetra=four Penta=five Hexa=six Hepta=seven Octo =eight

Molecular Names & Formulas You can always recognize a molecular compound by its name, because only a molecular compound has a name with prefixes. Identify which of the names below describe molecular compounds: 1. sodium sulfate 2. hydrogen monoxide 3. carbon monoxide 4. ammonium hydroxide 5. carbon tetrachloride 6. dinitrogen trioxide 7. calcium carbonate Hint: If there is only one of the first atom listed in a molecular formula, “mono-” is not needed. Mono- is not normally used for the first named element. Sodium sulfate if ionic. You can tell by the name of the polyatomic ion ending in -ate. Hydrogen monoxide is molecular. The mono- gives it away. Carbon monoxide is molecular. Ammonium hydroxide is ionic. Carbon tetrachloride is molecular. Dinitrogen tetroxide is molecular. Calcium carbonate is ionic.

Molecular Names & Formulas Write the name and formula of each.

The first diagram was carbon tetrahydride. What is its formula? This diagram had three carbons and eight hydrogen atoms, so it is tricarbon octahydride, A.K.A. propane. What is its formula? The diagram showed carbon dioxide. What is its formula? The last diagram had two hydrogen atoms and one oxygen atom, so it is ___hydrogen monoxide, A.K.A. water.

r053872/tutorial/formulas/formulas.html Try the tutorial listed below for more. Take notes and review your notes.