Molecular Compounds

Molecular CompoundsRecapIf the solution conducts electricity, the compound must contain ions.Salt, or sodium chloride, is an ionic compound.In ionic compounds, metals with one, two or three electrons in their outer shell lose electrons to non-metals, which often have five, six, or seven electrons in their outer shell.

If the solution does not conduct electricity, it must be a different kind of compound.Most of the compounds you encounter every day do not contain ions, rather they contain neutral groups of atoms called molecules.

Kitchen ExperimentHow can you tell the difference between salt and sugar without tasting it?Salt is an ionic compound and therefore salt water will conduct electricity. Sugar is a molecular compound and when mixed in water will not conduct electricity.

Molecular CompoundsMolecular Compounds are formed by the combination of two or more atoms held together with covalent bonds.Sugar is an example of a molecular compound. It is made up of molecules in which non-metal atoms share electrons to form stable arrangements.Water is another example of a molecular compound, it is two hydrogen atoms and oxygen atom. These atoms share electrons to make a stable molecule of water (H20).Examples of Molecular CompoundsSugarAspirinGasolineMethaneWaterAmmonia

Covalent BondsA covalent bond is formed when a shared pair of electrons held between two nonmetal atoms hold a molecule together.Many nonmetals form molecules this way.Ex: Chlorine gas(Cl2) is when two chlorine atoms, each with 7 electrons in its outer shells join and share an electron so each Cl atom can have a full outer shell.

Writing Formulas for Molecular CompoundsThe formulas of many molecular compounds can be predicted using a method similar to the one you used for ionic compounds.The number of electrons that metals and nonmetals transfer to become stable ions can be a clue to the formula of an ionic compound.The number of electrons that a nonmetal needs to share to become stable is a clue to the number of covalent bonds it can form.

The Combining Capacity of a nonmetal is a measure of the number of covalent bonds that it will need to form a stable molecule.Combining Capacities of Nonmetal Atoms4321HCNOFSiPSClAsSeBrIEx. Carbon has 4 electrons in the outer shellIf it loses 4 electrons to become stable it would have the same arrangement as Helium and form a positive ion If it gains 4 electrons it will resemble Neon and form a negative ion. It turns out that Carbon cannot form either ion so it has to share electrons to become stable. It will gain four electrons; it has a combining capacity of 4.Carbon example: Carbon shares it 4 electrons with four different Hydrogen atoms, the result is the natural gas Methane, CH4.

How would you write the formula for a compound formed between carbon and sulfur?Step 1 Write the symbols, with the left-hand element from the Combining Capacities Table first, with the combining capacity.4 2C SStep 2 Crisscross the combining capacities to produce subscripts.4 2 C2S4C S

Step 3 Reduce if possibleCS2

Naming Molecular CompoundsThe names of molecular compound often contain prefixes.These prefixes are used to count the number of atoms when the same two elements form different combinations.

ExampleCO2 Carbon dioxideCO Carbon monoxide

The prefixes di and mono differentiate between the two molecules.

Using Mono is not necessary when there is only one atom of the first element in a molecular compound.

QuestionsUsing your notes and the text book answer questions 1,2,3 and 4 on page 204.