Molecular Compounds (a.k.a. Covalent Compounds)

Ionic Compounds Review Ionic compounds are the combination of ions. E.g. Na+ + Cl-  NaCl. This formula represents the __________ of sodium ions and chloride ions not the exact number of them. They are composed of a ___________________ and form a crystal structure (e.g. NaCl and CaCl 2 which are both salts)

Molecular Compounds Consist of atoms covalently bonded together The elements involved are all __________

Some examples N 2 O  _____________ = Gas used at the dentist to relax patients NO 2  _____________ = poisonous toxin emitted from car exhaust

More Examples H 2 O  ______ CO 2  ____________ = Gas exhaled and created during combustion reactions CO  ____________________= Lethal gas created during incomplete combustion

Recall In ionic compounds, the non-metal rips away the electron(s) from the metal because the metals loosely hold their electrons This creates a positive and negative ion which attract each other making them stick together (opposites attract)

Molecular Compounds made up of a non-metal and a non-metal. also called _____________

Molecular Compounds ________ electrons (e - ) to form a ________________. Neg. e - are attracted to the Pos. nuclei of both atoms

Molecular Compounds Molecular compounds are formed when non metals share electrons to fill their outer electron orbit (shell). If we draw the Lewis Structure for Fluorine, We can see that it needs ________ It wants to share one electron with another atom. If it bonds with another fluorine atom We draw the shared pair of electrons between the two atoms. FF FF Shared electron pair  ______

Molecular Compounds Many molecular compounds are predictable. How will Oxygen bond with Hydrogen to form a molecule. Draw the Lewis Structure of both Atoms. ________________________ Clearly we need another Hydrogen atom Putting the shared electrons between the atoms. The molecule is H 2 O H O H H O H **The Oxygen atom has 8 valence electrons (full) and the Hydrogen has 2 valence electrons (full)

Molecular Compounds Not all molecular compounds are as predictable. How will Oxygen bond with Carbon? Draw the Lewis Structures of each atom. ___________________________ If we add one more Oxygen, each oxygen can share two. However, if Oxygen will share two and donate one of its other electrons pairs, Oxygen can bond with just on Carbon atom. OC O C O CO _____________

Types of Bonds O C O Carbon Monoxide – Triple Bond because _______pairs of electrons are shared H O H Water – Single bond because ______ pair of electrons are shared Carbon Dioxide – Double bond because _______pairs of electrons are shared CO

Molecular Compounds – Naming So Oxygen can form CO or CO 2 We need a more flexible naming system for covalent compounds to reflect the many different bonding possibilities. To name a covalent compound, 1.Starting with the atom that is to the left in the periodic table, (or lower) 2.Write the name of the atoms with the prefix indicating the number of that atom in the compound. 3.Change the ending of the last atom to – ide. The prefixes are, 1_______ 2_______ 3_______ 4_______ 5_______ 6_______ 7_______ Note, the mono is omitted on the first atom. CO _____________ CO 2 _____________

Memorize me! NumberPrefixNumberPrefix 1mono6_________ 2 7hepta 3tri8_________ 4 9nona 5penta10_________

Naming Example P 4 O 10  Phosphorus - use prefix tetra (4)  Oxygen – change ending – Oxide  Oxide – use prefix deca (10) = _________

Molecular Compounds - Naming Name the following compounds CF 4 _________ H 2 O _________ PF 5 _________ Write the chemical formula for, Sulphur Dioxide _________ DiCarbon Tetrahydride _________

Molecular Compounds – Diatomic Gases Molecular compounds show an incredible variety in structure, physical and chemical properties. There are categories that further divide covalent compounds into categories with common properties. Diatomic Gases – _________ The Halogens, Oxygen, Nitrogen and Hydrogen form diatomic gases. H 2 is called Hydrogen Gas not Dihydrogen.

Eg. N 2 - _________ O 2 - _________ Air

Writing Formulas  left-most element goes 1 st Carbon monoxide -Carbon (C)  no prefix therefore = C - Monoxide – Mono = 1 therefore, 1 oxygen atom = O = _________

Writing Formulas Nitrogen dioxide -Nitrogen (N)  no prefix therefore = N - Dioxide – Di = 2 therefore, 2 oxygen atoms = O 2 = _________

Writing Formulas DiCarbon Tetrahydride -Dicarbon (C)  Di = 2 therefore = C 2 - Tetrahydride (H)  Tetra = 4 therefore, 4 Hydrogen atoms = H 4 = _________

Exceptions that need to be Memorized! CH 4 – _________ H 2 O 2 – _________ H 2 O – Water

These Too! NH 3 – _________ O 3 – _________