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 CaCl2 which are both salts)
Molecular Compounds • Consist of atoms covalently bonded together • The elements involved are all __________
Some examples • N2O _____________ = Gas used at the dentist to relax patients
• NO2 _____________ = poisonous toxin emitted from car exhaust
More Examples • H2O ______ • CO2 ____________ = 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 ________
F
F
F 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.
F
Shared electron pair ďƒ ______
Molecular Compounds Many molecular compounds are predictable. How will Oxygen bond with Hydrogen to form a molecule. Draw the Lewis Structure of both Atoms. ________________________
H
H
O
H H O
Clearly we need another Hydrogen atom Putting the shared electrons between the atoms. The molecule is H2O
**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. ___________________________
C
O
C
O
O
_____________ 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.
C
O
_____________
H
Types of Bonds
H O C
Water – Single bond because ______ pair of electrons are shared O O
O
Carbon Monoxide – Triple Bond because _______pairs of electrons are shared
C
Carbon Dioxide – Double bond because _______pairs of electrons are shared
Molecular Compounds – Naming So Oxygen can form CO or CO2 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 _____________ CO2
_____________
Memorize me! Number
Prefix
Number
Prefix
1
mono
6
_________
2
_________ 7
hepta
3
tri
_________
4
_________ 9
nona
5
penta
_________
8
10
Naming Example • P4O10 Phosphorus - use prefix tetra (4) Oxygen – change ending – Oxide Oxide – use prefix deca (10) = _________
Molecular Compounds - Naming Name the following compounds
Write the chemical formula for,
CF4
Sulphur Dioxide
_________
_________
H2O
_________ PF5
_________
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. H2 is called Hydrogen Gas not Dihydrogen.
Eg. N2 - _________ O2 - _________
Air
Writing Formulas left-most element goes 1st 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 = O2 = _________
Writing Formulas DiCarbon Tetrahydride - Dicarbon (C) ďƒ Di = 2 therefore = C2 - Tetrahydride (H) ďƒ Tetra = 4 therefore, 4 Hydrogen atoms = H4 = _________
Exceptions that need to be Memorized! CH4 – _________
H2O2 – _________
H2O – Water
These Too! NH3 – _________ O3 – _________