Covalent Bonding

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Chemical Bond
A bond results from the attraction of nuclei for electrons
- All atoms are trying to achieve a stable octet
IN OTHER WORDS
- the protons (+) in one nucleus are attracted to the electrons (-) of another atom
This is Electronegativity
Three Major Types of Bonding
Ionic Bonding
- forms ionic compounds
- transfer of valence e-
Metallic Bonding
Covalent Bonding
- forms molecules
- sharing of valence e-
Ionic Bonding
Always formed between metal cations and non-metals anions
The oppositely charged ions stick like magnets
Metallic Bonding
Always formed between 2 metals (pure metals)
- Solid gold, silver, lead, etc…
Covalent Bonding
Pairs of e- are shared between 2 non-metal atoms to acquire the electron configuration of a noble gas.
Drawing molecules (covalent) using Lewis Dot Structures
Symbol represents the KERNEL of the atom (nucleus and inner electrons)
dots represent valence electrons
The ones place of the group number indicates the number of valence electrons on an atom.
Draw a valence electron on each side (top, right, bottom, left) before pairing them.
Covalent bonding
The atoms form a covalent bond by sharing their valence electrons to get a stable octet of electrons.(filled valence shell of 8 electrons)
Electron-Dot Diagrams of the atoms are combined to show the covalent bonds
Covalently bonded atoms form MOLECULES
General Rules for Drawing Lewis Structures
All valence electrons of the atoms in Lewis structures must be shown.
Generally each atom needs eight electrons in its valence shell (except Hydrogen needs only two electrons and Boron needs only 6).
Multiple bonds (double and triple bonds) can be formed by C, N, O, P, and S.
Central atoms have the most unpaired electrons.
Terminal atoms have the fewest unpaired electrons.
When carbon is one of you atoms, it will always be in the center
Sometimes you only have two atoms, so there is no central atom
Cl2 HBr H2 O2 N2 HCl
We will use a method called ANS (Available, Needed, Shared) to help us draw our Lewis dot structures for molecules
Rules for Naming Molecular compounds
The most “metallic” nonmetal element is written first (the one that is furthest left)
The most nonmetallic of the two nonmetals is written last in the formula
NO2 not O2N
All binary molecular compounds end in -ide
Molecular Compounds
Ionic compounds use charges to determine the chemical formula
The molecular compound‘s name tells you the number of each element in the chemical formula.
Uses prefixes to tell you the quantity of each element.
You need to memorize the prefixes !
Prefixes
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca
Molecular Compound Rules
If there is only one of the first element do not put (prefix) mono
Example: carbon monoxide (not monocarbon monoxide)
If the nonmetal starts with a vowel, drop the vowel ending from all prefixes except di and tri
- monoxide not monooxide
- tetroxide not tetraoxide
Bond Types
3 Possible Bond Types:
Ionic
Non-Polar Covalent
Polar Covalent
Use Electronegativity Values to Determine Bond Types
Ionic bonds
- Electronegativity (EN) difference > 2.0
Polar Covalent bonds
- EN difference is between .21 and 1.99
Non-Polar Covalent bonds
- EN difference is < .20
- Electrons shared evenly in the bond
Ionic Character
“Ionic Character” refers to a bond’s polarity
In a polar covalent bond,
- the closer the EN difference is to 2.0, the more POLAR its character
- The closer the EN difference is to .20, the more NON-POLAR its character
Polar vs. Nonpolar MOLECULES
Sometimes the bonds within a molecule are polar and yet the molecule itself is non-polar
Nonpolar Molecules
Molecule is Equal on all sides
- Symmetrical shape of molecule (atoms surrounding central atom are the same on all sides)
Polar Molecules
Molecule is Not Equal on all sides
- Not a symmetrical shape of molecule (atoms surrounding central atom are not the same on all sides)
Water is a POLAR molecule
ANY time there are unshared pairs of electrons on the central atom, the molecule is POLAR
VSEPR – Valence Shell Electron Pair Repulsion Theory
- Covalent molecules assume geometry that minimizes repulsion among electrons in valence shell of atom
- Shape of a molecule can be predicted from its Lewis Structure
5 Shapes of Molecules
Linear (straight line)
Trigonal Planar
Tetrahedral
Bent
Trigonal Pyramidal
Intramolecular Attractions
Attractions within or inside molecules, also known as bonds.
- Ionic
- Covalent
- Metallic
Intermolecular Attractions
Attractions between molecules
- Hydrogen “bonding”
- Strong attraction between special polar molecules (F, O, N, P)
- Dipole-Dipole
- Result of polar covalent Bonds
- Induced Dipole (Dispersion Forces)
- Result of non-polar covalent bonds
STRONG intermolecular force
- Like magnets
Occurs ONLY between H of one molecule and N, O, F of another molecule
Why does Hydrogen “bonding” occur?
Nitrogen, Oxygen and Fluorine
- are small atoms with strong nuclear charges
- powerful atoms
- Have very high electronegativities, these atoms hog the electrons in a bond
- Create very POLAR molecules
Dipole-Dipole Interactions
WEAK intermolecular force
Bonds have high EN differences forming polar covalent molecules, but not as high as those that result in hydrogen bonding. .21<EN<1.99
Partial negative and partial positive charges slightly attracted to each other.
Only occur between polar covalent molecules
Induced Dipole Attractions
VERY WEAK intermolecular force
Bonds have low EN differences EN < .20
Temporary partial negative or positive charge results from a nearby polar covalent molecule.
Only occur between NON-POLAR & POLAR molecules
Intermolecular Forces affect chemical properties
For example, strong intermolecular forces cause high Boiling Point
- Water has a high boiling point compared to many other liquids