Unit 8 – Covalent Bonding
To bond or not to bond?
• What is a chemical bond?
• Forces of attraction that hold groups of
atoms together
• Why do elements form bonds?
• Octet Rule
• Atoms gain, lose or share to have eight electrons
on the outer shell
Types of Bonds
•Ionic Bond
•Covalent Bond
Ionic Bonds
• Between a METAL and a NONMETAL
• Between a CATION and an ANION
• Most are CRYSTALLINE solids
• High melting points
• Good conductors
• They are called “salts”
Covalent Bonds
• Between a NONMETAL and a NONMETAL
• They are called molecules
• Low melting points
• Involve the sharing of electrons
• Non-polar- equal sharing of electrons
• Polar- unequal sharing of electrons
Differences of Bonds
IONIC
COVALENT
Types of
Elements
metal and nonmetal
two nonmetals
Electron
activity
Electrons transfer
Metals lose=cations
Non-metals gain=anions
Electrons are shared
Non-polar: Equally shared
Polar: unequally shared
Physical
State
solid
liquid or gas
Melting
Point
high
low
Yes/separates into
cations and anions
yes
(solution or liquid)
usually not
Solubility in
Water
Electrical
Conductivity
Electronegativity
Big differences
no
Small differences
Naming Covalent Compounds
• Only use a prefix with the first element when there
is more than one.
• ALWAYS use a prefix with the second element and
ends in -ide
• One- mono
Six- hexa
• Two- di
Seven- hepta
• Three- tri
Eight- octa
• Four- tetra
Nine- nona
• Five- penta
Ten- deca
• 11 – undeca
• 12 – dodeca
• 13 – trideca
• 14 – tetradeca
• 15 – pentadeca
• 16 – hexadeca
• 17 – heptadeca
• 18 – octadeca
• 19 - nonadeca
Practice Naming Covalent Compounds
• CO
• CO2
• N2O5
• NF3
Writing Covalent Compounds
• Write the symbol of the first element.
• If it has a prefix, put the number after the element
as subscript.
• Write the symbol of the second element
• Put the number represented by the prefix after it
as a subscript.
• DO NOT REDUCE! Leave it as it is.
Practice Writing Covalent Compounds
• Iodine pentafluoride
• Nitrogen tribromide
• Diphosphorus pentoxide
• Sulfur hexachloride
Activity
•Your partner is the person
across from you.
•Set of cards with 20 items
•Sort them into “Ionic” and
“Covalent” categories
•See if you can find all the
matches
Diatomic Molecules
• Molecule: another name for a compound which
has covalent bonds
• Diatomic molecule: covalent molecule with two of
the same atoms
• Seven you need to know: I2, Br2, Cl2, F2, O2, N2, H2
Lewis Dot for Covalent
Compounds
• Lewis Dot Review: What is a Lewis dot diagram?
• Draw the Lewis dot for the following:
S
N
C
Xe
He
Bell Work
11/10/14
• Log on to socrative.com
• Enter Room number 4f6c8fbc
• Wait for teacher to begin activity
• Get out your notes
AGENDA
Review
Lewis Dot Rules for Covalent Molecules
Examples
Activity - Practice
Socrative Exit Ticket
Review
• Triselenium tetranitride
• Tetracarbon Octahydride
• Lewis Dot for: P
• What happens to electrons in
covalent bonds?
Lewis Dot for Covalent Molecules
• Draw the Lewis dot diagram so every element is
SHARING 8 valence electrons.
• EXCEPTION #1: H only needs 2 valence electrons
• EXCEPTION #2: Be, B, and other Group 3 elements not
need 8 valence electrons
• EXCEPTION #3: Some elements when bonded with
certain other elements will have more than 8 valence
electrons. Called “expanded octet.”
• Covalent molecules can create:
•
•
•
•
Single bonds: sharing 2 electrons
Double bonds: sharing 4 valence electrons (2 pairs)
Triple bonds: sharing 6 valence electrons (3 pairs)
Cannot share more than 6 valence electrons!!!
Examples:
Steps for Lewis Dot Structures
1. Determine the total number of valence
electrons for all of the atoms in the formula
2. Use the electrons to satisfy all elements with 8
electrons (except for H, Be, B, and other Group 3
elements).
3. Share 2 electrons at a time (single bond)
4. When you run out of electrons, consider if you
need to share more!
* 4 electrons = double bond
* 6 electrons = triple bond
5. If all elements are satisfied and there are
leftover electrons, they are placed on cental
atom (expanded octet).
EXIT TICKET
•Socrative Quiz is Now
Activated.
•8 questions based on today’s
lecture
•Good Luck!!!
How To Determine Shapes of
Molecules:
• The shape of a molecule can determine
its physical and chemical properties.
• The shapes determine whether they can
get close enough to react.
VSEPR Theory
V alence
S hell
E lectron
P air
R epulsion
• repulsion between pairs of
electrons around an atom cause
them to be as far apart as
possible
• used to predict the geometry of
molecules
• Must first draw the CORRECT
Lewis Dot Structure
Molecular Shapes
• diatomic molecules will always be linear
• all other molecules can have different
shapes based on the number of charged
electron clouds around the central atom
• charge electron clouds include:
• bonding pairs
• lone pairs
Hybridization
• Hybrid: Two things combined and the result
characteristics of both.
• Hybrid cars?
• During bonding, atomic orbitals undergo
hybridization
• For example, when carbon bonds with four other
atoms, the four valence electrons in the 2s22p2
orbitals hybridize to form four identical sp3 hybrid
orbitals.
2 Electron Clouds Around Central Atom
• no lone pairs: linear
• CO2
O = C =O
3 Electron Clouds Around the Central Atom
• no lone pairs: trigonal
planar
• CH2O
• 1 lone pair: bent or
angular
• SO2
O=S - O
4 Electron Clouds
• no lone pairs: CH4
tetrahedral
• 1 lone pair: NH3
pyramidal
• 2 lone pairs: H2O bent or
angular
5 Electron Clouds
• no lone pairs: trigonal
bipyramidal
• PCl5
• 1 lone pair:
seesaw
• SF4
5 Electron Clouds
• 2 lone pairs:
• ClF3
T-shaped
• 3 lone pair: Linear
• I 3-
6 Electron Clouds
• no lone pairs: octahedral
• SF6
• 2 lone pairs:
square planar
• XeF4
Cl
• 1 lone pair:
square pyramidal
• SbCl52-
Cl
Cl
Sb
Cl
Cl
Three Types of Bonds
• Ionic – Electrons are __________ and
_____________
• Nonpolar Covalent – Electrons are
__________ ___________.
• Polar Covalent – Electrons are
_________ ____________.
Polar vs. Nonpolar
• Polar
• Nonpolar
• Definition: unequal • Definition: equal
sharing of electrons sharing of electrons
• In a polar
• Nonpolar
molecule there
molecule has 0
will be at least
free pairs from
one free pair for
the central atom
the central atom
Nonpolar/Polar/Ionic Bonds
Difference in Electronegativity
Type of Bond
0 – 0.6
0.6 – 1.8
1.8 +
Non-Polar
Polar
Ionic
Polar or Nonpolar Molecule?
• Step 1 – Draw the Lewis dot for your molecule
• Step 2 – Determine the hybridization, electronic
and molecular geometry of the molecule
• Step 3 – Determine if there are unshared pairs of
electrons.
• Step 4 -Determine if there is an overall positive and
negative end to the molecule
* If so, the molecule is Polar
* If not, the molecule is Nonpolar
Note: It is possible to have polar bonds, but
nonpolar molecule
Intra Versus Inter
•Intra??.........Within
•Inter??..........Between or Among
Intramolecular Forces
• These are the forces we have learned so far.
• These are the chemical bonds
• There are 3 types….what are they again?
___________________
___________________
___________________
• These are stronger than intermolecular
forces
Intermolecular Forces
•Attraction between
________________.
•There are Four types of
intermolecular forces (IMF).
IMF #1: Ionic Attraction
•Involves Ionic Bonds which have
a __________ and an
___________
•The _________ end of one
molecule is attracted to the
___________ end of its neighbor.
IMF #2: Dipole-Dipole Attraction
• Attraction between _____________
molecules based upon a difference
in ______________.
• The molecule must be __________
and be _________ (i.e. have a
________ pair of electrons)
IMF #3: Hydrogen Bonding
• A special kind of dipole-dipole
attraction involving _______
• Hydrogen MUST be bonded directly
to:
_________________
_________________
_________________
IMF #4: London Dispersion Force
•A weak force that holds together
molecules that are
_______________.
•Typically happens at
___________ temperatures.
EXAMPLES:
• H20
• N2
• SCl2
• H2S
• CaCl2