covalent bonding. covalent bond: –a bond formed by the sharing of electrons between atoms. (does...
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Covalent Bonding
Covalent Bonding• Covalent Bond:
– a bond formed by the sharing of electrons between atoms. (does NOT form charges)
– Made up of nonmetals• Molecule: a neutral group of atoms
joined together by covalent bonds. (Compounds formed with ionic bonds do NOT have molecules)
• Molecular Formula: chemical formula for a molecular compound. It shows how many atoms of each element a molecule contains.
Covalent Bonding• Examples:
ascorbic acid (vitamin C): C6H8O6
C_____, H_____, O_____,
trinitrotoluene (TNT): C7H5N3O6
C_____, H_____, N_____, O_____,
6 8 6
7 5 3 6
Molecular Nomenclature
• Prefix System (binary compounds)
1. Less electronegative atom comes first.
2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element.
3. Change the ending of the second element to -ide.
most
PREFIXmono-di-tri-tetra-penta-hexa-hepta-octa-nona-deca-
NUMBER123456789
10
Molecular Nomenclature
Only use
“mono” on the
second
element.
P2O5 =CO2 =
CO =
N2O =
diphosphorus pentoxide
carbon dioxide
carbon monoxide
dinitrogen monoxide
Naming Covalent Binary Compounds
PCl5N2H4
Cl2O7
IO2
phosphorous pentachloride = dinitrogen tetrahydride
=dichlorine heptaoxide =iodine dioxide =
Lewis Structures
• Electron Dot Diagrams–show valence e- as dots–distribute dots like arrows in an orbital diagram
–4 sides = 1 s-orbital, 3 p-orbitals–EX: oxygen
2s 2pO
X
Lewis Structures
• Octet Rule–Most atoms form bonds in order to obtain 8 valence e-
–Full energy level stability ~ Noble Gases
Ne
Diatomic Molecules• Diatomic Molecule: a molecule
consisting of two atoms.• Diatomic molecules in nature:
H2, N2, O2, F2, Cl2, Br2, I2
“HON and the Halogens”
• Structural Formula: represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms
• Unshared pair or lone pair: a pair of valence electrons that is not shared between atoms.
• Single Covalent Bond: formed by one shared pair of electrons.
• Double Covalent Bond: formed by two pairs of shared electrons.
• Triple Covalent Bond: formed by three pairs of shared electrons.
The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.
The hydrogen and oxygen atoms attain noble-gas configurations by sharing electrons.
The ammonia molecule has one unshared pair of electrons.
Methane has no unshared pairs of electrons.
Each oxygen atom has two unshared pair of electrons.
This is a double covalent bond.
Oxygen Molecule
Some covalently bonded substances DO NOT form discrete molecules, they form… Network Solids: solids in which all of the
atoms are covalently bonded.
Diamond, a network of covalently bonded carbon atoms
Graphite, a network of covalently bonded carbon atoms
Lewis Structures
Lewis structures are representations of molecules showing all electrons, bonding and nonbonding (lone pairs).
RULES FOR DRAWING LEWIS STRUCTURES (STRUCTURAL FORMULAS OR ELECTRON DOT STRUCTURES)
1. Total the number of valence electrons available in the molecule/polyatomic ion (adjust for charge). 2. Write the symbols for the given formula with some space between them. Put the one with the lowest electronegativity in the center and the others on each of the four sides.
Exception: Hydrogen can NEVER be in the center. If there is a Carbon atom, it is the center atom.
3. Draw one dash between the symbols to represent a bond and fill other octets with lone pairs. 4. Check for full octets, & count the total number of electrons used. The total number of electrons drawn in the structure must equal the number of electrons you counted in step 1.
If too many e-‘s in structure, erase lone pairs and make double and/or triple bonds. If too few e-‘s in structure, expand octet of central atom. Odd number of valence e-‘s in molecule = octet deficient (ie: BF3 & BF2).
5. If the molecule is a polyatomic ion and has an overall charge, put brackets around the structural formula and write the charge outside the brackets in the upper right corner.
Writing Lewis Structures**These are on your reference sheet**
Writing Lewis Structures
1. Total the number of valence electrons available in the molecule/polyatomic ion (adjust for charge)– If it is an anion, add one
electron for each negative charge.
– If it is a cation, subtract one electron for each positive charge.
PCl3
5 + 3(7) = 26
Writing Lewis Structures2. Write the symbols for the given
formula with some space between them. Put the one with the lowest electronegativity in the center and the others on each of the four sides.
• Exception: Hydrogen can NEVER be in the center.
• If there is a Carbon atom, it is the center atom.
3. Draw one dash between the symbols to represent a bond…
Writing Lewis Structures
3. … Fill the octets of all the outer atoms with lone pairs.
Writing Lewis Structures
4. Check for full octets & total number of electrons used.
…If too many e-s used, erase lone pairs and make multiple bonds.
…If too few e-s used, expand central atom octet.
…odd number of valence e-s = octet deficient
Writing Lewis Structures
Writing Lewis Structures
6. If the molecule is a polyatomic ion, put brackets around the structure and write the charge in the upper right corner.
Examples
• Cl2
• O2
• N2
#s of Covalent Bonds
Cl Cl
O O
N N
Single Bond: 2 e- shared
Double Bond: 4 e- shared
Triple Bond: 6 e- shared
Examples
• NH3
• CCl4
• H2S
• SO3
Examples
• ClO4-
Polyatomic Ions and covalent bonding “CHLORATE”
O
Cl O
O
Chlorine has 7 valence e-
Each oxygen has 6 valence e-
When ClO3 comes together they form 3 single covalent bonds
One additional electron completes chlorine with a full valence shell, making this a covalently bonded group with an ionic charge of -1
-1
Examples
• CO32-
O
C O
O
Polyatomic Ions and covalent bonding “CARBONATE”
Carbon has 4 valence e-
-2 Each oxygen has 6 valence e-
When CO3 comes together they form 2 single covalent bonds and 1 double covalent bond
Two additional electrons completes carbon with a full valence shell, making this a covalently bonded group with an ionic charge of -2
Examples
• PO43-
O
O P O
O
Polyatomic Ions and covalent bonding “PHOSPHATE”
Phosphorus has 5 valence e-
-3Each oxygen has 6 valence e-
When PO4 comes together they form 3 single covalent bonds
Three additional electrons completes phosphorus with a full valence shell, making this a covalently bonded group with an ionic charge of -3
VSEPR Theory
Most graphics from: http://wps.prenhall.com/wps/media/objects/602/616516/index.html
VSEPR Theory• VSEPR Theory (Valence-shell
electron-pair repulsion theory): the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.
http://wps.prenhall.com/wps/media/objects/602/616516/index.html
2 Charge Clouds
AX2 CO2
3 Charge Clouds
AX2E SO2
AX3 CH2O
Bent or
4 Charge Clouds
AX3E NH3
AX4 CH4
AX2E2 H2OBent or
Quiz
1. What is the geometry around the central atom in each of the following molecular models?
2. How many lone pairs (not shown) are around each central atom?
Above is a ball-and-stick molecular model representation of acetaminophen, the active ingredient in such over-the-counter headache remedies as Tylenol (red = O, gray = C, blue = N, ivory = H):
1. What is the molecular formula of acetaminophen?2. What is the geometry (angles) around each carbon and nitrogen?
(The lines between atoms indicate connections only, not whether the bonds are single, double, or triple.)
3. Indicate the positions of multiple bonds (double & triple) in acetaminophen.
104.5
120
107
120109.5120
120
120
120LP
LP
LP
LPLP
C8H9NO2
Polarity
Bond Polarity
• Most bonds are a blend of ionic and covalent characteristics.
• Difference in electronegativity determines bond type.
E difference: 0.0-0.4
E difference: 0.4-1.7
E difference: >1.7
Bond Polarity
• Electronegativity–Attraction an atom has for a shared pair of
electrons.–higher e-neg atom δ-
–lower e-neg atom δ+
Bond Polarity
• Electronegativity Trend – Increases up and to the right.
Table of Electronegativity
• Nonpolar Covalent Bond–e- are shared equally–symmetrical e- density–usually identical atoms
Bond Polarity
δ+ δ-
Bond Polarity• Polar Covalent Bond
–e- are shared unequally–asymmetrical e- density– results in partial charges (dipole)
• Ionic Bond–e- are transferred
Bond Polarity
• Nonpolar– e- shared equally
• Polar– e- shared unequally
• Ionic– e- transferred
Bond Polarity
E difference: >1.7
E difference: 0.4-1.7
E difference: 0.0-0.4
Bond Polarity
Examples:
• Cl2
• HCl
• NaCl
3.0-3.0=0.0Nonpolar
3.0-2.1=0.9Polar
3.0-0.9=2.1Ionic
+ -
+
Bond Polarity
• Nonpolar Covalent – equally shared e-
• Polar Covalent - partial charges, e- shared unequally
Polar Molecule• One end of the molecule is slightly negative and
the other end is slightly positive• Caused by the presence of a polar bond in the
molecule. (the structure is not symmetrical)• A molecule that has two poles is called a dipolar
molecule, or dipole.
How to Determine Molecular Polarity
Are There Polar Bonds?
Are the polar bondssymmetrical around
the molecule?
Non-PolarMolecule
NO
Check theMolecule Shape
YES
PolarMolecule
NO
Non-PolarMolecule
YES
The water dipole
The ammonia dipole
Self Test
• Is CO2 a covalent or ionic compound?• What is CO2 ’s name?• What is the electronegativity
difference between C and O?• Does CO2 have polar bonds?• Is CO2 a polar molecule overall?
. .O. .
C: :O
CHEMICAL FORMULA/Smallest unitIONIC COVALENT
MolecularFormula
CO2
FormulaUnit
NaCl
COMPOUND
2 elementsmore than 2
elements
TernaryCompound
NaNO3
BinaryCompound
NaCl
ION (charged particle)
1 atom 2 or more atoms
PolyatomicIon
NO3-
MonatomicIon
Na+
Bonding Summary
Ionic Covalent
Octet achieved by:
Transfer of electrons (forming + & - ions)
Sharing electrons
Made of:Metal cation (+) & Nonmetal
anion (-)Nonmetals (above metalloid
line) (no charges)
Characteristics: Brittle Small and very large molecules
Structure:Arranged in alternating
+ & - ions (crystal lattice)Individual molecules
Representative Particle:
Formula Unit: (lowest whole number ratio of
atoms)
Molecule: (group of joined atoms)
Bonding Summary
Ionic Covalent
Physical State: Solid Solid, Liquid, Gas
Melting Point: High Low
Electrical Conductivity:
Yes, when dissolved in water or melted
No
Bonding SummaryMetallic
Octet achieved by:
Valence e- delocalized around metal atoms
Made of:Metal cation (+) & Valence electrons
Characteristics:Maleable, ductile,
lustrous
Structure: “Electron Sea”
Representative Particle: Atom
Metallic
Physical State: Solid (except Hg)
Melting Point: High
Electrical Conductivity: Yes (any form)
Ionic Bonding - Crystal Lattice
Types of Bonds
Covalent Bonding - True Molecules
Types of Bonds
Diatomic Molecule
Metallic Bonding - “Electron Sea”
Types of Bonds
Quiz - answer the following on a sheet of paper1. The following ball-and-stick molecular model is a representation of
thalidomide, a drug that causes birth defects when taken by expectant mothers but is valuable for its use against leprosy. The lines indicate only the connections between atoms, not whether the bonds are single, double, or triple (red = O, gray = C, blue = N, ivory = H):
(a) What is the molecular formula of thalidomide?(b) Indicate the positions of the multiple bonds in thalidomide.(c) What is the geometry around each carbon and each nitrogen?