Covalent Bonding The joining of two or more elements through the sharing of valance electrons to...
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Transcript of Covalent Bonding The joining of two or more elements through the sharing of valance electrons to...
Covalent Bonding
The joining of two or more elements through the sharing of valance electrons to form a molecule
Purpose: To form a stable octet between the elements
Types of Covalent Bonds
• Non-Polar: equal sharing of the valance electrons.
• Polar: unequal sharing of the valance electrons.
Non-Polar
• Shape of molecule is symmetrical.
• Homonuclear molecules.•Diatomic molecules:
•N2, O2, F2, Cl2, Br2, I2, and H2
•Makes the #7
Polar
• Shape of the molecules is asymmetrical due to unequal sharing of the electrons.
• Heteronuclear: one nuclear charge is stronger than another.
• Polarity is the function of the change in electronegativity (EN)• Increase EN, = more ionic chstc.
Polar Molecules
Rank these in decreasing covalent characteristics:
H2O, N2, NO3- , NaBr2, CO2
Solution:
1. Identify the electronegativity for each element in the molecule.
2. Less covalent > 1.7 > more covalent.
N2 > NO3- > CO2 > H2O > NaBr2
Lewis Dot Structure
• Pictorial representation of valance electrons.
• Dot structure• Stick structure
Octet Rule
• Representative elements share electrons to take on a Noble gas electron configuration.
• Each element in a molecule will follow the octet rule.
Shared Electrons
• Formula to determine the number of shared electrons:
• N – A = S• N = # of electrons needed to form
a Noble gas configuration.• A = # of electrons available in the
valance.• S = # of electrons shared
Bonding• Sigma Bonds are the single
electron overlap of the s orbital.• Forms single bonds, end-to-end.• Pi Bonds are the overlap of the s
and p orbitals.• Forms double and triple bonds w/ s
end-to-end and p side-to-side.
Practice Problems
• CO2
• N2
• CS2
• HNO3
• NO31-
• Which are polar?• Which are non-polar?• Which are non-polar with polar bonds?
Resonance
• Equally acceptable formulas.
• HNO3
• NO31-
Limits to the Octet Rule
• Most beryllium compounds• Most Group IIIA elements• Compound which require more
than 8e- in the valance.• Compounds containing d or f
transitional elements• ‘S’ with an odd number of
electrons
Practice Problems
• CCl4• CO2
• N2O5
• N2O
• S3O5
• NF3
Naming Molecules
• Follows the rules as ionic compounds except prefixes are used to note ‘how many’.
• Table 8-3, page 248.
Molecular Structure
• VB Theory : Valance Bond Theory, orbital overlaps
• VSEPR Theory: Valance Shell Electron Pair Repulsion Theory• Electrons arrange to max the distance
between electrons• Bonding pairs v. Unshared pairs
Molecular Geometry
• Linear (2) • Trigonal Planar• Tetrahedral• Trigonal Pyramidal• Angular (Bent)• Trigonal Bipyramidal• Octehedral
Linear
• Formula AB2 w/ no unshared pairs
• VSEPR: bonding angle of 180o
• VB: sp overlap• Forms a polar bond and a non-
polar molecule.
Trigonal Planar
• Formula of AB3 and no unshared pairs.
• VSEPR: bonding angle of 120o
• VB: SP2 overlap• Polar bond w/ non-polar molecule
Tetrahedral
• Formula of AB4 w/ no unshared pairs.
• VSEPR: bonding angle of 109.5o
• VB: sp3 overlap• Forms polar bonds and non-polar
molecule.
Trigonal Pyramidal
• Formula AB3 w/ one unshared pair on A.
• General: subtract 2.5o for each unshared pair.
• VSEPR: bonding angle of 107o
• VB: sp3 overlap w/ a polar bond and a polar molecule
Angular (Bent)
• Formula AB2 w/ 2 unshared pairs on A
• VSEPR: bonding angle of 104.5o
• VB: sp3 overlap w/ polar bonds and polar molecule.
Linear
• Formula AB w/ 3 unshared pairs• VSEPR: bonding angle of 102o• VB: sp3 overlap w/ polar bonds and
polar molecule.
Trigonal Bipyramidal
• Formula AB5 w/ no unshared pairs
• VSEPR: bonding angles at 90o, 120o and 180o
• VB: sp3d overlap w/ polar bonds and polar molecule.
Octahedral
• Formula AB6 w/ no unshared pairs
• VSEPR: bonding angles of 90o, 120o and 180o
• VB: sp3d2 overlap w/ polar bonds and molecule
Molecules
Molecule VB VSEPR Shape NI3PH3
CH4
SF6
H2S
PF5
BeCl2