Transcript Covalent Lewis Structure PPT

Drill – 12/2
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Why do bonds form?
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What is electronegativity?
Drill – 12/7
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What type of bond will form between:
1.
2.
3.
Calcium & Chlorine
Chlorine and Carbon
Carbon & Calcium
Electronegativities:
Ca = 1.1 C = 2.5 Cl = 3.0
Drill – 12/7
Grab a textbook and use
values on pg. 161
What type of bond will form between:
1.
2.
3.
Calcium & Chlorine
Chlorine and Carbon
Carbon & Calcium
Covalent Bonding and
Molecular Compounds
Objectives
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SWBAT state the octet rule.
SWBAT apply the rules for writing Lewis
structures to molecules and polyatomic
ions, including those containing multiple
bonds.
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A molecular compound is a chemical
compound whose simplest units are
molecules
A molecule is a neutral group of atoms
that are held together by covalent
bonds
(Note: Molecular compound = nonmetal
atom + nonmetal atom)
Diatomic Molecules
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Certain elements always appear in
nature as diatomic molecules – two
atoms bonded together.
H2, N2, O2, F2, Cl2, Br2, I2
Or BrINClHOF
Demonstrating Covalent Bonding:
Electron Dot Notation
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How would we illustrate covalent
bonding by using electron-dot notation?
How many electrons in a bond?
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For example, between hydrogen and
hydrogen?
Sample Lewis Structure
H
••
F
••
••
atomic symbols
represent nuclei
and inner-shell
electrons
C
H
dots adjacent to only one
atomic symbol represent
unshared electrons or lone
pairs
H
dot-pairs or dashes
between two atomic
symbols represent
electron pairs in
covalent bonds
Writing Lewis Structures
What is a Lewis structure?
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A representations in which atomic symbols
represent nuclei and inner-shell electrons,
dot-pairs or dashes between two atomic
symbols represent electron pairs in covalent
bonds, and dots adjacent to only one atomic
symbol represent unshared electrons.
Method for Writing Lewis
Structures
1) Write the symbols for the atoms to show
which atoms are attached to which
2) Sum the valence electrons from all the atoms
- for an anion, add an electron to the total for
each negative charge
- for a cation, subtract an electron for each
positive charge
3) Determine the total number of electrons
needed to give each atom an octet (or duet
in the case of H) of electrons
4) Calculate the number of bonding
electrons (step 3 – step 2)
5) Calculate the number of unshared
electrons (step 2 – step 4)
6) Use all the above information to help
you draw your Lewis structure
Helpful Hints
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Remember: Your Lewis structure may
contain multiple bonds (single, double,
or triple)
When arranging your atoms, atoms are
often arranged with the least
electronegative atom in the center (C is
almost always your central atom; H is
NEVER central)
When in doubt, aim for symmetry
Example – H2O
1. Write the symbols in the correct order:
H
O
H
2. Sum all the valence electrons
1+1+6=8
3. Determine the electrons needed for each atom to
be stable
2 + 8 + 2 =12
4. Calculate bonding electrons (Step 3 – Step 2)
12 - 8 = 4
5. Calculate unshared electrons (Step 2 – Step 4)
8–4=4
6. Draw the Lewis Structure
Lewis Structure of Water (with
lone pairs)
Polyatomic Ions
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A polyatomic ion is a charged group of
covalently bonded atoms
Example: NH4+
When writing Lewis structures for polyatomic
ions, you must place brackets around the ion
and place the charge outside of the brackets
Practice Problem
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Write the Lewis structure for the
following:
PO43SO42-