COVALENT BONDS!

-Covalent Bonds- one or more bonds made between elements when the bond is made by the sharing of electrons

-Single Bond- sharing of 2 electrons between 2 elements

-Double Bond- sharing of 4 electrons between 2 elements

-Triple Bond- Sharing of 6 electrons between 2 elements

Drawing Lewis Dot Structures
1. Draw the Lewis Dot structure for each element
2. Place the element having the most unpaired electrons in the center
3. Bond as many single electrons to the center element as possible- keep the balance as you draw
4. Create double/triple bonds as necessary to reach the octet for all elements

Ex. Hydrogen has 1 valence electron and carbon has 4 so carbon goes in the middle*

external image Methanes.GIF

Drawing Ions (with a Charge)
-Caronate (CO3)-²
-The -2 means that you will have to add 2 extra electrons to have all elements reach the octet rule
1. Start by connecting oxygens to center with carbon
2. Add 2 electrons to help oxygen reach stable octet


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**Exceptions to the octet rule
-Elements with 3 valence electrons
For boron (B)-> Most are happy with 6 when bonding
For Nitrogen (N)-> Can be happy with 10 electrons
For Chlorine (Cl)-Good with 14 electrons

The Different Shapes of Molecules

Molecular Geometry
This describes the 3-D arrangement of atoms in a molecule. Int his case we use VSEPR
this is short for Valence- Shell- Electron- Pair- Repulsion
  • it is a set of procedures for predicting the 3-D shape of a molecule from the molecule's electron dot structure
  • the idea is that electron pairs in the electron dot structure want to be as far apart from each other as possible
  • bond length- distance between nuclei
  • bond angle- angle between adjacent bonds
VSEPR Theory
  • electron pairs repel each other whether they're in chemical bonds(bond pairs) or unshared (lone pairs). Electron pairs assume orientations about an atom to minimize repulsions
  • electron group geometry- distribution of the electron pairs
  • molecular geometry- distribution of the nuclei
Let's look at the different shapes of compounds in their 3-D form. Essentially, there are six possible shapes.
1) CO2
O=C=O
the angle between the elements is 180 degrees/ there are no lone pairs/ there are 4 bond pairs/ the EN is 1 which is polar
2) CH2O
O
ll
C
l l
H H
the angle between is 120 degrees/ there are no lone pairs/ 4 bond pairs/ the EN between C & O is 1 which is polar, the EN between C&H is .4 which is also polar
3) SO2
. .
S
ll l
O O
in this case, the electron pair is pushing the 2 bond pairs down/ the angle is still 120 degrees/ there is one lone pair/ three bond pairs/ the EN between S&O is 1 which his polar/ the name is angular/bent

1) Which of the following is a covalent compound?
A. Na2O
B. CaCl2
C. Cl2O
D. CsCl
E. Al2O3
answer: D
2) Which of the following contains covalent bonds?
A. BaO
B. IBr
C. Mg
D. LiBr
E. Cu
Answer: B
3) In which of these substances are the atoms held together by polar covalent bonding?
A. SrCl2
B. CsCl
C. ClF
D. TiF2
E. S8
Answer: C
4) Electronegativity is a measure of
A. the energy needed to remove an electron from an atom.
B. the energy released when an electron is added to an atom.
C. the magnitude of the negative charge on an electron.
D. the attraction by an atom for electrons in a chemical bond.
E. the magnitude of the negative charge on a molecule.
answer: D
5) Which of the following elements is the most electronegative?
A. S
B. Ru
C. Si
D. Te
E. Cs
answer: Ru
6) Which of the following elements is the least electronegative?
A. Si
B. Se
C. S
D. Sc
E. Sr
answer: Sr
7) Which of the following elements is the most electronegative?
A. Ne
B. Rb
C. P
D. I
E. Cl
answer: Cl
8) Arrange aluminum, nitrogen, phosphorus and indium in order of increasing electronegativity.
A. Al < In < N < P
B. Al < In < P < N
C. In < Al < P < N
D. In < P < Al < N
E. None of these orders is correct.
answer: C
9) Arrange calcium, rubidium, sulfur, and arsenic in order of decreasing electronegativity.
A. S > As > Rb > Ca
B. S > As > Ca > Rb
C. As > S > Rb > Ca
D. As > S > Ca > Rb
E. None of these orders is correct.
Answer: B
10) Select the most polar bond amongst the following.
A. C-O
B. Si-F
C. Cl-F
D. C-F
E. C-I
Answer: D
11) According to VSEPR theory, a molecule with the general formula AX2 will have a _ molecular shape.
A. linear
B. bent
C. trigonal planar
D. tetrahedral
E. triangular

Answer: A
12) According to VSEPR theory, a molecule with the general formula AX3 will have a molecular shape.
A. linear
B. bent
C. trigonal planar
D. tetrahedral
E. trigonal pyramidal
Answer: C
13) According to VSEPR theory, a molecule with the general formula AX4 will have a __ molecular shape.
A. bent
B. trigonal planar
C. trigonal pyramidal
D. square planar
E. tetrahedral
Answer: E
14) What is the molecular shape of N2O as predicted by the VSEPR theory?
A. trigonal pyramidal
B. trigonal planar
C. angular
D. bent
E. linear
Answer: D
15) What is the molecular shape of the thiocyanate anion, SCN-, as predicted by the VSEPR theory? (Carbon is the central atom.)
A. linear
B. bent
C. angular
D. trigonal
E. none of these choices is correct
Answer:
16) What is the molecular shape of ClCN as predicted by the VSEPR theory? (Carbon is the central atom.)
A. linear
B. bent
C. angular
D. trigonal
E. none of these choices is correct
17) What is the molecular shape of BeH2 as predicted by the VSEPR theory?
A. linear
B. bent
C. angular
D. trigonal
E. none of these choices is correct