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Chemical bonds form different shapes based on the arrangement of their atoms. To determine the shape of the molecule, the number of shared and lone pairs of electrons must be determined. To do this, you must count the available bonding electrons each atom has. Then you must determine central atoms and terminal atoms. Central atoms tend to lie closer to the left of the periodic table than terminal atoms. Terminal atoms typically form single covalent bonds. Shared pairs of electrons are represented by a dashed line. One dashed line indicates one shared pair, or one sigma bond. Two dashed lines indicate two shared pairs, or one sigma bond and one pi bond. Unshared pairs of electrons are represented by two dots. Unshared pairs go where they are needed. The objective of every atom in a Lewis structure is to have an octet, or eight electrons. Please refer to the attached image to help answer the questions. Select the best answer from the given choices.
Lewis structure #1 is the shape of water. Water has a bent linear shape due to the unpaired electrons on one end of the molecule. How many shared pairs of electrons does water have?
1
2
3
4
For the water molecule, which atoms are the terminal atoms?
Hydrogen
Oxygen
Nitrogen
Chlorine
How many unshared pairs of electrons does water have?
4
2
3
1
Lewis structure #2 is the shape of carbon dioxide. Carbon dioxide is linear, with a 180 degree bond angle. How many sigma bonds does carbon dioxide contain?
2
0
1
4
How many pi bonds does carbon dioxide contain?
3
9
6
2
What is the total number of shared electron pairs in carbon dioxide?
1
3
4
5
Does the central carbon atom have a full octet?
Might be possible
Definitely yes
Can’t say
No
Lewis structure #3 is the shape of ammonia. This shape is called trigonal pyramidal and it has a bond angle of 107.3 degrees. Identify the central atom in ammonia.
Oxygen
Carbon
Hydrogen
Nitrogen
