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Chemistry LibreTexts

1.0: General Chemistry review: atoms, electron configuration, and Lewis structures

Before you begin your study of organic chemistry, you may need to do some review of  General Chemistry because it will be assumed that you already understand some basic chemistry concepts.  A great way to review is to watch the following series of tutorials from Kahn Academy:


Here are some practice exercises to try before moving on: 

Exercise 1.1

How many protons and neutrons do the following isotopes have?

a)  31P, the most common isotope of phosphorus

b)  32P, a radioactive isotope of phosphorus used often in the study of DNA and RNA.

c)  37Cl, one of the two common isotopes of chlorine.

d) tritium (3H), a radioactive isotope of hydrogen, used often by biochemists as a 'tracer' atom.

e) 14C, a radioactive isotope of carbon, also used as a tracer in biochemistry.


Exercise 1.2

The electron configuration of a carbon atom is 1s22s22p2, and that of a sodium cation (Na+) is 1s22s22p6.  Show the electron configuration for:

a) a nitrogen atom                                       

b) an oxygen atom  

c) a fluorine atom                                   

d) a magnesium atom 

e) a magnesium cation (Mg2+)                 

f) a potassium atom   

g) a potassium ion (K+)                           

h) a chloride anion (Cl-)

i) a sulfur atom                                          

j) a lithium cation (Li+)

k) a calcium cation (Ca2+)


Exercise 1.3

Draw Lewis structures for the following species (use lines to denote bonds, dots for lone-pair electrons).  All atoms should have a complete valence shell of electrons.

a) ammonia, NH3

b) ammonium ion, NH4+

c) amide ion, NH2-

d) formaldehyde, HCOH

e) acetate ion, CH3COO-

f) methyl amine, CH3NH2

g) ethanol, CH3CH2OH

h) diethylether, CH3CH2OCH2CH3

i) cyclohexanol (molecular formula C6H12O, with six carbons bonded in a ring and an OH group)

j) propene, CH2CHCH3

k) pyruvate, CH3COCO2H

Exercise solutions