General Chemistry Principles, Patterns, and Applications, 2011

Hydrogen (H2) has a single bond between atoms. Oxygen (O2) has a double bond between atoms, indicated by two
lines (=). Nitrogen (N2) has a triple bond between atoms, indicated by three lines (≡). Each bond represents an
electron pair.
Table 2.1 The Number of Bonds That Selected Atoms Commonly Form to Other Atoms
Atom Number of Bonds
H (group 1) 1
O (group 16) 2
N (group 15) 3
C (group 14) 4
The structural formula for water can be drawn as follows:
Because the latter approximates the experimentally determined shape of the water molecule, it is more
informative. Similarly, ammonia (NH3) and methane (CH4) are often written as planar molecules:
As shown in Figure 2.3 "The Three-Dimensional Structures of Water, Ammonia, and Methane", however, the actual
three-dimensional structure of NH3 looks like a pyramid with a triangular base of three hydrogen atoms. The
structure of CH4, with four hydrogen atoms arranged around a central carbon atom as shown in Figure 2.3 "The
Three-Dimensional Structures of Water, Ammonia, and Methane", is tetrahedral. That is, the hydrogen atoms are
positioned at every other vertex of a cube. Many compounds—carbon compounds, in particular—have four bonded
atoms arranged around a central atom to form a tetrahedron.
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