http://www.ck12.org Chapter 3. Chemical Interactions
FIGURE 3.45
Q:How many more electrons does carbon need to have a full outer energy level?
A:Carbon needs four more valence electrons, or a total of eight valence electrons, to fill its outer energy level. A
full outer energy level is the most stable arrangement of electrons.
Q:How can carbon achieve a full outer energy level?
A:Carbon can form four covalent bonds. Covalent bonds are chemical bonds that form between nonmetals. In a
covalent bond, two atoms share a pair of electrons. By forming four covalent bonds, carbon shares four pairs of
electrons, thus filling its outer energy level and achieving stability.
How Carbon Forms Bonds
A carbon atom can form covalent bonds with other carbon atoms or with the atoms of other elements. Carbon often
forms bonds with hydrogen. Compounds that contain only carbon and hydrogen are called hydrocarbons. Methane
(CH 4 ), which is modeled in theFigure3.46, is an example of a hydrocarbon. In methane, a single carbon atom
forms covalent bonds with four hydrogen atoms. The diagram on the left in theFigure3.46 shows all the shared
valence electrons. The diagram on the right in theFigure3.46, called a structural formula, represents each pair of
shared electrons with a dash (–).
FIGURE 3.46
Methane (CH 4 )Carbon-Carbon Bonds
Carbon can form single, double, or even triple bonds with other carbon atoms. In a single bond, two carbon atoms
share one pair of electrons. In a double bond, they share two pairs of electrons, and in a triple bond they share three