Lesson 1: Meet carbon

Four hands to hold

Section 2 of 4

Atoms join together by sharing electrons. Each shared pair of electrons is a bond, and it holds the two atoms together.

Carbon has 4 electrons in its outer shell. Atoms like carbon are most stable with 8 outer electrons, so carbon shares 4 more: one from each of 4 partners. That means carbon usually makes 4 bonds. You can think of a carbon atom as having four hands to hold.

Carbon's 4 outer electrons, and methane On the left, the letter C with 4 dots around it, one on each side, for its 4 outer electrons. An arrow points right to methane: a C in the middle joined by 4 lines to 4 H atoms, above, below, left and right. Each line is one bond. C carbon: 4 outer electrons C H H H H methane: 4 bonds
In the drawing, carbon's 4 outer electrons are dots (left), and methane, CHâ‚„, shares one electron pair with each of 4 hydrogen atoms (right). The drawing is flat; methane's real shape is 3D, which lesson 3 explains.

Methane is the simplest carbon compound: one carbon atom holding four hydrogen atoms. Hydrogen has only one electron, so each hydrogen can make just one bond. It is the main gas in the natural gas that heats many homes.

Carbon does not have to hold four different atoms, and it does not have to use one hand per partner. It can also bond to other carbon atoms, or use two or three hands on the same partner. That is what lesson 2 is about.

Quick check

How many bonds does a carbon atom usually make?