Double and triple bonds

Lesson 1 said carbon can use two or three hands on the same partner. Here is what that looks like.

Two atoms can share two pairs of electrons. That is a double bond, drawn as two lines. They can even share three pairs: a triple bond, drawn as three lines.

Carbon still has 4 lines in total. In ethene, C₂H₄, the double bond uses 2 of each carbon's 4 lines, so each carbon has room for only 2 hydrogen atoms. In ethyne, C₂H₂, the triple bond uses 3, which leaves room for just 1.

Double bonds can join carbon to other atoms too. In carbon dioxide, CO₂, the carbon shares two pairs with each oxygen atom: two double bonds, so carbon still has 4 lines. You will meet the C=O double bond again in lesson 5.

Ethane, ethene and ethyne sound alike because chemists build names from parts. You will learn how the names work in lesson 4.