The Chemical Context of Life
Chapter 2
Chemical Elements
• Matter - any substance that has mass
and takes up space.
• Element - cannot be broken down to
other substances by chemical reactions.
• 92 naturally occurring
• life requires about 25 elements
– Most common elements (CHNOPS) = 98%
• Compound - substance consisting of 2
or more elements combined in a ratio.
Atoms and Molecules
• The simplest unit of matter that retains
its chemical properties is the atom.
• Atoms are composed of subatomic
– Protons
– Neutrons
– Electrons
• Atoms that are chemically combined are
called compounds or molecules.
Chemical Bonds
• Bond - formed by electrical interactions
atoms; behavior of electrons
• Two types of strong interactions
– ionic
– covalent
• Weak interaction
– hydrogen bonds
Exit Questions
• 1. Draw and label an atom. Include the
following labels: nucleus, energy levels,
neutrons, protons, and electrons.
• 2. What is the difference between an
ionic bond and a covalent bond?