Download Chapter 3

The Chemistry of Life
Chemical Basis of Life
Matter
Lesson Objectives
• Describe elements and compounds, and
explain how mixtures differ from
compounds.
• Define energy, and describe how energy
can be changed from one form to another.
• Identify three states of matter, and explain
how they differ.
Introduction
• Living things are made of matter.
• What is matter???
– Anything that occupies space and has mass
– Consists of chemical substances
CHEMICAL SUBSTANCES
• Material that has a definite chemical
composition
• Homogeneous, so the same chemical
composition is found uniformly throughout
the substance
– Elements
– Chemical Compounds
Elements
• Pure substance that cannot be broken down
into different types of substances
• Each element is made up of one type of atom
• There are almost 120 known elements
Chemical Compounds
• New substance that forms when atoms of two or more
elements react with one another in a chemical reaction
and bond
– atoms of a compound are held together by chemical bonds
(covalent or ionic)
• Covalent bonds: characterized by the sharing of pairs of electrons
between atoms
• Ionic bonds: bond in which one or more electrons from one atom are
removed and attached to another atom, resulting in positive and
negative ions
• The substances in a chemical compound can be
separated from one another by another chemical
reaction
Mixtures vs. Compounds
• Consists of more than one chemical substance;
unlike a compound, a mixture does not have a
fixed chemical composition
• Mixture are not formed through a chemical
reaction; substances in a mixture are not
changed into unique new substances
• Can be separated from each other without a
chemical reaction.
MATTER AND ENERGY
• Energy is a property of matter that is defined as
the ability to do work
• All living organisms need energy to grow,
develop, and reproduce
• Law of Conservation of Energy:
– Energy can never be created
or destroyed, it is always conserved
(changed from one form to another)
How Organisms Change Energy
• For example, plants obtain light energy from
sunlight and change it to chemical energy in
food molecules (photosynthesis)
• Chemical energy is energy stored in bonds
between atoms within food molecules
• Organisms eat and digest the food, they break
the chemical bonds and release the chemical
energy.
– About 90 percent of the energy they obtain from food
is converted to heat energy that is given off to the
environment.
Kinetic and Potential Energy
• Energy also constantly changes back and forth
between kinetic and potential energy
• Kinetic energy is the energy of movement
• Potential energy is the energy stored in an
object due to its position
States of Matter
• The amount of energy in molecules of
matter determines the state of matter.
– gas, liquid, or solid
What Determines a
Substance’s State?
• Temperature and air pressure
Changing States
• Matter constantly goes through cycles that
involve changing states; those important to
organisms are recycled on Earth
Lesson Summary
• Matter consists of elements and compounds. A
compound forms when elements combine in fixed
proportions and undergo a chemical reaction. A mixture
forms when substances combine in any proportions
without a chemical reaction.
• Energy is a property of matter. It cannot be created or
destroyed. Organisms obtain light energy from sunlight
or chemical energy from food and change the energy
into different forms, including heat energy.
• Matter can exist in one of several different states,
including a gas, liquid, or solid state. States of matter
differ in the amount of energy their molecules have.
When matter recycles, it changes state by gaining or
losing energy.