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.