Transcript 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.