Chapter 2: Chemistry of Life Section 1: Composition of Matter Section 2: Energy Section 3: Water and Solutions

Section 1: The Composition of Matter Matter is anything that occupies space and has mass. Mass is the quantity of matter that an object has. Weight and mass are not the same. Weight is the force produced by gravity acting on mass. Chemical changes in matter are essential to all life processes. Biologists study chemistry because all living things are made up of the same kinds of matter that makes up nonliving things.

Elements and Atoms Elements are substances that cannot be broken down chemically into simpler kinds of matter. Fewer than 30 of the more than 100 known elements are important to living things. 90% of the mass of all kinds of living things is composed of combinations of just four elements: oxygen, carbon, hydrogen, and nitrogen. Information about the elements is organized on the Periodic Table. Every element has a symbol derived from the first letter or letters. Most symbols come from the Latin names. The simplest particle of an element that retains properties of the element is an atom.

Structure of the Atom Atoms are so small that they cannot be observed, so scientists have constructed models that represent what we think they are like. Nucleus – the central region. Makes up the bulk of the atom. Has two subatomic particles called protons and neutrons. The proton is positively charged and the neutron has no charge. The atomic number is the number of protons found in the atom. The atomic mass is equal to the total number of protons and neutrons found in the nucleus of the atom.

Electrons – the negatively charges particles that orbit around the nucleus at very high speeds. All atoms have equal amounts of proton and electrons. The net electrical charge on an atom is zero. Electrons are high-energy particles that have very little mass. Isotopes – atoms of the same element that have different numbers of neutrons and therefore have different masses.

Compounds Compounds are made up atoms of two or more elements. Most atoms are not stable in their natural state so they tend to react with other atoms to form chemical bonds. Chemical bonds – are the attractive forces that hold atoms together. Covalent Bond – formed when two atoms share one or more pairs of electrons. A molecule is the simplest part of a substance that retains all the properties of the substance and can exist in a free state.

Ionic Bonds – a bond resulting from an attraction of electrical charges causing one atom to gain an electron and one to lose an electron. How can we predict which elements are reactive under normal conditions and which are unreative?

Energy Energy and Matter – Energy is the ability to do work Energy comes in various forms and change from one form to another. States of matter: all molecules are in constant motion. Solids move less rapidly than liquids and gases. Energy and Chemical Reactions Metabolism is the term used to describe all the chemical reactions in an organism. In a chemical reaction, one or more substances change to produce one or more different substances. Energy is absorbed or released when chemical bonds are broken and new ones formed.

In every chemical reaction there are reactants and products. For most chemical reactions to begin, energy must be added to the reactants. The amount of energy needed to start a reaction is called the activation energy. Catalysts are chemical substances that reduce the amount of activation energy needed for a reaction to occur. In living things, enzymes act as catalysts. Enzymes are a protein molecule that speed up metabolic reactions with being changed or destroyed.