All living things are made up of MATTER. MATTER: *has mass *takes up space *made up of Atoms *has three states: solid, liquid & gas *can be made up of two or more elements joined together (compound)

ICE

Atoms: The Building Blocks of Elements An atom is the smallest particle of an element that has the characteristics of that element. Atoms are the basic building blocks of all matter. An atom is made up of protons ( + charge) and neutrons (no charge) located in a central nucleus The nucleus is surrounded by electrons ( - charge)

The Structure of an atom The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e-) Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus. Nucleus This region of space is referred to as an electron cloud. Electron energy levels

Compounds A compound is a substance that is composed of atoms of two or more different elements that are chemically combined Table salt (NaCl) is a compound composed of the elements sodium and chlorine. MOLECULE: are the smallest unit of most compounds.

Electron arrangement determines the chemical properties of an atom Electrons are arranged in shells The outermost shell determines the chemical properties of an atom In most atoms, a full outer shell holds eight electrons Electrons occur in energy levels called electron shells Information about the distribution of electrons is found in the periodic table of the elements Atoms whose shells are not full tend to interact with other atoms and gain, lose, or share electrons

Electron arrangement determines the chemical properties of an atom Atoms want to fill their outer electron shells To accomplish this, the atom can share, donate, or receive electrons This results in attractions between atoms called chemical bonds Chemical bonds cause atoms to stay close together. Recall that a compound is a substance consisting of two or more different elements combined in a fixed ratio. Chemical bonds are responsible for holding atoms together. Student Misconceptions 1. The dangers posed by certain chemicals in our food and broader environment often misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Copyright © 2009 Pearson Education, Inc.

How covalent bonds form Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms. For many elements, an atom becomes stable when its outermost energy level is full. Sharing electrons with other atoms is one way for elements to become stable.

How covalent bonds form Two hydrogen atoms can combine with each other by sharing their electrons. Each atom becomes stable by sharing its electron with the other atom. Hydrogen molecule

How covalent bonds form Water molecule A covalent bond holds the two hydrogen atoms together. A molecule is a group of atoms held together by covalent bonds. It has no overall charge.

How ionic bonds form An atom (or group of atoms) that gains or loses (transfers) electrons has an electrical charge and is called an ion. An ion is a charged particle made of atoms. The attractive force between two ions of opposite charge is known as an ionic bond.

Chemical Reactions Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances. Ionic bond + + Chlorine atom Sodium+ Ion Chlorine― ion Sodium atom

Chemical Reactions All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism.