The Nature of Matter Read the lesson title aloud to the students.

Learning Objectives Identify the three subatomic particles that make up atoms. Explain how all isotopes of an element are similar and how they are different. Explain how compounds differ from their component elements. Describe the two main types of chemical bonds. Click to reveal each of the learning objectives. Tell students that all living organisms are made of elements, which are used to build the larger molecules of life. By the end of this lesson, students should be able to identify the components of an atom and how atoms can be bound to each other.

Atoms The subatomic particles that make up atoms are protons, neutrons, and electrons. Explain to students that this is an atom and that atoms are made of protons, neutrons, and electrons. Define each term. Tell students that protons are drawn as a “+” because they are positively charged. Ask: How many protons does this atom have? Click to highlight the protons. Answer: 6 Tell students that electrons are drawn as a “–” because they are negatively charged. Ask: How many electrons does this atom have? Click to highlight the electrons. Explain that because atoms have equal numbers of electrons and protons, they are electrically neutral. Address the misconception that electrons travel in fixed orbits around the nucleus. Explain that they travel in an electron cloud, not in fixed orbits. Explain that neutrons have no charge and are not designated with a “+” or “–.” Ask: How many neutrons does this atom have? Click to highlight the neutrons.

Elements An element is a pure substance that consists entirely of one type of atom. Atomic number = 6 Define atomic number. Ask: What is the atomic number of this atom? Ask for a volunteer to write the answer on the board. Click to reveal the answer. Explain that different elements have different numbers of protons. Carbon has an atomic number of 6. Define element.

Isotopes Because they have the same number of electrons, all isotopes of an element have the same chemical properties. 6 6 6 Explain to students that you will fill out this table together. Click to reveal the answer for each of the following questions. Ask: How many protons does carbon have? Click to reveal the answer for Carbon-12: 6 Ask: Does carbon always have 6 protons? Answer: Yes. Click to reveal the proton numbers of Carbon-13 and 14. Ask: How many electrons does carbon have? Ask: Does carbon always have 6 electrons? Click to reveal the electron numbers of Carbon-13 and 14. You may want to mention that carbon will form bonds with other atoms, and in those cases it will share electrons with the other atoms. Ask: How many neutrons does carbon have? Explain to students that the number of protons plus the number of neutrons is called the mass number (this is the “-12”). Ask: What is the mass number of the second isotope of carbon on this list? Answer: 13 Ask: How many neutrons does this isotope have? Click to reveal the answer for Carbon-13: 7 Ask: How many neutrons does Carbon-14 have? Click to reveal the answer: 8 Define and discuss radioactive isotopes. 6 6 7 6 6 8

Chemical Compounds A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed. Tell students that chemical compounds are usually shown using a chemical formula. Water, for example, is shown H2O. To illustrate the second point, students that both oxygen and hydrogen are gases, yet when they combine (sometimes explosively), they form a liquid.

Ionic Bonds An ionic bond is formed when one or more electrons are transferred from one atom to another. Begin with a review of subatomic particles. Ask: How many electrons does sodium have? Click to reveal the answer: 11 Ask: What is the overall charge of sodium? Click to reveal the answer: 0 Ask: How many electrons does chlorine have? Click to reveal the answer: 17 Ask: What is the overall charge of chlorine? Explain that a sodium atom easily loses its one valence electron and that chlorine easily picks up this electron. This changes the number of electrons in each atom. Draw students’ attention to the diagram on the right. Ask: How many electrons does sodium have now? Click to reveal the answer: 10 Ask: What is the overall charge of sodium now? Click to reveal the answer: +1 Ask: How many electrons does chlorine have now? Click to reveal the answer: 18 Ask: What is the overall charge of chlorine now? Click to reveal the answer: -1 Explain that the positive and negative charges attract and the atoms form an ionic bond. -10 -18 -11 -17 +1 -1

Covalent Bonds A covalent bond is formed when atoms share electrons. Electrons in oxygen: 8 Total electrons: Tell students that hydrogen has 1 proton. Ask: How many electrons would hydrogen have? Answer: 1 Click to highlight each hydrogen atom’s electron. Tell students that oxygen has 8 protons. Ask: How many electrons would oxygen have? Ask for a volunteer to write the answer on the board. Click to reveal the answer: 8 Ask: If each hydrogen in this image has 1 electron and the oxygen has 8, how many electrons are present in total? Ask for a volunteer to write the answer on the board. Click to reveal the answer: 10 Click to highlight the electrons that are shared between oxygen and hydrogen. Tell students that these electrons form the covalent bonds. Use familiar phenomena as analogies to help students understand and distinguish between ionic and covalent bonds. Explain that ionic bonds can be summarized as “opposites attract.” You may want to use magnets to demonstrate this type of attraction. Covalent bonds are like two people sharing the same umbrella. Challenge students to think of other analogies for covalent bonds. Ask for volunteer students to share his or her analogy. 10

Van der Waals Forces Van der Waals forces are intermolecular forces of attraction due to a slight attraction between oppositely charged regions of nearby molecules. Ask students if they ever wondered how a lizard could walk up a wall. Explain to them how van der Waals forces make this feat possible. Check that students understand how the three different images in the slide are related. Ask: How could weak intermolecular forces between the gecko’s feet and the wall prevent gravity from pulling the gecko off the wall? Answer: There are so many fibers that the total van der Waals forces are strong enough to counter the force of gravity.