1. Lesson Overview Lesson Overview The Nature of Matter Lesson Overview 2.1 The Nature of Matter

2. Lesson Overview Lesson Overview The Nature of Matter THINK ABOUT IT What are you made of? Just as buildings are made from bricks, steel, glass, and wood, living things are made from chemical compounds. When you breathe, eat, or drink, your body uses the substances in air, food, and water to carry out chemical reactions that keep you alive. The first job of a biologist is to understand the chemistry of life.

3. Lesson Overview Lesson Overview The Nature of Matter Atoms What three subatomic particles make up atoms? Protons – positively charged, found in nucleus neutrons – no charge, found in nucleus electrons – negatively charged, found outside nucleus

4. Lesson Overview Lesson Overview The Nature of Matter Atoms The study of chemistry begins with the basic unit of matter, the atom. The concept of the atom came first from the Greek philosopher Democritus, nearly 2500 years ago.

5. Lesson Overview Lesson Overview The Nature of Matter Atoms Democritus asked -can you divide a substance without limit? -does there come a point at which you cannot divide the substance without changing it into something else? Democritus thought -there had to be a limit, -called the smallest fragment the atom, -from the Greek word atomos, meaning “unable to be cut.”

6. Lesson Overview Lesson Overview The Nature of Matter Atoms Atoms are incredibly small: -Placed side by side, 100 million atoms would make a row only about 1 centimeter long—about the width of your little finger! -Despite its extremely small size, an atom contains subatomic particles that are even smaller.

7. Lesson Overview Lesson Overview The Nature of Matter Protons and Neutrons Protons and neutrons -have about the same mass (about 1 atomic mass unit), -Protons-positively charged, -Neutrons-no charge at all, -found in the nucleus at the center of the atom, -held together by strong forces.

8. Lesson Overview Lesson Overview The Nature of Matter Electrons Electron-negatively charged (–) -1/1840 the mass of a proton -in constant motion in the space surrounding the nucleus -attracted to the positively charged nucleus -remain outside the nucleus because of the energy of their motion.

9. Lesson Overview Lesson Overview The Nature of Matter Electrons Why are atoms neutral? -atoms have equal numbers of electrons and protons, -positive and negative charges balance out The carbon atom shown has 6 protons and 6 electrons.

10. Lesson Overview Lesson Overview The Nature of Matter Elements and Isotopes How are all of the isotopes of an element similar? They have the -same number of protons and electrons, -same chemical properties. Isotopes of an atom are different only because they have -different masses, -different numbers of neutrons in the nucleus.

11. Lesson Overview Lesson Overview The Nature of Matter Elements and Isotopes A chemical element is a pure substance that consists entirely of one type of atom. More than 100 elements are known, but only about two dozen are commonly found in living organisms. The element mercury is shown to the right.

12. Lesson Overview Lesson Overview The Nature of Matter Elements and Isotopes Elements are represented by one- or two-letter symbols. For example: -C stands for carbon, -N for nitrogen, -Al for aluminum, and -P for phosphorus. Notice the first letter of the symbol is capitalized and the second letter is lowercase.

13. Lesson Overview Lesson Overview The Nature of Matter Elements and Isotopes The number of protons in the nucleus of an element is called its atomic number. Carbon’s atomic number is 6, meaning that each neutral atom of carbon has six protons and, consequently, six electrons.

14. Lesson Overview Lesson Overview The Nature of Matter Isotopes Isotopes - atoms of an element that have different numbers of neutrons (& different masses). For example, although all atoms of carbon have six protons, some have six neutrons, some seven, and a few have eight.

15. Lesson Overview Lesson Overview The Nature of Matter Isotopes Mass number = Proton number + neutron number Isotopes are identified by their mass numbers; for example, carbon-12, carbon-13, and carbon-14.

16. Lesson Overview Lesson Overview The Nature of Matter Isotopes Atomic mass - weighted average of the masses of an element’s isotopes, in which the abundance of each isotope in nature is considered. Why do all isotopes of an element have the same chemical properties? -Because all isotopes of an element have the same number of protons and electrons.

17. Lesson Overview Lesson Overview The Nature of Matter Radioactive Isotopes Some isotopes are radioactive, meaning their nuclei are unstable and break down at a constant rate over time. Uses for radioactive isotopes: -determine the ages of rocks and fossils by analyzing the isotopes found in them. -detect and treat cancer -kill bacteria that cause food to spoil. -labels or “tracers” to follow the movements of substances within organisms.

18. Lesson Overview Lesson Overview The Nature of Matter Chemical Compounds In what ways do compounds differ from their component elements? The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed.

19. Lesson Overview Lesson Overview The Nature of Matter Chemical Compounds Compound - substance formed by the chemical combination of two or more elements in definite proportions. -Scientists show the composition of compounds by a kind of shorthand known as a chemical formula. -Water has the chemical formula H 2 O (2H : 1O), -Table salt, has the chemical formula NaCl (1Na : 1 Cl)

20. Lesson Overview Lesson Overview The Nature of Matter Compounds & Elements are Different Sodium -is very reactive, -is a silver-colored metal, -is soft enough to cut with a knife, -reacts explosively with cold water. Chlorine -is very reactive, -is a poisonous, greenish gas, -was used in battles during World War I.

21. Lesson Overview Lesson Overview The Nature of Matter Compounds & Elements are Different Sodium chloride -table salt, -is a white solid, -dissolves easily in water, -is not poisonous, -is essential for the survival of most living things.

22. Lesson Overview Lesson Overview The Nature of Matter Chemical Bonds What are the main types of chemical bonds? Two main types of chemical bonds are -ionic bonds -covalent bonds.

23. Lesson Overview Lesson Overview The Nature of Matter Chemical Bonds The atoms in compounds are held together by various types of chemical bonds. Bond formation involves the electrons that surround each atomic nucleus. Valence electrons -electrons that are available to form bonds, -found in the outermost energy level of the atom.

24. Lesson Overview Lesson Overview The Nature of Matter Ionic Bonds Ionic bonds - formed when one or more electrons are transferred from one atom to another, -atoms that lose electrons have a positive charge, -atoms that gain electrons have a negative charge, -positively and negatively charged atoms are known as ions.

25. Lesson Overview Lesson Overview The Nature of Matter Ionic Bonds Ionic bonds form between sodium and chlorine to form NaCl, table salt.

26. Lesson Overview Lesson Overview The Nature of Matter Ionic Bonds A sodium atom easily loses its one valence electron and becomes a sodium ion (Na + ).

27. Lesson Overview Lesson Overview The Nature of Matter Ionic Bonds A chlorine atom easily gains an electron (from sodium) and becomes a chloride ion (Cl - ).

28. Lesson Overview Lesson Overview The Nature of Matter Ionic Bonds These oppositely charged ions have a strong attraction for each other, forming an ionic bond.

29. Lesson Overview Lesson Overview The Nature of Matter Covalent Bonds Covalent bonds -electrons are shared by atoms instead of being transferred, -moving electrons travel about the nuclei of both atoms, -Single covalent bond – 2 atoms share 2 electrons -Double covalent bond – 2 atoms share 4 electrons -Triple covalent bond – 2 atoms share 6 electrons

30. Lesson Overview Lesson Overview The Nature of Matter Covalent Bonds Molecule -the smallest unit of a covalent compound. This diagram of a water molecule shows that each hydrogen atom is joined to water’s one oxygen atom by a single covalent bond. Each hydrogen atom shares two electrons with the oxygen atom.

31. Lesson Overview Lesson Overview The Nature of Matter Covalent Bonds When atoms of the same element join together, they also form a molecule. Oxygen molecules in the air you breathe consist of two oxygen atoms joined by covalent bonds. The atoms in a molecule always share their electrons.

32. Lesson Overview Lesson Overview The Nature of Matter Van der Waals Forces Because of their structures, atoms of different elements do not all have the same ability to attract electrons. Some atoms have a stronger attraction for electrons than do other atoms. When the atoms in a covalent bond share electrons, the sharing is not always equal. Even when the sharing is equal, rapid movement of electrons can create regions on a molecule that have a tiny positive or negative charge.

33. Lesson Overview Lesson Overview The Nature of Matter Van der Waals Forces When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. Van der Waals forces -intermolecular forces of attraction -named after the scientist who discovered them -not as strong as ionic or covalent bonds -hold molecules together, especially when large.

34. Lesson Overview Lesson Overview The Nature of Matter Ch 2.1 Assessment Questions (page 38) 1.(a) Describe the structure of an atom. An atom is an extremely small particle with a nucleus in the center. The nucleus contains protons (+) and neutrons (no charge). Smaller particles called electrons (-) are in constant motion in the space surrounding the nucleus. (b) An atom of calcium contains 20 protons. How many electrons will it have? 20 (proton number = electron number in atoms)

35. Lesson Overview Lesson Overview The Nature of Matter Ch 2.1 Assessment Questions (page 38) 2. (a) Why do all isotopes of an element have the same chemical properties? Because they all have the same number of protons and electrons. (b) Compare the structure of carbon-12 and carbon-14. Each isotope has 6 protons and 6 electrons. However, carbon-12 has 6 neutrons and carbon-14 has 8 neutrons.

36. Lesson Overview Lesson Overview The Nature of Matter Ch 2.1 Assessment Questions (page 38) 3. (a) What is a compound? A compound is a substance formed by the chemical combination of 2 or more elements in definite proportions. (b) Water (H 2 O) and hydrogen peroxide (H 2 O 2 ), both consist of hydrogen and oxygen atoms. Explain why they have different chemical and physical properties. The two compounds have different properties because they contain hydrogen and oxygen in different proportions.

37. Lesson Overview Lesson Overview The Nature of Matter Ch 2.1 Assessment Questions (page 38) 4. (a) What are 2 types of bonds that hold the atoms within a compound together? Ionic bonds (transfer of electrons) and covalent bonds (sharing of electron pairs) (b) A potassium atom easily loses its one valence electron. What type of bond will it form with a chlorine atom? It will form an ionic bond, since the potassium will transfer its one valence electron to the chlorine atom. This will result in both atoms becoming ions and obtaining a full valence electron level.

38. Lesson Overview Lesson Overview The Nature of Matter Ch 2.1 Assessment Questions (page 38) 5. Why do you think it is important that biologists have a good understanding of chemistry? Since living things are made up of elements and chemical compounds, we need to know about the behavior of these elements and compounds. In addition, the survival of living things depends on chemical reactions that take place inside and outside their bodies. For both these reasons, biologists need to have an understanding of chemistry in order to understand living things.