2. 6.1 Section Objectives – page 141 Relate the structure of an atom to the identity of elements. Section Objectives: Relate the formation of covalent and ionic chemical bonds to the stability of atoms.

3. 6.1 Section Objectives – page 141 Section Objectives: Distinguish mixtures and solutions. Define acids and bases and relate their importance to biological systems.

4. An element is a substance that can’t be broken down into simpler chemical substances. Section 6.1 Summary – pages 141-151 Elements Everything – whether it is a rock, frog, or flower – is made of substances called elements.

5. Section 6.1 Summary – pages 141-151 Of the naturally occurring elements on Earth, only about 25 are essential to living organisms. Carbon, hydrogen, oxygen, and nitrogen make up more than 96 percent of the mass of a human body. Natural elements in living things

6. Section 6.1 Summary – pages 141-151 Trace elements Trace elements such as iron and copper, play a vital role in maintaining healthy cells in all organisms. Plants obtain trace elements by absorbing them through their roots; animals get them from the foods they eat.

7. Section 6.1 Summary – pages 141-151 Table 6.1 Some Elements That Make Up the Human Body ElementSymbol Percent By Mass in Human Body Element Symbol Percent By Mass in Human Body Molybdenum Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Sodium Chlorine Magnesium Selenium Iron Zinc Copper Iodine Manganese Boron Chromium Cobalt Fluorine O C H N Ca P K S Na Cl Mg 65.0 18.5 9.5 3.3 1.5 1.0 0.4 0.3 0.2 0.1 Fe Zn Cu I Mn B Cr Mo Co Se F trace

8. An atom is the smallest particle of an element that has the characteristics of that element. Section 6.1 Summary – pages 141-151 Atoms: The Building Blocks of Elements Atoms are the basic building blocks of all matter.

9. All nuclei contain positively charged particles called protons (p + ). The center of an atom is called the nucleus (NEW klee us). Section 6.1 Summary – pages 141-151 The structure of an atom Most contain particles that have no charge, called neutrons (n 0 ).

10. Section 6.1 Summary – pages 141-151 The Structure of an atom Nucleus Electron energy levels The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e - ) This region of space is referred to as an electron cloud.

11. The Periodic Table 11 atomic number (# protons) Na chemical symbol 22.990 atomic mass (#protons and neutrons)

12. Section 6.1 Summary – pages 141-151 The Structure of an atom Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus.

13. Section 6.1 Summary – pages 141-151 Electron energy levels Electrons exist around the nucleus in regions known as energy levels. The first energy level can hold only two electrons. The second level can hold a maximum of eight electrons. The third level can hold up to 18 electrons. Nucleus 8 protons (p+) 8 neutrons (n 0 ) Oxygen atom

14. Section 6.1 Summary – pages 141-151 Electron energy levels Atoms contain equal numbers of electrons and protons; therefore, they have no net charge.

15. Section 6.1 Summary – pages 141-151 Atoms of the same element always have the same number of protons but may contain different numbers of neutrons. Isotopes of an Element Atoms of the same element that have different numbers of neutrons are called isotopes (I suh tophs) of that element.

16. Section 6.1 Summary – pages 141-151 A compound is a substance that is composed of atoms of two or more different elements that are chemically combined. Compounds and Bonding Table salt (NaCl) is a compound composed of the elements sodium and chlorine.

17. Section 6.1 Summary – pages 141-151 An atom (or group of atoms) that gains or loses electrons has an electrical charge and is called an ion. An ion is a charged particle made of atoms. How ionic bonds form The attractive force between two ions of opposite charge is known as an ionic bond.

18. Section 6.1 Summary – pages 141-151 Chemical Reactions

19. Section 6.1 Summary – pages 141-151 Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms. How covalent bonds form 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.

20. Section 6.1 Summary – pages 141-151 Two hydrogen atoms can combine with each other by sharing their electrons. How covalent bonds form Each atom becomes stable by sharing its electron with the other atom. Hydrogen molecule

21. Section 6.1 Summary – pages 141-151 How covalent bonds form Click image to view movie.

22. Section 6.1 Summary – pages 141-151 How covalent bonds form The attraction of the positively charged nuclei for the shared, negatively charged electrons holds the atoms together. Hydrogen molecule

23. Section 6.1 Summary – pages 141-151 A covalent bond holds the two hydrogen atoms together. How covalent bonds form A molecule is a group of atoms held together by covalent bonds. It has no overall charge. Water molecule

24. Section 6.1 Summary – pages 141-151 Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances. Chemical Reactions All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism.

25. Section 6.1 Summary – pages 141-151 In a chemical reaction, substances that undergo chemical reactions, are called reactants. Writing chemical equations Substances formed by chemical reactions, are called products.

26. Section 6.1 Summary – pages 141-151 A molecule of table sugar can be represented by the formula: C 12 H 22 O 11. Writing chemical equations The easiest way to understand chemical equations is to know that atoms are neither created nor destroyed in chemical reactions. They are simply rearranged.

27. A mixture is a combination of substances in which the individual components retain their own properties. Section 6.1 Summary – pages 141-151 Mixtures and Solutions Neither component of the mixture changes.

28. Section 6.1 Summary – pages 141-151 A solution is a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent). Mixtures and Solutions Sugar molecules in a powdered drink mix dissolve easily in water to form a solution.

29. Section 6.1 Summary – pages 141-151 Chemical reactions can occur only when conditions are right. Acids and bases A reaction may depend on: - energy availability - temperature - concentration of a substance - pH of the surrounding environment

30. Section 6.1 Summary – pages 141-151 The pH is a measure of how acidic or basic a solution is. Acids and bases A scale with values ranging from below 0 to above 14 is used to measure pH. More acidic NeutralMore basic

31. Section 6.1 Summary – pages 141-151 Substances with a pH below 7 are acidic. An acid is any substance that forms hydrogen ions (H + ) in water. Acids and bases A solution is neutral if its pH equals seven. More acidic NeutralMore basic

32. Section 6.1 Summary – pages 141-151 Substances with a pH above 7 are basic. A base is any substance that forms hydroxide ions (OH - ) in water. Acids and bases pH 11

33. Section 1 Check Question 1 Which of the following is an element? D. water C. sodium chloride B. carbon A. chlorophyll

34. Section 1 Check The answer is B. An element can't be broken down into simpler chemical substances. Chemical elements combine in different ways to form a variety of substances useful to living things.

35. Section 1 Check Table 6.1 Some Elements That Make Up the Human Body ElementSymbol Percent By Mass in Human Body Element Symbol Percent By Mass in Human Body Molybdenum Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Sodium Chlorine Magnesium Selenium Iron Zinc Copper Iodine Manganese Boron Chromium Cobalt Fluorine O C H N Ca P K S Na Cl Mg 65.0 18.5 9.5 3.3 1.5 1.0 0.4 0.3 0.2 0.1 Fe Zn Cu I Mn B Cr Mo Co Se F trace

36. Section 1 Check The smallest particle of an element that has the characteristics of that element is a(n) __________. Question 2 D. atom C. nucleus B. electron A. proton

37. Section 1 Check The answer is D. Atoms are the basic building blocks of all matter and have the same general structure, including a nucleus and electrons. Elements found in both living and nonliving things are made of atoms. Nucleus Electron energy levels An atom has a nucleus and electrons in energy levels.

38. Section 1 Check Which of the following can contain two types of particles? D. electrons Question 3 B. protons C. neutrons A. nucleus

39. Section 1 Check The answer is A. The nucleus is the center of the atom and may contain both positively charged particles and particles that have no charge. Nucleus 8 protons (p+) 8 neutrons (n 0 ) Oxygen atom

40. Section 1 Check Question 4 B. Sodium and chlorine atoms have no overall electrical charge. A. Sodium and chlorine are sharing electrons in their outer energy levels. Sodium and chlorine combine to form table salt. What do you know to be true?

41. Section 1 Check Question 4 D. Sodium and chlorine atoms in table salt have full outer energy levels. C. Sodium and chlorine are less stable in the compound sodium chloride. Sodium and chlorine combine to form table salt. What do you know to be true?

42. Section 1 Check The answer is D. Sodium and chlorine atoms combine because the resulting compound, table salt, is more stable than the individual atoms. Sodium loses an electron in its outer energy level, chlorine gains that electron in its outer energy level, and an ionic bond is formed.