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The Chemical Basis of Life Chapter 4

The Chemical Basis of Life Chapter 4. Life requires about 25 chemical elements. Concept 4.1. Objectives List the most common elements in living things. Compare and contrast elements and compounds Key terms matter element trace element compound. Elements C, H, O, N

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The Chemical Basis of Life Chapter 4

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  1. The Chemical Basis of LifeChapter 4

  2. Life requires about 25 chemical elements Concept 4.1

  3. Objectives • List the most common elements in living things. • Compare and contrast elements and compounds • Key terms • matter • element • trace element • compound

  4. Elements • C, H, O, N • Matter: anything that occupies space and has mass • Element: a pure substance that cannot be broken down into other substances by chemical means. • Trace elements: elements that make up less than 0.01 percent of your body mass. (e.g. Iodine, Iron, etc)

  5. Compounds • H20, (Na + Cl -- NaCl) • Compound: is a substance containing two or more elements that are chemically combined in a fixed ratio. • (activity 4.1) • Fluoridation

  6. Concept Check 4.1 1. List the four most abundant elements in your body, in order of decreasing percent of body mass. 2. How are elements and compounds different? 3. Give an example showing the importance of trace elements to the human body.

  7. Chemical properties are based on the structure of atoms. Concept 4.2

  8. Atoms • C6H12O6 • Atom: the smallest possible particle of an element. • Proton: is a subatomic particle with a single unit of positive electrical charge (+). • Electron: is a subatomic particle with a single unit of negative electrical charge (-). • Neutron: is electrically neutral, meaning it has no electrical charge.

  9. Atoms • Nucleus: An atoms central core where protons and neutrons are tightly packed together. • All atoms of a particular element have the same number of protons, known as the element's atomic number.

  10. Isotopes • Isotopes: have the same number of protons in their atoms but different numbers of neutrons. • Radioactive isotope: one in which the nucleus decays (breaks down) over time, giving off radiation in the form of matter and energy.

  11. Electrons and Reactivity (activity 4.2)

  12. Concept Check 4.2 1. Describe three kinds of subatomic particles and tell how they are arranged in an atom. 2. What is an isotope? Explain how radioactive isotopes are useful to researchers. 3. Describe the significance of the number of electrons in an atom's highest energy level. 4. Explain the significance of an element's atomic number.

  13. Chemical bonds join atoms to one another. Concept 4.3

  14. Ionic Bonds • Ionic bonds: occur when an atom transfers an electron to another atom. • Ions: atoms (or groups of atoms) that have become electrically charged as a result of gaining or losing electrons.

  15. Covalent Bonds • Covalent bond: forms when two atoms share electrons. • Number of bonds = number of shared e- • Molecules: two or more atoms held together by covalent bonds

  16. Chemical Reactions • Chemical reactions: changes which result in the formation of one or more new substance • Reactants: The starting materials for the reaction (hydrogen and oxygen) • Products: The ending materials (water)

  17. Concept Check 4.3 1. Describe how an ionic bond forms. How is this process different from the formation of a covalent bond? 2. In a molecule represented by the chemical formula C6H12O6, how many atoms of each element are present? 3. What information does a chemical equation provide about a chemical reaction? 4. A carbon atom has 4 electrons in its highest energy level. How many hydrogen atoms could become bonded to a single carbon atom? .

  18. Life depends on the unique properties of water. Concept 4.4

  19. Objectives • Describe the structure of a water molecule. • List and describe water's unique properties. • Distinguish between an acid and a base. • Explain how Earth's conditions are fit for life. • Key terms • polar molecule • hydrogen bond • cohesion • adhesion • thermal energy • temperature • solution • solvent • solute • aqueous solution • acid • base • pH scale • buffer

  20. The Structure of water • Polar molecule: A molecule in which opposite ends have opposite electric charges • Water is a compound consisting of polar molecules. “hogs” • Hydrogen Bond: A weak attraction between the hydrogen atom of one molecule and a slightly negative atom within another molecule. • Water tension activity

  21. Water's Life-Supporting Properties • Cohesion and Adhesion • Cohesion: The tendency of molecules of the same kind to stick to one another. • Adhesion attraction that occurs between unlike molecules is called

  22. Temperature Moderation • Thermal energy is the total amount of energy associated with the random movement of atoms and molecules in a sample of matter. • Temperature is a measure of the average energy of random motion of the particles in a substance.

  23. Low Density of Ice • Density is the amount of matter in a given volume. • In most substances, the solid state is more dense than the liquid state. • Ice is less dense than cold liquid form.

  24. Water's Ability to Dissolve Other Substances • Solution: a uniform mixture of two or more substances. • solvent: substance in a solution that dissolves the other substance and is present in the greater amount • solute: substance in a solution that is dissolved and is present in a lesser amount • aqueous solution: solution in which water is the solvent • Water is the main solvent inside all cells, in blood, and in plant sap. • Dissolve a half a cup of sugar in a cup of water?

  25. Figure 4-16 Sodium chloride dissolves as Na+ and Cl- ions become attracted to water molecules and break away from the surface of the solid. Water can also dissolve many nonionic compounds, such as sugars.

  26. Acids, Bases, and pH • In aqueous solutions, a very small percentage of the water molecules themselves break apart into ions. • Hydrogen ions (H+) & Hydroxide ions (OH-) • For life, the right balance of H+ ions and OH- ions is critical. • Some chemical compounds contribute additional H+ ions to an aqueous solution while others remove H+ ions from it.

  27. Acids, Bases, and pH • A compound that donates H+ ions to a solution is called an acid. • E.g: Hydrochloric acid (HCl), the acid in your stomach. In an aqueous solution, hydrochloric acid breaks apart completely into H+ and Cl- ions. • A compound that removes H+ ions from an aqueous solution is called a base. • E.g: Sodium Hydroxide (NaOH), does this by adding OH- ions, which then combine with H+ ions and form water molecules.

  28. The pH scale • The pH scale describes how acidic or basic a solution is.

  29. Buffers • buffer: substance that maintains a fairly constant pH in a solution by accepting H+ ions when their levels rise and donating H+ ions when their levels fall • E.g blood (pH 7.4) An Environment Fit for Life • The abundance of liquid water is one example of how conditions on Earth provide a favorable environment for life.

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