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The Chemical Basis of Life

The Chemical Basis of Life

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The Chemical Basis of Life

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  1. The Chemical Basis of Life (Chapter 2.0 – 2.16)

  2. Learning Objectives • Describe the component parts of an atom and how they are distributed in the atomic structure. • Explain atomic number and mass number • Memorize the atomic number of carbon, hydrogen, oxygen, sodium, and chlorine • Given the number of electrons, protons, and neutrons of an atom, provide the mass number • Explain matter, chemical element, compound, trace element. • Given a simple chemical equation, identify elements, compounds, and molecules. Identify reactants and products. • Explain isotopes and radioactive isotopes. • Explain how radioactive isotopes, although potentially harmful, have valuable medical applications. • Name the five most common elements found in the human body by common name and chemical symbol • Name seven trace elements found in the human body • Explain how electron arrangement determines the chemical properties of an atom. • Understand the number of electrons it takes to fill the innermost and outermost shells of an atom.

  3. Learning Objectives (cont’d) • Provide examples of how ionic and covalent bonds are formed between atoms • Describe the structure of a water molecule and explain how this contributes to its role as a universal solvent. • Understand how polarity and hydrogen bonds contribute to the unique properties of water •  Explain what is meant by pH. • Understand the difference between an acid and a base, and the importance of pH in living systems. Determine the pH of your saliva (in class activity) • Determine if a solution is neutral, acidic, or basic given its pH. • Explain the role of buffers in biological fluids • Be prepared to provide an example of a basic chemical reaction. Explain what is meant by a balanced equation • Explain how we can know that this equation is “balanced” by looking at the reactants and products .

  4. Parts of an atom • Nucleus: consists of protons and neutrons • Protons: positively charged • Neutrons: neutral charge • Electrons: negatively charged and occupy energy shells around the nucleus • Video: What is an Atom? (2:14 min) •

  5. Atomic Number and Mass Number • Atomic number = the total number of protons and in the nucleus (in an uncharged atom, # protons = # electrons) • Mass number = # of protons + # neutrons in the nucleus • ie. Mass number = atomic number + # neutrons

  6. Check your understanding What is the atomic number? What is the mass number? How many protons? How many electrons? How many neutrons?

  7. Remember this

  8. What is matter? • Matter is anything that occupies space and has mass • Usually, an atom is the smallest unit of matter

  9. What is a chemical element? • A chemical element is a substance that cannot be broken down into smaller components by chemical reactions • All atoms of an element have the same number of protons (ie. same atomic number)

  10. Common elements in the human body • O2: Oxygen (60%) • C: Carbon (18%) • H: Hydrogen (10%) • N: Nitrogen (3%) • Ca: Calcium (2%)

  11. What is a trace element? • A trace element is a chemical element that is only present in minute amounts in an environment • In living organisms, certain elements are only required in trace amounts for metabolism

  12. Important trace elements • P: Phosphorus (1%) • K: Potassium (0.4%) • S: Sulfur (0.3%) • Na: Sodium (0.15%) • Cl: Chloride • Mg: Magnesium (0.05%) • Fe: Iron

  13. Isotopes and Radioisotopes • Isotopes are elements that have the same number of protons, but different number of neutrons • Radioisotopes are isotopes of an element with an unstable nucleus • Radioactivity is due to the nuclear reaction to make the isotope stable resulting in a radioisotope’s halflife

  14. Medical Applications of Radioisotopes • For diagnostic scanning • different organs in the body will concentrate certain radioisotopes to produce an image • eg. CT vs PET scans 2. To treat cancer • Radioisotopes can be applied externally or internally to directly target a tumor site Video: What is cancer radiotherapy? (2:29 min)

  15. Chemical Properties of an Atom • The valence electrons in the outermost energy shell(s) determine the chemical properties of an atom • The interaction of the valence electrons between atoms form compounds Video: Valence Electrons (2:03 min)

  16. Ions • An ion is a charged atom with an unequal number of protons versus electrons • Cations are positively charged ions with more protons than electrons (eg. Na+) • Anions are negatively charged ions with more electrons than protons (eg. Cl-)

  17. What is a compound? • A chemical compound is composed of two or more separate elements • Different elements combine by forming chemical bonds to make compounds

  18. Chemical bonds • Ionic bondsare formed due to the electrostatic attraction between two oppositely charged ions • Covalent bonds are formed when electrons are shared between atoms Video: Chemical bonding (2:14 min)

  19. Water • Water is a polar molecule because it is negatively charged at one end and positively charged at the other end due to unequal sharing of electrons • Because of its polarity, water can form a Hydrogen bond between the Hydrogen of one water molecule and the Oxygen of another molecule Video: Water molecules (1:17 min)

  20. Properties of Water • Universal solvent – other polar or charged molecules dissolve easily, most chemical reactions occur in water • Transporter – dissolved molecules can be transported throughout living organisms (eg. blood) • Cohesiveness – water molecules are attracted to each other due to hydrogen bonding (eg. capillary action and transpiration) • Temperature regulator – H-bonds absorb and release heat to regulate temperature in living systems (eg. sweat) • Insulator – water is less dense as a solid than a liquid, so floating ice insulates lakes and oceans

  21. pH • pH is a logarithmic measurement of the relative concentration of H+ and OH- ions in a solution • Acids have excess H+ ions in solution and a pH less than 7 • Bases have excess OH- ions in solution and a pH more than 7

  22. Buffers • Buffers resist pH changes by taking up excess H+ or OH- ions to maintain a constant pH • eg. Bicarbonate ions (HCO3-) in our blood maintain a pH of approximately 7.4

  23. Try this • What is the pH of your saliva? • Are the following acidic or basic? Gastric juice pH 2.5 Intestinal juice pH 9.5 • What is the difference in the relative concentration of H+ between gastric juice and intestinal juice?

  24. Chemical Equations

  25. Test your understanding In the above chemical equation, What are the elements? What are the compounds? What are the molecules? What are the reactants? What are the products?

  26. Balancing Equations An equation is “balanced” if the number of atoms for each element is equal between reactants and products

  27. Practice balancing equations Video: How to balance chemical equations (5:00 min)