Chapter 2

1. Chapter 2 The Chemistry of Life

2. Ch 2-1 • Goals: • Describe 3 subatomic particles • Explain how isotopes are similar • List the functions of radioactive isotopes • Explain the relationship between atoms, molecules, and compounds • Describe 2 types of chemical bonds and how they form

3. Atoms • Atom -the smallest component of an element that still has properties of the element • consists of a positively charged nucleus- center of the atom containing the protons (+) and neutrons (neutral) • surrounded by a negatively charged cloud of cloud of electrons • "+" and "-" charges strongly attract • Elements are pure substances made up of just one type of atom

4. Atoms • Proton • particle in the nucleus with a positive charge of +1 • Neutron • non-charged (neutral) nuclear particle with the same mass as the proton • Electron • negatively charged particle (-1) with a mass 1/1840 of that of a proton • Orbit the nucleus

5. Protons, Neutrons, and Electrons • Altering the number of any one of the 3 subatomic particles yields different results • Change the # of protons • Changes the atom type entirely • Recall atomic # determines the element • Change the # of neutrons • Forms an isotope • Increases or decreases atomic mass • Change the # of electons • Forms an ion (either cation (+) or anion(-)) • Important for ionic bond formation

6. Isotopes • Isotopes- atoms of the same element that differ in the number of neutrons they contain are known as isotopes

7. Isotopes • Some are radioactive • Their unstable nuclei break down at a constant rate giving off radiation • Uses of isotopes include: • Analyzing the age of rocks and fossils • Treating cancer • Eliminate bacteria from food • “Tracers” to follow movement of substances in the body

8. Radioactive Tracers • Radioisotopes of hydrogen, carbon, phosphorus, sulfur, and iodine have been used extensively to trace the path of biochemical reactions • In medicine, tracers are applied in a number of tests in autoradiography and nuclear medicine • including single photon emission computed tomography (SPECT) • positron emission tomography (PET) • scintigraphy • The urea breath test for Helicobacter pylori commonly used a dose of 14C labeled urea to detect H. pylori infection • If the labeled urea was metabolized by H. pylori in the stomach, the patient's breath would contain labeled carbon dioxide. In recent years, the use of substances enriched in the non-radioactive isotope 13C has become the preferred method, avoiding patient exposure to radioactivity

9. Electrons • Atoms have no net charge • equal numbers of electrons and protons • The number of electrons determines the chemical properties of an element • Electron energy levels • electrons exist around the nucleus in regions known as energy levels • 1st level – holds a max. of 2 electrons • 2nd level – holds a max. of 8 electrons • 3rd level- holds 18 electons • And so on… • The general formula is that the nth shell can in principle hold up to 2n2electrons… http://en.wikipedia.org/wiki/Electron_shell#List_of_elements_with_electrons_per_shell

10. Electrons • An atom’s ability to form bonds is determined by the electrons in the outermost energy level or “shell” • We refer to this shell of electrons as valence electrons • Valence electrons are the basis for Lewis dot structures Li

11. Electrons • Valence electrons can be determined easily by looking at the Periodic Table • The group number tells us the number of valence e- • Often written in Roman numerals above each family (column) All in group I have 1 valence electron

13. Compounds • A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. • NaCl (table salt) • C6H12O6(glucose) • properties of a compound are different from those of its individual elements

14. Chemical Bonds • The atoms in compounds are held together by chemical bonds • forces of attraction that hold atoms together (chemical energy) • formed or broken during chemical reactions • energy is usually required to make bonds • energy usually released when bonds are broken • Ex: ATP to ADP

15. Chemical Bonds • Form because atoms with unfilled outer electron shells are unstable • can react with other atoms • Reactive atoms form chemical bonds to stabilize their outer shells • The main types of chemical bonds are: • ionic bonds – atoms transfer (give up or accept e-) • Loss or gain of e- forms ions with opposite charge • covalent bonds –atoms share electrons with other atoms

17. Chemical Bonds • Ionic bonds- form between metals and nonmetals, involve the transfer of electrons to form a positive cation (metal) and negative anion (nonmetal) which attract due to their opposite charges and form a bond

18. Chemical Bonds • Covalent bonds- form between 2 nonmetals, involve the sharing of electrons, can result in the formation of single, double, or even triple bonds • The structure that results when atoms are joined together by covalent bonds is called a molecule.

19. Van der Waals Forces • Sharing of electrons is not always equal creating regions on molecules with slight positive or negative charges • When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules

20. Ch 2-2 • Goals: • Explain why water molecules are polar • Explain the roles of solutions and suspensions in living things • Describe how the pH scale works • Contrast acids and bases • Describe the importance of buffers in living things

21. Mixtures • Mixture – combination of substances in which the individual components retain their own properties • Solution – a type of mixture where ions are evenly dissolved in a liquid • Ex: salt water; salt is the solute and water is the solvent • Blood is a suspension because it contains cells and other undissolved particles in solution

22. Water • Water is the strongest solvent known because it is polar • Polarity results from an uneven sharing of electrons between the oxygen and hydrogen atoms.

23. Hydrogen Bonds • Because of the partial positive and negative charges, polar molecules can attract each other • Hydrogen bonds form between the oxygen of one water molecule and the hydrogen of another

24. Cohesion of Water Molecules • Cohesion is an attraction between molecules of the same substance. • Hydrogen bonding causes cohesion in water molecules

25. Adhesion • Adhesion is an attraction between molecules of different substances.