Chapter 2

1. Chapter 2 The Chemical Context of Life

2. Matter • Matter is the amount of “stuff” in an object. • Matter is anything that contains mass and occupies space. • Mass is the amount of matter in an object, weight is the force of gravity acting upon the object.

3. Elements • Elements are the fundamental units of matter. When you get to the atomic level, you cannot break it down any further and still maintain properties of the element. Going further will give you protons, neutron, and electrons.

4. Compounds • Compounds are mixtures of two or more different atoms combined in fixed ratios.

5. Atoms • Are the fundamental units of matter. • They are comprised of protons, neutrons, and electrons.

6. Living Matter • 96% of living matter is made up of C, H, N, and O. • The remaining 4% comes from P, S, Ca, K and a few trace elements.

7. Trace Elements • Trace elements are elements that are required in extremely small quantities for normal bodily functioning. • They are usually cofactors that assist in enzyme functioning.

8. Atomic Number • This is the number of protons within an atom.

9. Mass Number • The mass number is the number of protons plus the number of neutrons.

10. Isotopes • Isotopes are atoms of the same element with different numbers of neutrons.

11. Atomic Mass • The atomic mass of an atom is the average mass of a mixture of its isotopes. • Even though the mass of the element is different, the atom behaves exactly the same in chemical reactions.

12. Radioactive Isotopes • These are isotopes in which the nucleus decays giving off particles and energy. • Radioactive carbon is very commonly used by biologists as is radioactive H. • These are called tracers and often are used to date old objects and assist in the mapping of metabolic processes.

13. Radioactive Isotopes--Decay • There are three main types of radioactive decay of radioactive isotopes: a decay b decay • Decay a and b decay are of most importance.

14. a Decay • Alpha decay occurs when an atom emits a He atom with no electrons, He2+. • These particles are hazardous if ingested, or if any substance which produces them is ingested (radon). • Otherwise they are not very harmful because your dead skin cells absorb them and they cause no harm.

15. b-decay • In b-decay, the decaying element ejects a positron (same mass as an electron, but with a positive charge) from the nucleus--it is called a b-particle. • These are what are often used in patients/organisms as tracers.

16. b-decay and Tracers • The metabolically active tissue of interest takes up the tracer. • When it undergoes decay, a positron is emitted and shortly after combines with an electron producing a photon that can be detected and formed into an image by the scanner.

18. Interactions of Atoms • Most atoms with the exception of the Noble gases are reactive because they contain an incomplete outer energy shell. • The interaction of the elements is what gives rise to a chemical bond. • There are two main categories of chemical bonds: • 1. Ionic • 2. Covalent

19. Covalent Bonds • In a covalent bond, electrons are shared and the result is a molecule. • Single bonds, double bonds, and triple bonds can occur resulting in molecules. • H2 is a single bond, H-H • O2 is a double bond, O=O • C2H2 is a triple bond, H-C≡C-H

21. Covalent Bonds • Covalent bonds

22. Electronegativity • Remember that electronegativity is the number that represents an atoms “desire” to have electrons. • The more electronegative an element, the more likely it is to steal an electron and form an ionic compound with an element.

23. Covalent Bonds • There are two types: • Polar covalent--electrons are not shared equally. The more electronegative atom hogs the electrons giving it a slightly negative charge. H2O for example. H is slightly positive, O is slightly negative. • Non-polar covalent--atoms share electrons equally. CO2, and CH4.

26. Ionic Bonds • In ionic bonds, atoms steal electrons from one another forming compounds that have very high melting points. • When an electronegative atom steals an electron, it has an overall negative charge and is called an anion. • The atom that gave up the electron is now positive and is called a cation. • Since opposites attract, an ionic compound is formed and is called a salt.

28. Ionic Bonds • Ionic Bonds

29. Chemical Reactions • When chemical reactions occur, reactants combine to form products. • 6CO2 + 6H2O --> C6H12O6 + 6O2 • Reactants Products

30. Van der Waals Interactions • Van der Waals interactions are weak intermolecular forces that occur between atoms of compounds and molecules. • There are three different types: • 1. Dispersion forces. • 2. Dipole interactions. • 3. Hydrogen bonds.

31. Van der Waals Interactions • Van der Waals forces are very weak individually, but in large number they are very strong. • The gecko example from the book and H-bonding that creates surface tension that allows water striders to walk on water.

32. 1. Dispersion Forces • Dispersion forces are the weakest: these forces generally increase as the number of electrons increases. • The halogens are an example. • Chlorine is a gas, bromine is a liquid, and iodine is a solid.

33. 2. Dipole Interactions • Dipole interactions are a little stronger and these result from the interactions of polar molecules. • SiO2 is a very polar molecule, they are attracted to other SiO2 molecules.

34. 3. Hydrogen Bonds • Hydrogen bonds are the strongest dipole interactions. Hydrogen bonds are seen in H-containing compounds that are bonded to very electronegative atoms. • H2O