1. The Nature of Molecules Our study of life begins with physics and chemistry – as life, itself, is a chemical machine

2. 1 st, some definitions MatterMatter = any substance having mass and which takes up space; all matter is composed of atoms AtomsAtoms = the simplest/smallest component of matter; composed of nucleus and electron orbital(s) Atomic number –# of protons = Atomic number Atomic mass –# of protons + neutrons = Atomic mass Naturally-occurring atoms on Earth = 90 Diagram of typical atomic structure: Atomic #/mass of: H, He, C, O, N, S, P, Ne

3. Fig. 2.2.a

4. Isotopes All atoms of an element contain the same number of protons, but not the same number of neutrons Atoms possessing different numbers of neutrons are isotopes –Ex: Carbon has 3 isotopes (99% have 6 neut’s) = 12 C there is also 13 C and 14 C ( 14 C is a radioactive isotope with a half-life of 5730 years) Isotopes are commonly used in research and in medicine

5. Fig. 2.3

6. Electrons Negatively charged particle(s) which orbit the nucleus Electrons may be lost or gained from one atom to another to form a charged atom or ion….e.g., Na + Cl (formation of cation/anion) # of electrons determines the behavior, hence chemical activity of an atom

7. Fig. 2.4

8. Electrons and energy levels There are discrete energy levels surrounding the nucleus of an atom; one level contains only 1 orbit of electrons, others contain 4 different orbits of electrons (each orbit is filled with 2 e-’s) The filling of orbitals and energy levels relates to the chemical behavior of atoms valenceThe number of electrons of an atom relates to its valence Valence relates to how one atom reacts with anotherValence relates to how one atom reacts with another

9. Fig. 2.7

10. Fig. 2.5 ***Inner energy shells (those closest to the nucleus) contain electrons with lower energy than the outer energy shells ***important concept as it will be discussed in the Light Dependent reaction of Photosynthesis

11. The elements of biology biomolecules CHONPSThe large biomolecules which comprise life are composed, primarily, of 6 elements: CHONPS (98.9%) = all having low atomic masses….check it out…… Examples of biomolecules: through covalent bondsThese elements contain valences that dictate how they react with other atoms of elements => through covalent bonds.

12. Chemical bonding Bonding occurs between interacting atoms in several ways; mainly through: Ionic bonding – loss/gain of electron from one atom to another = Ionic bonding (found in salts and other crystalline molecules) Or covalent bonding -sharing of electrons between atoms = covalent bonding (found in biomolecules)

13. Fig. 2.8.a Sodium (Na) losses an e- and Chlorine (Cl) gains an e-; hence charged atoms (ions) form and are attracted to one another Ionic bonding of NaCl (Sodium chloride)

14. Page 24 Covalent bonding of some common gases

15. Lastly, some definitions: moleculeA group of at least 2 atoms joined together by a chemical bond is called a molecule compoundA molecule that contains more than one element is called a compound