The Chemical Context of Life

1. The Chemical Context of Life • Atomic structure • The periodic table • Chemical bonding • Important elements in living organisms

2. A. Atomic Structure • Matter • Anything that takes up space and has mass • Atom • The smallest stable particle of matter • Composed of protons, neutrons, and electrons

3. A. Atomic Structure • Protons • Positively charged • Atomic mass  1 atomic mass unit • Located in the nucleus of an atom • Neutrons • Electrically neutral • Atomic mass  1 atomic mass unit • Located in the nucleus of an atom

4. A. Atomic Structure • Electrons • Negatively charged • Atomic mass: very small, almost negligible • Located in electron shells (orbitals) around the nucleus • In a neutral atom, the number of electrons and protons is the same • Atoms can lose or gain electrons during chemical bonding

5. A. Atomic Structure • Element • A substance composed of only a single type of atom • Atomic number of an element • The number of protons in its atoms • The atomic number is the same for all atoms of an element • Mass number of an element • The number of protons plus the number of neutrons in its atoms • The atoms of an element may have a variable number of neutrons

6. A. Atomic Structure • Isotopes of an element • Different forms of an element with the same atomic number but with different mass numbers • The atoms of some isotopes are stable • Other isotopes are radioactive, having unstable atoms that spontaneously break apart (decay) to form other atoms • When radioactive atoms decay, energy is released

7. A. Atomic Structure • For example, carbon has three isotopes • Carbon-12, with 6 protons and 6 neutrons, is the most common form of carbon • Carbon-13, with 6 protons and 7 neutrons, is stable (non-radioactive) and rare • Carbon-14, with 6 protons and 8 neutrons, is unstable (radioactive) and rare

8. B. The Periodic Table • In the periodic table • Elements are listed in order of their atomic numbers • Elements are designated by standard one or two-letter abbreviations • Elements in the same vertical column often have very similar chemical bonding properties

9. C. Chemical Bonding • Chemical bonding occurs when two or more atoms combine • Atoms combine by exchanging or sharing electrons in their outermost electron shell • Chemical compound • Formed when the atoms of two or more different elements combine by chemical bonding • Properties of a compound are usually very different than those of its elements

10. C. Chemical Bonding • Ionic bonds • Formed when electrons are completely transferred from one atom to another • The atom that gains electrons becomes a negative ion (anion) • The atom that loses electrons becomes a positive ion (cation) • Example: Sodium chloride Na + Cl  Na+ Cl–

11. C. Chemical Bonding • Covalent bonds • Form when two atoms share one or more pairs of electrons • Molecule: consists of two or more atoms that are joined by covalent bonding • Covalent bonds are generally more stable than ionic bonds in aqueous (water) solution

12. C. Chemical Bonding • Other types of atomic & molecular interactions • Polar interactions • Attraction between partially charged (polar) molecules and other polar or charged molecules • Similar to ionic bonding • Hydrogen bonding • Interaction between a hydrogen atom and two strong electronegative groups • Hydrophobic interactions • Attraction between molecules that are insoluble in water

13. D. Important Elements • See table in the textbook • Major covalent constituents of biomolecules:C H N O P S