1. Biology 102 Lecture 2: Atoms, molecules and life

2. Lecture outline [0. See notes for Lecture 1 for first part of today’s lecture] Characteristics of living organisms Characteristics of living organisms Basic atomic structure Basic atomic structure Electron shells Electron shells The Periodic Table of the elements The Periodic Table of the elements The formation of chemical bonds The formation of chemical bonds

3. 1. Characteristics of living organisms 1. Have complex, organized structure made mostly of organic molecules. 2. Respond to stimuli from their environment 3. Actively maintain their complex structure/ internal environment (homeostatis) 4. Acquire and use materials and energy/ convert to different forms 5. Grow 6. Reproduce themselves (involves DNA) 7. Have the capacity to evolve.

4. 2. Basic atomic structure Atoms: The smallest unit of an element which has characteristics of that element. Atoms: The smallest unit of an element which has characteristics of that element.  Example: One atom of gold is still gold Element: Cannot be broken down or converted to other substances by ordinary chemical means. Element: Cannot be broken down or converted to other substances by ordinary chemical means. Atoms are made of subatomic particles Atoms are made of subatomic particles  Number and configuration of these subatomic particles give each element its unique properties

5. Subatomic particles Protons: positively charged particles (+1) Protons: positively charged particles (+1)  Number of protons identifies an atom  “Atomic number” on periodic table  Example: Ir (iridium) = 77; has 77 protons  Located in the nucleus of the atom Neutrons: particles without charge Neutrons: particles without charge  The number of neutrons is variable  Different isotopes of the same element have different numbers of neutrons  Neutrons are also located in the nucleus  Mass number: Sum of protons and neutrons  Example: Carbon-12 isotope: 6 protons and 6 neutrons Electrons: negatively charged particles (-1) Electrons: negatively charged particles (-1)

6. 3. Electron shells Electrons: negatively- charged particles (-1) Electrons: negatively- charged particles (-1)  Orbit around nucleus  Shown as “ring” in 2-D, but orbits can be complex shapes  Several levels of “electron shells”  In a neutral atom, the number of electrons equals the number of protons Audesirk, Fig. 2-1 Audesirk, Fig. 2-2

7. 4. The Periodic Table The Periodic Table is organized according to the number of electron shells, and the number of electrons per shell

8. The first 18 elements Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

9. 5. The formation of chemical bonds CHEMICAL BONDS: Attractive forces that hold atoms together in molecules CHEMICAL BONDS: Attractive forces that hold atoms together in molecules The way atoms react with each other to form bonds depends upon the emptiness or fullness of their electron shells The way atoms react with each other to form bonds depends upon the emptiness or fullness of their electron shells The most stable state: a completely empty or completely full outer shell. The most stable state: a completely empty or completely full outer shell. Achieved in three ways: Achieved in three ways:  Lose electrons and thus empty outer shell  Gain electrons and thus fill outer shell  Share electrons

10. Types of chemical bonds Ionic bonds Ionic bonds  One atom completely loses an electron, while the other gains an electron  Ex: Na + Cl - (sodium chloride, or salt)  Note their locations on the Periodic Table! Once the exchange occurs, + attracts – and the ions (charged particles) stick together. Covalent bonds Covalent bonds  Two atoms share electrons  Ex: Carbon-carbon bonds (plus other examples)  Note where carbon is in the Periodic Table! Hydrogen bonds (Will introduce next time) Hydrogen bonds (Will introduce next time)

11. Can tell how atoms will react with each other based on their position in the table! Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings