1. The Chemical Context of Life
Chapter 2 Notes
The Chemical Context of Life

2. What is life made of?
Organisms are composed of __________: anything that takes up space or has mass
___________: a substance that cannot be broken down by chemical reactions
___________: substance consisting of two or more elements in a fixed ratio

3. Essential Elements for Life
Life requires about 25 elements
4 of those make up 96% of living matter
_______________________________________________________
Trace Elements are those that are required in only minute quantities
-ex. Iron, iodine

5. What are elements made of?
_________: smallest unit of matter that still retains the properties of an element
___________________: Protons (+), Neutrons (0), Electrons (-)
Protons and Neutrons have a mass of 1 dalton. Electrons have no mass

6. Atomic Number and Mass ___________________: # of protons
_______________: sum of protons + neutrons
__________________: different forms of an element (same # of protons, more neutrons)
-ex. Carbon-12 (99%), Carbon-13 (1%), Carbon-14 (<1%)

7. Isotopes C-12 and C-13 are stable. C-14 is unstable, and radioactive.
Radioactive Isotope: atom that will decay giving off particles and energy.
Carbon-14 will decay into Nitrogen
Radioisotopes are useful in science and medicine

8. Electrons and Energy
An atom’s electrons vary in the amount of energy they possess.
____________: the ability to do work.
_______________: energy that matter stores because of its position or location
Electrons have potential energy because of their position in relation to the nucleus.

9. Potential Energy (a) A ball bouncing down a flight
of stairs provides an analogy
for energy levels of electrons
Third shell (highest energy
level)
Second shell (higher
energy level)
Energy
absorbed
First shell (lowest energy
Atomic
nucleus
lost

10. Electron Shells
The different states of potential energy that electrons have in an atom are called energy levels or electron shells.
- the first shell has the lowest energy. The second shell has more than the first, etc.
__________________: those in the outermost shell

11. Electrons and Chemical Properties
Hydrogen 1H 2
Atomic number
Helium
2He He
Atomic mass
4.00
First
shell
Element symbol
Electron-
distribution
diagram
Lithium
3Li
Beryllium
4Be
Boron 5B
Carbon 6C
Nitrogen 7N
Oxygen 8O
Fluorine 9F
Neon
10Ne
Second
shell
Sodium
11Na
Magnesium
12Mg
Aluminum
13Al
Silicon
14Si
Phosphorus
15P
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Third
shell

12. Chemical Bonds
Atoms will bond with others to gain stability (fill valence shell)
________________: sharing of a pair of valence e- by two atoms
-ex. Hydrogen atoms will share their electrons. They become H-H

13. Covalent Bonds

14. Types of Covalent Bonds
__________________: the attraction of an atom for the electrons of a covalent bond
____________________: when the electrons are shared equally
____________: when one atom is bonded to a more electronegative atom

15. Polar Covalent Bonds
 – + H O
H2O

16. Unequal sharing of electrons
_________: a charged atom formed when two atoms are so unequal in their attraction for electrons that one atom will strip the electrons from its partner
cation has a positive charge, anion has a negative charge (ca+ion; a negative ion)
_________: bond formed when cations and anions attract each other
Compounds formed by ionic bonds are salts

17. Ionic Bonding Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom
Sodium ion
(a cation)
Chloride ion
(an anion)
Sodium chloride (NaCl)

18. Weak bonding
The advantage of weak bonding is that the contact can be brief
_______________: H is covalently bonded to an electronegative atom and attracted to another electronegative atom.
-ex. Water and ammonia

19. Hydrogen Bonding
  +
Water (H2O)
Ammonia (NH3)
Hydrogen bond

20. Weak bonding
Nonpolar molecules may have positively and negatively charged regions at any moment
_______________: enables nonpolar molecules to attract each other
May form between regions of the same protein help form shape

21. Molecular Shape
Molecules have characteristic shape and size Shape determines how molecules recognize and respond to one another Ex: opium and endorphins

22. Forming and Breaking Bonds
________________: making and breaking of chemical bonds.
- starting material is reactants
- ending material is products
All reactions are reversible

23. Forward and Reverse Reactions
__________________: point at which reactions offset one another.
No net effect on concentration
Affected by concentration of reactants or products

24. Atoms and Molecules