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

2. Concept 2.1
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. Concept 2.1
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

4. Concept 2.1

5. Concept 2.2
_________: 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. Concept 2.2
___________________: # of protons _______________: sum of protons + neutrons __________________: different atomic forms of an element. -ex. Carbon-12 (99%), Carbon-13 (1%), Carbon-14 (<1%)

7. Concept 2.2
C-12 and C-13 are stable. C-14 is unstable, and radioactive. It will decay giving off particles and energy. Carbon-14 will decay into Nitrogen

8. Concept 2.2
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. Concept 2.2 (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. Concept 2.2
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. Concept 2.2 1H 2He 3Li 4Be 5B 6C 7N 8O 9F 10Ne 11Na 12Mg 13Al 14Si 15P
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. Concept 2.3
Atoms will bond with others to gain stability ________________: sharing of a pair of valence e- by two atoms -ex. Hydrogen atoms will share their electrons. They become H-H

13. Concept 2.3

14. Concept 2.3
__________________: 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. Concept 2.3
 – + H O
H2O

16. Atoms and Molecules
_____________: when two atoms are so unequal in their attraction for electrons that one atom will strip the electrons from its partner
_________: a charged atom; cation has a positive charge, anion has a negative charge (ca+ion; a negative ion)
Compounds formed by ionic bonds are salts

17. Concept 2.3 Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom
Sodium ion
(a cation)
Chloride ion
(an anion)
Sodium chloride (NaCl)

18. Atoms and Molecules
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. Concept 2.3
  +
Water (H2O)
Ammonia (NH3)
Hydrogen bond

20. Atoms and Molecules
________________: making and breaking of chemical bonds. - starting material is reactants - ending material is products __________________: point at which reactions offset one another.

21. Atoms and Molecules