Chapter 2: The Molecules of Cells
Chapter 2: The Chemical Basis of Life
Chemical and Physical systems make up biological ones
matter –
element –
92 naturally occurring, 13 synthetic
25 of these elements are essential to life
98% of body weight of living organisms made up of 6 elements: carbon - C
hydrogen - H
nitrogen - N
oxygen - O
phosphorus - P
sulfur - S
sodium – Na
chlorine – Cl
Trace elements are
Structure of elements:
made up of atoms –
1. nucleus –
protons –
atomic number:
Ex: 1 is Hydrogen = 1 proton
8 is Oxygen = 8 protons
6 is Carbon = 6 protons
neutrons –
ATOMIC WEIGHT or MASS NUMBER =
Mass number – atomic number = # of neutrons
ex: hydrogen’s atomic weight = 1
has 1 proton and 0 neutrons
oxygen’s atomic weight = 16
has 8 protons and 8 neutrons
2. electron shells –
electrons –
Valence e-‘s – those available for
CHEMISTRY ! ! – interacting
with e-’s of other atoms
In biological systems, most stable e- configuration is 2-8-8 e-‘s in outermost e- shell.
It is the number of electrons in outer shells ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Isotopes –
ex: Carbon 12 – 6 protons and 6 neutrons
atomic no. = 6; mass no. = 12
Carbon 14 – 6 protons and 8 neutrons
atomic no. = 6; mass no. = 14
• used in radioactive carbon to follow the fate of C in cycles like photosynthesis.
- some isotopes are stable
- some isotopes are radioactive, give off energy and particles
although dangerous but have uses in medicine and research
Compound –
Molecule –
water = H2O
2 atoms of hydrogen; 1 atom of oxygen
glucose = C6H12O6
6 atoms carbon, 12 atoms hydrogen,
6 atoms oxygen
atoms bond together to fill their outermost shell
sometimes 2 atoms share electrons
sometimes atoms give/take electrons to/from other atoms
Ion –
• ex: H+, Na+, Ca+2, Cl-, O-2
There are 2 types of chemical bonds:
1. Ionic bonds –
occurs when atoms --------------------------------------------------------
these bonds easily come apart when the molecules are dissolved in water
• ex: salt – NaCl
2. Covalent bonds –
3 types of covalent bonds:
1. single bonds –
2. double bonds –
3. triple bonds –
Chemical Formulae to Memorize
H2 Hydrogen (gas)
O2 Oxygen (gas)
H2O Water
CO2 Carbon dioxide
NaCl Sodium chloride
C6H12O6 Glucose
H+ Hydrogen ion
OH- Hydroxide ion
Na+ Sodium ion
CL- Chloride ion
K+ Potassium ion
Chemical reactions rearranges matter to give you a product, it does not change it.
Water –
water is a polar molecule –
water forms H-bonds:
water is only substance on earth that exists in nature in 3 states: --------------------------------------------------------------------------------------------------
water is less dense -------------------------------------------------------------------------------------------------------------------------------------------------
Water molecules stick together because of H bonds this is called --------------------------------------------------. Therefore water beads up and has surface tension.
water is the ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------.
water temperature changes slowly – it has a high heat of vaporization, and a high specific heat, allows water to regulate tempr. on earth.
Acids & Bases
Acid –
have sharp, sour taste
ex: lemon juice, vinegar, tomato juice, coffee, soft drinks, and stomach acid (HCl)
Base –
have bitter taste and slippery feel
ex: milk of magnesia, calcium hydroxide (active ingredient in antacids), ammonia, lye (NaOH -- sodium hydroxide, main ingredient in Drano)
weaker acids and bases release fewer H+ and OH- ions than stronger acids and bases
The pH Scale (potential of Hydrogen)
pH scale from 0 to 14
measures concentration -----------------------------------------------------------------------------------------------------------------------------------
0 to 6.9 is ----------------------, 0 is the strongest acid
7.0 is --------------------, equal numbers of H+ and OH- ions present
7.1 to 14 is -------------------------------------------------- 14 is the strongest base
scale is logarithmic; change in one unit of pH
indicates a 10x change in H+ concentration
buffers –
salts –
ACID PRECIPITATION: rain, snow with pH< 5.6
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