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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