Download Topic 3.1: Chemical Elements and Water

Topic 3: The Chemistry of Life
SL and HL
Topic 3.1: Chemical Elements and Water
A. Basic Atomic Structure
Matter: anything that takes up space and has mass
Element: (atoms) a substance that cannot be broken down by ordinary means. The material
making up matter.
There are 92 naturally occurring elements, of these 25 are essential to life. 4 of these make up
96% of living matter ( Carbon, Hydrogen, Oxygen,and Nitrogen). The rest are called trace
elements. These are required in minute amounts( Zinc, Cobalt, Iron, Magnesium).
Molecules: Two or more different atoms combined.
Atomic Number: The total number of protons or electrons in an atom.
Atomic Mass: The total number of neutrons and protons in an atom.
Neutral atoms: electron # = proton #
Ions: # of electrons & protons differ
Cation: positive charge, electron(s) lost
Anion: negative charge, electron(s) gained
B. Chemical Bonding
Chemical Bonding: Atoms will interact with each other depending on their incomplete
valence shell.
There are several types of chemical bonds:
Covalent Bond: These bonds are the strongest of the bonds. They are formed by the sharing
of electrons. There are several subsets of covalent bonding:
a). Nonpolar: Here the electrons are shared equally, thus eliminating a positive and
negative end on the molecule.
1). double nonpolar: O2
2). triple nonpolar: N3
b). Polar covalent bond: Here the electrons are shared unequally, causing the
molecule to develop a positive end (where the electrons spend less time) and a
negative end (where the electrons spend more time). This has to do with the
electronegativity of the atom. The more electronegative the atom the more it will hold
on to the electrons. Oxygen is very electronegative (electronegative - the power of an
atom in a molecule to attract electrons to itself). Hydrogen is not.
Ionic Bond: These bonds are formed by the taking of electrons.
Anion: negative ion, Cl- and (OH-)
Cation: positive ion, Na+ and (NH4)+.
Molecules formed form ionic bonds are called ionic molecules
Molecules formed from covalent bonds are called covalent molecules
Non-Polar Covalent Bond
Polar Covalent Bond
C. The importance of some elements for life
Hydrogen, Oxygen, Carbon are the most common molecules in living cells
a. Carbon
-Can make four covalent bonds with other atoms
-This allows carbon to form complex
molecules with other elements.
-This molecule forms the basis of life.
Without carbon life would not exist!
-Forms 4 bonds with other molecules.
b. Oxygen
- Forms two covalent bonds with other
molecules.
-Oxygen allows organisms to get more energy
from food.
-It is also important in holding complex
molecules together.
c. Hydrogen
-Forms one covalent with other molecules.
-Most common element in the universe.
-Also helps to stabilize and hold molecules
together.
d. Nitrogen
-needed for proteins in plants and animals
-promotes growth of leaves and stems in plants
e. Sulfur
-needed for proteins in plants and animals
f. Phosphorus
-needed for nucleic acids in plants and animals
-also needed in plants for converting sugars to other molecules
g. Iron
-needed by haemoglobin (which carries oxygen in red blood cells)
-required for the synthesis of chlorophyll
h. Sodium and Potassium
-needed for transmitting nervous impulses in neurons and for cell respiration in
animals
-Potassium – needed for photosynthesis and cell respiration in plants
D. The importance of water for life
-Water is made up of hydrogen and oxygen
-Water has slightly negative and slightly positive areas
-This gives water it’s unique properties which make life
possible.
Properties of water
Thermal Properties
Cohesive Properties
Solvent Properties