Download Essential Chemistry for Biology

Essential Chemistry for Biology
Matter: Elements and Compounds
Matter is anything that occupies space and has mass
Matter on Earth is found in three physical states
solid, liquid, and gas
Mass is a measure of the amount of material in an object
An element is a substance that cannot be broken down into other substances by chemical
reactions
All matter is composed of chemical elements
All biologists have to have a basic understanding of chemistry
There are 92 naturally-occurring elements
All living organisms are made of atoms of basic naturally-occurring elements
~25 are essential for life
Atoms
Each element consists of one kind of atom
The atom is the fundamental unit of matter
Atomic structure
All atoms are composed of three subatomic particles
Protons - positively charged particles
Neutons - neutral particles
Electrons - negatively charged particles
Protons and neutrons are found in the nucleus of the atom
Electrons orbit the nucleus
Number of protons = atomic number
This determines the chemical properties of the element
Number of protons + neutrons = mass number
Atoms are electrically neutral
Isotopes
All atoms of a particular element have the same atomic number
However, they can vary in the number of neutrons
Atoms of the same element with different numbers of neutrons are called isotopes
They have the same chemical properties but different physical properties
Many elements can combine to form compounds
This is due to the interactions of atoms of the elements
It all has to do with the electrons
The chemical reactivity of an atom is determined by its electron configuration
Atoms whose outer shells are not full tend to interact with other atoms
They readily participate in chemical reactions
They are reactive!
The electron configuration follows specific rules
2, 8, 8, 18
Chemical bonding and molecules
Chemical bonds hold atoms together
These form when atoms share or after they transfer electrons
Ionic bond
Covalent bond
Occurs when two atoms share electrons
Water molecules
H atoms exert a weak pull on the shared electrons and the O atom exerts a strong
pull
Therefore, the water molecule exhibits polarity; it is polar
Water
The properties of water are due to the properties of the water molecule
The major contributing factor is the polarity of the water molecule
Hydrogen Bonds
The polarity of water results in weak electrical attractions between neighboring water
molecules
These weak attractions are called hydrogen bonds
Cohesion
Responsible for surface tension
It also allows the transport of water from the roots to the leaves of tall trees
Water resists changes in temperature
Temperature is a measure of the average speed of molecules
Water is an excellent solvent for other charged or polar substances
When something is dissolved in water, we have an aqueous solution
Consider sugar or salt dissolved in water
The substance dissolved is the solute
But by the same token, water is not a good solvent for nonpolar molecules
Hydrophilic compounds interact well with water
Hydrophobic compounds do not
Chemical Reactions
Cells constantly rearrange molecules by
breaking existing chemical bonds and
forming new ones
Such changes in the chemical composition of matter are called chemical reactions
Chemical reactions include
reactants or starting materials
products or end materials
Chemical reactions
can rearrange matter
but cannot create or destroy matter
Acids, bases, pH
In aqueous solutions, some water molecules dissociate into ions (H+ and OH-)
Organisms need the correct balance of these H+ and OHAcids (more H+), bases (less H+)
pH scale
Even slight changes in pH can be harmful to organisms
Because of this many biological fluids contain buffers to maintain correct pH ranges
When CO2 dissolves in seawater, it reacts with the water to form an acid lowering
ocean pH and greatly affecting marine environments