Chapter 2: The Chemical Context of Life
Matter Anything that has mass and
occupies space.
Smallest particle of an element (still retains elemental properties)
Atom
Compound Compound - Elements combined
in fixed ratios. A compound has characteristics
beyond those of its combined elements.
Macroelements Elements needed in large amounts or
quantities. Macro = Large Examples:
C HOPKNS CaFe Mg NaCl
Microelements
Elements needed in very small quantities. Also known as trace elements. Micro = small Examples:
Cu, Co, Zn, Mo, I, Mn
Atomic Subparticles Protons
+ charge, 1 Dalton mass Neutrons
no charge, 1 Dalton mass Electrons
- charge, essentially no mass
Atomic Number The number of protons in the nucleus. Each element has its own atomic
number. If you change the atomic number, you no
longer have the same element.
Isotopes
Atoms of the same element with different atomic mass
Caused by changes in the number of neutrons Used as “tracers”, used to kill cancer/bacteria
cells, used to determine age of fossils/geological formations
Types of Isotopes Radioactive
Where the nucleus decays spontaneously, giving off particles and energy.
HeavyHas a stable nucleus, but masses more
than the standard isotope for the element.
Energy The ability to do work THINK = ATP ATP is how living organisms have the
ability to do workThey USE ATP!!!
Potential Energy Is the energy that matter stores
simply because of its position or location
Electrons have potential energy because of their position relative to the nucleus
Electron Energy Levels
Energy levels around the nucleus of an atom
1st level can have 2 electrons and has the lowest potential energy
Other levels can hold more than 2 electrons and have higher energy levels
Electron Orbitals The three dimensional space
where an electron is found 90% of the time.
Different orbitals have different shapes.
Each orbital can hold only 2 electrons.
Chemical Behavior Of An Atom Is determined by its electron
configuration in the energy levels and orbitals
This determines who is can bond with (if anyone!)
Valence Electrons The electrons in the outermost energy
level Electrons available chemical bonds Atoms/Elements with same # of valence
electrons will react similarly and will have similar characteristics
Octet Rule The most stable condition is to have
an outer level of 8 electrons Exception - 1st level is stable with
only 2 electrons When stable - no chemical reactions
will take place Ex: Ne, He, (Noble gases)
Chemical Bonds Forces that join atoms together to form
molecules Usually caused by sharing or
transferring valence electrons
Bond Formation Depends On: The number of valence electrons
that must be gained, lost, or shared to reach the stable condition.
Electronegativity
The attractiveness of a specific kind of atom towards e- in another atomImportant in covalent bonds
Periodic Table trend: More electronegativity = stronger pull of e-He has highest ENIncreases as you go right and up the table
Nonpolar Covalent When electrons are shared equally
between atoms Very strong bond Important in many molecules found in
living things Ex: carbon to hydrogen, hydrogen to
hydrogen, oxygen to oxygen
Nonpolar Covalent Can be single, double, or triple between
two atoms Each nonpolar covalent bond involves a
pair of electrons
Polar Covalent When electrons are shared unequally
between atoms Results in “polar” molecules that have
charged areas Use δ symbol Ex: Water, H to O bonds
Ionic Bonds Formed when electrons are transferred
from one atom to another and ions are formed
Ex: NaCl Why? Two atoms electronegativity
are SO different that one atom gains e- completely
Two Types of Ions
Cations - have lost electrons (p+ > e-) giving them a positive charge.Ex: Sodium (Na+)
Anions - have gained electrons (p+ < e-) giving them a negative charge.Ex: Chlorine (Cl-)
Ionic Bonds Formed when cations (+) and anions (-)
attract each other Weak chemical bond
Why? Environment easily affects strength of this bond
Ex: Salt Solid in air/gas; Dissolves in liquid
Hydrogen Bonds When a hydrogen atom bonded to one
molecule is attracted to the slightly negative area (often N or O) of another molecule
Very weak individual bondCan be a “strong” force if there are many H
bonds.
Hydrogen bonds Remember:
H bonds occur BETWEEN MOLECULES (not b/t atoms within ONE molecule)
Ex: H bonds hold water molecules together
Van der Waals
Result of e- ability to move at high speeds Creates “spots” where there are “pools” of
+ and – charges Weak chemical “bond” Ex: gecko’s feet
Bond type
B/t atoms w/in ONE
molecule?
B/t more than one different
molecules?
Weak or Strong
Polar covalent
Yes No Strong
Nonpolar covalent
Yes No Strong
Ionic Yes No Weak
Hydrogen No Yes (attraction of H in one to -
atom in another)
Weak (unless LARGE #)
Van der Waals
No Yes Weak
Molecular Shape Each molecule on Earth has a
characteristic shapeDetermined by the positions of the
atom’s orbitals Shape related to function
Molecular Shape
Molecular shape is crucial because it determines how most molecules of life recognize and respond to one another.
Ex: Viruses (reproduction), bacteria
(reproduction), hormones/cell recognition
Chemical Reactions The making and breaking of chemical
bonds Reactions do not destroy matter, they
only rearrange it
Parts of the Equation
Reactants: - the starting materials Products: - the ending materials Note - all atoms of the reactants must
be accounted for in the products
2 H2 + O2 2 H2O
Chemical Equilibrium When the conversion of reactants to
products is balanced to the reverse reaction
Ex:
3 H2 + N2 2 NH3
Chemical equilibrium
Reversible rxn When concentrations of react and prod
STOPS changingDoesn’t necessarily mean concentrations
are equal!!!!! Rxn still continues
Summary We will now put elements together to
form molecules and build the next level in the hierarchy
Ch 3, 4, 5 (Properties of Water and Macromolecules)
Summary Continued Recognize macro-elements and micro-elements
and their roles in biological organisms. Differentiate between elements and compounds. Identify the basic principles of atomic structure and
how they determine the behavior of an element. Identify the main types of chemical bonds. Discuss the relative strength of different types of
chemical bonds. Recognize that chemical reactions make and
break chemical bonds.