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

Element Matter made up of only one type of

atom. 92 natural elements. Each element has a symbol.

Compound Compound - Elements combined

in fixed ratios. A compound has characteristics

beyond those of its combined elements.

Question? What elements are necessary for life? Life requires about 25 chemical

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 Model

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.

Atomic Mass The number of protons and neutrons in

the nucleus. The atomic mass can change.

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.

Electron Orbitals

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)

Electrons of the first elements

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.

Chemical Bond Types Nonpolar Covalent Polar Covalent Ionic Hydrogen van der Waals forces

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

Ionic

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

Hydrogen Bonds

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

Chemical Equations A way to represent what is happening in

a chemical reaction

Ex: 2 H2 + O2 2 H2O

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.