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Chapter 2The Nature of Molecules


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The Nature of Molecules

Element substance that cannot bedegraded by ordinary means into asubstance having different properties.

Matter any substance that has mass andoccupies space.

All substances are composed of matter,and . . .

All matter is composed of atoms.


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The Structure of Atoms

Atom the smallest unit of matter that isunique to a particular element.

Atoms are composed of three subatomic

particles: Protons

Neutrons

Electrons


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Atoms contd

Atoms (typically) have one electron for eachproton.

Atoms are neutral if the number of protons

equals the number of electrons. Atomic number

Atomic mass


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Isotopes

Isotopes

Most atoms in nature exist as different

isotopes. Isotopes have the same atomic number,

but differ in mass.

All isotopes of an element interact withother atoms in the same way.

Carbon can have six (12C), seven (13C),or eight (14C) neutrons.


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Electrons

Electrons determine the chemical

behavior of atoms!


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Electrons

Electrons circle the nucleus of an atom inorbitals.

Orbitals volumes of space around thenucleus in which electrons are likely to be at

any instant. The shell closest to the nucleus has ____

orbital holding one or two electrons, maximumof ____.

The next shell can have ____ orbitals with____ electrons per orbital, holding a maximumof ____ electrons.


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Electron behavior influences atombonding

Atoms may acquire extra electrons . . . Share them . . .

Or donate them to another atom.

The outcome depends on the number andarrangement of electrons in an atom.

Atoms will react with other atoms only whenthere are vacancies in their outermost electron

shells. An atom is _____ when its outermost electron shell

is completely full.

An atom is _____ when its outermost electron shell

is only partially full.


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Ions

Ion an atom in which the number of protonsdoes not equal the number of electrons.

The atom becomes electrically charged.

Anion

Cation


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Oxidation-Reduction

Oxidation-reduction reactions electrontransfers between molecules.

Oxidation

Reduction


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The Periodic Table

Arranged in order by atomic number, theelements exhibit a predictable pattern.

The chemical behavior of each atom isgoverned by the number of electrons inthe outer shell.


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The Periodic Table

Non-reactive element (inert element) - Allorbitals are filled with the maximum number ofelectrons (helium, neon, argon).

Highly reactive elements elements with

seven electrons in their outermost orbitals.These elements tend to gain electrons(flourine, chlorine, bromine).

Also reactive are elements with one electron in

their outer orbital. They tend to lose electrons(sodium, potassium)

Octet rule rule of eight. Atoms tend to filltheir orbitals


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Chemical Bonds

Chemical bond a union between theelectron structures of an atom.

Chemical bonding occurs when two

particles can exchange or combine theirouter electrons in such a way that isenergetically favorable.

There are three types of chemical bonds: Ionic

Covalent

Hydrogen


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Ionic Bonds

Ionic bond


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Covalent Bonds

Covalent bond


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Polar Covalent Bond

Polar covalent bond


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Hydrogen Bonds

Hydrogen bond a bond in which an atominteracts weakly with a hydrogen atomalready taking part in a polar covalent

bond.

Hydrogen bonds are weak, but . . .

The additive effects of many weakinteractions can create strength.


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Properties of Water

Polarity

Stabilizes temperature

Cohesion Good solvent


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Polarity of Water

Water is a polar molecule because of theslightly negative charge at the oxygen endof the molecule, and a slightly positive

charge at the hydrogen end. Water molecules form hydrogen bonds

with each other.

Each hydrogen bond is relatively weak,but the cumulative effects of many of themcreate strength.


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Water Stabilizes Temperature

Water stabilizes temperature because itcan absorb considerable heat before itstemperature changes.

High specific heat Specific heat the amount of energy needed to

raise the temperature of one gram of a substance1oC.

High heat of vaporization Heat of vaporization the amount of heat required

to convert liquid water into vapor.


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Cohesion

Hydrogen bonds hold water moleculestogether.

Cohesion imparts surface tension at thesurface of lakes and ponds.

Cohesion allows plants to pull waterthrough the root system.


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Water is a Good Solvent

Water is capable of dissolving a widerange of substances.

Polar water molecules are attracted toionic compounds AND polar compounds(these compounds will dissolve in water).

Hydrophilic

Hydrophobic


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Acids, Bases, and Buffers

The pH scale a scale that indicates theconcentration of H+ in a solution. pH a measure of the hydrogen ion (H+)

concentration in a solution. The ______ the H+ concentration, the _____

the pH.

The scale extends from 0 (acidic) to 7

(neutral) to 14 (basic).


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Acids vs. Bases

Acid

Acidic solutions have pH values 7.


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Buffers

Buffer molecules combine with, or releasehydrogen ions to prevent drastic changes in pH.

Bicarbonate is one of the bodys major buffers

If the blood becomes too acidic, bicarbonate acceptshydrogen ions (H+) to form carbonic acid.HCO3

- + H+ H2CO3 If the blood becomes too basic, carbonic acid

releases hydrogen ions that combine with the excesshydroxide ions (OH-) forming water.H2CO3 + OH

- HCO3- + H2O


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Works Cited

Raven, Peter H., George B. Johnson, JonathanB. Losos, and Susan R. Singer. Biology. 7thed. New York: McGraw-Hill, 2005.

Starr, Cecie. Basic Concepts in Biology. 4th ed.

Brooks/Cole, 2000.

Diagrams and Photos: Raven, Peter H., George B. Johnson, Jonathan

B. Losos, and Susan R. Singer. Digital ContentManager 2.0. Biology. 7th ed. New York:McGraw-Hill, 2005.

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