Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies The Nature of Molecules Chapter 2 Copyright © McGraw-Hill Companies Permission required for reproduction or display

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Outline Atoms  Basic Structure  Chemical Behavior - Ionic Bonds - Covalent Bonds - Hydrogen Bonds pH Scale

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Nature’s building materials All things (including cells) are made of atoms We must understand chemistry in order to understand living things  Life processes include chemical reactions

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Any substance that has mass and occupies space is known as matter.  Composed of atoms. - Orbiting cloud of electrons (-). - Dense nucleus formed of protons (+) and neutrons (neutral).  Number of protons determines chemical character because it dictates number of electrons available for chemical activity.

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Atoms Mass - Amount of a substance. Weight - Force gravity exerts on a object. Atomic number – Number of protons Atomic Mass - Equal to the sum of masses of protons and neutrons.  Measured in daltons. - Protons and neutrons both weigh approximately 1 dalton, while electrons weigh 1/1840 of a dalton.

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Atoms with the same atomic number have the same chemical properties.  Atoms of an element that possess a different number of neutrons are called isotopes. - Some are unstable, radioactive  As they give off radioactive energy, they decay  Half life – time for ½ of material to decay  Example: 14 C has a half life of 5600 years

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Atoms Electrons –  Number of electrons determines the chemical properties of an atom  Atoms with the same number of protons and electrons are electrically neutral.  Electrons are maintained in orbits by their attraction to the positively charged nucleus. - Ions - Atoms in which the number of electrons does not equal the number of protons.  Cation - Net positive charge.  Anion - Net negative charge.

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chemical Behavior of Atoms Orbital - Area around a nucleus where an electron is most likely to be found. Because electrons are attracted to the nucleus, it takes energy to maintain them in orbitals.  Contain potential energy due to relative position. - Example: grapefruit in hand vs. grapefruit on top of tall building - Example: During photosynthesis, sunlight excites electrons in chlorophyll molecules

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Chemical Behavior of Atoms Moving an electron to a higher orbital requires an input of energy, while moving an electron closer to the nucleus releases energy.  Oxidation - Loss of an electron.  Reduction - Gain of an electron.  In organisms, energy is stored in high energy electrons that are transferred from one atom to another in redox reactions

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Kinds of Atoms Mendeleev (19 th century) arranged the 92 naturally occurring elements.  Arranged according to atomic mass.  Discovered that the elements in the table had a pattern of chemical properties that repeats in groups of eight based on interactions of electrons in outer shell (Valence Electrons).  The arrangement is the Periodic Table

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Kinds of Atoms For most atoms, the outer energy level contains a maximum of eight electrons.  Octet Rule - Atoms tend to establish completely full outer energy levels. - Inert - Elements possessing a full complement of electrons in the outer shell. - Reactive - Atoms lacking a full complement of electrons in the outer shell.

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Ionic Bonds Ionic bonds form when atoms of opposite electrical charges attract each other.  Donation of an electron.

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Covalent Bonds Covalent bonds form when two atoms share one or more pairs of valence electrons.  Give rise to discrete molecules.

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Covalent Bonds Bond Strength  Strength of a bond depends on the number of shared electrons. - Single Bond - Double Bond - Triple Bond

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chemical Reactions Chemical Reactions occur because of the formation and breaking of chemical bonds.  Reactants - Original molecules.  Products - Resultant molecules. Chemical reactions influenced by:  Temperature  Concentration of Reactants and Products  Catalysts

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Review Atoms  Basic Structure  Chemical Behavior - Ionic Bonds - Covalent Bonds - Hydrogen Bonds Chemistry of Water Properties of Water pH Scale

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display