Ch 2 The Chemical Context of Life

I. OverviewA. All living organisms are subject to the

laws of chemistry & physics.B. A basic knowledge of both helps us to

better understand how living things work.1. What class of levers do you find most often in the human body?2. Why use those?3. How do moth species recognize mates of the same species?4. Read the test case on the “Devil’s gardens” in the rain forest in Ch 2.

Section 2.1 The nature of MatterA. Matter- anything that has mass and

takes up space1. Matter consists of chemical elements in pure form or in combinations called compounds2. All organisms have mass & take up space, therefore all organisms are made of matter

B. Matter is made of elements.1. Elements are substances that can’t be broken down into other substances by chemical reactions

C. A compound is a substance consisting of two or more different elements chemically combined in a fixed ratio. 1. Compounds will have chemical and physical characteristics different from those of their elements.2. ex. Salt is made of Sodium (Na) and Chlorine (Cl). Sodium explodes in water, chlorine is a poison. Salt is a harmless, edible compound.

D. The smallest unit of an element is an atom.

E. The smallest unit of a compound is a molecule.

Making Salt

II. Essential Elements of LifeA. 25 of the 92 elements are

essential to life.B. Carbon, hydrogen, oxygen and

nitrogen make up 96% of all living matter.

(CHON) or (CHONS)

C. Calcium, potassium, phosphorous, and sulfur makes up most of the remaining 4%.

(CaPSK)

D. Trace elements make up about 0.05%.

What happens when essential elements are missing?

Insufficient nitrogen in plants

Iodine deficiency in people

III. An element’s properties depend on the structure of its atoms.

A. An atom is the smallest unit of matter that retains the properties of an element.

B. Atoms are made of subatomic particles which include:1. Neutrons: 0 charge, found in the nucleus2. Protons: + charge, found in the nucleus3. Electrons: - charge, found in the cloud

around the nucleusC. Atomic number- the number of

protons in an element’s nucleus- the number is unique for each element

D. All atoms of an element have the same number of protons, but may have different numbers of neutrons in the nucleus.

E. Isotopes- when two atoms of an element have different numbers of neutrons

F. Radioactive isotopes- may decay spontaneously giving off particles & energy. These isotopes are used for

1. dating fossils2. diagnosing medical problems3. tracing atoms through metabolic processes

Highlighted area represents cancerous throat tissue.

IV. Energy Levels of ElectronsA. Energy-an ability to do work or cause

changeB. Potential energy- energy due to the

position or structure of matter1. Electrons’ potential energy is due to their energy level or position in an electron shell.2. Electrons losing energy, fall to a lower shell.

C. The chemical behavior of an atom is due to the distribution of its electrons in the electron shells, especially the valence electrons

D. An atom’s bonding capacity is called its valence.

E. Valence electrons are those in the outermost or valence shell of the atom.

F. Elements with a full valence shell are chemically inert.

V. Electron Orbitals

A. An orbital is a three dimensional space where electrons are found 90% of the time.

B. Each electron shell has a specific number of orbitals

Section 2.3 The formation and function of molecules depend on chemical bonding between atoms A. Atoms with incomplete outer shells

(8 electrons) give, take, or share electrons

B. Such interactions form chemical bonds.

C. Chemical bonds- attractive forces holding atoms close together, making molecules

D. Molecules consist of two or more atoms held together by chemical bonds.

II. Covalent BondsA. Covalent bond- the sharing of a pair of

valence electrons by two atoms1. The shared electrons each count as part of each other’s valence shell

B. Types of covalent bonds1. Single covalent bond- made by the sharing of one pair of electrons2. Double covalent bond- made by the sharing of two pairs of electrons3. Triple covalent bond- made by the sharing of three pairs of electrons

C. Covalent bonds can form between atoms of the same or atoms of different elements

III. Showing chemical bonds

A. Structural formula- a notation used to represent atoms & bonding in a moleculeex. H H

B. Molecular formula- an abbreviated formula for a compoundex. H2

IV. PolarityA. Electronegativity- how strongly an atom

attracts electrons; it depends on the element’s position in the Periodic Table; the greater the electronegativity, the stronger the pull on the electrons

B. Nonpolar covalent bond- electrons are shared equally between the two atoms

C. Polar covalent bond- one atom is more electronegative than the other; the electrons are unequally shared

D. Polar compounds- compounds that have polar covalent bonds. Due to unequal electron sharing, one atom has a slight negative charge, the other has a slight positive charge

E. Water- a polar molecule

1. -Indicates a partially positive charge on the atom

2. -Indicates a partially negative charge on the atom

3. So, the oxygen atom is slightly negative (it has the electrons most of the time) and the hydrogen atoms are partially positive.

V. Ionic bondsA. When there is a large difference in

the electronegativity of the two atoms, one may take the valence electron(s) from the other.

B. After the transfer of electrons, the two atoms have charges

C. Ion- a charged atom or moleculeD. Cation- a positively charged ion (J)E. Anion- a negatively charged ion (L)F. Ionic bond- a chemical bond

formed by the attraction between an anion and a cation. (Breaks easily to form ions)

IONIC BONDS ILLUSTRATIONThe red electron on sodium is transferred to Chlorine. This leaves 8 electrons in the remaining outer electron shell for sodium and completes the valence shell for chlorine with the 8th electron, making an ionic bond.

VI. Weak bondsA. Chemical bonds vary in strength. Going

from strongest to weakest, the order iscovalentionichydrogenVanderwaals

B. Covalent bonds form most of a cells bonds.

C. Weak bonds are used to 1. reinforce the shapes of large molecules2. help molecules adhere to each other

D. Hydrogen bonds- form when the hydrogens of one polar molecule are attracted to strongly electronegative atoms of a nearby polar molecule.

E. In cells, nitrogen and oxygen are electronegative

Hydrogen bonds between polar molecules

D. Unequally shared electrons in a molecule or atom cause “hot spots” of positive or negative charge

E. Vanderwaals interactions- are attractions between molecules that are close together as a result of these “hot spots”.

F. This is what gives us the strong attracti ve forces between the ridges on a geko’s toe pads & a wall.

VII. Molecular shape & functionA. The function of a molecule depends on

its shape. Examples include DNA & proteins.

B. The shape of a molecule depends on the positions of the valence electron orbitals for each of the atoms in the molecule.

C. In covalent molecules, the s & p orbitals may affect each other (hybridize) to make specific shapes.

Molecular Shapes

D. Biological molecules recognize & react with each other based on the specific shape of the molecules.

E. Molecules with similar shapes can have similar biological effects(see picture to the left)

VIII. Section 2.4 Chemical ReactionsA. Chemical reactions- making &

breaking chemical bonds to make new molecules

B. Reactants- starting molecules of a reaction

C. Products- final molecules of a reaction

D. Some chemical reactions go to completion & all reactants are converted to products

E. Some reactions are reversible; the products of the forward reaction become the reactants of the reverse reaction.

F. Chemical equilibrium- is when the forward & reverse reactions occur at equal rates.

G. Some reactions are not reversible but may be paired with an opposite reaction. An example is photosynthesis & respiration.

H. Photosynthesis- sunlight powers the conversion of carbon dioxide and water into glucose and oxygen.

CO2 + H2O C6H12O6 + O2

I. Respiration- the breakdown of glucose using oxygen into carbon dioxide, water, and usable energy

C6H12O6 + O2 CO2 + H2O

Acknowledgements: This presentation is drawn almost entirely from the materials provided by Reese Campbell 8th ed. DVD materials & notes