Announcements:

Test question will come from my lecture notes and the same topics in the book.

This has been the 1882nd visit to this site since August 26, 1996.

A. Matter consists of chemical elements in pure form and in combinations called compounds.

Matter = Anything that takes up space and has mass.

92 elements in Nature, 25 essential to Life.

(see Table 2.1 in book)

4 elements make up 96% of living matter C, O, H, N

(see Fig. 2.3 - Corn N deficiency)

Remaining 4% is made up of: P, S, Ca, K, and a few others

There are also very important TRACE ELEMENTS = Elements needed in very small amounts, but which play very important functons (B, Cr, Co, Cu, F, I, etc.).

e.g.

Iron (Fe) needed by all forms of life for aspects of respiration
Hemoglobin contains Fe
Electron carriers in respiration often contan Fe

Iodine (I) needed only by Vertebrates for the proper function of the thyroid gland.
Iodine deficiency causes goiter = abnormal thyroid growth

(see Fig. 2.4 in Book).

Compound = A substance composed of 2 or more elements in a fixed ratio.

Compounds have unique properties beyond those of the individual elements.

e.g. NaCl (sodium chloride)

Atom = Smallest unit of matter that retains the properties of an element.

Atomic structure: 3 main types of subatomic particles
protons, neutrons and electrons

1) Proton, charge of +1, Mass of 1 dalton, (dalton = 1.7 x 10-24 grams) (454 grams in a pound)

In an uncharged (neutral) atom, Number of protons (= ATOMIC NUMBER) = number of electrons

2) Neutron, no charge, mass = 1 dalton

ATOMIC MASS = Protons + Neutrons

3) Electron, charge = -1, Mass is very small = 1/2000 daltons,

(See Figure 2.5)

ALL atoms of a given element have the same number of Protons, but not nec. the same number of neutrons

ISOTOPES = Atoms of an element with same atomic number but differesnt atomic mass.

For C = 12C, 13C, 14C

99% of Cs are 12C

ELECTRON ORBITALS = 3-D space in which electrons can be found most of the time.
1st shell holds 2 electrons = 1 orbital (2 elements in row 1 of periodic table)
2nd shell holds max of 8 electrons = 4 orbitals (8 elements in 2nd row '' ''' ''' '')

Outer shell = VALENCE SHELL = determines chemical interactions

NOBLE GASES have filled outer shells so don't interact with other elements
Orbitals are most stable when full (= 2 per orb.)

SEE PERIODIC TABLE IN BOOK

(= FIGURE 2.9, pg. 32)

Elements short of electrons can add them, lose some or share some = Basis for chemical bonds

MOLECULES = Two or more atoms held together by chemical bonds.

CHEMICAL BOND = Attractions that hold molecules together

3 main types: 1) ionic bonds,
2) covalent bonds,
3) weak bonds (weak but important in Biology, e.g. Hydrogen bonds)

(Figs. 2.10 and 2.11)

H2 as an example

Methane as an example (CH4) DRAW = natural gas

Electronegativity = attraction of an atom for electrons

EXAMPLE of NaCl

(see Figs. 2.12 and 2.13)

Cl is more electronegative than Na so it pulls an electron completely away from Na resulting in a - charge on Cl and a + charge on Na they are thus ionized.

We say that Na+ is a CATION (= has a + charge) and Cl- is an ANION (= has a - charge)

Ionic bonds result from the attraction of opposites (i.e. + for -) as a result of complete transfer of e- (or more than one in some cases).

3) WEAK BONDS (e.g. hyrdrogen bonds, Van der Waals and hydrophobic interactions)

- Make chemical signalling possible because they can be easily made and broken.

- Help stabilize the 3-D shape of large macromolecules (e.g. proteins and DNA).

i) HYDROGEN BOND = formed by the charge attraction between the partial positive charge of a H (in a molecule like water) and a electronegative atom in another molecule.

(see Fig. 2.14)

- Around 20 times weaker than a covalent bond.

When atoms form into molecules orbitals rearrange into the most stable configuration called hybrid orbitals.

Hybrid orbitals can be thought of as tear drops that are spread as far apart from each other as possible.

The structure of water:

(See FIG. 2.15)
showing polar covalent bond,
i.e. e- spend more time around the O than the Hs

Also the 3-D spacing of the four orbitals makes the molecule asymmetrical.

Tetrahedron

(See FIG. 2.15)

O and H thus form what we call POLAR COVALENT BONDS, that is, the e- spend more time around the O than the Hs --- O is more electronegative

Like Mickey Mouses ----- SHOW PARTIAL - and +

Hydrogen Bonds between water molecules
(see FIG. 3.1)
each water molecule can bond with 4 other water molecules,
H bonds are constantly breaking and reforming in water.