The Harmony of the Worlds

 

            If we lived on a planet where nothing ever changed, there would be little to do. There would be nothing to figure out. There would be no impetus for science. And if we lived in an unpredictable world, where things changed in random or very complicated ways, we would not be able to figure things out. Again, there would be no such thing as science. But we live in an in-between universe, where things change, but according to patterns, rules, or, as we call them, laws of Nature. And so it becomes possible to figure things out.

                                                                        - Carl Sagan

 

What is life?

 

Order               Evolutionary adaptation Response to Environment

 

Regulation        Energy processing         Growth & development

 

Reproduction

 

 

Is it alive?

 

The oldest seed datable by carbon-14 that has been germinated into a viable plant was a date palm seed about 2000 years old, recovered from excavations at Herod the Great's palace on Masada in Israel. Water bears can enter a state of dehydration for over a decade and “return to life” when moisture levels increase. Human cancer cells are “immortal.”

 

TAXONOMY (see note online from Sept. 21)

 

Chemical Basis of Life

•         All matter is composed of atoms

•         Matter can be classified as

Pure substances: elements and compounds

Mixtures: homogenous (solutions: coffee) and heterogeneous (more than one visible phase: hot chocolate and marshmallows)

           

Elements and Life

•         Life requires about twenty-five elements

•         The four most abundant are Carbon, Oxygen, Hydrogen, and Nitrogen

•         Sulphur and Phosphorus are important in biological molecules

THINK   *SPONCH*

•         Sodium, calcium, and potassium are the most important metals

 

 

Don’t be confused!

A molecule consists of two or more non-metallic atoms.  Some elements always occur in Nature as molecules: oxygen, chlorine, hydrogen, etc. These are the diatomic elements. The atoms may be the same or different (as in water, H2O).

 

A compound consists of two or more elements.

      Water is a molecular compound. Table salt, or sodium chloride—NaCl, is an ionic compound.

 

Elements

•         Consist of one type of atom only

•         An atom is the smallest part of an element that still retains the properties of the element

•         Atoms are made from protons, neutrons, and electrons

•         Elements are identified by the number of protons in their atoms

 

   ¹²₆C

 

(Elements are represented by international symbols. The number at top left is the mass. The number at bottom left is the atomic number)

Atomic number = number of protons

Atomic mass = number of protons and neutrons

 

The number of electrons equals the number of protons in a (neutral) atom.

 

Can you identify this element?

 

4 electrons        4 protons          5 neutrons

 

Number of protons = atomic number                 Protons + neutrons= atomic mass

 

(The element is beryllium, symbol Be)

 

A Model of a Silicon Atom

Atomic number 14

 

The nucleus consists of 14 protons and 14, 15 or 16 neutrons

 

All the mass comes from the nucleus (protons + neutrons)

 

Atoms with the same number of protons but different number of neutrons are ISOTOPES. Some are radioactive, but all have the same chemical properties.

 

14 electrons orbit the nucleus in layered shells of energy.

 

The outside (valence electrons) dictate the chemical behaviour of the element.

(There are only 100 known elements—some are synthetic—and hundreds of thousands of compounds. Elements combine through chemical bonds to produce new substances with different properties.)

 

Chemical bonding

 

Atoms become stable when their valence shell is either full or empty of electrons.

•         Non-metals may share electrons with each other to fill their valence shell. These bonds are covalent.

•         Metals will donate electrons to non-metals. In the process, ions are formed. Ions of opposite charges (+ and – ) attract each other.

 

Covalent Bonds

 

Sometimes more than one pair of electrons is shared.

 

Covalent bonds are not always a 50/50 share of electrons.

 

In a molecule of water, the oxygen atom attracts the shared electrons more strongly. The oxygen becomes a bit more negatively charged. The hydrogens become a bit more positively charged. The covalent bond is polar.

 

(Remember that electrons will be attracted to the protons in each nucleus)

 

Ionic bond formation

 

Metallic elements will donate electrons to non-metallic elements. Each will form a stable ion. Losing and gaining electrons throws off the balance between positive charges (protons) in the nucleus and negative charges (orbiting electrons).

In common table salt, the sodium atom loses an electron and becomes the positively charged sodium ion (11 protons and 10 electrons). The chlorine atom gains an electron and becomes the negatively charged chloride (notice the change in spelling) ion.

 

Compounds, again

 

Molecular compounds are made of molecules

            H₂O, CO₂, C₆H₁₂O₆, NH₃, CH₄  (but not H₂—it’s an element!)

            each molecule has the same element composition and properties as the compound.

 

Ionic compounds are made of positive ions (cations ) and negative ions (anions ).

            NaCl, KBr, Na₂S, MgBr₂— also known as salts

 

Interactions between molecules

•         Weak interactions keep molecules together in liquid and solid form

•         Hydrogen bonds are the strongest of these interactions

 

-O-H ^{. . .} O=

=N-H ^{. . .}  O=C-

(also with Fluorine, a very strong attractor of electrons)

 

 (The solid lines mean that a pair of electrons is shared. The dotted line means there’s a temporary attraction between the slightly positive hydrogen and the slightly negative oxygen, or nitrogen, or fluorine)

 

Water and Life

 

•         Important characteristics and properties due to hydrogen bonding

Surface tension

Cohesion

Adhesion

Universal solvent

 

Water is less dense as a solid. (Remember a suitcase with crumpled clothes vs. folded clothes? Hydrogen bonds in ice are fixed and rigid and the molecules are less densely packed. In a liquid form, the H-bonds break and re-form often and can be more densely packed.) Ice floats!

 

Hydrophilic and hydrophobic

Nonpolar molecules (hydrocarbons) are hydrophobic ("water-fearing"). They do not dissolve in water.

Polar and ionic molecules are hydrophilic (water-loving).

Portions of large molecules may be hydrophobic and other portions of the same molecule may be hydrophilic.

Polar molecules may “dissociate” in water, separating into positive and negative ions.

 

(That ends the “chemistry review”)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                  

 

 

 

 

 

 

Name	Symbol	Charge	Mass (amu)	Location
proton	p+	+1	1	Nucleus
neutron	n0	0	1*	Nucleus
electron	e-	-1	negligible	outside nucleus

*more accurately 1.008