BIOLOGY II

CHAPTER 2 NOTES

 

 

I.                 MATTER consists of CHEMICAL ELEMENTS in PURE FORM and in COMBINATIONS called COMPOUNDS.

  

Chemistry is fundamental to an understanding of life, because living organisms are made of matter.

 

MATTER = Anything  that takes up space and has mass.

 

MASS = A measure of the amount of matter an object contains.

 

WEIGHT = is the measure of how strongly an object is pulled by earth’s gravity, and it varies with distance from the earth’s center.

 

 

II.             Life requires about 25 chemical elements

 

Element = A substance that cannot be broken down into other substances by chemical reactions.

* All matter is made of elements.

                             *92 naturally occuring.

*Desiginated by a symbol of one or two letters.

 

 

 

About 25 of the 92 naturally occuring elements are essential to life. Biologically important elements include:

 

C  = carbon     ¾   

O  = oxygen         ½ make up 96% of living

H  = hydrogen     ½  matter.

N  = nitrogen  ¾

 

Ca = calcium

P  = phosphorus

K  = potassium

S  = sulfur                       make up the

Na = sodium                        remaining 4% of

Cl = chlorine                      an organism’s

Mg = magnesuim                weight.

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Trace elements

 

Trace element – Element required by an organism in exetremely minute quantities.

́           Though in small quantity, are indispensable for life.

́           For example: B, Cr, Cu, F, I, Fe, Mn, Mo, Se, Si, Sn, V and Zn.

 

 

Elements can exist in combinations called compounds.

 

Compound = A pure substance composed of two or more elements combined in a fixed ratio.

́           For example: NaCl(sodium chloride).

́           Has unique emergent properties beyond those of its combined

elements.  (Na and Cl have very different properties from NaCl.)

 

 

III.         Atomic structure determines the behavior of an element.

 

Atom =  Smallest possible unit of matter that remains the physical

and chemical properties of its element.

́           Atoms of the same element share similar chemical 

          properties, made up of subatomic particles.

 

 

 

 

A.         Subatomic particles

The three most stable subatomic particles are:

 

1. Neurons[no charge (neutral)].

2. Protons[+1 electrostatic charge].

                  3. Electrons[-1 electrostatic charge].

 

Neutron                  Proton                     Electron

 

no charge              +1 charge                 -1 charge

 

found together  in a dense core              orbit around

called the nucleus(positively                 nucleus(held by 

charged because of protons)                  charge attraction)

 

1.009 dalton           1.007 dalton             1/2000 dalton    

 

masses of both are about the same         mass is so small, usually

(about 1 dalton)                                      not used to calculate

                                                               atomic mass.

 

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 The dalton =  is a unit used to express mass at the atomic level.

    One dalton(d) is equal to 1.67 X 10-24 g.

 

If an atom is electrically neutral, the number of protons equals the number of electrons, which yields an electrostatically balanced charge.

 

B.          Atomic Number and Atomic Weight

 

Atomic number = Number of protons in an atom of a particular element.

́           All atoms of an element have the same atomic number.

́             Written as a subscript to the left of the element’s symbol

́           In a neutral atom, # protons = # electrons.

 

Mass number =Number of protons and neutrons in an atom.

́           Written as a superscript to the left  of an element’s symbol

́           Is approximate mass of the whole atom, since the mass of a proton 

and the mass of a neuron are both about 1 dalton.

́           Can deduce the number of neutrons by subtracting atomic number 

from mass number.

́           Number of neutrons can vary in an element, but number of protons

is constant.

́           Is not the same as an element’s atomic weight, which is the     weighted mean of the masses of an element’s constituent isotopes.

 

 

C.         Isotopes

 

Isotopes = Atoms of an element that have the same atomic number but different mass number.

́           Have the same number of protons, but different number of neutrons.

́           Under natural conditions, elements occur as mixtures of iosotopes.

́           Different isotopes of the same element react chemically in the same

way.

́           Some isotopes are radioactive.

 

Radioactive =unstable isotope in which the nucleus spontaneously decays emitting sub-atomic particles and/or energy as radioactivity.

́           Loss of nuclear particles may transform one element to another

́           Has a fixed half life.

 

Half life = Time for 50% of radioactive atoms in a simple to decay.

Biological application of radioactive isotopes include:

1.Dating geological strata and fossils.

·        Radioactive decay is at a fixed rate.

·        By comparing the ratio of radioactive and stable isotopes in a fósil with the radio of isotopes in living organisms, one can estimate the age of a fósil.

·        The radio of C to C is frequently used to date fossils less than 50,000 years old.

2.Radioactive tracers

·        Chemicals lebelled with radioactive isotopes are used to trace the steps of a biochemical reaction or to determine the location of a particular substance within an organism.

·        Radioactive isotopes are useful as biochemical tracers because they chemically react like the stable isotopes and are easily detected at low concentrations.

·        Isotopes of P,N and H were used to determine DNA structure.

·        Used to diagnose disease (e.g PET scanner).

·        Because radioactivity can damage cell molecules, radioactive isotopes can also be hazardous.

 

                                       3.Treatment of cancer

*e.g. radioactive cobalt.

 

 

D.         Energy Levels

 

Electrons = Light negatively charged particles that orbit around nucleus.

·        Equal in mass and charge

·        Are the only stable subatomic particles directly involved in chemical reactions.

·        Have potential energy because of their position relative to the positively charged nucleus.

 

Energy = Ability to do work.

 

 

Potential Energy = Energy that matter stores because of its position or location.

·        There is a natural tendency for matter to move to the lowest state of potential energy.

·        Potential energy of electrons is not infinitely  divisible, but exists only in discrete amounts called quanta.

·        Different fixed potential energy states for electrons are called energy levels or electron shells.

·        Electrons with lowest potential energy are in energy levels closest to the nucleus.

·        Electrons with greater energy are in energy levels further from nucleus.

 

Electrons may move from one energy level to another. In the process, they gain or lose energy equal to the difference in potential energy between the old and new energy level.

 

 

F. Electron Orbitals

 

Orbital = Three dimensional space where an electron will most likely be found 90% of the time.

·        Viewed as a three dimensional probability cloud- a statistical concept.

·        No more than two electrons can occupy same orbital.

 

First energy level:

·        Has one spherical s orbital(1s orbital).

·        Holds a maximum of two electrons.

 

Second Energy Level:

·        Holds a maximum of 8 electrons.

·        One spherical s orbital(2s orbital).

·        3 dumbbell-shaped p orbitals each oriented at right angles to the other two(2px, 2py, 2pz orbitals).

 

Higher energy levels:

·        Contain s and p orbitals.

·        Contain additional orbitals with more complex shapes.