Download Atomic Structure I. History A. prehistory The four elements B

Atomic Structure
I. History
A. prehistory
The four elements
B. Aristotle v. Democritus (@370BC)
1. Continuous v Discontinous "atom" theories of matter
C. Dalton (1803)
1. The "atom"
2. Law of Definite Proportions
3. Law of Multiple Proportions
D. Thompson (1897)
1.Cathode ray tube / discovered electron
2. Plum Pudding model
E. Millikan
1. Oil drop experiment (mass of an e-)
F. Rutherford (1909)
1. Gold foil experiment
2. Three conclusions
G. Bohr
1. Model explained light emission
a. PEL's, quantum #'s
b. Bright line spectrum
i. ground state
ii. excited state
iii. quanta
2. EMR spectrum and discussion
a. energy, wavelength, frequency
b. Calculations
i. c= frequency x wavelength
ii. E=hv
c. Balmer, Lyman, Paschen Series
3. Absorption Spectrum v. Emission spectrum
4. IR, UV-Vis Spectroscopy
H. Faraday - discovered the charge of 1 mole electrons
I. Schrodinger (Wave/Quantum-Mechanical model)
orbital=region of greatest probability
II. Concepts
A. Subatomic Particles
1. PEN chart
2. Role of each
B. Isotopes
1. Atomic Masses
2. Average atomic mass
3. Gram Formula Mass
C. Ions
1. cations
2. anions
Atomic Structure
I.
History timeline
A.
Prehistory (Earth, Water, Wind, Fire)
B.
Continuous v. Discontinuous Theory of Matter
1.
Aristoltle v. Democritus
A: All matter is continuous and exists in a state of flux, changing from one form to
another
CONCRETE WALL - no beginning or end
D: An ingenious escape was proposed in the fifth century B.C. by Democritus. He
hypothesized that all matter (plus space and time) is composed of tiny indestructible
units, called atoms. This idea seems motivated by the question of how finely one can
go on cutting up matter. While Democritus performed no experiments and had only
the flimsiest evidence for postulating the existence of atoms, his theory was kept alive
by the Roman poet Lucretius which survived the Dark Ages to be discovered in 1417.
The atoms in Democritus theory themselves remain unchanged, but move about
in space to combine in various ways to form all macroscopic objects. Early
atomic theory stated that the characteristics of an object are determined by the
shape of its atoms. So, for example, sweet things are made of smooth atoms,
bitter things are made of sharp atoms.
BRICK WALL - small
building blocks
C.
John Dalton (1803) English scientist and schoolteacher
1.
History:
It was John Dalton, in the early 1800's, who determined that each chemical element is
composed of a unique type of atom, and that the atoms differed by their masses. He
devised a system of chemical symbols and, having ascertained the relative weights of
atoms, arranged them into a table. In addition, he formulated the theory that a
chemical combination of different elements occurs in simple numerical ratios by
weight, which led to the development of the laws of definite and multiple proportions.
He then determined that compounds are made of molecules, and that molecules are
composed of atoms in definite proportions. Thus, atoms determine the composition of
matter, and compounds can be broken down into their individual elements.
2.
Law of Definite proportions:
Elements combine in specific mass ratios to make up matter
H(g) + O(g)
3.
ex. H2O + electricity -->
2:16 or 1:8 ratio
Law of Multiple Proportions:
Some elements combine in more than one mass ratio, but it is always a whole number
multiple:
ex. H2O --> H:O 1:8
H2O2 --> H:O 2:32 1:16
Oxygen ratio is 2
4.
Daltons Atomic Theory
a.
Matter is composed of extremely small particles called atoms
b.
Atoms of a given element are identical
c.
Atoms can not be subdivided, created or destroyed
d.
Atoms of elements can be combined in certain ratios to form compounds
e.
Chemical reactions result from the rearrangement, combination or separation of
atoms
D.
JJ Thompson (1897)
1.
Used Crooke's Ray Tube to discover the electron.
a.
b.
The simplest version of a cathode ray tube consists of a gas-filled glass tube in
which two metal plates, one negatively charged (the cathode) and the other
positively charged (the anode), have been placed. When a very large voltage is
placed across the electrodes, the neutral gas inside the tube will ionize into a
conducting plasma, and a current will flow as electrons travel from the cathode to
the other side.
The cathode ray tube was used in the experiments of Röntgen and
J. J. Thomson that led to the discoveries of X-rays and the electron,
respectively. Cathode ray tubes remain familiar objects today as a result of the
popularity of the neon sign.
c.
E.
Proposed the Plum Pudding Model
Robert Millikan
Discovered the charge of an electron through his oil-drop experiment. (click on <-- to read about
the experiment)
F.
Ernest B. Rutherford (1909)
1.
Gold-Foil Experiment
Rutherford, and his assistants Hans Geiger and Ernie Marsden, bombarded a thin sheet of
gold foil with positively charged alpha particles to test Thompson's atomic theory. A ZnS
fluorescent screen was used to detect the alpha particles.
a.
b.
c.
Observations:
(1)
Most particles went straight through the golf foil undeflected
(2)
Many particles were deflected a high angles
(3)
A few were deflected back at angles up to 180o
Conclusions:
(1)
atoms are composed of primarily empty space
(2)
there is a small, dense and positively charged nucleus
(3)
electron's are located outside the nucleus (somewhere)
Theory Limitations:
Though Rutherford's model of the atom made great strides it did not explain two
common occurrances
1) when metals are heated why do they glow various colors? red, orange, yellow, white
2) when various salts are put into a flame why do they give off unique colors?
G. Neils Bohr (Danish Physicist, student of Rutherford) 1913
To solve the above dilemmas Bohr suggested a new twist to the model of the atom. Bohr
concluded:
1.
Conclusions:
a.
Electrons are not arranged haphazardly around the nucleus, but are instead found
in specific energy levels he called
Quanta = Principle Energy Levels = Periods.
b.
The energy associated with PEL's increases as you proceed away from the nucleus.
c.
Electrons absorb energy (any kind: heat, light, electrical, chemical) to jump to a
higher energy level then release that energy in the form of light (electromagnetic
radiation) when they jump back down.
This is sometimes referred to as the Planetary Model of the atom.
2.
Electromagnetic Radiation:
a.
c = freq x wavelength
c = speed of light (3.0x108m/s)
f = frequency (Hertz, #waves/second)
lambda = wavelength (meters)
ex: What is the frequency of an orange spectral line (wavlength=600nm)?
Solution:
f= c/w.l.
f= (3.0x108m/s)/(6x10-7m)
f= 5.0x1014 Hz
b.
Energy = h x freq
h = Plank's constant = 6.626x10-34 J*s
cool website animation
ex. 1) What is the energy needed to create a spectral line with a wavelength of
848nm?
2) What is the energy needed to create a spectral line with a frequency of
1.3x1013Hz?
Solutions:
1) E = h * f
2) E = h * f
c.
and
c = freq x wavelength
Lyman, Balmer and Paschen series
QuickTime™ and a
decompressor
are needed to see this picture.
d.
Photoelectric effect:
so
3.
Bright Line Spectrum (website of elements spectrum)
H. Edwin Schrodinger: Wave-Mechanical model
nuclear forces
spark notes SAT on quantum mechanical model
An orbital - the region of greatest probability of finding an electron.
II. Concepts:
A.
B.
Subatomic particles
1.
p,e,n chart
2.
role of each
Isotopes (isotope maker website)
Definition: atoms of the same element having different atomic mass.
practice sheet
1.
Atomic Mass: the mass of 1 atom of a given element (amu)
2.
Average atomic mass: the average of all existing isotopes of an element
a.
calculations
(1)
avg. atomic mass = (mass1)(abundance1) + (mass2)(abundance2) + etc.
EXAMPLES:
(a)
Rubidium has two common isotopes, 85Rb and 87Rb. If the
abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%,
what is the average atomic mass of rubidium?
avg.a.m.= (85amu)(.722)+(87amu)(.278)=85.56 amu
(b)
Uranium has three common isotopes. If the abundance of
0.01%, the abundance of
235U
234U
is 0.71%, and the abundance of
99.28%, what is the average atomic mass of uranium?
is
238U
is
avg.a.m.= (234amu)(.0001)+(235amu)(.0071)+(238amu)(.9928)=
237.98 amu
3.
C.
Gram Formula Mass: the mass of 1 mole of atoms (g/mole)
Ions: charged atoms
1.
Cations (+ ions): atoms that LOSE electrons become positive
a.
Metals have an abundance of e-s and will lose them to achieve the electron
configuration of the nearest noble gas.
(1)
practice:
2.
Anions (- ions): atoms that GAIN electrons become negative
a.
practice:
3.
additional practice: