Models of the Atom – Please Match 2- Thomson’s plum-pudding model (1897) 1- Rutherford’s model (1909) 4- Bohr’s model (1913) 3-Charge-cloud model (present)
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Models of the Atom – Please Match
2- Thomson’s plum-pudding model (1897)
1- Rutherford’s model (1909)
4- Bohr’s model (1913)
3-Charge-cloud model (present)
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125
5- Democritus’s model
(400 B.C.)
A
B
C
D
E
Early Greek Theory
All matter was composed of four elements: fire, air, water and earth.
Stone = mostly earth Rabbit = mostly water and fire Theory that certain substances are
made up of a combination of “elements”
Greek Model
Greek philosopher 460-371 b.c. Idea of ‘atomos’
Atomos = ‘indivisible’ ‘Atom’ is derived
No experiments to support idea
Democritus’s model of atom
No protons, electrons, or neutrons
Solid and INDESTRUCTABLE
Democritus“To understand the very large,
we must understand the very small.”
Early Ideas on Elements
Robert Boyle stated... A substance was an element unless
it could be broken down to two or more simpler substances.
Air therefore could not be an element because it could be broken down in to many pure substances.
Subatomic particles
Electron
Proton
Neutron
Name Symbol ChargeRelative mass
Actual mass (g)
e-
p+
no
-1
+1
0
1/1840
1
1
9.11 x 10-28
1.67 x 10-24
1.67 x 10-24
Structure of the Atom
There are two regions1. The Nucleus
With protons and neutrons Positive charge Almost all the mass
2. Electron Cloud Almost all the volume Where electrons are found
Single Atom
Water Molecule
The Sad State of Chemistry Humor
Two atoms are walking down the street.One atom says to the other, “Hey! I think I lost an electron!”The other says, “Are you sure??”“Yes, I’m positive!”
A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”
Size of an atom
Atoms are incredibly tiny.Measured in picometers (10-12 meters)
Hydrogen atom, 32 pm radius
Nucleus tiny compared to atomRadius of the nucleus near 10-15 m.Density near 1014 g/cm3
IF the atom was the size of a stadium, the nucleus would be the size of a marble.
California WEB
The Atomic Theory of Matter In 1803, Dalton proposed that elements
consist of individual particles called atoms.
His atomic theory of matter contains five hypotheses:
Elements are made of tiny particles called atoms. All atoms of a given element are identical.
The atoms of a given element are different from those of any other element
Atoms of one element can combine with atoms of another element to form compounds. A given compound always has the same relative number and types of atoms.
Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
Legos are Similar to Atoms
Lego's can be taken apart and built into many different things.
H
H
O
O
O
O
H
H
H
H
H
HH2
H2
O2
H2O
H2O
+
Atoms can be rearranged to form different substances (compounds).
Chemical Formulas
A compound contains atoms from two or more elements
Always contains the same relative numbers of atoms of each element
The types and number of atoms is expressed in a chemical formula
Carbon & Oxygen
1 Carbon atom 2 Oxygen
atoms
CO2
CO2
Practice
Try These: NH3 2H2O
Mg(NO2)2
NH3 : 1 Nitrogen, 3 Hydrogen atoms
2H2O : (2 water molecules)
4 H, 2 O atomsMg(NO2)2 : 1 Mg, 2 N, 4 O
atoms
More Practice
P4O10
12 H atoms
4 Au, 6 C, and 18 O atoms
Write the chemical formula for four phosphorus atoms and ten oxygen atoms
Write the number of hydrogen atoms in (NH4)2C8H4O2
Write the number and types of atoms in 2Au2(CO3)3
J.J. Thompson’s A Cathode Ray Tube
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58
Cathode RayExperiment
Thompson’s 1897 Experiment Using a cathode ray tube,
Thomson was able to deflect cathode rays with an electrical field.
The rays bent towards the positive pole, indicating that they are negatively charged.
Cathode Ray Experiment
Deflectionregion
Drift region
Displacement
+
-Anodes / collimators
Cathode
Volts
Thomson Model of the Atom
J.J. Thomson discovered the electron and knew that electrons could be emitted from matter (1897).
William Thomson proposed that atoms consist of small, negative electrons embedded in a massive, positive sphere.
The electrons were like raisins in a plum pudding, called the ‘plum pudding’ model of the atom.
Feeling overwhelmed?
Read Chapter 4!
"Teacher, may I be excused? My brain is full."
Chemistry
Ernest Rutherford (1871-1937)
Learned physics in J.J. Thomson’ lab.
Noticed that ‘alpha’ particles were sometime deflected by something in the air.
Gold-foil experimentAnimation by Raymond Chang – All rights reserved.
Rutherford’s Apparatus
beam of alpha particles
radioactive substance
gold foil
circular ZnS - coatedfluorescent screen
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
Rutherford Scattering In 1909 Rutherford fired (alpha) particles at
a very thin sample of gold foil. According to the Thomson model the
particles would only be slightly deflected. Rutherford discovered that they were
deflected by large angles and could even be reflected straight back to the source.
particlesource
Lead collimator Gold foil
What he expected…
Because he thought the mass was evenly distributed in the atom.
- -
-
-
-
What he got…richochetingalpha particles
The Predicted Result:
expected path
expected marks on screen
mark onscreen
likely alphaparticle path
Observed Result:
Density and the Atom
Since most of the particles went through, the atom was mostly empty.
Because the alpha rays were deflected so much, the positive pieces it was striking were heavy.
Small volume and big mass = big density
This small dense positively charged area is the nucleus
California WEB
Actual Results of Gold-Leaf Experiment
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57
n +
YES! WE'RE FINALLY DONE WITH HISTORY OF THE ATOM!!
Electrons are in constant motion around the nucleus, protons and neutrons jiggle within the nucleus, and quarks jiggle within the protons and neutrons. This picture is quite distorted. If we drew the atom to scale and made protons and neutrons a centimeter in diameter, then the electrons and quarks would be less than the diameter of a hair and the entire atom's diameter would be greater than the length of thirty football fields! 99.999999999999% of an atom's volume is just empty space!
Website “The Particle Adventure”
The Modern Atom Model
Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels
The Planetary Model
+
Nucleus
Electron
Orbit
The Bohr model of the atom, was built upon the incorrect idea that electrons orbit the nucleus like planets around the sun.
Bohr Model of Atom
The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation.
Increasing energyof orbits
n = 1
n = 2
n = 3
A photon is emittedwith energy E = hf
e-e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
An unsatisfactory model for the hydrogen atom
According to classical physics, lightshould be emitted as the electron circles the nucleus. A loss of energywould cause the electron to be drawncloser to the nucleus and eventuallyspiral into it.
Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 294
Cartoon courtesy of NearingZero.net
Subatomic Particles
Quarks component of
protons & neutrons
6 types (flavors)3 quarks = 1 proton or 1 neutron
He
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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