chem1 chapter 5 - atom
DESCRIPTION
intro to chemistryTRANSCRIPT
Atoms
Engr. Yvonne Ligaya F. Musico
TOPIC
Evolution of the Different Atomic TheoriesStructure of Atom and Properties of AtomThe Quantum NumbersThe Electron Configuration of Atoms
Evolution of Different Atomic Theories
The History of the Discovery of the Atom
The Greek Model of the AtomDalton’s Atomic TheoryThomson ModelRutherford ModelBohr ModelModern Atomic Theory
The Greek Model of the Atom
Beginning with Democritus, who lived during the late 5th and early 4th centuries BC,
Greek philosophers developed a theory of matter that was not based on experimental
evidence, but on their attempts to understand the universe in philosophical
terms.
The Greek Model of the Atom
According to this theory, all matter was composed of tiny, indivisible particles called atoms (from the Greek word atomos, meaning “indivisible”).
The Greek Model of the Atom
According to the ancient Greeks, atoms were all made of the same basic material,
but atoms of different elements had different sizes and shapes
The Greek Model of the Atom
The sizes, shapes, and arrangements of a material’s atoms determined the material’s
properties.
The Greek Model of the Atom
Other than the atoms, matter was empty space. Atoms and empty space were
believed to be the ultimate reality.
Dalton’s Atomic Theory
Late 1700’s - John Dalton-EnglandTeacher- summarized results of his
experiments and those of others.
Dalton’s Atomic TheoryCombined ideas of elements with that of
atoms.
Dalton’s Atomic Theory
All matter is made of tiny indivisible particles called atoms.
Atoms of the same element are identical, those of different atoms are different.
Dalton’s Atomic Theory
Atoms of different elements combine in whole number ratios to form compounds.
Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.
Just How Small an Atom
Think of cutting a piece of lead into smaller and smaller pieces
How far can it be cut?An atom is the smallest particle of an element
that retains the properties of that elementAtoms-very small
still observable with proper instruments
Thomson Model
J. J. Thomson - English physicist. 1897
Made a piece of equipment called a cathode ray tube.
It is a vacuum tube - all the air has been pumped out.
Thomson’s Experiment
Voltage source
+-
Vacuum tube
Metal Disks
Thomson’s Experiment
Voltage source
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Thomson’s Experiment
Voltage source
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Thomson’s Experiment
+-Voltage source
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Thomson’s Experiment
Voltage source
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Thomson’s Experiment
Passing an electric current makes a Passing an electric current makes a beam appear to move from the beam appear to move from the negative to the positive endnegative to the positive end
Voltage source
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Thomson’s Experiment
Passing an electric current makes a Passing an electric current makes a beam appear to move from the beam appear to move from the negative to the positive endnegative to the positive end
Voltage source
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Thomson’s Experiment
Passing an electric current makes a Passing an electric current makes a beam appear to move from the beam appear to move from the negative to the positive endnegative to the positive end
Voltage source
+-
Thomson’s Experiment
Voltage source
By adding an electric field
Thomson’s Experiment
Voltage source
By adding an electric fieldBy adding an electric field
+
-
Thomson’s Experiment
Voltage source
By adding an electric fieldBy adding an electric field
+
-
Thomson’s Experiment
Voltage source
+
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Thomson’s Experiment
Voltage source
By adding an electric fieldBy adding an electric field
+
-
Thomson’s Experiment
Voltage source
By adding an electric fieldBy adding an electric field
+
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Thomson’s Experiment
Voltage source
By adding an electric field he found By adding an electric field he found that the moving pieces were negativethat the moving pieces were negative
+
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Other Particles
Proton - positively charged pieces 1840 times heavier than the electron – by E. Goldstein
Neutron - no charge but the same mass as a proton – by J. Chadwick
Rutherford Model
Ernest Rutherford -English physicist. (1910)
Believed in the plum pudding model of the atom
Wanted to see how big they are.
Rutherford’s Experiment
Used radioactivity.Alpha particles - positively charged
pieces- helium atoms minus electronsShot them at gold foil which can be
made a few atoms thick.When an alpha particle hits a
fluorescent screen, it glows.Here’s what it looked like
Rutherford’s Experiment
Lead block
Uranium
Gold Foil
Fluorescent Screen
Rutherford’s Experiment
What he expected??
The alpha particles to pass through without changing direction very much.
Rutherford’s Experiment
Because……
…the positive charges were thought to be spread out evenly. Alone they
were not enough to stop the alpha particles.
Rutherford’s Experiment
What he expected……..
Rutherford’s Experiment
Because…
He thought the mass was evenly distributed in the atom
Rutherford’s Experiment
Rutherford’s Experiment
Since he thought the mass was evenly distributed in the atom
Rutherford’s Experiment
What he got
Rutherford’s Experiment
How he explained it!
+
Atom is mostly empty.Small dense, positive piece
at center.Alpha particles
are deflected by
it if they get close enough.
Rutherford’s Experiment
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Rutherford’s Experiment
Since most of the particles went through, it was mostly empty space.
Because the pieces turned so much, the positive pieces were heavy.
Small volume, big mass, big density.This small dense positive area is the
nucleus.
Bohr Model
Bohr Model
Line-Emission Spectrum
ground state
excited state
ENERGY IN PHOTON OUT
Bohr Model
e- exist only in orbits with specific amounts of energy called energy levels
Therefore…
e- can only gain or lose certain amounts of energy
only certain photons are produced
Bohr’s Model
1
23
456Energy of photon
depends on the difference in energy levels
Bohr’s calculated energies matched the IR, visible, and UV lines for the H atom
Other Elements
Each element has a unique bright-line emission spectrum.“Atomic Fingerprint”
HeliumBohr’s calculations only worked for
hydrogen!
Modern Atomic Theory
ATOM
NUCLEUS ELECTRON
(-) CHARGEPROTONS NEUTRONS
(+) CHARGE NEUTRAL
QUARKSLEPTONS BOSONS
Most of the Atom’s MassAtomic number equals the number of….
Equal in a neutral atom
Subatomic Particles
Quarkscomponent of
protons & neutrons
6 types
3 quarks = 1 proton or 1 neutron
He
Summary of the Model of the Evolution of Atom
Structure and Properties of Atoms
Structure of Atoms
Electrons Negatively chargeMoving around the nucleus
Nucleus Protons – positively chargeNeutrons – neutral
Properties of Subatomic Particles
Name Symbol Charge Relative
mass
Actual
mass (g)
Electron e- -1 1/1840 9.11 x 10-28
Proton p+ +1 1 1.67 x 10-24
Neutron n0 0 1 1.67 x 10-24
Counting the Pieces
Atomic Number number of protons in the nucleusnumber of protons determines kind of atom
(since all protons are alike!)the same as the number of electrons in the
neutral atom.Mass Number
the number of protons + neutrons.These account for most of mass
Number of Electrons
An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons
Atomic Symbols
Contain the symbol of the element, the mass number and the atomic number.
XNumberMass
NumberAtomic
Atomic Symbols
Show the mass number and atomic number
Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11
Atomic Number on the Periodic Table
11
Na
Atomic Number
Symbol
All atoms of an element have the same number of protons
11
Na
11 protons
Sodium
Subatomic Particles in Some Atoms
16 31 65 O P Zn
8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n8 e- 15 e- 30 e-
Learning Check
State the number of protons for atoms of each of the following:A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons
B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons
C. Barium1) 137 protons 2) 81 protons 3) 56 protons
Solution
State the number of protons for atoms of each of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium
3) 56 protons
Isotopes
Atoms with the same number of protons, but
different numbers of neutrons.
Atoms of the same element (same atomic number)
with different mass numbers
Isotopes of chlorine
35Cl 37Cl17 17
chlorine - 35 chlorine - 37
Isotopes
© Addison-Wesley Publishing Company, Inc.
Relative Atomic Mass
12C atom = 1.992 × 10-23 g
atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
1 p = 1.007276 amu1 n = 1.008665 amu1 e- = 0.0005486 amu
Average Atomic Mass
weighted average of all isotopeson the Periodic Tableround to 2 decimal places
100
(%)(mass(mass)(%) )
Avg.AtomicMass
Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70%
25Mg = 25.0 amu 10.13%
26Mg = 26.0 amu 11.17%
Atomic mass (average mass) Mg = 24.3 amu
Mg24.3
Learning Check
Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Solution
Avg.AtomicMass
100
(18)(0.20)(17)(0.04))(16)(99.76 16.00amu
Learning Check
Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Solution
Avg.AtomicMass
100
(37)(2)(35)(8)35.40 amu
Learning Check
Gallium is a metallic element found in
small lasers used in compact disc players.
In a sample of gallium, there is 60.2% of
gallium-69 (68.9 amu) atoms and 39.8% of
gallium-71 (70.9 amu) atoms. What is the
atomic mass of gallium?
Solution
Avg.AtomicMass
100
8)(70.9)(39.2)(68.9)(60.69.7 amu
Atomic Mass
Listed on the periodic table
Gives the mass of “average” atom of each element compared
to 12C
Average atom based on all the isotopes and their abundance %
Atomic mass is not a whole number
Atomic mass is the weighted average mass of all the atomic
masses of the isotopes of that atom.
Na22.99
Atomic Mass on Periodic Table
11
Na
22.99
Atomic Number
Symbol
Atomic Mass
Learning Check
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium __________
B. aluminum __________
C. lead __________
D. barium __________
E. iron __________
Solution
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium _40.1 amu _
B. aluminum _27.0 amu _
C. lead _207.2 amu_
D. barium _137.3 amu_
E. iron _55.8 amu__
Finding an Isotopic Mass
A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?
Finding an Isotopic Mass
Assign X and Y values:X = % 10B Y = % 11B
Determine Y in terms of XX + Y = 100Y = 100 - X
Solve for X:X (10.0) + (100 - X )(11.0) = 10.8
100 100
Multiply through by 10010.0 X + 1100 - 11.0X = 1080
Finding an Isotopic Mass
Collect X terms
10.0 X - 11.0 X = 1080 - 1100
- 1.0 X = -20
X = -20 = 20 % 10B
- 1.0
Y = 100 - X
% 11B = 100 - 20% = 80% 11B
Learning Check
Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass)
1) 30% 2) 70% 3) 100%
Solution
2) 70%
Solution
62.9X + 6490 = 64.9X = 6350-2.0 X = -140
X = 70%