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Ch. 4 - Atomic Structure
I. Subatomic Particles(p.113 - 114)
Subatomic Particle Properties
Particle Symbol Location Charge Relative Mass (amu)
Actual Mass (g)
electron
proton
neutron
e-
p+
n0
Electron cloud
nucleus
nucleus
–
+
0
1/1840
1
1
9.11 x 10-28
1.67 x 10-24
1.67 x 10-24
approx 0
Symbols
Elements are listed by their chemical symbols
Symbols are usually either one capital letter like C for Carbon, or one capital and one lowercase letter like Ne for Neon
Periodic Table
The periodic table gives much information we need to learn more about the atom of each element
Atomic Number
Atomic number = # of protons in an atomWhole number shown on periodic tablePeriodic table is arranged by atomic
number
Atomic Mass
The average atomic mass is the number at the bottom of this square
Found by averaging the natural abundances of its isotopes
Atom Math
Protons Electrons
Protons Neutrons
# n0 = Atomic mass – Atomic number
Subatomic Particles
POSIT IVECHARG E
PROT ONS
NEUT RALCHARG E
NEUT RONS
NUCLEUS
NEG AT IVE CHARG E
ELECT RONS
AT OM
Most of the atom’s mass.
NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
ATOM
#n0 = Atomic mass- Atomic #
equal in a neutral atom
Atomic Numberequals the # of...
Ch. 4.3 - Atomic Structure
II. How Atoms Differ (p. 114 - 121) Mass Number Isotopes Relative Atomic Mass Average Atomic Mass
A. Mass Number
mass # = protons + neutrons
always a whole number
NOT on the Periodic Table!
© Addison-Wesley Publishing Company, Inc.
B. Isotopes
Atoms of the same element with different numbers of neutrons
C126
Mass #
Atomic #
Isotope notation:
Isotope name: carbon-12
Element name Mass #
B. Isotopes
Chlorine-37
atomic #:
mass #:
# of protons:
# of electrons:
# of neutrons:
17
37
17
17
20
Cl3717
Isotope notation:
Natural Abundances of Isotopes
Most elements are found as mixtures of isotopes
Relative abundance of each isotope is the same in each source
Ion: an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative charge.
Cation: has a positive charge, due to the loss of electrons
Anion: has a negative charge, due to the gain of electrons
C. Relative Atomic Mass
12C atom = 1.992 × 10-23 g
1 p = 1.007276 amu
1 n = 1.008665 amu
1 e- = 0.0005486 amu
© Addison-Wesley Publishing Company, Inc.
atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
D. Average Atomic Mass
weighted average of all isotopeson the Periodic Table
100
(%)(mass(mass)(%) )
Avg.AtomicMass
Avg.AtomicMass
D. Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
100
(18)(0.20)(17)(0.04))(16)(99.76 16.00amu
Avg.AtomicMass
D. Average Atomic Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
100
(37)(20)(35)(80)35.40 amu
Atomic Theory
Development of our understanding
of the atom
Early ModelsBattle of Philosophers
Aristotle vs. Democritus-Matter is infinite - Matter is composed of
extremely small particles
-4 Basic ‘elements’ - Called these particles ‘atoms’
- Earth (From ‘atmos’ meaning invisible)
-Air
-Fire *Eventually after many years
-Water Democritus is proven right
Early Models Dalton’s model was the “Billiard Ball”
Published an Atomic Theory1. All matter is composed of atoms that are
indivisible (did not know about protons, electrons, or neturons)
2. Atoms of a given element have same size, mass and chemical properties and are different from those of another element (no longer true, b/c of isotopes)
3. Different atoms combine in whole number ratios to form compounds and are separated, combined and rearranged in chemical reactions
4. In chemical reactions atoms can combine or separate, but are neither created or destroyed
Law of Definite Proportions Law of Definite Proportions Each compound has a specific ratio of Each compound has a specific ratio of
elementselements It is a ratio by mass It is a ratio by mass Water is always 8 grams of oxygen for Water is always 8 grams of oxygen for
each gram of hydrogen each gram of hydrogen
Law of Multiple ProportionsLaw of Multiple Proportions if two elements form more than one if two elements form more than one
compound, the ratio of the second compound, the ratio of the second element that combines with 1 gram of element that combines with 1 gram of the first element in each is a simple the first element in each is a simple whole number.whole number.
What?What? Water is 8 grams of oxygen per gram of Water is 8 grams of oxygen per gram of
hydrogen.hydrogen. Hydrogen Peroxide is 16 grams of Hydrogen Peroxide is 16 grams of
oxygen per gram of hydrogen.oxygen per gram of hydrogen. 16 to 8 is a 2 to 1 ratio16 to 8 is a 2 to 1 ratio True because you have to add a whole True because you have to add a whole
atom, you can’t add a piece of an atom. atom, you can’t add a piece of an atom.
Parts of AtomsParts of Atoms J. J. Thomson - English physicist. 1897J. J. Thomson - English physicist. 1897 Made a piece of equipment called a Made a piece of equipment called a
cathode ray tube.cathode ray tube. It is a vacuum tube - all the air has been It is a vacuum tube - all the air has been
pumped out.pumped out.
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Vacuum tube
Metal Disks
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Passing an electric current makes a Passing an electric current makes a beam appear to move from the negative beam appear to move from the negative to the positive endto the positive end
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Passing an electric current makes a Passing an electric current makes a beam appear to move from the negative beam appear to move from the negative to the positive endto the positive end
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Passing an electric current makes a Passing an electric current makes a beam appear to move from the negative beam appear to move from the negative (cathode) to the positive end (anode)(cathode) to the positive end (anode)
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Passing an electric current makes a Passing an electric current makes a beam appear to move from the negative beam appear to move from the negative (cathode) to the positive end (anode)(cathode) to the positive end (anode)
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field By adding an electric field
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field By adding an electric field
+
-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field By adding an electric field
+
-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field By adding an electric field
+
-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field By adding an electric field
+
-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field By adding an electric field
+
-
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electric field he found By adding an electric field he found the ratio of electrical charge to mass (e/m) for an electron
The e/m ratio is (negative) 1.76 x 108coulombs per gram (or C/g in SI units).
+
-
Thomsom’s ModelThomsom’s Model Thomson always found the same Thomson always found the same
value for the value for the e/me/m ratio no matter ratio no matter what the tube materials or the gas what the tube materials or the gas inside.inside.
Reinforced the notion that the Reinforced the notion that the electrons are a fundamental electrons are a fundamental component of mattercomponent of matter..
‘ ‘Plum Pudding’ model: a thin Plum Pudding’ model: a thin positive fluid, which contains most positive fluid, which contains most of the mass, w/ negative electrons of the mass, w/ negative electrons embedded to balance the chargeembedded to balance the charge
Millikan used oil drop experiment Would spray a fine mist of oil droplets above a
pair of parallel plates. Some of the oil drops would pass through the hole in the top plate.
He then used X-rays to knock electrons off of the air molecules in the barrel and some of those electrons attached themselves to the oil drops. The oil drops, which were now negative, could now be affected by the electrical field. He then could now measure the charge of the oil drops.
Millikan found that all the values he obtained were whole-number multiples of -1.60 x 10-19 coulomb. This value must be the charge of an electron.
The electron’s charge was -1.60 x 10-19 coulombs Using two values and solving for m
- 1.60 x 10-19 coul = - 1.76 x 108 coul/g
m m = 9.11 x 10-28 grams (a negligible mass even in the smallest atom)
Confirmed the negative charge of an electron Determined mass of the electron
Rutherford’s experimentRutherford’s experiment Ernest Rutherford English physicist. (1910)Ernest Rutherford English physicist. (1910) Believed in the plum pudding model of the Believed in the plum pudding model of the
atom.atom. Wanted to see how big they are using Wanted to see how big they are using
radioactivityradioactivity Alpha particles - positively charged pieces Alpha particles - positively charged pieces
given off by uranium given off by uranium Shot them at gold foil which can be made a Shot them at gold foil which can be made a
few atoms thick few atoms thick
Lead block
Uranium
Gold Foil
Florescent Screen
He ExpectedHe Expected The alpha particles to pass through The alpha particles to pass through
without changing direction very muchwithout changing direction very much BecauseBecause The positive charges were spread out The positive charges were spread out
evenly. Alone they were not enough to evenly. Alone they were not enough to stop the alpha particlesstop the alpha particles
What he expected
Because, he thought the charge was evenly distributed in the atom
What he got
+
How he explained it
+ Atom is mostly emptyAtom is mostly empty Small dense,Small dense, positive piecepositive piece at at
center (nucleus) center (nucleus) Proposed planetary model… (not as refined as the Proposed planetary model… (not as refined as the
solar sytem model)solar sytem model) Refined the concept of the nucleus & concluded it was Refined the concept of the nucleus & concluded it was
composed of positively charged particles called protonscomposed of positively charged particles called protons James Chadwick: discovered a neutral James Chadwick: discovered a neutral atomic atomic particle particle
with a mass close to a proton. Thus was discovered the with a mass close to a proton. Thus was discovered the neutron. neutron.
Moving Forward… Neils Bohr said electrons move in orbits
Found in energy levels Explains bright-line spectrum Called “Solar System Model” where
Electrons move in orbits around the nucleus
What we believe nowHeisenberg/Schrodinger
Heisenber Uncertainty Principle: You can know either the eˉ position or velocity
but not both Schrodinger said the eˉ are located in orbitals,
(regions of probability) around the nucleus… not orbits
“Electron Cloud” model