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Transcript
Atomic Theory
Defining the Atom
• The Greek philosopher Democritus
(460 B.C. – 370 B.C.) was among the first
to suggest the existence of atoms (from
the Greek word “atomos”)
– He believed that atoms were indivisible
and indestructible
– His ideas did agree with later scientific
theory, but did not explain chemical
behavior, and was not based on the
scientific method – but just philosophy
Dalton’s Atomic Theory (experiment based!)
John Dalton
(1766 – 1844)
1) All elements are composed of
tiny indivisible particles called
atoms
2) Atoms of the same element are
identical. Atoms of any one
element are different from
those of any other element.
3) Atoms of different elements combine in
simple whole-number ratios to form
chemical compounds
4) In chemical reactions, atoms are combined,
separated, or rearranged – but never
changed into atoms of another element.
Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small
particles called atoms. All atoms of a given
element are identical, having the same size,
mass and chemical properties. The atoms of one
element are different from the atoms of all other
elements.
2. Compounds are composed of atoms of more
than one element. The relative number of atoms
of each element in a given compound is always
the same.
3. Chemical reactions only involve the rearrangement
of atoms. Atoms are not created or destroyed in
chemical reactions.
2.1
2
2.1
16 X
+
8Y
8 X2Y
2.1
Structure of the Nuclear Atom
Dalton Wasn’t Exactly Correct…..
• One change to Dalton’s atomic
theory is that atoms are divisible
into subatomic particles:
–Electrons, protons, and neutrons
are examples of these fundamental
particles
–There are many other types of
particles, but we will study these three
Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray
tube to deduce the presence of a negatively
charged particle: the electron
J.J. Thomson, measured mass/charge of e(1906 Nobel Prize in Physics)
2.2
Cathode Ray Tube
2.2
Thomson’s Atomic Model
J. J. Thomson
Thomson believed that the electrons
were like plums embedded in a
positively charged “pudding,” thus it
was called the “plum pudding” model.
Modern Cathode Ray Tubes
Television
Computer Monitor
Cathode ray tubes pass electricity
(electrons) through a gas that is
contained at a very low pressure.
Mass of the Electron
Mass of the
electron is
9.11 x 10-28 g
The oil drop apparatus
1916 – Robert Millikan determines the mass
of the electron: 1/1840 the mass of a
hydrogen atom; has one unit of negative
charge
Measured mass of e(1923 Nobel Prize in Physics)
e- charge = -1.60 x 10-19 C
Thomson’s charge/mass of e- = -1.76 x 108 C/g
e- mass = 9.10 x 10-28 g
2.2
(Uranium compound)
2.2
2.2
(1908 Nobel Prize in Chemistry)
 particle velocity ~ 1.4 x 107 m/s
(~5% speed of light)
1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron (-)
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
2.2
Rutherford’s Findings
Most of the particles passed right through
 A few particles were deflected
 VERY FEW were greatly deflected

“Like howitzer shells bouncing
off of tissue paper!”
Conclusions:
a) The nucleus is small
b) The nucleus is dense
c) The nucleus is positively
charged
Rutherford’s Model of
the Atom
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
“If the atom is the Houston Astrodome, then
the nucleus is a marble on the 50-yard line.”
2.2
The Rutherford Atomic Model
• Based on his experimental evidence:
– The atom is mostly empty space
– All the positive charge, and almost all the
mass is concentrated in a small area in the
center. He called this a “nucleus”
– The nucleus is composed of protons and
neutrons (they make the nucleus!)
– The electrons distributed around the nucleus,
and occupy most of the volume
– His model was called a “nuclear model”
Chadwick’s Experiment (1932)
H atoms - 1 p; He atoms - 2 p
mass He/mass H should = 2
measured mass He/mass H = 4
· In 1932 James proved the existence of neutral particles in an
atom
· James said that the neutrons were just about the same weight as
protons
· He discovered this by using alpha rays, which are charged, and
therefore repelled by considerable electrical forces present in the
nuclei of heavier atoms
· Chadwick led the way to the starting of penetrating and splitting
the nuclei of atoms.
· Also led the way to the fission of uranium 235, which eventually
created the atomic bomb
HOMEWORK
1. Describe JJ Thompson’s CRT (Cathode Ray Tube)
experiment & how it showed that atoms contain
particles he called “electrons.”
2. Describe JJ’s model of the atom.
3. Explain Rutherford’s scattering experiment and
what it helped to prove. Also, how did it disprove
Thompson’s model?
4. Describe Rutherford’s atomic model.
5. What led to Chadwick’s discovery.
mass p+ = mass no = 1840 x mass e-
Mass (amu)
0
1
1
2.2
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different
numbers of neutrons in their nuclei
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
(T)
U
2.3
2.3
Do You Understand Isotopes?
How many protons, neutrons, and electrons are
14
in 6 C ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are
11
in 6 C ?
6 protons, 5 (11 - 6) neutrons, 6 electrons
2.3
Ions: Atoms with different number of
protons (p+) and electrons (e-)
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
Do You Understand Ions?
How many protons and electrons are in
27 3+
13 Al
?
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in
78 234 Se
?
34 protons, 36 (34 + 2) electrons
2.5
Practice:
1) Write the elemental symbol if 10 p+, 11no, 10e21Ne
2) Write the elemental symbol if 20p+, 20no, 18e40Ca2+
2.5
Noble Gas
Halogen
Group
Alkali Metal
Alkaline Earth Metal
Period
2.4
Chemistry In Action
Natural abundance of elements in Earth’s crust
Natural abundance of elements in human body
2.4
A molecule is an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
2.5
An ion is an atom, or group of atoms, that has a net
positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
2.5
A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
2.5
2.5
2.6
A molecular formula shows the exact number of
atoms of each element in the smallest unit of a
substance
An empirical formula shows the simplest
whole-number ratio of the atoms in a substance
molecular
empirical
H2O
H2O
C6H12O6
CH2O
O3
O
N2H4
NH2
2.6
ionic compounds consist of a combination of cations
and an anions
• the formula is always the same as the empirical formula
• the sum of the charges on the cation(s) and anion(s) in each
formula unit must equal zero
The ionic compound NaCl
2.6
Formula of Ionic Compounds
2 x +3 = +6
3 x -2 = -6
Al2O3
Al3+
1 x +2 = +2
Ca2+
1 x +2 = +2
Na+
O22 x -1 = -2
CaBr2
Br1 x -2 = -2
Na2CO3
CO322.6
2.6
2.7
Polyatomic Ions
+1
-1
-2
-3
Ammonium
NH4
Nitrate
NO3
Carbonate
CO3
Phosphate
PO4
Acetate
C2H3O2
Sulfate
SO4
Phosphite
PO3
Cyanide
CN
Sulfite
SO3
Hydroxide
OH
Dichromate
Cr2O7
Permanganate
MnO4
Chlorate
ClO3
Bicarbonate
HCO3
Nitrite
NO2
WRITING FORMULAE (DIATOMIC
& POLYATOMIC)
Polyatomic
Mixed
1) Potassium Nitrate
2) Sodium Sulfate
3) Potassium Dichromate
4) Ammonium Phosphate
5) Copper I Carbonate
6) Iron (III) Cyanide
7) Silver Sulfite
8) Tin (II) Nitrite
9) Calcium Hydroxide
10) Boron Acetate
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Sodium Sulfide
Sodium Bicarbonate
Potassium Oxide
Potassium Permanganate
Magnesium Chloride
Calcium Chlorate
Iron (II) Phosphate
Copper Nitride
Ammonium Phosphide
Aluminum Acetate
Chemical Nomenclature
• Ionic Compounds
– often a metal + nonmetal
– anion (nonmetal), add “ide” to element name
BaCl2
barium chloride
K2O
potassium oxide
Mg(OH)2
magnesium hydroxide
KNO3
potassium nitrate
2.7
• Transition metal ionic compounds
– indicate charge on metal with Roman numerals
FeCl2
2 Cl- -2 so Fe is +2
iron(II) chloride
FeCl3
3 Cl- -3 so Fe is +3
iron(III) chloride
Cr2S3
3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide
2.7
Hydrates:
– ionic compounds with Water Molecules
contained in their crystalline structure.
CuCl2 · 2 H2O
Copper Chloride Dihydrate
Fe(SO3) · 5 H2O
Iron (II) Sulfate Pentahydrate
Cu(NO3)2 · 4 H2O
Copper Nitrate Tetrahydrate
2.7
Hydrates:
– USE PREFIXES TO DENOTE THE #
OF WATER MOLECULES
1 =
mono
6 =
hexa
2 =
di
7 =
hepta
3 =
tri
8 =
octa
4 =
tetra
9 =
nona
5 =
penta
10 = deca
• Molecular compounds
• nonmetals or nonmetals + metalloids
• common names
• H2O, NH3, CH4, C60
• element further left in periodic table
is 1st
• element closest to bottom of group is
1st
• if more than one compound can be
formed from the same elements, use
prefixes to indicate number of each
kind of atom
• last element ends in ide
2.7
Molecular Compounds
HI
hydrogen iodide
NF3
nitrogen trifluoride
SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
TOXIC!
Laughing Gas
2.7
2.7
An acid can be defined as a substance that yields
hydrogen ions (H+) when dissolved in water.
HCl
•Pure substance, hydrogen chloride
•Dissolved in water (H+ Cl-), hydrochloric acid
An oxoacid is an acid that contains hydrogen,
oxygen, and another element.
HNO3
nitric acid
H2CO3
carbonic acid
H2SO4
sulfuric acid
HNO3
2.7
2.7
2.7
2.7
A base can be defined as a substance that yields
hydroxide ions (OH-) when dissolved in water.
NaOH
sodium hydroxide
KOH
potassium hydroxide
Ba(OH)2
barium hydroxide
2.7
2.7