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Atomic Theory
“Atom” means uncuttable.
It isn’t.
--but it is the smallest particle of
an element
Early models of the atom
• Classical
model
• “Plum
pudding”
model
• Solar
system
model
You need to know these people
•
•
•
•
•
•
•
Democritus
Dalton
Rutherford
Millikan
Thomson
Chadwick?
Curie
You will need to know the
contributions of…
• Democritus—first used the
term “atom”
• Considered four “elements”: earth, air, fire
and water (it could translate as
“characteristics”)
• The physical shape of the “atom” gave
substances their physical properties.
• “Atoms” are not changed in mixtures
You will need to know the
contributions of…
• Dalton—modern atomic theory
• -all matter is made of atoms
• -atoms of one element are identical, atoms of
different elements are different
• -atoms form compounds in simple whole
number ratios
• -chemical reactions are rearrangements of
atoms, the atoms are not changed
• -compounds with different ratios of atoms
are different compounds
You will need to know the
contributions of…
• Dalton—modern atomic theory
The
law of
• -all matter is made of atoms
definite
• -atoms of one element are identical, atoms of
proportions
different elements are different
• -atoms form compounds in simple whole
number ratios
The law of
• -chemical reactions are rearrangements
of
multiple
atoms, the atoms are not changed proportions
• -compounds with different ratios of atoms
are different compounds
The mass of a proton=1 dalton
• It’s about the same mass as a neutron (an
electron is about 1/1800th of that mass)
• ~1.7 x 10-24g
It’s also called an atomic mass unit (1amu)
You will need to know the
contributions of…
• Rutherford-Gold foil experiment
-showed
atom is
mainly empty
space
-mass and
(+) charge in
the center
You will need to know the
contributions of…
• Thomson—
cathode
“rays”
• = stream of
electrons
• He calculated
the charge/mass
ratio of electron
You will need to know the
contributions of…
• Millikan—oil drop experiment
•determined
the charge
(& therefore
the mass) of
an electron
You will need to know the
contributions of…
• Curie—
• -described
radioactive
decay of
atoms
You will need to know the
contributions of…
• Chadwick—
• -discovered neutrons
Cloud chamber—
the straight track
shows that it has no
charge
19
39.0983
K
Potassium
Atomic Number =
number of protons
Name
19
39.0983
K
Potassium
Average atomic
mass, in amu/atom
Symbol
Atomic number and mass number
Atomic number
Atomic mass number
# electrons
Atomic number and mass number
Atomic number is the number of protons—
determines the element
Atomic mass number = #protons + #neutrons
# electrons = # protons, in an atom
Atomic number and mass number
Atomic number is the number of protons—
determines the element
Atomic mass number = #protons + #neutrons
# electrons = # protons, in an atom
An atom gains, loses, or shares electrons to
form chemical bonds
Protons, neutrons, electrons
Name
Proton
Neutron
Electron
Symbol Mass Charge Location
Protons, neutrons, electrons
Name
Symbol Mass Charge Location
(about)
Proton
p
1 amu
+1
in nucleus
0
in nucleus
(about)
Neutron
n
1 amu
(about)
Electron
e-
0 amu
-1
around
nucleus, in
electron cloud
Name
Symbol
Atomic Atomic # p
#n
Number Mass
(most
Number
likely)
Sulfur
K
20
17
#
e-
Name
Symbol Atomic Atomic # p # n # eNumber Mass
(most
Number
likely)
Sulfur
S
16
32
16 16 16
Potassium
Calcium
K
19
39
19 20 19
Ca
20
40
20 20 20
Chlorine
Cl
17
35
17 18 17
What is an isotope?
What is an isotope?
“the same”
“place”
Isotope (or nuclide) Notation
39
19
K
This is potassium-39
atomic number = 19
19 protons, making it potassium,
20 neutrons,  mass number of 39
Isotope (or nuclide) Notation
39
19
K
42
19
K
This is potassium-42
atomic number = 19
19 protons, making it potassium,
23 neutrons,  mass number of 42
What is an isotope?
Same
Different
What is an isotope?
Same
Element
Atomic number
# protons
# electrons
Ion charge
Chemical properties
(mostly)
Different
Mass
Mass number
# neutrons
Radioactivity
What is the atomic number and
mass number?
Proton
Neutron
Electron
(A)
23
28
21
(B)
7
7
10
(C)
52
71
54
(D)
38
49
36
What is the atomic number
and
These aren’t
mass number?atoms!
Proton
Neutron
Electron
(A)
23
28
21
(B)
7
7
10
(C)
52
71
54
(D)
38
49
36
Write the nuclide designation
Proton
Neutron
Electron
(A)
23
28
21
(B)
7
7
10
(C)
52
71
54
(D)
38
49
36
Write the nuclide designation
(A)
(B)
51
23
14
7
(C)
(D)
+2
V
-3
N
123
52
87
-2
Te
+2
Sr
38
\What is the mass number and
atomic number?
3
2
He
59
26
+2
Fe
80
Br
35
-
111
47
+
Ag
40
238
20
94
+2
Ca
Pu
How many p, n, e- in each?
3
2
He
59
26
+2
Fe
80
Br
35
-
111
47
+
Ag
40
238
20
94
+2
Ca
Pu
Average atomic mass
• --A weighted average of the naturally
occurring isotopes
Average atomic mass
• --A weighted average of the naturally
occurring isotopes
Ex: 99.63% N-14 (mass=14.003 amu/atom)
.37% N-15 (mass=15.000 amu/atom)
Average atomic mass
• --A weighted average of the naturally
occurring isotopes
Ex: 99.63% N-14 (mass=14.003 amu/atom)
.37% N-15 (mass=15.000 amu/atom)
Avg= (.9963x14.003) +(.0037x15.000)=
Average atomic mass
• --A weighted average of the naturally
occurring isotopes
Ex: 99.63% N-14 (mass=14.003 amu/atom)
.37% N-15 (mass=15.000 amu/atom)
Avg= (.9963x14.003) +(.0037x15.000)=
=13.951 + .056 = 14.007 amu / atom
Average atomic mass
• What is the average atomic mass of
carbon:
• 98.89% C-12 (12.000 amu/atom)
• 1.11% C-13 (13.003 amu/atom)
Average atomic mass
• What is the average atomic mass of
carbon:
• 98.89% C-12 (12.000 amu/atom)
• 1.11% C-13 (13.003 amu/atom)
12.011 amu/atom
How common is S-32?
• S-32 has a mass of 31.972 amu/atom
• S-34 has a mass of 33.967 amu/atom
• (less common nuclides are ignored)
• The average atomic mass of sulfur is
32.060 amu/atom
A) 5%
B) 35%
C) 65%
D) 95%
How common is Cl-37?
• Cl-35 has a mass of 34.969 amu/atom
• Cl-37 has a mass of 36.966 amu/atom
• The average atomic mass of chlorine is
35.453 amu/atom
A) 25%
B) 50%
C) 75%
D)100%
The Periodic Table of Elements
The Periodic Table of Elements
• Dmitry Mendeleev
(Дми́трий Ива́нович Менделе́ев)
• Noticed physical and chemical
properties repeated every seven
elements (by atomic mass)
• Predicted the discovery of gallium
and germanium
The Periodic Table of Elements
• Dmitry Mendeleev
(Дми́трий Ива́нович Менделе́ев)
• Noticed physical and chemical
properties repeated every seven
elements (by atomic mass)
• Predicted the discovery of gallium
and germanium
Periodic properties seen by Mendeleev:
He predicted the
properties of
unknown elements,
later discovered
Know these
features:
Period
Series
Group
Family
Alkali metals
Alkaline earth
metals
Transition
elements
Representative
elements
Halogens
Noble gasses
Lanthanide series
Actinide series
The Periodic Table of
Elements
A period
A series
A group or family
The alkali metals
The alkaline earth metals
Transition elements
Representative elements
The Halogens (salt-makers)
The Noble Gasses
The Periodic Table of Elements
Boron
Family
Carbon
Family
Nitrogen
Family
Oxygen
Family
The Periodic Table of Elements
Lanthanide
series
Actinide
series
The Periodic Table of Elements