Download The Evolution of the Atomic Model

The Evolution of the Atomic Model
1897:
discovered by J.J. Thomson
Facts Leading to Model:
• Atoms contained electrons.
• Atoms of elements are neutral.
1907:
1932:
Therefore, he proposed
that electrons were
surrounded by a cloud
of positive electricity.
discovered by J.J Thomson & E. Goldestein
discovered by J. Chadwick
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The Evolution of the Atomic Model:
The Rutherford Experiment
In 1909, Thomson’s Plum Pudding Model was still
widely accepted. Rutherford was studying alpha (α
α)
particles, which consist of 2 protons & 2 neutrons
These results do not agree
with the Thomson Plum
Pudding Model.
Rutherford’s Proposal
These results agree with the
Thomson Plum Pudding Model.
Ernest Rutherford
Hans Geiger
The Anatomy of an Atom
Conclusion from Rutherford Experiment:
Atoms are mostly empty space, where the majority of
the mass was located in a small dense positive region.
Symbol: e –
Charge: -1
Mass: 0.0005486 amu
Recalling what we know
about attraction and
repulsion, what about the
nucleus is bothersome?
Symbol: p +
Charge: +1
Mass: 1.007 amu
Symbol: n
Charge: 0
Mass: 1.008 amu
Overall Charge: positive
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Section 2.1
Atomic Shorthand Notation
Mass
Number
Charge
(0,+, or -)
atomic number: equivalent to the
# of protons in the nucleus. If the
atom is neutral, it is represents
the # of electrons surrounding the
nucleus.
mass number: sum of protons
and neutrons
Atomic
Number
127
53 I
charge: 0 ∴ neutral
mass number: 127
atomic number: 53
Determine the # of p+, n, and e- for…
Given this information, calculate the # of
protons, neutrons, and electrons.
23
11 Na
199
79 Au
# p+ = atomic number = 53
# n = mass number – atomic number = 74
Since this atom is neutral, # e- = # p+ = 53
Isotopes & Atomic Weight
same number of p+
different number of n
proton
neutron
12C
Isotope
13C
# Protons
14C
# Neutrons
12C
13C
14C
Explain why 14N and 14C are not isotopes of each other.
3
Atomic Mass: Non-weighted vs. Weighted
Notice that the atomic mass of carbon on the periodic table is
not equivalent (but close) to the mass of the 12C atom! This is
because the
on the periodic table are weighted
average masses of atoms in the naturally occurring element.
Carbon Isotopes
Mass amu
% Abundance in Nature
12C
12.000
98.892 %
13C
13.0035
1.108 %
14C
14.00317
1 × 10-10 %
6
C
12.011
Notice that the atomic mass
is close to the mass of the
most abundant isotope!
Given the atomic mass of Mg, predict which isotope is most abundant in nature.
12 amu + 13.0035 amu + 14. 00317 amu
39.00652 amu
=
= 13.002173 amu = 13.0022 amu
3
3
Since 12C is the most
abundant, it contributes
the most to the average!
0.98892(12 amu) + 0.01108 (13.0035 amu) + (1 × 10-8 )(14.00317 amu) = 12.011119 amu = 12.0111amu
Atomic Mass: Non-weighted vs. Weighted
Given the atomic mass of Mg, predict which isotope is most abundant in nature.
Magnesium
Isotopes
Mass
amu
24Mg
23.98
25Mg
24.99
26Mg
25.98
12
Mg
24.305
Given the atomic mass of Tl, predict which isotope is most abundant in nature.
Thallium
Isotopes
Mass
amu
203Tl
202.97
205Tl
204.97
81
Tl
204.4
4
The Bohr Model & Quantum Mechanics
NOVA scienceNOW | Amazing Atoms | PBS
http://www.youtube.com/watch?v=xqNSQ3OQMGI
656.3 nm
n = 3 to n = 2
486.1 nm
n = 4 to n = 2
434.0 nm
410.0 nm
Based on Balmer’s emission line studies of the hydrogen atom and
Planck’s work, Bohr proposed…
a planetary model in which e- could only occupy certain energy levels.
energy levels differed in a step like manner.
electrons can occupy different energy levels by absorbing or emitting
energy.
Niels Bohr
1885 - 1962
Electron Configuration
: description of the lowest available energy
orbitals occupied by an atom’s electrons.
: represented as numbers.
The higher the number the greater the
distance from the nucleus. Electrons
prefer to fill an energy level with the
lowest energy.
: represented as lower case
letters (s, p, d, f, g, h). Each orbital can
hold a maximum of 2 electrons. Electrons
prefer to fill an energy level with the
lowest energy.
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Writing Electron Configurations
Provide the ground state electron configurations for the elements below:
Neutral hydrogen
has one electron.
1
H
1.0079
6
C
Neutral carbon
has six electrons.
12.011
Writing Electron Configurations
Write the ground state electron
configurations for the element below:
15
P
30.9737
Determine whether the ground state electron
configuration for nitrogen is correct.
7
N
14.0067
6