Ariana Garcia-Minsal
Dalton's Atomic Theory - (1808)
His atomic theory could be summarized as:
1) Matter is composed of tiny and indivisible particles
called atoms.
2) All atoms of a particular element are identical in size
and in mass. Atoms of different elements are different in
size and in mass.
Dalton's Atomic Theory - (1808)
His atomic theory could be summarized as:
3) Atoms of different elements can physically mix
together or can chemically combine in simple wholenumber ratios to form compounds.
4) Chemical reactions occur when atoms are separated
from each other, joined, or rearranged in a different
combination. Atoms of one element, however, are never
changed into atoms of another element as a result of a
chemical reaction.
Discovery of the Electron
In the years between approximately 1860 and 1935 the internal
structure of the atom was elucidated: see video
In 1897, J.J. Thomson used a cathode ray tube
to deduce the presence of a negatively charged
particle.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
ATOMIC MODELS
J.J. Thomson: In 1904, J. J. Thomson proposed an atomic
model best known as the “raisin-pudding model”. He
described the atom as a uniformly positive sphere of
matter in which electrons were embedded somewhat like
raisins in a pudding.
The Nuclear Atom
See video
The Nuclear Atom
Rutherford’s major conclusions from the particle scattering experiment
1. The atom is mostly empty space.
2. It contains a very small, dense center called
the nucleus.
3. Nearly all of the atom’s mass is in the
nucleus.
4. The nuclear diameter is 1/10,000 to
1/100,000 times less than atom’s radius.
The Nuclear Atom
The atom is mostly empty space.
Two regions
Nucleus contains protons and neutrons.
Electron cloud- region where you might
find an electron.
NUCLEAR MODEL:
In 1911, Ernest Rutherford proposed the first
nuclear model. The atoms consisted of a very
tiny center, or nucleus, that contains all the
positively charged particles and nearly all the
mass of the atom. The electrons were
distributed throughout the extra nuclear part of
the atom. According to this model “the
volume” of the atom is largely an empty space.
Particle
Mass (amu) Charge
-
0.00054858
-1
+
Proton (p,p )
1.0073
+1
0
1.0087
0
Electron (e )
Neutron(n,n )
Sub-atomic Particles
Z - atomic number = number of protons
determines type of atom.
n A - mass number = number of protons +
neutrons.
n Number of protons = number of electrons if
neutral.
n
Symbols
A
X
Z
23
Na
11
11 protons
11 electrons
12 neutrons
Isotopes: Atoms with the same number
of protons, but different number of
neutrons
16
8
O
99.762%
1
1
H
O
17
8
0.038%
2
1
H
18
8
0.200%
O
3
1
H
H
Cu
Be
C
P
N
Mass Spectroscopy
The spectrum obtained from this technique
allows us to know the abundance of each isotope
in a sample.
P
e
r
c
e
n
t
a
b
u
n
d
a
n
c
e
80
60
40
20
0
63
Atomic mass
65
The atomic weight of an element is
the weighted average of the masses of
its stable isotopes
Example: Naturally occurring Cu
consists of 2 isotopes. It is 69.1% 63Cu
with a mass of 62.9 amu, and 30.9%
65Cu, which has a mass of 64.9 amu.
Calculate the atomic weight of Cu to
one decimal place.
atomic weight  (69.1)(62.9)  (30.9)(64.9)
100
atomic weight  63.5 amu for copper