Download Atomic Structure ppt

Atomic Theory
Atomic History







Ancient Greeks
John Dalton
JJ Thomson
Ernest Rutherford
James Chadwick
Neils Bohr
Erwin Schrödinger
Ancient Greeks (~ 400 B.C.E)

Democritus (460 – 370 B.C.E.)


All matter is made of tiny,
indestructible units called
ATOMOS
Aristotle (384 – 322 B.C.E) &
Plato (428 – 348 B.C.E)

Completely disagreed with
Democritus. Public opinion
sided with these guys that all
matter was made of EARTH,
AIR, FIRE, & WATER
John Dalton (1766 – 1844) &
Dalton’s Atomic Theory

John Dalton

Chemist & Physicist who
made a living teaching
 His theory is backed by many
experiments

Theory





Elements are made of
particles called atoms
All atoms of an element are
identical
Atoms of 1 element are diff.
from atoms of another element
Atoms of elements can
combine to form compounds
with simple, whole number
ratios
Atoms can’t be destroyed or
created, they’re just
rearranged in a chemical
reaction
JJ Thomson (1856 – 1940) & the
Cathode Ray Experiment (1890s)

Physicist who used a
cathode ray tube to
show that atoms of
any element can be
made to give off tiny
negative particles
(ELECTRONS)
JJ’s Model- The Plum Pudding Model
(Chocolate Chip Cookie anyone?)
Ernest Rutherford (1871 – 1937) &
Gold Foil Experiment (1911)

Ernest
the positive α (alpha) particles to
pass straight through to the back of the
detector. He was surprised when they
bounced off at strange angles.
 He surmised that the alpha particles were
bouncing off a small + charge in the Gold
atoms. He called that part the NUCLEUS!
 Expected
Gold Foil Experiment
Some More Stuff Ernie Did

In 1918 – He experimented by
bombarding N2(g) with alpha
particles. 1 of the results was
that a whole lot of H2(g) was
created. What’s going on?

Ernie figured out that the H
atoms must have come from
inside the N2. That means that
ATOMS ARE DIVISIBLE!!!!!!!!
He eventually isolated those H
atoms and discovered they
were actually PROTONS
Ernie found a friend- James
Chadwick (1932).

Ernie’s assistant, James Chadwick found the
NEUTRON in 1932.
 He
put some Be in a chamber with Po (gives off alpha
particles). The alpha particles hit the Be which gave
off some particles at high, high speeds. At first he
thought they were gamma (γ) rays but they moved too
fast for gamma rays. He worked his way thru some
calculations and discovered they were not, but some
neutral particles that he named (NEUTRONS)
Chadwick- Rutherford Model
Neils Bohr (1885 – 1962) and the
Bohr Planetary Model

Developed a theory of
the H atom, saying
that electrons moved
in specific ORBITS
around the nucleus.
Each orbit has a
specific amount of
energy to it.
Erwin Schrödinger, Albert Einstein, Neils Bohr, &
Werner Heisenberg: Modern Model of the Atom
(Wave Mechanical Model)

States that electrons
exist in a state
described by an
ORBITAL
 An
area where there is
a 90% probability of
finding an electron
ATOMIC STRUCTURE
Physical structure
 Atomic Number
 Mass Number
 Isotopes
 Atomic Mass
 Calculating Atomic Mass

Atomic Structure




An atom is the defining
part of what makes an
element, an element.
Cannot be broken down
chemically.
Atoms are mostly empty
space!
Atoms are very, very
small!
If an atom were 2 miles
wide, the nucleus would
be the size of a baseball!
Atomic Structure
Particle
Relative Mass
(Actual Mass)
Relative Charge
Proton
1836
+1
(1.67262158 × 10-27
kg)
Neutron
1839
0
(1.67492729 × 10-27
kg)
Electron
1
(9.10938188 × 10-31
kg)
-1
Atomic Number & Mass Number

Atomic Number (Z) =
# of protons (p+)
=

# electrons (e-)
Mass Number (A)
= # of p+ + # n0
How many p+, n0, and e-?
238
92
U
23
11
Na
Isotopes


Atoms of an element that
have different #’s of
neutrons.
An element is composed
of varying percentages
(abundances) of isotopes
Isotopes

Examples
 11H
2
1H
 63Li
7
3Li
3
1H
Atomic Mass

Weighted average of all the masses of
each isotope of the element.
A.M. =
(% isotope 1)(Mass isotope 1) + (% isotope 2)(Mass isotope 2) +
(% isotope 3)(Mass isotope 3) + ….

Examples

Calculate the average atomic mass of gold
of 197Au weighs 197
 50% of 198Au weighs 198
 50%