Atomic Theory & the Periodic Table A Review
Jan 03, 2016
Atomic Theory & the Periodic Table
A Review
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
Expected 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!
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: 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(1.67262158 × 10-27 kg)
+1
Neutron 1839(1.67492729 × 10-27 kg)
0
Electron 1(9.10938188 × 10-31 kg)
-1
Atomic Number & Mass Number
Atomic Number = # of protons (p+) = # electrons (e-)
Mass Number
= # of p+ + # n0
How many p+, n0, and e-?
238 23
11 Na92 U
Isotopes
Atoms of an element that have different #’s of neutrons.
11H 2
1H 31H
63Li 7
3Li
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 50% of 197Au weighs 197 50% of 198Au weighs 198