Transcript Atomic Theory

What do I need to know for the test?
 460 BC-created the 1st Atomic Theory of Matter (not
modern atomic theory however)
 HIS THEORY
 Matter is composed of empty space through which atoms




move
Atoms are solid, homogeneous, indestructible, and
indivisible
Different kinds of atoms have different sizes and shapes
The differing properties of matter are due to the size, shape,
and movement of atoms
Changes in matter result from changes in groupings of atoms
and NOT from changes in the atoms themselves
Dalton revived Democritus’s
ideas in the 19th century. Much
time has passed.
Dalton’s Model
 Father of the Modern Atomic Theory
 5 parts
 Each element is composed of tiny, indestructible




particles called atoms
All atoms for a given element have the same mass and
properties
Atoms cannot be created, divided into smaller particles,
or destroyed
Atoms combine in whole number ratios to form
compounds
In a reaction, atoms are separated, combined, and
rearranged
 He used a cathode ray tube experiment to discover
electrons.
 He measured both magnetic and electric fields on the
cathode rays and observed that there was a teeny tiny
particle, much smaller than the Hydrogen atom 
Electron
 Plum Pudding Model
 Negatively charged electrons are distributed throughout
a uniform positive charge
Plum Pudding Model
Cathode Ray
 Discovered the charge (-1) of an electron by doing the
oil drop experiment
 http://www.suite101.com/content/millikan-oil-drop-
experiment-a124624
Oil Drop
 He was interested in studying how alpha particles (+
charge ) interact with atoms
 Rutherford thought that, in his experiments, only a
few positively charged alpha particles would slightly
deflect and the rest would go straight through.
 Using the Gold Foil Experiment he discovered that
some of those particles deflected at large angles and
even bounced straight back at him.
 That means that the plumb pudding model was wrong
and there was a small dense center to an atom called a
NUCLEUS!
 Which means that the electrons floated around in
empty space….so he also discovered the orbital theory
of electrons, in other words, electrons orbit the
nucleus (small charge) in circular paths
Gold Foil Experiment
 Mendeleev was the first to put all the known elements
into some sort of arrangement. His periodic table is
NOT the periodic table we know today.
 He arranged the table in order of atomic mass, NOT
number.
 Arranged the periodic table according to atomic
number NOT atomic mass (Mendeleev)
 This is our periodic table that we use today
 Periodic Law-Elements close to one another have
similar properties.
 Bohr’s Model is based on the light emission spectrum
of Hydrogen…
 He proposed that a hydrogen atom has only certain
allowable energy levels. (energy is quantized)
 Lowest energy level is ground state
 When an electron is excited it moves up to an excited state
 He proposed that electrons can only orbit in certain
circular paths (like planets)
 Each path is a different energy level
Bohr’s Energy
Levels
 When an electron falls from an excited state to the
ground state, light is emitted….
 His model explained Hydrogen’s spectrum, but not any
other element
 Louis went one step further than Bohr…
 Theorized that all moving particles have wave like
characteristics, even electrons!
 Went further with the wave/particle theory
 Discovered electron clouds (s, p, d, f)
 Explains that electrons move like waves and not in a
fixed patterns
 At any given time, an electron can be found
somewhere within its electron cloud. (90% of the
time)
 Essentially discovered neutrons (no charge) and how it
pairs with protons in a mass called a nucleus