Transcript 1. models of the atom

What is an atom?
Agenda for Thursday March 31st
1. Models of the Atoms
Atoms
 Atom – smallest unit of an element that maintains the
properties of that element
 What are Atoms composed of?
Particle
Charge
Location
Proton
Positive (+)
Nucleus
Neutron
Neutral (0)
Nucleus
Electron
Negative (-) Electron Cloud
Democritus
 400 BC
 1st atomic theory
 All things composed of small particles
 no technology to support his claim
 His theory came from observations
 turned out to be surprisingly accurate
Dalton
1766-1844
Matter is made of tiny spheres called
atoms
There are different types of atoms
These atoms combine to form
molecules
John Dalton proposed an atomic theory
1.
2.
3.
4.
5.
matter is composed, indivisible particles (atoms).
all atoms of a particular element are identical
different elements have different atoms
atoms combine in certain whole-number ratios
In a chemical reaction, atoms are rearranged to
form new compounds;
1. not created, destroyed, or changed into atoms of other
elements
Mendeleev
(1834-1907)
Organized the first Periodic
Table by observing patterns
in atomic structure.
Predicted the characteristics of elements not yet found
His predictions were all correct!
J.J. Thomson
 1890s
 Used a cathode ray tube to add to Dalton’s theory
 J.J. Thomson: in 1890s proved that atoms made up of smaller
particles
 Discovered electrons
 Chocolate chip cookie model: electrons placed randomly
throughout the atom
Rutherford
1849-1919
The Gold Foil Experiment
Shot beam of positive particles at
layer of gold foil.
Almost ALL went right through.
Some scattered.
What does this mean?
Atoms are mostly empty space,
with a small dense, POSITIVE core.
Electrons scattered around it.
Also credited with the discovery of Protons
Rutherford’s Model
 He calls the dense center of the atom the nucleus.
 His model is called the nuclear model
 It looks like a peach that is cut in half
Bohr 1885-1962
Discovered that electrons move
around nucleus in orbits
Chadwick (1891-1974)
 Proved the existence of Neutrons
 Do not have a charge. Neutral.
 Worked on Manhattan Project
Erwin Schrodinger
 Electrons do not orbit the nucleus in set paths; they exist in an
electron cloud
 Don’t know the exact path, just the place it’s most likely to be
NO!!
More accurate
Timeline
Democritus – all things composed of small particles
Dalton – atoms
Mendeleev – periodic table
Thomson – electrons
Rutherford – dense, positively charged nucleus, mostly empty space
Bohr – electrons orbit in paths
Chadwick – neutrons
Schrodinger – electron cloud model
Positive and Negative charges
 There are 2 types of charges: positive and negative
 Protons – positively charged
 Electrons – negatively charged
 Opposite charges attract
 Like charges repel
Charges
 Opposite charges cancel each other out
 3+ charges will cancel out 3- charges for an overall 0 charge
 5+ charges with 4- charges gives a 1+ charge overall
Summary of subatomic particles
Particle
Charge
Location
Proton
Positive (+)
Nucleus
Neutron
Neutral (0)
Nucleus
Electron
Negative (-)
Electron Cloud
Ernest Rutherford
 1909
 Gold foil experiment
 Said each atom had a center called the nucleus that contained
protons. Electrons existed outside of the nucleus.
Niels Bohr
 Said that electrons exist outside of the nucleus in energy levels
 Electrons orbit the nucleus in paths