Download ATOMIC STRUCTURE: Atomic History

ATOMIC
STRUCTURE: Atomic
History
What is an Atom
• Smallest part of matter that exists
• Retains the properties of the element
that it is a part of
• Cannot be broken down any further
• Consists of at least one electron,
proton, and neutron
Dalton’s Atomic Theory of
Matter
Dalton’s Atomic Theory Has 4
Points
• 1. All elements are composed of matter
• 2. All atoms of an element are identical
• 3. Atoms of different elements are made
up of different materials
• 4. Compounds are formed by combining
atoms of different elements
People Associated With
Discovering Atomic Structure
JJ Thomson “Plumb-Pudding
Model”
• Around 1897
• Credited with discovering the electron
• Famous experiment is the “Cathode-Ray
Tube Experiment”
• Theory was that all of the charge of an
atom is in a dense area located in the
middle of the structure
Rutherford “Gold-Foil
Experiment”
• Around 1910 ish
• Credited with discovering the nucleus of
an atom
• Used the Gold Foil Experiment to
determine the location and charge of an
atom’s nucleus
What is the Gold-Foil
Experiment?
• Major experiment in chemistry
• Shot alpha-particles at gold foil and observed
what happened
• Basically 2 main things were observed:
• 1. Most of the alpha particles went through
the gold foil and hit the phosphor screen
behind the foil
• 2. Some of the alpha particles hit some unseen
object and bounced back or in random
directions away from the gold foil
What are the conclusions of the
Experiment?
• 1. Atoms are mostly empty space: Have
large volume
• 2. Atoms have a dense positive core called
the nucleus and this is where the mass of
the atom is located.
Rutherford’s Model of the
Atom
What is wrong with the model?
• Electrons are protons are together in the
middle of the atom
• Can’t happen due to the attractions that
take place between the oppositely charged
particles
• Had to be a better model that somehow
separated the two particles from each
other.
Bohr Model “Planetary Model”
What is the model
• Uses the Rutherford model as its basis
• Around 1915ish
• Places the electrons outside of the nucleus
away from the protons
• Electrons are in orbits around the nucleus
similar to the way the planets rotate
around the sun
• All of model is OK EXCEPT for 1 key fact
What is correct/incorrect
about the model?
• Correct:
1. Nucleus
2. Electrons in orbits away from nucleus
3. Protons in nucleus
Incorrect:
1. Electrons are not stationary in orbits
2. Electrons can move around within an orbit to any
random spot that they find, and can also move
between levels within an atom
4. Wave Mechanical Model
• Modern model of the atom (1936-on)
• Nucleus contains protons/neutrons so it is positive
• Electrons are in regions of highest probability outside of
the nucleus called orbitals
• Electrons can move anywhere within the orbital they are
assigned to based on energy
• If the atom gains energy, electrons can gain energy and
jump to a higher level as well
• Electrons that jump always return home, similar to a dog
that quickly runs away from home.