Date post: | 16-Dec-2015 |
Category: |
Documents |
Upload: | norman-wilemon |
View: | 223 times |
Download: | 1 times |
The Structure of the Atom
Honors ChemistrySection 3.2
Demonstrate the Think Tube
The Think Tube
The smallest particle of an element that still retains the properties of that element.
Made of two regionsNucleus
In center of atomExtremely smallMajority of Mass of AtomProtons/Neutrons
Electron CloudContains electrons
Atom
The Atom
Parts of the Atom
Video
Properties of Subatomic Particles
How did we find the electron?J.J. Thomson – late 1800’sUse the Cathode Ray Tube
Thomson's Experiment
Thompson's Experiment
Video
Cathode Rays move away from a negative charge
Cathode Rays move away from a magnetic field in the same manner as a wire carrying a negative charge
Found the Cathode Rays have mass – could move a paddle wheel in their path
Charge to mass ratio of Cathode Rays the same regardless ofType of metal used in electrodesType of gas used in tube
Thomson's Observations
Cathode Rays are negatively chargedCathode Rays must be a fundamental particle
of matterCalculated the charge to mass ratio of the
particlesParticles later named electrons
Thomson's Conculsions
Robert Millikan
Millikan's Experiment
Video
Determined the fundamental charge on matter (the electron)
Used Thomson’s charge to mass ratio to determine the mass of an electron
Verified that electrons are negative
Millikan's Results
Atom is divisibleOne of the basic subatomic particles is the
negatively charged electronAtom is electrically neutral, so it must contain
positive charges to balance out the electronsElectrons have an extremely small mass,
therefore there must be other massive particles in the atom
Results
Thomson's and Millikan's Model
Demo the Cloud Chamber
Radiation Demonstration
Ernest Rutherford - 1911
α particles are positively charged and massiveHe nucleus
Rutherford's Results
Rutherford's Experiment
Video
Nucleus existed at the center of the atomSmall – extremely smallMassiveDensely PackedPositive
Electrons are in orbit around the nucleus.
Rutherford's Conclusions
All nuclei (execpt H) have protons and neutrons
Proton – positiveCharge equal and opposite the electronMass about the same as a neutron1.673 x 10-27 kg (1836 x the mass of an
electron)Neutron – electrically neutral
1.675 x 10-27 kgAtom neutral so # protons = # electronsThe number of protons determines the
identity of the element
Early 1900's Atomic Theory
When two protons are extremely close to each other, there is a strong attraction between them.
A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together.
The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are referred to as nuclear forces.
Forces in the Nucleus
Nuclear Forces
• The radius of an atom is the distance from the center of the nucleus to the outer portion of its electron cloud.
• Because atomic radii are so small, they are expressed using a unit that is more convenient for the sizes of atoms.
• This unit is the picometer, pm.
The Size of an Atom