Atomic Structure Define the atom Structure of the Nuclear Atom Distinguish between atoms.
Structure of Atom
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Atom
Smallest particle of an element
Atomic Structure – arrangement of smaller particles within an atom
Two Main Regions In Atom
Nucleus – very small dense central region
protons – positively charged particles
neutrons – neutral particles
● Electron Cloud – large region around nucleus
electrons – negatively charged particles
Discovery of Electrons
JJ Thomson – used Crooke’s Tube (cathode ray tube)Gas under low pressure in a sealed glass tubeHas a positive end (Anode) and negative end (Cathode)When anode and cathode are connected to the + and – terminals of a battery, the tube produces a beam of particles called electrons
Thomson’s Atom
Plum-pudding model
Since total atom is neutral, there must be an equal number of + and - charges
Atom is a positively charged area with negative electrons randomly spread throughout
Nucleus
Ernest Rutherford – Gold foil experiment
Shot positive charged particles at a very thin piece of gold foil
How he explained it
+
Atom is mostly empty spaceSmall dense, positive piece at centerAlpha particles are
deflected by it if they get close enough
Rutherford’s Model Of Atom
Positively charged nucleus containing protons and neutrons with negatively charged particles in orbit around it
Electrons stay in orbit due to attraction between + and – charges
Problems With Rutherford Model
Charged particle when moving in a curved path give off light so they lose energy
If they lose energy, they would gradually get closer and closer to the nucleus and crash into it
Bohr Model of Atom
Similar to Rutherford model, but in this model electrons orbit in specific, well defined energy levelA gain or loss of energy moves the electron from one energy level to anotherPositively charged protons and neutral neutrons held together tightly by the Strong Nuclear Force