atomic theory timeline
Published on Nov 19, 2015
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PRESENTATION OUTLINE
BEGINNING OF ATOMIC THEORY TIMELINE
- Democritus suggested that there was a smallest particle that is indivisible.
- The Greek word for indivisible is Atomas.
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DALTON
- Dalton tested the idea and then was able to come up with a theory.
- He said that each element is made up of tiny indestructible particles called atoms.
- He said that all atoms of an element are identical and have the same mass.
- He said that atoms combine in simple, whole number ratios to form molecules or compounds.
- Dalton was able to determine the relative masses of an atom using assumed formulas.
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THOMSON
- Thomson was the first to discover that atoms were made up of small particles
- These particles were called electrons and the mass of the atoms was due to the mass of the electrons
- He added that an atoms structure had electrons suspended in a positively charged field.
- The field must be positive to balance out the negative charge of electrons.
- He called his model the plum pudding model.
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RUTHERFORD
- Rutherford used alpha particles and gold foil to see if the atom was empty.
- In his expiriment, 98% of the particles went straight through the gold foil.
- 2% went through but were deflected and 0.01 bounced straight back.
- Rutherford concluded that there was a tiny, dense positevly charged center in the atom.
- The deflected particles had hit this center which is called the nucleus.
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RUTHERFORD CONTINUED
- The nucleus of the the atom had the same mass as the atom.
- The electrons weigh so little that there weight practically contributes nothing to the atoms mass.
- The nucleus is positively charged which is why some of the alpha particle bent.
- The positive charge also balances the negative charge of the electrons.
- Rutherford wrongly believed that the electrons were dispersed in the atom like water droplets.
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BOHR MODEL
- The Bohr model shows the way electrons travel around the nucleus.
- The further away an electron is from the nucleus, the more energy it has.
- The Bohr model only worked perfectly for hydrogen atoms.
- The mathematics of the Bohr are only accurate for the hydrogen spectrum.
- It doesn't account for electron-electron encounters and so a better theory was needed.
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THE QUANTUM-MECHANICAL MODEL
- Erwin Schrödinger discovered an equation.
- The equation was able to predict the probability of where an electron with a certain energy would be.
- An orbital is a region with high probability of finding an electron when it has a specific energy.
- There are four subshells: s,p,d, and f
- Each subshell has an orbital with a different shape.
Photo by John Twohig Photography
