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Chemistry. First Quiz Notes

Terms in this set (20)

atom
the smallest particle of an element that has all the properties of an element.
Democritus
Greek philosopher who was the first person to propose the idea that "all matter is made up of small indivisible particles"
He called the particles "atoma" which means "indivisible units"
proposed this idea nearly 2500 years ago
John Dalton
1803-developed Atomic Theory:proposed that all matter is made of tiny, indivisible particles and that the atoms of the same element are identical to each other but differ from atoms of other elements.
Model-atom is a solid sphere
Modern Atomic Theory
an updated version of John Dalton's atomic theory. It recognizes the existence of subatomic particles-protons, neutrons, and electrons, and differing masses of atoms of the same element (isotopes)
J.J. Thomson
1898- used a gas discharge tube (cathode ray tube), proposed that electrons were fundamental constituents of the atom. Basically discovered electrons."Plum Pudding" Model of the atom
Ernest Rutherford
1911- discovered 2 things.
1. that the atom has a dense central core with a positive charge called the nucleus.
2. He correctly concluded that the atom is mostly empty space with the electrons located outside of the nucleus.
He also performed the Gold Foil Experiment.
Problem with Rutherford's theory
Rutherford proposed that the electrons were not attracted to the positive nucleus because they travelled in a circular orbit around the nucleus (like the moon orbiting the earth).
Problem: Electrons are negatively charged and a charged particle moving in a curved path must emit some form of energy such as light. This would cause the electrons to spiral into the nucleus and cause the collapse of the atom
Neils Bohr
1913- modified Rutherford's model. Proposed that electrons are located in definitely Energy Levels around the nucleus and that these levels represent the only areas where the electrons can be located. The energy of the electron is quantized (or has a discrete specific amount of energy). He proposed that the only way an electron can lose energy is by "dropping" from one energy level to another.
A characteristic color of light is produced when....
electrons "drop" from the excited state to the ground. (fireworks, neon lights)
Problem with Bohr's Model
The model proposed by Bohr could only explain the existence of the spectral lines ("finger prints" of the atom) of the simplest element, Hydrogen (it could not predict the energy levels of electrons in atoms with more than one electron). Bohr's model was modified with many of his fundamental ideas still intact.
Why are electrons restricted to certain energy levels?
The wavelength of an electron must "fit" inside the atom so as to not cancel itself. This happens only at certain discrete energy levels.
*electron is travelling as a wave.
Max Planck and Albert Einstein
1900- Light is made up of bundles of energy called Quanta or Photons (particle nature of light). Modern theory of light: it can behave both as waves and particles.
Basically the wave has a particle property
Louis de Broglie
1924- If light has particle-like characteristics, particles can have wavelike characteristics.
Electrons follow the particle/wave theory.
Basically, he believed the opposite of Planck and Einstein.
Werner Heisenberg 1927
Heisenberg Uncertainty principle: It is impossible to know the exact location and velocity(momentum) of a small particle(electron) at the same time.
We can only state the Probability of finding a particle (electron) at a particular place at a particular time.
Erwin Schrodinger 1926
He arrived at a set of Quantum Numbers that correspond to a certain energy and describe a region of space around the nucleus (orbital) where an electron having that energy can be found.
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