Who was the first scientist to provide a picture of the arrangement of the electrons in an atom?
Niels Bohr
How is a continuous spectrum formed?
Shining white light through a prism and viewing it on a screen.
What is an emission line spectrum?
Black background with coloured lines on it.
Explain Bohr's Theory.
Electrons revolve around the nucleus in fixed paths called orbits.
It neither gains or loses energy when on these orbits.
They are said to be in their ground state.
If energy is provided, the electron absorbs this energy and jumps to a higher energy level (orbit).
This is called the excited state.
The energy absorbed is the difference between the ground state and the excited state.
In the excited state, the electrons are unstable and only remain for a short period of time.
As they fall back to a lower orbit or energy level, the excess energy is released in the form of light.
As only definite amounts of energy are emitted, this implies that the electrons can occupy only definite energy levels.
The frequency of the light is equal to the formula E = hf
Why do electrons not remain in the excited state?
They are unstable so they must return to their original ground state.
Define the energy level.
An energy level is defined as the fixed energy value that an electron in an atom may have.
Define ground state.
The ground state of an atom is the one in which the electrons occupy the lowest available energy levels.
Define an excited state.
The excited state of an atom is one in which the electrons occupy higher energy levels than those available in the ground state.
Why can the Lyman and Paschen series not be viewed normally?
They are not found in the visible spectrum.
Where is the Lyman series located?
Ultraviolet region - when an electron falls to the n=1 energy level
Where is the Paschen series located?
Infrared region - when an electron falls to the n=3 energy level
What is the name of the series of lines in the visible spectrum?
Balmer series - when the electron falls to the n=2 energy level.
In E=hf, what does h and f stand for?
h = Plancks constant f = frequency of light
What is Atomic Absorption Spectrometry?
Passing white light through a gas sample of an element before it goes through the prism. Bohr noticed that there were place lines found in the continuous spectrum.
Give 2 uses for Emission line spectrum and Atomic Absorption Spectrometry.
Emission for the identification of elements and used in fireworks
Absorption for the identification of elements and finding the concentration of elements
What are energy sublevels?
A sublevel is a subdivision of a main energy level and consists of one or more orbitals of the same energy
How were they discovered?
Scientists noticed that the emission lines were not all singular. Upon inspection, some were actually made of 2 lines or 3 lines etc.
When listing the sublevels, 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, why does the 4s come before the 3d?
It takes more energy to get into the 3d sublevel.
Who discovered that electrons travel in a wave motion?
De Broglie
What outcome does this have for the electron?
Makes it difficult to pinpoint the location of the electron.
What is Heisenberg’s Uncertainty Principle?
Heisenberg's Uncertainty Principle: states that it is impossible to measure at the same time both the velocity and position of the atom.
Give 3 limitations of Bohr’s theory.
Only works for hydrogen.
Did not take into account the wave nature of the electron.
Did not consider the sublevels
Define an atomic orbital.
An orbital is a region in space where there is a high probability of finding an electron.
What was the name of the scientist who calculated the probability of finding electrons in a particular sublevel?
Schrodinger
What shape is the S orbital?
Spherical
What shape are the P orbitals?
Dumbbell shape
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