Chapter 2 Flashcards
What is the use of a mass spectrometer?
It is used to determine the relative atomic masses (Ar) of elements and to determine the structure of organic compound
What are the steps of a mass spectrometer?
- the sample is first vaporised to form a gas
- it is then bombarded by high energy elections to make positive ions (+1)
- the positive ions are then accelerated in an electric field
- the positive ions are then deflected in a magnetic field depending on their mass to charge ratio (m/z)
- ions with a higher mass to charge ratio are deflected less in a magnetic field - finally, the positive ions reach the detector, where they produce a mass spectrum
Bohr Model of an atom suggests….
electrons exist in energy levels or principal energy levels and can transition between these energy levels by absorbing or emitting exact amounts of energy. The principal energy levels are assigned numbers with n = 1 being closest to the nucleus and of lowest energy.
The Pauli exclusion principle states…
two electrons cannot have the same quantum number. Simply put, two electrons can only occupy the same atomic orbital if they have opposite spins.
Draw how orbitals spin
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/2.2.4.1%20Two-electrons-in-the-same-orbital.a3ab008e7b8fdabfcabb.jpeg?w=1344&h=666&auto=compress
Heisenberg’s uncertainty principle states…
it is not possible to know, at the same time, the exact position and momentum of an electron. Instead, we can only state the probability that an electron will be somewhere in a given region of space.
Draw the graphs of orbitals s, px, py and pz
https://kognity-prod.imgix.net/media/edusys_2/content_uploads/s%20and%20p.5c710295e447111752e7.png?w=675&auto=compress
Atomic Orbital
a region of space where there is a high probability of finding an electron
The Afbau principle states…
electrons fill atomic orbitals of lowest energy first
What order should sub-levels be filled?
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s
Exceptions to the Afbau principle
Chromium:
- expected: 1s2 2s2 2p6 3s2 3p6 4s2 3d4
- reality: 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Copper:
- expected: 1s2 2s2 2p6 3s2 3p6 4s2 3d9
- reality:1s2 2s2 2p6 3s2 3p6 4s1 3d10
Line Spectra and elements
Different elements have different characteristic line spectra
Electromagnetic Radiation
In order: radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), x-rays and gamma rays. These different types of EM radiation can be classified according to their energy, wavelength or frequency, going from longest wavelength to shortest
Speed of light equation
3 x 10^8 = frequency (Hz) x wavelength (λ)
Energy, frequency and wavelength
Higher energy = higher frequency = shorter wavelength.
Lower energy = lower frequency = longer wavelength.
Infrared radiation
Infrared radiation has a longer wavelength, lower frequency and lower energy than visible light. Infrared radiation feels warm on the skin.
Visible radiation
The visible region encompasses radiation of intermediate frequency. It is visible to the naked eye and takes on 7 different colours; red, orange, yellow, green, blue, indigo and violet.
UV
The UV region encompasses UV radiation, which has a shorter wavelength and therefore a higher frequency and energy than visible light. This is the type of non-visible radiation emitted by the sun, which is dangerous for human skin.
Dispersion
When white light passes through a prism, a continuous spectrum is produced. This separation of the white light into its component colours is known as dispersion.
What does continuous spectrum show?
It shows all the wavelengths or frequencies of visible light
What does an absorption line spectrum show?
It is similar to continuous spectrum, but it differs from a continuous spectrum in that some of the wavelengths of visible light are missing, shown by the black lines on the coloured background.
What does an emission line spectrum show?
An emission line spectrum is characterised by having coloured lines on a black background
How are emission line spectra made?
By absorbing or emitting energy, electrons can transition between the energy levels. If a high voltage is passed through a gas, the electrons in the gaseous atoms become excited and transition to higher energy levels. As the electrons fall back down to lower energy levels, the transitions are accompanied by an emission of energy. This results in the formation of an emission line spectrum.
How are absorption line spectra made?
Absorption line spectra are produced when electrons absorb energy and transition to higher energy levels. Similar to the process of emission line spectra.
Visible light and the use of energy while transitioning between energy levels
Electron transitions from n = 2 to higher energy levels absorb energy that corresponds to the wavelength or frequency of visible light. Electron transitions from n = 2 to n = 3, for example, absorb energy that corresponds to the wavelength of red light. Similarly, electron transitions from n = 2 to n = 5 absorb energy that corresponds to the wavelength of blue light.
Draw a emission graph and an absorption graph
Emmision: https://kognity-prod.imgix.net/media/edusys_2/content_uploads/Nuclear%20fusion.b219db78a98f7654bd3c.png?w=825&auto=compress
Absorption: https://kognity-prod.imgix.net/media/edusys_2/content_uploads/24.3.1.6%20Electron%20transitions%20from%20n%202%20produce%20an%20absorption%20spectrum%20in%20the%20visible%20range.59943a304955f89826e5.png?w=825&auto=compress
Energy equation
Energy (J) = h (Planck’s constant: 6.63 × 10-34 J s) x frequency (Hz)
What can be deduced when looking the hydrogen emission line spectrum?
- Electron transitions to the n = 1 energy level emit energy that corresponds to the wavelength or frequency of ultraviolet (UV) radiation.
- Electron transitions to the n = 2 energy level emit energy that corresponds to the wavelength or frequency of visible light.
- Electron transitions to the n = 3 energy level emit energy that corresponds to the wavelength or frequency of infrared (IR) radiation.
Lines in emission and absorption graphs
the longer the arrow, the greater the amount of energy emitted (or absorbed in the case of an absorption line spectrum)
How line spectra give evidence for the model of an atom
We have seen that the line spectra are at characteristic frequencies for a given element. This shows that a given atom only emits certain energies, and the conclusion is that there are only certain energy levels available for the electrons in the atom. Electrons can transition from one energy level to another, but not to somewhere ‘in between’. Examination of line spectra gives evidence for the model of the atom in which electrons are arranged in different energy levels
