1. Emission spectrum
Continuous spectrum
When a beam of white light passes through a prism, a continuous spectrum will be formed like in Figure 1.
Continuous spectrum will show all colors.
Figure 1: Formation of continuous spectrum
Absorption spectrum
When white light passes some particles, some energies (related to some colors) will be absorbed due to the electronic transition from lower energy level to higher energy, and absorption spectrum will be produced. (Figure 2)
Figure 2: Formation of absorption spectrum
Emission spectrum
Light is one form of energy. Other energy, such as electricity and heat, can promoted electrons to higher energy as well. When electrons are in the excited state, they are unstable, and easy to back to ground state. Meanwhile, some energies (related to some colors) will be released and emission spectrum is formed. (Figure 3)
Figure 3: Formation of emission spectrum
In our daily life, neon lights and flame tests (or fireworks) are other examples of emission spectrum.
Both absorption and emission spectra are line spectrum. (Figure 4)
Figure 4: Classification of spectra
Terms
ground state:
Excited state:
Questions
1) Distinguish the difference between continuous spectrum and line spectrum.
Continuous spectrum will show all colors (frequency or wavelength).
Line spectrum will show some specific colors (frequency or wavelength).
2) Distinguish difference between absorption spectrum and emission spectrum.
Absorption spectrum is a continuous spectrum which is loss some specific colors.
Emission spectrum is a black background and show some specific colors.
3) Draw the energy level diagram for hydrogen, and draw a series of lines to represent the electronic transition in emission spectrum in visible region.
4) Draw four lines in the following emission spectrum of hydrogen.
5) Describe the features of emission spectrum.
6) Explain why discrete lines related to existence of energy level.
7) Explain why lines are converged at higher energy.
2. Orbital, sub-level and energy level
Traditionally, we think electrons are moving around the nucleus in a fixed energy level which is a 2-D circle. According to Heisenberg’s uncertainty, it is impossible for us to determine the accurate position and velocity of one electron. Scientist states the terms of orbital to describe a region and the dash line represents 95% probability to find electron in it (Figure ).
Figure: A diagram to represent one type of orbital
There are four types of orbital: s, p, d and f. Different orbital has different shape. Figure shows shapes for two orbitals. s-orbital is a sphere, and p-orbital is a dumbbell. But p-orbital has three different directions: x, y and z-axis direction.
Figure: Shapes for s and p-orbital
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Terms
Orbital: a region for
Sub-level:
Questions
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3. Electron configuration
Figure: A periodic table to deduce electron configuration (click to enlarge)
Figure can help us to deduce electron configuration quickly. 15P is used to be an example to show the process for condensed electron configuration.
Step 1: find the noble gas before the element you are required. P is a period 3 element, and Neon is the noble gas in period 2. [Ne] is used to describe the electron configuration of Ne which is 1s2 2s2 2p6, and it is the electron configuration for phosphorus besides valence electrons.
Step 2:
Terms
electron arrangement
electron configuration:
full electron configuration:
condensed electron configuration:
Sub Heading 2
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