Electron+arrangement

=Electromagnetic Spectrum = toc Electromagnetic spectrum is the spectrum that has radiation of all different frequencies, ranging from radio waves to gamma rays. As you go from radio waves to gamma rays on the spectrum The frequency of the radiation increases while the wavelength decreases. As the frequency increases, in going from radio waves to gamma rays, it means that the energy of the wave also increases.



An electromagnetic spectrum is known as a continuous spectrum. This is because waves of all frequencies are present. //Example:// ** R a i n b o w ** is an example of //continuous spectrum//, since light of all different frequencies are present in it. However, we can also have a // l in e spectrum //, which shows only light of a particular frequency. A line spectrum has bright areas with dark spaces in between. The bright areas represent light of a particular frequency which is being emitted. 

=Energy levels in an atom = As we had said earlier, the electrons orbit the nucleus in shells, which are called energy levels. The closest one to the nucleus is the first energy level, then we have the second, third etc. The electrons move around in the energy levels. The energy of the energy level increases the further away from the nucleus it is. So the energy levels near the nucleus have the lowest energy.

//**Note**// how the distance between the energy levels isn’t uniform. The further away from the nucleus they are, the closer the energy levels. This is because the further away from the nucleus the energy levels have very small difference in energy, so they are closer. While the ones near the nucleus are closer because they have a higher difference in their energy.

Now we know that there is a difference of energy between the energy levels. So, for an electron to move from one energy level to another, it has to either gain/lose energy. An electron can go(jump) to a //higher energy level//, when it //gains energy//. It usually does so by //absorbing light// of a particular frequency. (When the black electron moves from shell 1 to shell 3) An electron can go(jump) to a //lower energy level//, when it //loses energy//. When this happens the energy that has been lost is usually //emitted// in the form of //light// of a particular frequency. (When the green electron moves form shell 3 to shell 1).

=Emission spectrum = <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The electron in an atom can move from the first energy level to any other energy level or vice versa. Since there is a distinct amount of energy difference between the different energy levels, then the electrons can only lose/gain a certain amount of energy for them to move from one energy level to another. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Note:** that the energy change when the electron moves from one energy level to another is proportional to the frequency of the wave which is produced.

//<span style="font-family: Tahoma,sans-serif;">An emission spectrum shows the light of different frequencies which are emitted when the electron jumps from a high energy level to a lower one. //

= **<span style="font-family: Tahoma,sans-serif;">The hydrogen emission spectrum ** =

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The diagram shows the energy levels for a hydrogen atom. We have from energy level 1 and onwards. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">When an electron jumps from a higher energy level to a lower one it loses energy and this energy is given out as light of a particular frequency.


 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">If an electron from any energy level falls to the first energy level (shown by <span style="color: #008000; font-family: Tahoma,sans-serif; font-size: 14pt;">green arrows <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">) then light in the ultraviolet region is emitted. The higher the energy level from which the electron falls the higher the frequency of the light emitted as can be seen by the lines appearing to the left (where the frequency of the light is higher).
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">If an electron from any energy level falls to the second energy level (shown by blue arrows ) then light in the visible region is emitted. The higher the energy level from which the electron falls the higher the frequency of the light emitted as can be seen by the lines appearing to the left (where the frequency of the light is higher).
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">If an electron from any energy level falls to the third energy level (shown by brown lines ) then light in the infrared region is emitted. The higher the energy level from which the electron falls the higher the frequency of the light emitted as can be seen by the lines appearing to the left (where the frequency of the light is higher).


 * //<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">So, why do the lines emitted on the spectrum(the orange lines) tend to come closer to each other?? //**

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">This is because the higher up you go the closer the energy levels become to each other and therefore the difference in their energy is small. So the difference in frequency of the light emitted when an electron falls from the 5th level to the 1st level, is a little bit smaller compared to frequency of the light emitted when an electron goes from the 6th level to the 1st level. Thus, as the frequency of the light emitted is slightly different each time, it means that the lines will appear closer to each other.

=<span style="color: #2a099f; font-family: Tahoma,sans-serif; font-size: 14pt;">Electron arrangement around the nucleus =

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">So how exactly are the electrons arranged around the nucleus? //

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">We had earlier said that electrons orbit the nucleus in shells or energy levels. Each energy level has a capacity of electrons that it can have.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">- The first energy levels can hold a maximum of 2 electrons

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">- Other energy levels can hold upto a maximum of 8 electrons

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">So, when you are given the atomic number of an atom (that is neutral so that the atomic number is equal to the number of electrons) you can find its electronic arrangement.

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Example: //

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Aluminium (Al) has atomic number 13. So there are 13 electrons.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">We represent this as follows:

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The first shell is filled with 2 electrons (2,)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">We have 11 electrons left. The second shell takes 8 electrons. (2,8)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">We have 3 electrons left. These go into the third shell. (2,8,3)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">This is shown as follows: 2,8,3

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">This shows the number of electrons in each shell, starting from the first shell with a space in between. //

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Another easy way of getting the electronic structure of an atom is to use the periodic table (provided on page 6 of the data booklet):


 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The period of an atom tells you the number of electron shells that it has. (a period is a horizontal row in the periodic table). Eg: Sodium is in period 3 so it has 3 electron shells.
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The group of an atom tells you the number of electrons in its outer shell (these are also known as valence electrons). (a group is a vertical column in the periodic table). Eg: Sodium is in group 1 so it has 1 electron in its outer shell.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Using the above information we know that sodium has 3 electron shells and 1 electron in its outermost shell—that means that there is one electron in the 3rd shell and the previous two shells are full. So we have;

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Electronic structure of Na is 2,8,1

By the end of this lesson you should be able to:
 * Know the variation of wavelength, frequency and energy across the electromagnetic spectrum
 * Distinguish between a continuous spectrum and a line spectrum
 * Have an understanding of the emission spectrum of hydrogen
 * deduce the electronic configurations of atoms having up to an atomic number of 20

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The photo at the top of the page:"the electromagnetic spectrum" has been taken from @http://www.kollewin.com/blog/electromagnetic-spectrum/ (accessed 05/03/2012)