The structure of atoms
Both protons and neutrons are known as nucleons
Composition f the nucleus
Number of protons= atomic number Z
Number of protons and neutrons= mass number A
Same number of protons, different number of neutrons.
E.G. 1 H 2 H 3 H
1 1 1
The Electromagnetic spectrum
Consists of a large number of different waves, all of which travel at the same speed in a vacuum (3x108ms-)
Electromagnetic waves are an inseperable combination of varying electrical and magnetic fields which are perpendicular to eah other and to the direction of the wave, ans do are classed as transverse waves.
Y-rays: 10-13 +
X-rays: 10-8 - 10-13
Ultrviolet: 10-6.5 - 10-8
Visable: 7.8x10-7 - 3.9x10-7
Infrared: 10-3 - 10-6
Microwaves: 10-1 - 10-3
The larger the wavelength, the smaller the frequency: c=f x /|
Energy of a photon
E= H x f OR E= h x c / /|
E= energy of 1 photon (quantum)
f= frequency (Hz) Unit s-1 (vibraions per second)
h= plans constant= 6.6x10-34Js-
The electron volt
The energy gained by an electron when it is accelerated through a potential difference of 1V
ev x 1.6x10-19 = J
J/ 1.6x10-19= eV
Energy levels and the origin of spectra
The higher energy levels are still there even if they're not occupied by any electrons.
Ground state= all of the electrons occupy the lowest availale energy level
Energy levels are given a number, n, called the quantum number
About potential energy
An electron has a negative value for its PE whilst in orbit around an atom since work must be done to remove it (to infinity, where PE=0)
Atoms aren't always in their "ground state". If an elecron in orbit is given just the right amount of energy, it may move to a higher energy level. The atom is now said to be in an excited state. This can be done by:
2.Photons of certain frequency
What happens next?
The electron will stay in the higher energy level for a short time, before it returns to the ground state.
This happens either directly or via intermediate energy levels.
The electron emits the difference in energy, E2-E1, between the higher energy level, E2, and the lower energy level, E1, as a single photon
E2- E1= hf
White light source= all the wavelengths (continuous spectrum), filament light bulb, spectrometer.
Absorption spectrium= continuous spectrum that contains some dark bands. Absorption of a photon excites the electron.
Fraunhafer= darker lines on the colour, produced by the suns atoms absoribing the specific wavelenghts.
Dark lines remains because atoms emit the absorbed light in random directions so the continuous spectrium doesn't absorib the colours back.
Emission spectrum= produce specific colours/wavelenghts in random directions
Used for: protein/DNA identification, flame tests.
Consists of very few narrow lines on a dark background. Each line corresponds to a specific wavelength.
Produced by low-density gases and vapours.
The atoms in these gases and vapours are so far apart that they don't interact, and their energy levels don't "overlap".
Any excited electron can only move to lower energy levels within that 1 atom, and there is a very limited amount of different wavelengths produced.
Several lines grouped together into bands.
The line within each band are closer together at one side, making this side sharper and brighter.
Produced by gases and vapours whose molecules contain more than 1 atom.
Since these atoms are bonded together, their energy levels "overlap".
This means that there are a greater number of transitions available to any excited electron since there are energy levels available from the other neighbouring atoms.
Procuced by hot solids and liquids and high-density gases.
Atoms are so close that it interacts with many others, and any 1 atom may find many other energy levels overlapping into its own energy levels.
Any excited electrons have a limitless number of availbale energy levels that they can move down into.
Almost every wavelenght of light is produced.
Very short wavelenght electromagnetic waves (1x10-10m)
X rays are produced in an X-ray tube ("Tube" because its a glass container and we can get the air out of it.
How an X-ray tube works
Setting an electron up to a very high speed.
The heat of the filament knocks the electrons out, leaving positive ions, the electrons are attracted to the positive ions and so move back.
Try and attract the electrons back out with another charge- anode
the electrons start accelerating towards the Tungsten target.
X-rays can only come out of one small point due to the Lead shielding
There is a partial vacuum to prevent the electrons colliding with the air.
Properties of X-rays
They travel in straight lines at the speed of light (in a vacuum)
They have a wavelength of 1x10-10m
Effect photographic film
Can penetrate through materials.
Calculating the kinetic energy for an electron str
Work done = Kinetic energy gained
Since W.D= e x V,
e x V = KE gain
If the energy is needed in eV, then divide the answer withe 'e'. KEgain (in eV)= V
KE= 1/2 mv2
A whole range of different wavelengths are produced
usual way of showing this range of x-rays is to plot a graph of intensity vs wavelength