Atomic Structure Flashcards
What is a positive ion called?
Cation (this is right). The atom has lost electrons, whereas the anode in electrolysis would be gaining them which is why the positive electrode is called an an anode.
What is a negative ion called?
Anion
What are isotopes?
Isotopes are different atoms of the same element with different mass numbers i.e. different numbers of neutrons in the nucleus.
What is the same about 2 isotopes and what is different?
Isotopes have the same chemical properties (they react in the same way) but different physical properties (different melting points and boiling points).
This is because they have the same number of electrons but different numbers of neutrons and so move at different speeds because some are heavier than others.
What is the relative atomic mass of an element?
The relative atomic mass of an element is the average of the masses of the isotopes in a naturally occurring sample of the element relative to the mass of a 1/12 of an atom of carbon-12.
How do you calculate relative atomic mass from two isotopes?
You take their percentage and times it by their atomic mass and then add it to the other isotope times that isotopes atomic mass and put it over 100.
What does a mass spectrometer show?
It shows us how many of each isotope in a sample. The number of peaks shows how many isotopes we have, and the height (or more properly the area under each peak) is proportional to its abundance in the sample.
What is the K shell?
The lowest energy level or shell, the one closest to the nucleus.
What is a shorthand for how many electrons in an element?
2n^2 with n being the principle quantum number meaning the number of the outer shell.
How do electrons fill shells?
The general rule for filling these energy levels is that the electrons fill them from the lowest energy to the highest (from the nucleus out). The first two energy levels must be completely filled before an electron goes into the next energy level. The third main energy level is, however only filled to 8 before electrons are put into the fourth main energy level. This scheme works for elements with atomic number up to 20.
What is frequency?
v (frequency) = speed of light/wavelength
What are photons?
Photons are how we describe light or electromagnetic energy when it acts or displays the properties of a particle.
What is the evidence for energy levels in atoms?
- Hydrogen atom spectrum
- Ionisation energies
What is the hydrogen atom spectrum and what does it show?
When hydrogen gas at low pressure is subjected to a very high voltage, the gas glows pink. The glowing gas can be looked at through a spectroscope, which contains a diffraction grating and separates the various wavelengths of light emitted from the gas. Because light is emitted by the gas, this is called an emission spectrum. In the visible region, the spectrum consists of a series of sharp, bright, lines on a dark background. This is a line spectrum as opposed to a continuous spectrum which consists of all the colours merging into each other.
The lines get closer together at higher/frequency. Passing an electric discharge through a gas causes an electron to be promoted to a higher energy level (shell). The electron in the higher state is excited and unstable at this higher level and therefore will fall to a lower level, as it does this it releases energy as a photon of light. So each line in the spectrum comes from the transition of an electron from a high energy level to a lower one. The fact that a line spectrum is produced provides evidence from electrons being in energy levels (shells): i.e. electrons in an atom are allowed to have only certain amounts of energy. Each line in the spectrum comes from the transition of an electron from a high energy level to a lower one.
It depends where the excited electrons are falling back down to, if they are falling all the way back to one they release lots of energy and that has a high frequency and is therefore ultraviolet. If they are falling to 2 then it produces visible and if they are falling back to 3 it produces infra red.
The lines in the emission spectrum get closer together at higher frequency/energy. Eventually they come together and converge. This is the convergence limit, the lines merge to form a continuum. Beyond this point the electron can have any energy and so must be free from the the influence of the nucleus. It is not normally observed in the spectrum but can be worked out.
What is the difference between a line spectrum and a continuous spectrum?
In the visible region, the spectrum consists of a series of sharp, bright, lines on a dark background. This is a line spectrum as opposed to a continuous spectrum which consists of all the colours merging into each other.
Line spectrum - only certain frequencies/wavelengths of light present.
Continuous spectrum - all frequencies/wavelengths of light present.
How is an emission spectrum formed?
Passing an electric discharge through a gas causes an electron to be promoted to a higher energy level (shell). The electron in the higher state is excited and unstable at this higher level and therefore will fall to a lower level, as it does this it releases energy as a photon of light. So each line in the spectrum comes from the transition of an electron from a high energy level to a lower one. The fact that a line spectrum is produced provides evidence from electrons being in energy levels (shells): i.e. electrons in an atom are allowed to have only certain amounts of energy. Each line in the spectrum comes from the transition of an electron from a high energy level to a lower one.
How are different lines produced in the hydrogen emission spectrum?
A hydrogen spectrum looks like a series of coloured lines across a black background, however there are parts of the emission spectrum that we cannot see, there are infrared and ultraviolet sections. These sections have their own convergence, and then start agains spaced out at the next part of the electromagnetic spectrum. So in the ultraviolet region the lines get closer and closer together and then they return to being spaced out much further to the right in the visible part.
The different series of lines occur when electrons fall back down to different energy levels. Falling down to shell 3 produces infra red, falling down to 2 produces visible and falling down to 1 produces ultraviolet.
Why are different electromagnetic waves produced by the hydrogen emission spectrum?
It depends where the excited electrons are falling back down to, if they are falling all the way back to one they release lots of energy and that has a high frequency and is therefore ultraviolet. If they are falling to 2 then it produces visible and if they are falling back to 3 it produces infra red.
Why do we use the hydrogen emission spectrum?
It provides evidence for electrons being in energy levels but we particularly use hydrogen because it is simple as it only has one electron.
What is the convergence limit and what does it show?
The lines in the emission spectrum get closer together at higher frequency/energy. Eventually they come together and converge. This is the convergence limit, the lines merge to form a continuum. Beyond this point the electron can have any energy and so must be free from the the influence of the nucleus. It is not normally observed in the spectrum but can be worked out.
