Topic 2: Atomic Structure Flashcards
What is the relative charge of a neutron proton and electron?
Neutron: 0
Proton: +1
Electron: -1
What does the atomic number tell us?
The atomic number defines an element – it is unique to that particular element
If the overall charge on an atom is 0 what is the number of protons relatie to electrons in an atom?
number of protons in an atom = number of electrons
How to calculate the mass number (A)?
number of protons + neurotrons
WHat does the A and Z stand for?
A: mass number
Z: atomic number
Define ions
Ions are charged particles that are formed when an atom loses or gains an electron(s)
What is a positive and negative ion called?
Cation and Anion
How is a cation formed?
when an atom loses electrons = positive ion
How is an anion formed?
when an atom gains electrons = negative ion
Define isotopes
Isotopes are different atoms of the same element with different mass numbers: i.e. different numbers of neutrons in the nucleus
Do isotopes have the same chemical properties and physical properties?
Isotopes have the same chemical properties (they react in exactly the same way) because they have the same numbers of electrons, and chemical reactions depend only on the number and arrangement of electrons and not on the composition of the nucleus.
but different physical properties (e.g. different melting and boiling points) because, for example, the different masses mean that their atom move at different speeds.
What are the subatomic particles?
Protons, neutrons and electrons
What is the relative atomic mass (Ar)?
the average of the masses of the isotopes in a naturally occurring sample of the element to the mass of 1/12 of an atom of carbon-12
Why do we quote the average mass for an atom and what is it called?
Because of the different isotopes present, it is most convenient to quote an average mass for an atom – this is the relative atomic mass (Ar)
What is Ar
Relative atomic mass
What is the use of a mass spectrometer?
It is an instrument that can be used to measure the proportion of each isotope present in a sample of an element
What are the processes that goes on in the mass spectrometer? (5)
- Heating filament to vaporize inserted sample into gas
- Electron beam to ionize sample to bombard it with high energy electrons to produce positively charged ions (electrons will knock off the electrons)
- Positive ions are accelerated in the electric field
- Deflection -magnetic field causes a deflection, affected by charge (more charge, more deflection), mass (heavier, harder to change direction = straight trajectory). Both affect how much it curves around.
- Detector
- Vaporization
- Ionization
- Acceleration
- Deflection
- Detection
Whaty is the readout from a mass spectrometer called?
mass spectrum
What can be see in a mass spectrum of an element?
one peak for each individual isotope
the height of each peak (more properly, the area under each peak) is proportional to the number of atoms of this isotope in the sample tested
How do i measure the Ar of this?
How are electrons in an atom arranged?
They are arranged in energy levels (shells) around the nucleus
Which energy level has the lowest energy?
The first energy level or first shell, the one closest to the nucleus
What changes as the shells get further from the nucleus?
they increase in energy
What is the maximum number of electrons in each shell given by?
2n^2
What is the general rule for filling energy levels?
The general rule 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 numbers up to 20.
What are various forms of electromagnetic radiation usually regarded as?
They are usually regarded as waves that travel at the speed of light in a vacuum but vary in the frequency/energy/wavelength
What are particles of electromagnetic radiation called?
Photons
What are the colours of the spectrum in order of increasing energy?
Red < orange < yellow < green < blue < indigo < violet
What is an emission spectrum?
It is the light emitted by a gas that is seen through a spectroscope, which contains a diffraction grating and separates the various wavelengths of light emitted from the gas.
By first subjecting a gas to a very high voltage at low pressure, the gas will glow a certain colour. And by looking at this glowing gas through a spectroscope, which contains a diffraction grating and separates the various wavelengths of light emitted from the gas.
Describe the electromagnetic spectrum
- Wavelength (red has high, violet has low)
- Energy photons (red has low, violet has high)
- Frequency (red has low, violet has high)
What is a line spectrum
when the spectrum consists of a series of sharp, bright lines on a dark background?
only certain frequencies/wavelengths of light present
What is the difference between a line spectrum and a continuous spectrum?
Light spectrums only contain frequencies/wavelengths of light present
Continuous spectrum shows all frequencies/wavelengths of light present
Continuous shows all the colours, has all the frequencies and a line spectra has selected frequencies
How is an emission spectrum formed?
It’s formed by passing an electric discharge through a gas causing an electron to be promoted to a higher energy level (shell)
electon is unstable in this higher level and will fall to a lower energy level
when an elecron falls from a higher to a lower energy level in an atom, a photon of light is emitted
What happens when energy is given to an electron at its ground state?
The electron will be promoted to a higher energy level. When they are in a higher energy level than the ground state, this is called an excited state
How is the line in the spectrum determined?
When the electron falls back to the ground state, the energy is given out in the form of a photon of light. This contributes to a line in the spectrum.
Each line in the spectrum comes from the transition of an electron from a high energy level to a lower one.
What evidence shows that electrons are in energy levels (shells)?
The fact that a line spectrum is produced provides evidence for electrons being an energy levels
Electrons in an atom are allowed to have only certain amount of energy
When do different series of lines occur?
The different series of lines occur when electrons fall back down to different energy levels
Which levels do electrons fall to in the infrared, visible, ultraviolet region? What does this tell us about the energy differences?
Ultraviolet: All transitions involve electrons falling down to level 1
Visible: to level 2
Infrared: to level 3
We can deduce that the energy difference between level one and any other level is bigger than that between level two and any other higher levels
What is the convergence limit? What does it form? What happens to the electron’s energy?
The convergence limit is the frequency (or wavelength) at which the spectral lines converge. The lines merged together to form a continuum. Beyond this point the electron can have any energy and so it must be free from the influence of the nucleus, i.e. electron is no longer in the atom
What is the shape of the 1s orbital and 2s orbitals
s orbitals are sphere, 2s is bigger than 1s
What do p orbitals look like?
They have a dumb-bell shape.
What do d orbitals look like?
Clover
What do f orbitals look like?
What is the Pauli exclusion principle?
The maximum number of electrons in an orbital is two. If there are two electrons in an orbital, they must have opposite spin
What is the Hund’s rule?
Electrons fill orbitals of the same energy (degenerate orbitals) so as to give the maximum number of electrons with the same spin.
What is the Hund’s rule?
Electrons fill orbitals of the same energy (degenerate orbitals) so as to give the maximum number of electrons with the same spin.
What are the two exceptions in electron configurations?
Chromium and copper
both with only one electron in the 4s sub-level
