2. Atomic Structure Flashcards
Where is the mass of an atom concentrated?
The mass of an atom is concentrated in the nucleus
Why is the mass of an atom concentrated in the —?
because the nucleus contains the heaviest subatomic particles (the neutrons and protons)
Why is the mass of an electron not counted?
The mass of the electron is negligible
What is the nucleus’ charge and why?
The nucleus is also positively charged due to the protons
how do electrons contribute to the structure of an atom?
Electrons orbit the nucleus of the atom, contributing very little to its overall mass, but creating a ‘cloud’ of negative charge
What holds an atom together?
The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it is what holds an atom together
What are the subatomic particles? 3 examples
The protons, neutrons and electrons that an atom is made up of are called subatomic particles
Why can we not measure subatomic particles’ masses “normally”?
These subatomic particles are so small that it is not practical to measure their masses and charges using conventional units (such as grams)
How are subatomic particles measured?
Instead, their masses and charges are compared to each other, and so are called ‘relative atomic masses’ and ‘relative atomic charges’
What are the relative atomic mass/charge?
These are not actual charges and masses, but rather charges and masses of particles relative to each other
What mass are protons and neutrons assigned and why?
Protons and neutrons have a very similar mass, so each is assigned a relative mass of 1
What is the mass of an electron and why?
Electrons are 1836 times smaller than a proton and neutron, and so their mass is often described as being negligible
What is the relative charge of a(n):
- proton
- neutron
- electron
- +1
- 0
- -1
What is the atomic number?
he atomic number (or proton number) is the number of protons in the nucleus of an atom and has the symbol Z
What is the atomic number equal to? What specific case is this only applicable to?
The atomic number is also equal to the number of electrons that are present in a neutral atom of an element
What is the mass number?
The mass number (or nucleon number) is the total number of protons + neutrons in the nucleus of an atom, and has the symbol A
How can we calculate the number of neutrons?
Number of neutrons = mass number – atomic number
What are protons and neutrons also called and why?
Protons and neutrons are also called nucleons, because they are found in the nucleus
What are isotopes?
Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
How do we represent isotopes?
The way to represent an isotope is to write the chemical symbol (or the word) followed by a dash and then the mass number
e.g carbon-12
What type of charge does an atom have?
An atom is neutral and has no overall charge
What charge do ions have and why?
Ions on the other hand have either gained or lost electrons causing them to become charged
How is the mass of an element given regarding all of its isotopes?
Because of this, the mass of an element is given as relative atomic mass (Ar) by using the average mass of all of the isotopes
How can the relative atomic mass of an element be calculated?
The relative atomic mass of an element can be calculated by using the percentage abundance values
How can we find out the percentage abundance of an isotope?
can be read off the mass spectrum
How would we calculate the relative atomic mass of an atom including all of its isotopes?
(% abundance x massA) + (% abundance x massB) / 100
What is the electromagnetic spectrum?
The electromagnetic spectrum is a range of frequencies that covers all electromagnetic radiation and their respective wavelengths and energy
What is an electromagnetic spectrum divided into?
It is divided into bands or regions
What type of chemistry is an electromagnetic spectrum important?
very important in analytical chemistry
What does an electromagnetic spectrum show the relationship between?
The spectrum shows the relationship between frequency, wavelength and energy
What is frequency?
Frequency is how many waves pass per second
What is wavelength?
wavelength is the distance between two consecutive peaks on the wave
How can we tell that radiation is dangerous?
Gamma rays, X-rays and UV radiation are all dangerous – you can see from that end of the spectrum that it is high frequency and high energy, which can be very damaging to your health
What type of energy, wavelength and frequency does radio waves, micro waves and infrared have?
lower energy
long wavelength
low frequency
What type of energy, wavelength and frequency does ultraviolet, x-rays and gamma rays have?
higher energy
short wave length
high frequency
What distinguishes light waves?
All light waves travel at the same speed; what distinguishes them is their different frequencies
What symbol represents the speed of light?
c
What is the speed of light?
The speed of light is constant and has a value of 3.00 x 108 ms–1
What is the symbol of frequency?
symbol ‘ν‘
What is frequency inversely proportional to?
frequency is inversely proportional to wavelength
What is the symbol for wavelength?
λ
what equation links, frequency, wavelength and the speed of light?
The equation that links them is c = νλ
What can use the equation to calculate? c = νλ
Since c is constant you can use the formula to calculate the frequency of x given the wavelength, and vice versa
what is a continous spectrum?
a continuous spectrum in the visible region contains all the colours of the spectrum
What does a line spectrum show?
a line spectrum only shows certain frequencies
What does a line spectrum tell us?
This tells us that the emitted light from atoms can only be certain fixed frequencies – it is quantised
Why can light emitted by atoms only be certain frequencies?
Electrons can only possess certain amounts of energy – they cannot have any energy value
Where do electrons move?
Electrons move rapidly around the nucleus in energy shells
Can electrons jump energy levels, why/when?
If their energy is increased, then they can jump to a higher energy level
The process is reversible, so electrons can return to their original energy levels
What happens when electrons jump energy levels?
When this happens, they emit energy
Is the frequency emitted by electrons when they jump up a level different?
The frequency of energy is exactly the same, it is just being emitted rather than absorbed:
What does it mean if an electron is in an excited state?
higher energy and further from nucleus
How is the frequency of energy expressed from
a) ground state -> excited state
b) excited state -> ground state
a) absorption (of energy)
b) emission (of energy)
What is the frequency of the energy emitted by an electron?
The energy they emit is a mixture of different frequencies
What (could) the mix of frequencies emitted by an electron link to?
This is thought to correspond to the many possibilities of electron jumps between energy shells
What can be done if the emitted energy is in the visible region of a spectrum?
What is the result?
If the emitted energy is in the visible region, it can be analysed by passing it through a diffraction grating
The result is a line emission spectrum
What do the lines on a line emission spectra represent?
Each line is a specific energy value
What do the varying lines on a line emission spectra suggest?
This suggests that electrons can only possess a limited choice of allowed energies
What are the lines on a line emission spectra called?
These packets of energy are called ‘quanta‘ (plural quantum)
What part of the le spectrum do the lines get closer together?
the lines get closer together towards the blue end of the spectrum (the higher energy end)
What is it called when lines towards of the le spectrum get closer together?
why?
This is called convergence and the set of lines is converging towards the higher energy end, so the electron is reaching a maximum amount of energy
What does the maximum energy of an atom correspond to?
This maximum corresponds to the ionisation energy of the electron
Who was the first to observe the lines in the blue section on an le spectrum?
These lines were first observed by the Swiss school teacher Johannes Balmer, and they are named after him
What do the lines at the end of an le spectrum show?
We now know that these lines correspond to the electron jumping from higher levels down to the second or n = 2 energy level
Who found out why there were convergent lines on an le spectrum? what was the name of the theory?
Balmer could not explain why the lines were formed – an explanation had to wait until the arrival of Planck’s Quantum Theory in 1900
How did Niels Bohr make use of Planck’s Quantum theory?
Niels Bohr applied the Quantum Theory to electrons in 1913, and proposed that electrons could only exist in fixed energy levels
What theory did the line emission spectrum of hydrogen help provide?
The line emission spectrum of hydrogen provided evidence of these energy levels
What do the families of lines on the line emission spectrum of hydrogen show?
it was deduced that the families of lines corresponded to electrons jumping from higher levels to lower levels
give the region and energy for the jump n(alpha) -> n1
region - infrared
energy - low
give the region and energy for the jump n(alpha) -> n2
region - visible
energy - in between high and low?
give the region and energy for the jump n(alpha) -> n3
region - ultraviolet
energy - high
What is the electron configuration?
The arrangement of electrons in an atom
How are electrons arranged around the nucleus?
Electrons are arranged around the nucleus in principal energy levels or principal quantum shells
What is used to number the energy levels?
Principal quantum numbers (n)
What does it mean the:
a) lower
b) higher
the principal quantum number is?
a) The lower the principal quantum number, the closer the shell is to the nucleus
b) The higher the principal quantum number, the lesser the energy of the shell
How many electrons (not exact number) can each principle quantum number hold?
Each principal quantum number has a fixed number of electrons it can hold
How many electrons can n=1 hold?
2
How many electrons can n=2 hold?
8
How many electrons can n=3 hold?
18
How many electrons can n=4 hold?
32
What is the mathematical relationship between the number of electrons and the principal energy level?
2n^2
What are principal quantum shells split into? What are they called?
are split into subshells which are given the letters s, p and d
What number of electrons does an element need to have an f subshell?
57
How does the energy of the electrons in the subshells change?
The energy of the electrons in the subshells increases in the order s < p < d
Do the subshells and principal quantum shells overlap?
The order of subshells overlap for the higher principal quantum shells
What do the subshells contain?
subshells contain one or more atomic orbitals
Where do orbitals exist?
Orbitals exist at specific energy levels and electrons can only be found at these specific levels, not in between
How many electrons can occupy 1 atomic orbital?
by a maximum of two electrons
WHat is the ground state?
The ground state is the most stable electronic configuration of an atom which has the lowest amount of energy
How is the ground state achieved? What principle?
This is achieved by filling the subshells of energy with the lowest energy first (1s) – this is called the Aufbau Principle
What order do the subshells follow after n=3?
The order of the subshells in terms of increasing energy does not follow a regular pattern at n= 3 and higher
What do the principal quantum shells increase in with increasing principal quantum number?
The principal quantum shells increase in energy with increasing principal quantum number
Eg. n = 4 is higher in energy than n = 2
How do the subshells increase in energy?
The subshells increase in energy as follows: s ＜ p ＜ d ＜ f
WHat is the exception for the pattern of increase in energy for subshell?
The only exception to these rules is the 3d orbital which has slightly higher energy than the 4s orbital, so the 4s orbital is filled before the 3d orbital
What level of energy do orbitals in the same subshell have and what are they called?
All the orbitals in the same subshell have the same energy and are said to be degenerate
How many orbitals can (x) subshell hold?
a) s
b) p
c) d
d) f
1
3
5
7
What are the maximum number of electrons in each subshell?
s 1 x 2 (can hold 2 electrons)
p 3x2 = 6
d 5x2 = 10
f 7x2 = 14
What shape do the s orbitals have?
The s orbitals are spherical in shape
What changes the size of an s orbital?
The size of the s orbitals increases with increasing shell number
E.g. the s orbital of the third quantum shell (n = 3) is bigger than the s orbital of the first quantum shell (n = 1)
What shape are the p orbitals?
The p orbitals are dumbbell-shaped
How many p orbitals does each shell have?
Every shell has three p orbitals except for the first one (n = 1)
What axes do the p orbitals occupy?
The p orbitals occupy the x, y and z axes
How are the p orbitals oriented?
point at right angles to each other, so are oriented perpendicular to one another
How does the shape of a p orbital change with increasing shell number?
The lobes of the p orbitals become larger and longer with increasing shell number
What does the electron configuration give us information about?
The electron configuration gives information about the number of electrons in each shell, subshell and orbital of an atom
How are the subshells filled?
The subshells are filled in order of increasing energy
How do electrons move?
Electrons can be imagined as small spinning charges which rotate around their own axis in either a clockwise or anticlockwise direction
What is the spin of the electron represented by?
The spin of the electron is represented by its direction
What does electron spin create?
The spin creates a tiny magnetic field with N-S pole pointing up or down
What is spin-pair repulsion?
Electrons with the same spin repel each other which is also called spin-pair repulsion
Why do electrons occupy separate orbitals in the same subshell first?
Therefore, electrons will occupy separate orbitals in the same subshell first:
to minimise this repulsion and have their spin in the same direction
What do electrons pair up with? WHat is this rule called?
They will then pair up, with a second electron being added to the first p orbital, with its spin in the opposite direction
This is known as Hund’s Rule
What does the principal quantum number indicate?
The principal quantum number indicates the energy level of a particular shell but also indicates the energy of the electrons in that shell
What is the Pauli Exclusion Principle?
An orbital can only hold two electrons and they must have opposite spin – the is known as the Pauli Exclusion Principle
What is the reasoning for the Pauli Exclusion Principle?
This is because the energy required to jump to a higher empty orbital is greater than the inter-electron repulsion
For this reason, they pair up and occupy the lower energy levels first
How can the electron configuration be represented (apart from using electron shellS)?
orbital spin diagrams
What does each box represent?
orbital spin diagrams
Each box represents an atomic orbital
How are the boxes arranged?
orbital spin diagrams
The boxes are arranged in order of increasing energy from lower to higher (i.e. starting from closest to the nucleus)
How are the electrons represented?
orbital spin diagrams
he electrons are represented by opposite arrows to show the spin of the electrons
What does writing out the electronic configuration tell us?
Writing out the electronic configuration tells us how the electrons in an atom or ion are arranged in their shells, subshells and orbitals
What does the full electron configuration describe?
The full electron configuration describes the arrangement of all electrons from the 1s subshell up
What does the shorthand electron configuration describe?
The shorthand electron configuration includes using the symbol of the nearest preceding noble gas to account for however many electrons are in that noble gas, followed by the rest of the electron configuration
How are positive ions formed?
Positive ions are formed by removing electrons from the outer subshell
how are negative ions formed?
Negative ions are formed by adding electrons to the outer subshell
Do transition metals fill 4s or 3d orbital first?
The transition metals fill the 4s subshell before the 3d subshell, but they also lose electrons from the 4s first rather than from the 3d subshell
What two elements are an exception to the Aufbau principle?
chromium and copper
What is the electronic configuration for Cr?
Cr is [Ar] 3d5 4s1
What is the electronic configuration for Cu?
Cu is [Ar] 3d10 4s1
Why are chromium and copper exceptions?
This is because the [Ar] 3d5 4s1 and [Ar] 3d10 4s1 configurations are energetically favourable
What did Rutherford’s experiment reveal?
Rutherford’s experiment revealed that atoms have a nucleus
What did Rutherford do in his experiment?
In his experiment, he shot alpha particles straight towards a sheet of gold foil. Around this foil was a florescent screen that would flash when alpha particles hit the screen
What did Rutherford predict?
It was predicted that these alpha particles would go straight through the gold foil and not get deflected
What actually happened in Rutherford’s experiment?
However, a small percentage of particles were deflected through angles much larger than 90 degrees. Some particles even were scattered back
What 2 things did Rutherford’s experiment prove?
The atom was mostly empty space instead of a solid (plum pudding model)
This also showed that atoms had a nucleus, as alpha particles would sometimes get deflected backwards when they would hit the nucleus
What are the chemical properties of isotopes i.e are they different?
Chemical properties depend on the outer shell of electrons.
Since isotopes still have the same number of electrons, these properties will remain the same
What are the physical properties of isotopes i.e are they different?
Physical properties depend on their nuclei.
Since the number of neutrons changes, properties such as density, rate of diffusion, melting and boiling change. The mass will also change
Why are many isotopes radioactive?
Many isotopes are radioactive because the nuclei are more prone to breaking down spontaneously. Radiation is emitted when this happens
What are 3 examples of radioisotopes?
carbon-14
cobalt-60
iodine-131/idodine-125
WHat is a mass spectrometer?
A mass spectrometer is an instrument that can be used to measure the individual masses of atoms
What can a mass spectrometer measure in terms of isotopes?
A mass spectrometer separates individual isotopes from a sample of atoms and determines the mass of each isotope
What are the 6 (general) stages of mass spectrometry?
- vaporisation
- separation of particles
- ionisation
- acceleration
- deflection
detection
WHat happens in vaporisation?
mass spectrometry
Vaporization: The sample is heated and vaporized, and passed through into an evacuated tube (this separates particles)
What happens in ionisation?
mass spectrometry
The atoms/molecules are then bombarded by a stream of high energy electrons, knocking electrons off the particles, resulting in ions with a 1+ charge
- WHat happens in acceleration?
mass spectrometry
The positively charged ions are then accelerated along the tube by means of the attraction to negatively charged plates.
The ions pass through the slits, which control the direction and velocity of their motion
What happens in deflection?
mass spectrometry
Deflection: The ions are then passed into a very strong magnetic field, deflecting the ions in a curved path
WHat happens in detection?
mass spectrometry
Detection: The ions are detected electronically by a device that measures the location and the number of particles
What does the deflection or path of an ion in a mass spectrometer depend on?
mass spectrometry
Absolute mass of the ion
Charge of the ion
Strength of magnetic field
Velocity (speed) of ions
How are the masses of an isotope presented?
mass spect..
This information is presented as a mass spectrum. In a mass spectrum showing the number of isotopes of an element:
What does the number of peaks show?
mass spectrum
The number of peaks indicates the number of isotopes
What does the position of each peak on the horizontal axis show?
mass spectrum
The position of each peak in the horizontal axis indicates the relative isotopic mass
What do the relative heights of the peaks correspond to?
mass spectrum
The relative heights of the peaks correspond to the relative abundance of the isotopes
What 4 mmain ideas does the Bohr model support?
Electrons orbit the nucleus in ring like paths around the nucleus at fixed energy levels. The higher the energy level the farther away the electron is from the nucleus and the higher the energy
Orbits further from the nucleus exist at higher energy levels
Bohr said that electrons are quantized, meaning electrons can only occur in one energy level or another but nothing in between. The ground state is the energy level an electron normally occupies
Electrons can only move from one orbital to another orbital at one time. When electrons absorb energy they move up to a higher energy level. This is called the excited state.
When the electron returns to a lower energy level they emit energy. These emissions are not always visible to the naked eye
`What is one weakness of Bohr’s model?
One weakness of Bohr’s model was that he could not offer a reason why only certain energy levels were allowed
