Ionisation Energies Flashcards
where did the evidence that different energy levels in which electrons can exist within atoms initially come from
- atomic emission spectra
- done by a spectroscope
what happened when elements in a gaseous state were given energy by heating or having an electric current run through them
- the electrons in their atoms moved to higher energy levels
- they would eventually move back down to their original energy level
- while emitting electromagnetic radiation
what is a spectroscope specifically measuring
the electromagnetic radiation emitted by the electrons in an atom
a spectroscope shows a series of different coloured lines with a black background behind them. what does this show
- it shows that atoms, specifically electrons, dont emit radiation across the whole of the electromagnetic spectrum
- instead, only specific frequencies are emitted
- which are unique to the element
what types of atoms radiate the same set of frequencies
atoms of the same element
what is the emission spectrum produced called due to its nature
a line spectrum
what does the fact that only certain frequencies of electromagnetic radiation are emitted from electrons support
- the notion that the energy of electrons in atoms can only have certain well defined values
- rather than a continuous range of values
- this is the basis of the quantum theory where the energy levels of electrons is said to be quantised
what is ionisation energy
the measure of the energy required in order to remove an electron from the atom of an element
how do successive ionisation energies support the existence of quantum shells (simple)
- the successive ionisation energies of an element increases steadily
- but big jumps occur at defined places
if sodium has an atomic number of 11, why is the ionisation energy of the 2nd electron much higher than the first ionisation energy and the 10th even more of a larger jump in terms of their ease of removal
- the first electrons is easier to remove than the second
- there is a steady increase in the ionisation energy for the next 8 electrons
- but then a big jump from the ninth to the tenth and 11th
- as the tenth is even harder to remove
why do the differences in the ease of removal of the electrons and therefore their ionisation energies vary like so
- the 10th and 211th electron are in the first quantum shell
- this means that they have the lowest energy
- meaning it requires alot more ionisation energy to excite them enough to escape
- the second quantum shell consists of the previous 8 electrons which sit at slightly higher energy levels
- and therefore require less energy on order to ionise
- the first electrons is in the third quantum shell so it has the most energy out of all the electrons
- meaning that it requires the least energy to ionise
what are the three factors that impact the ionisation energy of an electron in an atom or just the energy an electron has
- the nucleus or nuclear charge
- the shielding
- the distance between the electron and the nucleus (orbitals)
what does a larger nuclear charge lead to and why
- it leads to a larger ionisation energy
- because for a given distance and shielding, the electrostatic forces of attraction between the positively charged nucleus and electron is stronger
- meaning that it would require more energy to overcome this attraction and have the electron escape its pull
what is shielding in an atom
- the repulsion between electrons in an atom
- especially from the electrons at lower quantum shells
what does an increase in the electrons in the lower quantum shells relative to an electron lead to
increased shielding
what does an increase in shielding lead to and why
- it leads to less ionisation energy being required
- because the force repelling the electron, in the outer most shell, outwards and away from the nucleus is stronger
- meaning that the pull of the nucleus is less influential to the electrons
- so it can escape from its orbit easier with less energy needed
what does an increase in the distance between the electron and the nucleus lead to and why
- it leads to less ionisation energy being required
- as more distance between them means that the electrostatic force of attraction the electron would feel from the nucleus is weaker
- meaning it can escape from its orbit with less energy being required
what is the mathematical way of defining ionisation energy
the energy of the electron when removed - the energy of the electron in its original orbital
what can an electron feel an electron-electron repulsion by
- electrons that are in the same orbital (albeit tiny)
- electrons in different orbitals within a given quantum shell
- electrons in adjacent quantum shells
why does electron- electron repulsion lead to a decreased ionisation energy and what is the false reason
- it is not because it ‘cancels out’ from the electrostatic pull of the nucleus or sets up a barrier
- it just raises the energy of the electrons involved (the ones above) above the value they would have if there was no repulsion between them
- which would therefore lead to less ionisation energy that would normally be needed
how do the ionisation energies and energy levels of the electrons of elements change across periods
- the ionisation energies generally increase across periods
- due to the energy levels of the electrons decreasing
how do the factors that impact the energy levels of electrons and therefore their ionisation energies change across periods
- as you move across a period, the nuclear charge increases
- which leads to an increase attraction between the electrons and the nucleus
- so the electrons have a lower energy level meaning an increased ionisation energy
- however, one more electron is added to the same quantum shell
- which increases the shielding (electron-electron repulsion)
- this puts the outer electron about to be ionised at a higher energy level leading to lower ionisation energies
- the orbital the outer electron is in and therefore the distance doesnt change
which of the changing factors proves to be more significant
- the increase in nuclear charge
- leading to an overall decrease in the energy levels of the electrons across periods
- and therefore an increase in their ionisation energies
what periods does the general increase in ionisation energies apply to and what changes this trend
- it applies to periods 2 and 3 mainly
- until you start to get into d-block elements in the 3rd quantum shell
how does the energy of the electrons and therefore their ionisation energies change down groups
- the energy of electrons increase down groups
- which means that the ionisation energy required decreases
how do the factors that impact the energy levels of electrons and therefore their ionisation energies change down groups
- as you go down a group the nuclear charge increases
- this means that the energy level of the outer electron is lower which leads to higher ionisation energies
- however, one new full quantum shell is added as you go down a group once
- this means that there is an increase in shielding or electron-electron repulsion
- meaning the energy level of the outer electron is increased
- the extra shell also means that the outer electron has moved up an orbital leading to increased distances between it and the nucleus
- this means that the electron feels less of a pull so it sits at an even higher energy level
which of the changing factors proves to be more significant
- the combination of the increased shielding and distance is more significant than the increase in nuclear charge
- so there is a general increase in the energy of the outer electrons and therefore a decrease in ionisation energy own group 1
what groups is this trend repeated in
- 2 beryllium to barium
- 5, nitrogen to bismuth
- 6, oxygen to polonium
- 7, flourine to astatine
- 8 neon to radon
