7.2 Ionisation Energies
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What is first ionisation energy?
energy required to REMOVE 1 ELECTRON from EACH ATOM in 1 MOLE of GASEOUS ATOMS to form 1 MOLE of GASEOUS 1+ IONS
What are the factors affecting ionisation energy?
ATOMIC RADIUS NUCLEAR CHARGE NUMBER OF SHELLS
How does increasing ATOMIC RADIUS affect ionisation energy?
￪ atomic radius = • weaker electrostatic attraction between electrons + nucleus • Outer electrons require less energy to remove • Less endothermic ionisation energy
How does increasing NUCLEAR CHARGE affect ionisation energy? (moving across period)
￪ nuclear charge = • more protons in nucleus • stronger electrostatic attraction between electrons + nucleus • Outer electrons require more energy to remove
How does increasing the SHELL NUMBER affect ionisation energy?
￪ number of shells = • greater shielding effect • more repulsion of outer electrons by inner shells • weaker electrostatic attraction between outer electrons + nucleus • Outer electrons require less energy to remove
Which effect is greater, nuclear charge or shielding?
shielding
Is ionisation energy always exothermic or endothermic and why?
endothermic energy must be put into system in order to overcome electrostatic attraction to remove electron
Across a period, ionisation energy generally increases, why?
￪ no. of protons ￪ nuclear charge same shielding stronger electrostatic attraction of outer electrons to nucleus ￬ atomic radius
If element A has a greater nuclear charge than element B, element B will have a _____ ionisation energy IF A has more shells.
higher
Across a period, ionisation energy generally _____. this means different things for reactivity depending on whether the element reacts by gaining or losing an electron.
increases
_____ electrostatic attraction of outer electrons to nucleus = high ionisation energy
strong
_____ electrostatic attraction of outer electrons to nucleus = low ionisation energy
weak
For metals, a low ionisation energy means a _____ reactivity. Explain this trend.
high react by losing electrons if electrostatic attraction is weak + ionisation energy is low, electrons are more easily lost
Is the 2nd ionisation energy higher or lower than the first? Why?
higher after first electron lost, atom is 1+ cation & same amount of positive charge attracting less negative charge stronger electrostatic attraction of outer electrons to nucleus requires more energy to remove
2nd ionisation energy is _____ than 1st.
greater
What do successive ionisation energies give an indication of?
GROUP of the element
How can you tell the group of an element based on it’s successive ionisation energies?
successive ionisation energies increase because of cation formation LARGE JUMP = electron being removed from lower shell
Why does taking an electron from a lower shell have a significantly larger ionisation energy?
lower shell = closer to nucleus STRONGER ELECTROSTATIC ATTRACTION of outer electrons to nucleus more ENERGY REQUIRED to overcome electrostatic attraction + remove electron
Why is the ionisation energy of group 3 less than group 2?
electron in group 3 is in 2p orbital further from nucleus weaker electrostatic attraction requires less energy to remove than 2nd electron
Why is the ionisation energy of group 6 less than group 5?
electron in group 6 is the first in the p block to share an orbital with another electron repulsion within orbital requires less energy to remove than 5th electron (which does not share an electron)
More reactive metals have a _____ ionisation energy.
lower (react by losing electrons, more easily lost if ionisation energy is lower)