3.7.2: ionisation energies Flashcards
what’s the first ionisation energy?
the energy required to remove 1 electron from each atom in 1 mole of gaseous atoms
what does ionisation energy measure?
how easily an atom loses electrons to form positive ions
what’s the formula for ionisation energies?
X (g) –> X+ (g) + e-
what are 4 factors affecting ionisation energy?
PROTONS (nuclear charge): the more protons there are in the nucleus the greater the attraction between the nucleus and outer electrons
RADIUS: the greater the distance between the nucleus and outmost electron the weaker the nuclear attraction (this has a large effect)
SHIELDING: the more shielding the weaker the attraction between the nucleus and outermost electrons; electrons are negatively charged so inner shell electrons repel outer shell electrons (shielding effect) which reduces the attraction between the nucleus and outer electrons
(attraction between nucleus and outermost electrons)
what’s the trend in first ionisation energy across the period?
first ionisation energies increase across periods because the shielding stays the same but the number of protons increase which pull the electrons closer to the nucleus and decrease the radius so theres more of an attraction between the nucleus and outermost electron and more energy is needed to remove it
what’s the trend in first ionisation energy down a group?
first ionisation energy decreases down a group so less energy is required to remove the outermost electron; although the nuclear charge increases this is outweighed by the fact the radius of the atoms increase, and the shielding increases so the attraction between the nucleus and outermost electron decreases
why are trends in first ionisation energies important?
they provide important evidence for the existence of shells and sub-shells
why is there a drop in ionisation energy in group 3 elements?
because the 2p subshell is starting to be filled - the 2p subshell has a higher energy level so its easier to remove the outermost electron
why’s there a drop in ionisation energy at group 6 elements?
because the p orbitals begins to pair electrons which creates electron pair repulsion so it’s easier to remove outermost electron
why is there a drop in ionisation energy from the noble gases to the next group 1 metal?
because the number of shells has increased which means there’s a larger distance between the outermost electrons and the nucleus and a weaker force of attraction between the nucleus and outermost electrons so it’s easier to lose the outermost electron
what’s successive ionisation energies?
the energy required to remove an electron from each ion in 1 mole of gaseous X+ ions to form X+1 + ions
what’s the trend in successive ionisation energies?
ionisation energies increase because as more electrons are lost the remaining electrons are pulled closer to the nucleus as there’s more nuclear attraction so more energy is required to remove outermost electron
what can successive ionisation energies be used for?
to make predictions about the number of electrons, group of element and identity of an unknown element
