ionisation energy Flashcards
What does it mean if an atom is ionised?
when it loses one or more electrons to form a positive ion
What is 1st ionisation energy?
the energy needed to remove one electron from a mole of gaseous atoms of an element from each atom
What is the ionisation energy units ?
KJmol-1
How would you write the first and second ionisation energy as an equation?
X (g) –> X+1 (g) + e-
2nd:
X+ (g) —> X+2 (g) + e-
What are the 3 factors that affect ionisation energy?
nuclear charge
atomic radius
sheilding
How does nuclear charge affect ionisation energy?
the stronger the positive nuclear charge, the more strongly the electrons will be attracted so the higher the ionisation energy with all other factors being equal
How does atomic radius affect ionisation energy?
the increases distance the decreases attraction to the nucleus so a lower ionisation energy
Why does atomic radius depend what shell the outer electrons are in?
the higher the shell, the higher the average distance from the nucleus
Why does atomic radius depend on outer electrons being in the same shell?
the distance is still not equall due to different nuclear charges felt by the electrons so the higher to nuclear charge, the smaller the atomic radius
How does sheilding affect ionisation energy?
makes the electron being sheilded easier to remove
the higher the shell the greater extent of sheilding
with other things being equal, the attraction to the nucleus will be weaker ans the ionisation energy will be lower
What is sheilding?
an electron being removed is repelled by other electrons in the inner shells
the higher the shell the outer electron is in, the greater the no of inner shells so the greater the extent of sheilding
What happens to ionisation energy across a period?
increases across a period because of decreasing atomic radius
What is periodicity?
an approximately repeating trend across each period
What happens to ionisation energy down a group?
decreases because:
- extra shell = further from the nucleus
- atomic radius increases
- outer electrons experiences more sheilding
- these effects outweigh the increasing nuclear charge so the outer electron is less attracted to the nucleus
Where are the two places where the down a group trend that IE decreases does not apply?
between group 2 and 3 elements
between group 5 and 6 elements
Why does ionisation energy decrease between group 2 and 3?
the highest energy electron is in the p-subshell for the g3 element but in the s-subshell for the g2 element
the p-subshell is slighty higher energy so it is slightly easier to remove the outer electron from the g3 element
Why does ionisation energy decrease between group 5 and 6?
the highest energy electron is in a paired subshell for g6 but not in g5 element
repulsion between paired electrons raises their energy so it makes them slightly easier to remove from g6
Why is the 2nd ionisation energy higher than the first?
once 1 electron has been removed, there are fewer electrons left so they repel each other and the remaining electrons are more attracted to the nucleus
Why is there a big change in ionisation energies of the same element?
happens after a shell has been emptied so the next electron to be removed is closer to the nucleus and harder to remove
How do you log Ionisation energies on your calculator?
shift, squared, log (insert no)
Why would you need to log ionisation no.s?
they are too large and spread out to plot for graphs and to compare data
