Periodicity Flashcards
1st ionisation energy
the energy required to remove 1 electron from each atom in 1 mole of gaseous atoms
what are successive ionisation energies
the energy required to remove each electron in turn from each atom in 1 mole of gaseous atoms
what is the magnitude of ionisation energy influenced by
nuclear charge, atomic radius, shielding
nuclear charge
the greater the nuclear charge, the greater the attraction on the outer electrons so more energy is required to remove electron - larger ionisation energy
atomic radius
the further the electron from the nucleus the weaker the attraction (less energy required to remove electron - smaller ionisation energy)
shielding
full inner shells of electrons exert a repelling effect on the outer electrons as they are both negatively charged. this reduces the attraction between the nucleus and outer electron (less energy required to remove electron - smaller ionisation energy)
successive ionisation energies
steady increase in amount of energy needed to remove successive electrons
when an electron is removed
the remaining electrons are pulled closer to nucleus - the nucleus attracts remaining electrons more strongly so more energy is needed to remove them (higher i.e)
inner electron removed
there is a big jump in i.e when an electron is removed from an inner shell. the inner electron is much closer to the nucleus and is less shielded than the outer electron, so experiences a greater attraction and has a higher i.e
1st and 2nd i.e and 9th and 10th i.e
this shows clearly where an electron is being removed from an inner shell
1st i.e trend down a group
- nuclear charge increases
- atomic radius increases so electron is further from nucleus
- shielding increases as number of full inner shells increases
- increase in distance and shielding outweigh increased nuclear charge
- nuclear attraction on outer electron decreases
so first ionisation energy DECREASES
1st i.e general trend across period
- nuclear charge increases
- atomic radius decreases so outer electron is closer to the nucleus
- shielding stays same as electrons are in same shell
- nuclear attraction on outer electron increases
- first ionisation energy INCREASES
decrease between groups 2 and 3 (Be and B)
- Be: 1s2 2s2 B: 1s2 2s2 2p1
- 2p orbitals have slightly more energy than 2s
- s electrons provide slightly greater shielding of the p electron
- less energy needed to remove outer electron from B than Be despite increase in nuclear charge
decrease between groups 5 and 6 (N and O)
- N: 1s2 2s2 2p3 O: 1s2 2s2 2p4
- spin pairing occurs in 2p subshell of oxygen
- paired electrons in a 2p orbital of oxygen repel eachother
- less energy needed to remove outer electron from O than N despite increased nuclear charge
what creates nuclear charge
more protons in a nucleus leading to a greater attraction between nucleus and electrons
what is an orbital
the space where an atom can hold two electrons with opposite spins
what did dmitri mendeleev do
in 1869 he noticed that if the elements are arranged in ascending order of atomic mass with new rows started at the correct points then elements with similar properties are grouped in vertical columns
group number
number of outer shell electrons