trends in atomic radius and first ionisation energy Flashcards
how do we measure atomic radius ?(why cant we just measure it normally)
you can not measure the atomic radius of an isolated atom because there is not clear point around it at which the electron density drops to zero .instead half the distance between the centres of a pair of atoms is used .
what are the general rules for atomic radius in the periodic table ?
it decreases across each period and jumps back up when starting the next one
atoms get larger down any group
why does atomic radius deacrease across a period ?
there are more electrons and protons so the increased charge between them pulls the electrons closer to the nucleus
why does atomic radius increase down a group ?
going down a group , the atoms have one extra main level of electrons compared to the one before so outer main level is further from the nucleus and atomic radii increase
what is first ionisation energy ?
the energy required to convert one mole of isolated gaseous atoms into one mole of singly positively charged gaseous ions . (to remove one electron from each atom )
give the equation for first ionisation energy
E(g) -> E+(g) + e-(g) (E stands for any element )
describe the periodicity of first ionisation energy ?
generally increase across a period.
decrease going down a group
explain why first ionisation energy increases across period ?
number of protons increases but electrons enter the same main level .so charge increases so it’s increasingly difficult to remove an electron .
why does first ionisation energy decrease going down a group ?
the number of filled inner levels down the group . this results in increased shielding .the electron is removed at an increasing distance from the nucleus and therefor is held less strongly so the outer electron gets easier to remove going down a group because they are further away from the nucleus
why is there a drop in ionisation energy from one period to the next ?
a new main level starts and so there is and so there is and increase in atomic radius ., the outer electron is further from the nucleus .less strongly attracted and easier to remove
which groups do ionisation energy drop between ?
group 2 and 3
group 5 and 6
why does ionisation energy drop between group 2 and 3?
for the first ionisation energy magnesium looses a 3s electron. Aluminium looses a 3p electron.
The P electron is in a higher energy level then the s electron so it takes less energy to remove it
explain the drop in ionisation energy between group 5 and 6?
it i easier to remove an electron from a pair of electrons than it is to remove it singly as it is already being repelled
phosphorus has no paired electron in its P orbital
sulfur has two of the electrons paired in its P orbitals
is seconds ionisation energy higher or lower than first ionisation energy ?
higher
