periodicity

Question 1

the periodic table

essential idea

Answer 1

the arrangement of elements in the periodic table helps to predict their electron configuration

Question 2

physical properties

Answer 2

1) DISTANCE from the nucleus to the outer shell- this is largely determined by the number shells
2) SHIELDING by inner electrons- INNER SHELLS reduce the effect of the nucleus due to repulsion
3) NUCLEAR CHARGE- the greater the actual nuclear charge, the greater
4) SUB SHELLS & ELECTRON PAIRING - if trends cannot be explained by considering the above factors then look for the difference in sub shells or electron pairing

Question 3

Atomic radius

Answer 3

• atomic radius is measured as half the distance between 2 bonded atoms
• on descending a group the atomic radius increases
• across a period the atomic radius decreases

Question 4

Ionic radius

Answer 4

• distance between nucleus and outer most electrons of postive metal cations or negative non metal anions
• ionic radius increases descending a group
• metal cations are smaller than their atoms coz they have lost their outer shell electrons.
• non metal anions tend to be larger than their atoms as they have gained electrons into their outer energy levels

across a period metal cations get smaller

non metal anions also get smaller but are larger than the cations

Question 5

ionisation energy

Answer 5

the minimum amount of energy required to remove 1 mol of electrons from 1 mol of gaseous atoms
M -> M+ + e-

on descending a group ionisation energy decreases

across a period ionisation energy generally increases

Question 6

Electronegativity

Answer 6

Electronegativity is the ability of an atom to attract a pair of electrons towards itself with a covalent bond

descending a group electronegativity decreases

across a period electronegativity increases

Question 7

Electron affinity

Answer 7

the first electron affinity is the energy change when one mol of electrons is added to one mol of gaseous atoms