atomic structure

Question 1

why do electrons occupy the 4s orbital first before the 3d orbital?

Answer 1

4s orbital is at a lower energy level than the 3d orbital

Question 2

explain the electronic configuration of Cr

Answer 2

instead of 3d^4 4s^2 is 3d^5 4s^1
by the time Cr is reached, 3d and 4s orbitals are about equal in energy
by having one electron each in the 3d and 4s orbital, inter electronic repulsion is minimised,
hence 3d^5 4s^1 more stable

Question 3

explain the electronic configuration of Cu

Answer 3

instead of 3d^9 4s^2 is 3d^10 4s^1
the fully filled 3d subshell is unusually stable due to symmetrical charge distribution around the metal centre,
hence 3d^10 4s^1 more stable

Question 4

why does atomic radius decrease across a period

Answer 4

across period,
increasing protons so greater nuclear charge but e are added to the valence shell so SE remains constant, hence ENC increases valence e more tightly held, smaller in size

Question 5

why does atomic radius increase down a group

Answer 5

down group,

• no. of e shells increases
• distance between nucleus and valence e increases
• shielding effect increases
• despite increasing nuclear charge,
• electrostatic attraction between nucleus and valence e decreases, resulting in increase in size of e cloud

Question 6

why cations smaller than atoms

Answer 6

cations have 1 less occupied e shell

- distance between nucleus and valence e decreases

Question 7

why anions bigger than atoms

Answer 7

anions have more electrons, inter electronic repulsion increases

Question 8

explain ionic radius of isoelectronic ions across a period

Answer 8

decreases across period, (Na+ to Si4+, P3- to Cl-)

• no. of protons increases, hence nuclear charge increases
• valence e experience same shielding effect
• ENC increases
• electrostatic attraction between nucleus and valence e increases, resulting in decrease in size of e cloud

Question 9

define first ionisation energy

Answer 9

the energy required to remove 1 mole of electrons from 1 mole of gaseous M atoms to form 1 mole of gaseous M+ ions

Question 10

is ionisation energy endo or exo

Answer 10

endo, they are alw positive as they absorb energy to overcome attraction between electron and the nucleus

Question 11

explain general trend of IE across a period (1/radius)

Answer 11

generally increase across period,

• no. of e shells remain the same
• no. of protons increases hence nuclear charge increases
• shielding effect constant, ENC increases
• electrostatic attraction between nucleus and valence e increases, hence requiring more energy to remove valence e

Question 12

explain the 2 irregularities of IE across period

Answer 12

1. grp 2 & grp 13 (Al

Question 13

explain general trend of IE down a grp

Answer 13

decrease down a grp,

• no. of e shells increases
• distance between valence e and nucleus increases
• shielding effect increases
• despite increasing nuclear charge, electrostatic attraction between nucleus and valence e decreases, hence less energy required to remove valence e

Question 14

explain trend in successive IE of an element

Answer 14

increases,
once the first e removed from neutral atom, each successive e removed from an ion of increasing positive charge which attracts the e more strongly

Question 15

for graphs of IE

Answer 15

highest IE: grp 1
lowest IE:grp 2
from there you count the group

Question 16

define EN

Answer 16

is the ability of an atom to attract shared electrons towards itself

Question 17

explain trend of EN across a period (1/radius)

Answer 17

increases,

• no. of e shells remain the same
• no. of protons increases hence nuclear charge increases
• shielding effect constant, ENC increases
• electrostatic attraction between nucleus and shared e increases

Question 18

explain trend of EN down a grp (1/radius)

Answer 18

decreases,

• no. of e shells increases
• distance between nucleus and shared e increases
• shielding effect increases
• despite increasing nuclear charge, electrostatic attraction between nucleus and shared e decreases