Structure atomique

Question 1

Define mass/nucleon number

Answer 1

Total no of protons & neutrons in atom

Question 2

Define atomic number

Answer 2

no of protons in an atom (unique for each element)

Question 3

Define isotopes

Answer 3

atoms of same element containing same no of protons but diff no of neutrons

Question 4

Letting p be proton no, n be no of nucleus and e be no of electrons,
mass no=?
atomic no=?

Answer 4

mass no = p+n
atomic no = p (=e for atoms, which are neutral)

Question 5

electron is … in mass than proton

Answer 5

lighter

Question 6

How do subatomic particles behave in electric field?

Answer 6

protons (+) deflected to -ve plate
electrons (-) deflected to +ve plate
neutrons (neutral) not deflected at all
(direction of deflection depends on charge)

Question 7

In electric field,
Angle of deflection proportional to…?

Answer 7

magnitude of charge/mass (written as q/m)

*extent of deflection for electrons much more than protons due to its much smaller mass

Question 8

Each electron shell is assigned a principal quantum number, n, where n=1,2,3…
First shell is closest to nucleus and has… energy
As n increases, distance of orbital to nucleus and hence size of orbital…

Answer 8

lowest,
increases

Question 9

The larger the value of n
the … electron is to nucleus,
the … strongly electron is bound to nucleus
the … the … of electron

Answer 9

further,
less,
higher, energy level

Question 10

What are subshells? Explain

Answer 10

• grp of orbitals with same energy lvl (degenerate) but diff orientation in space
• labelled s, p, d or f
• generally order of energy lvl of subshell within each quantum shell is: s<p<d<f

Question 11

Describe shape of s, p and d orbitals

Answer 11

s orbital
- spherical
- non-directional
- size increases with n

p orbital (3 types)
- dumb-bell
- directional (towards x, y, z axes)
- three p orbitals hv diff orientation in space
- size increases with n

d orbitals (5 types)
- 4 of 5 orbitals hv four lobes (butterfly shape)
- fifth orbital (dz²) hv 2 lobes along z axis, doughnut centred in xy plane
- directional
- diff orientation in space
- size increases with n

Question 12

Each orbital holds up to how many electrons?

Answer 12

2

Question 13

What’s special abt 4s subshell?

Answer 13

4s subshell hv lower energy lvl than 3d subshell (when not occupied by electrons)

Once occupied, 4s hv higher energy lvl than 3d subshell due to repulsion and close energy gap btw 4s and 3d subshells

Question 14

Elucidate relative energy lvl of orbitals. What happens to the orbitals energy lvl as n increases?

Answer 14

• In atom, orbitals hv diff energy lvl, w nearest orbital to nucleus hv lowest energy lvl
• As n increases, energy lvl come closer to each other
  => overlapping of subshells happen. First overlap occur btw 3d and 4s subshells, meaning 4s orbitals fill up b4 3d orbitals

Question 15

What are the exceptions for Chromium and Copper?

Answer 15

Cr: 3d^5 4s^1 instead of 3d^4 4s²

Cu: 3d^10 4s^1 instead of 3d^9 4s^2

Question 15

Two electrons in each orbital must be in …?

Answer 15

opposite spins

Question 16

Define First and Second Ionisation Energy

Answer 16

1st: Energy needed to remove 1 mol of e- fr one mole of 1 mol gaseous atoms of element to form 1mol singly +vely charged gaseous ions

2nd: Energy needed to remove 1 mol of e- fr one mole of 1 mol of singly +vely charged gaseous ions to form 1mol doubly charged gaseous ions

Question 16

What are the equations for 1st and 2nd ionisation energy?

Answer 16

1st: X(g) -> X+(g) + e-

2nd: X+(g) -> X2+(g) + e-

NOTE:
X(g) -> X2+(g) + 2e- is not 2nd ionisation energy, but sum of both 1st and 2nd

Question 17

What factors affect ionisation energy of elements?

Answer 17

1. Nuclear Charge
   more protons, stronger
2. Screening/ Shielding effect
   shield valence e- by inner shell e-

=>
Effective nuclear charge is net electrostatic attraction btw + nucleus and valence e- to remove
- Combined effect of nuclear charge & screening effect, approximated by
eff. nuclear charge = nuclear charge - shielding effect

stronger eff nuclear charge,
stronger electrostatic force of attract n btw nucleus and valence e-,
higher ionisation energy

Question 18

Across period, explain how does ionisation energy change in general?

Answer 18

Increase from left to right across period since:
- no. of proton increase, so nuclear charge increase
- number of electrons increase but oni within same valence shell, so shielding effect remains relatively constant
- eff nuclear charge increase, so stronger electrostatic attraction btw nucleus and valence electrons
- Thus, more energy needed to remove valence e-, and first ionisation energy generally increases

Question 19

Expound on exceptions from general trend of increasing 1st IE across period

Answer 19

Period 3 elements
1. 1st Ionisation Energy (IE) of grp 13 element < 1st IE of grp 2 element
eg aluminium < Mg
- Since 3p valence e- to remove from aluminium has higher energy than 3s valence e- in Mg
- So, less energy needed to remove 3p e- in Aluminium than 3s e- in Mg, so 1st IE of aluminium lower than that of Mg

2. 1st IE of grp 16 element < 1st IE of grp 15 element
   eg that of S< that of P
   - Inter-electron repulsion present btw paired e- in 3p orbital of S atom.
   - So, less energy required to remove valence e- from S, and 1st IE of S < that of P

Question 20

Down a group, elaborate how IE changes

Answer 20

Trend: IE decrease down grp
Down grp,
- no of protons increase, so nuclear charge increase
- BUT, no of e- shells & shield effect oso increase
- So, valence e- experience weaker electrostatic forces of attract n to nucleus
- Less energy needed to remove valence e-, and 1st IE decrease down grp

Question 21

Between periods (ie btw grp 18 and grp 1 of next period), elucidate how IE differs

Answer 21

1st IE btw grp 18 element (noble gas) and succeeding grp 1 element of next period decrease significantly
eg 1st IE of Na < that of Ne

• Na hv more protons, so higher nuclear charge than Ne
• BUT, valence 3s e- in Na experience stronger shield effect due to more inner shell of e- than 2p e- in Ne
• So, valence 3s e- in Na further away fr nucleus & experience weaker electrostatic attract n to nucleus
• Less energy needed to remove 3s e- in Na than 2p e- in Ne, & 1st IE of Na lower than that of Ne

Question 22

Success ionisation energy always … for same atom
i.e. 1st IE … 2nd IE … 3rd IE

Why?

Answer 22

increases

1st IE < 2nd IE < 3rd IE

-after remove first e-, less e- than protons
- remaining e- more strongly attracted to constant +ve nuclear charge (since no of protons unchanged)
- So, electrostatic attract n btw nucleus and remaining e- increase
- more energy needed to remove e-

Question 23

What does sharp increase in IE mean?

How about smaller jumps in IE?

Answer 23

Sharp increase: change in principal quantum shell (eg. valence, vs inner shell)

Smaller jumps: change in subshell (eg. 2p e- more energy than 2s e-, so 2s e- need more energy to be removed)

Question 24

(trend) Which grps have each high 2nd, 3rd and so on IE?

Answer 24

Grp 1 - high 2nd IE
Grp 2 - high 3rd IE
Grp 13 - high 4th IE
Grp 14 - high 5th IE
Grp 15 - high 6th IE
Grp 16 - high 7th IE
Grp 17 - high 8th IE