02: Atomic Structure

Question 1

Sub-Atomic Particles

Behaviour in an Electric Field

Answer 1

• Protons → deflected towards (-)vely-charged plate by x°
• Neutrons → NO deflection
• Electrons → deflected towards (+)vely-charged plate by y°

y° > x°

Question 2

Angle of Deflection, AOD

Formula

Answer 2

lq/ml

q = charge of particle
m = mass of particle

• Larger q, stronger attraction to the oppositely-charged plate, –> greater AOD
• Larger m, more difficult for particle to deviate to oppositely-charged plate –> smaller AOD

Question 3

Isotopes

Definition

Answer 3

Atoms that contain the same number of protons but different number of neutrons.

Question 4

Electron Shells (ES)

Answer 4

ES have their own Principal Quantum Number (PQM) n; subshells that contain orbital(s).

As n increases,
- the ES is further from the Nucleus
- the Electrostatic Attraction, EA, between e^- and nucleus decreases
- energy level of the ES increases
- orbital becomes more diffused

Question 5

S Subshell Orbitals

S orbitals

Answer 5

Shape: Spherical
Directionality: Absent

Question 6

P Subshell Orbitals

P orbitals

Answer 6

Name(s): p_x, p_y, p_z
Shape: Dumbbell
Directionality: Present

Question 7

D Subshell Orbitals

D orbitals

Answer 7

Name(s): d_xz, d_xy, d_yz, d_{x² - y²}, d_z²
Shape:
d_xz, d_xy, d_yz –> 4-lobed with lobes pointing between the axes
d_{x² - y²} –> 4-lobed with lobes aligned to the x- & y-axis
d_z² –> Dumbbell with a Donut-shaped Ring at its waist (aligned to the y-axis) that is aligned to the z-axis
Directionality: Present

Question 8

Electronic Configuration, EC

Ways of Writing

Answer 8

1. Electron Shells/ Energy Level Notation, eg. Si: 2.8.4
2. s, p, d, f Notation, eg. Si: 1s^2s 2p⁶ 3s² 3p²/ [Ne] 3s² 3p²
3. Electrons-in-Boxes

[Ne] is the EC of Neon

Question 9

Electronic Configuration

Rules

Answer 9

1. Aufbau’s Principle
   ES filled in this order of 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d…
2. Hund’s Rule
   Orbitals in a subshell must be singly-occupied by e^- of parallel spins before pairing occurs.
3. Pauli Exclusion Principle
   2 e^- in the same orbital are of opposite spins.

Explanations behind the filling of 4s orbital before 3d orbital & e^- spin are OUT OF SYLLABUS!

Question 10

Anomalous Electronic Configurations

Chromium, Cr and Copper, Cu

Answer 10

Expected EC of Cr: [Ar] 3d⁴ 4s²
Actual EC of Cr: [Ar] 3d⁵ 4s¹

Expected EC of Cu: [Ar] 3d⁹ 4s²
Actual EC of Cu: [Ar] 3d¹⁰ 4s¹

Reason: Actual EC is more stable than Expected EC

Question 11

Ground State

Definition

Answer 11

Atom has the lowest overall energy level.

Question 12

Excited State

Definition

Answer 12

≥ 1 e^- absorbed energy and is promoted to a higher energy level, resulting in an unstable excited atom.

Question 13

Isoelectronic Species

Definition

Answer 13

Species with the same total number of e^-

Question 14

Shielding Effect

Answer 14

1. e^- are -ve-charged
2. e^- in the inner ES repel those in other ES.
3. other ES e^- cannot experience the full effect of the actual nuclear charge.

e^- in the same ES provide poorer shielding effect to one another.

Question 15

Explaining Trends & Variations

using Electrostatic Effects

Answer 15

1. No. of ES
   a. no. of ES increases
   b. PQN of VS increases
   c. Distance between Nucleus and valence electron, VE increases
   d. EA between Nucleus and VE decreases
2. Nuclear Charge, Z
   a. EA between Nucleus and VE increases
3. Shielding Effect, SE by inner e^- [not affected when electrons are added to outer shell]
   a. no. of inner e^- ES increases
   b. SE experienced by VE increases
   c. EA between Nucleus and VE decreases

Explaining trends:
- across a period, only F2 & F3 apply
- down a period, all 3 factors apply but F1 is said to have minor influence.

Question 16

Atomic Radius

Definition

Answer 16

Half the shortest inter-nuclear distance found in the structure of the element.

Atomic Radius is dependent on the bonding or interaction of atoms with its neighbours.

Question 17

Atomic Radius

Types

Answer 17

1. Metallic - between 2 neighbouring atoms in the metal
2. Covalent - between 2 covalently bonded atoms
3. Van De Waal’s - between atoms that are not chemically bonded

Question 18

Trends & Variations

Atomic Radii

Answer 18

Down a Group: Increases
Across a Period: Decreases

Question 19

Ionic Radius

Definition

Answer 19

Radius of spherical Ion in an Ionic Compound

Question 20

Trends & Variations

Ionic Radii

Answer 20

Cationic Radius: r_cation < r_atom
Anionic Radius: r_anion > r_atom
Isoelectronic Species across a Period: Decreases

Important: Sharp Increase from Al³⁺ to P^3-

Question 21

Trends & Variations

1st Ionisation Energy, IE down a group & across a period

Answer 21

Down a Group: generally Decreases
Across a Period: generally Increases
Irregularity 1: Group 2 & 13
Irregularity 2: Group 15 & 16

Question 22

Trends & Variations

Successive IE of an Element

Answer 22

Increases

Question 23

Successive IE of an Element

Deducing Group Number

Answer 23

Look for large jump in IE.

Medium jump in IE indicates different subshell

Question 24

Trends & Variations

Electronegativity, EN

Answer 24

Down a Group: Decreases
Across a Period: Increases