Atomic Structure

Question 1

Angle of Deflection

Answer 1

Proportionate to q/m

Larger the charge (q) of particle, stronger the attraction towards oppositely charged plate, greater angle of deflection

Larger the mass (m) of particle, more difficult to cause it deviate towards oppositely charged particle, smaller angle of deflection

Question 2

Isotopes and characteristics

Answer 2

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

Same number of electrons hence same chemical properties

Different number of neutrons so different physical properties due to different masses

Question 3

Relationship between electronic shells and electrons

Answer 3

Electronic shells (series of energy levels surrounding nucleus, described by principal quantum number) -> Comprises one or more subshells

Subshells (s, p, d, f) -> Comprises 1 (p subshell), 3 (p subshell), 5 (d subshell) or 7 (f subshell) orbitals

Orbital (Represents a region in space where there is high probability of finding an electron, distinctive geometrical shape) -> Can accommodate 2 electrons

Question 4

As n (principal quantum no.) increases….

Answer 4

1. Greater distance between electronic shell and nucleus
2. Higher energy level of electronic shell
3. Weaker electrostatic attraction between nucleus and electron
4. Larger size of orbital, orbital becomes more diffuse

Question 5

Types, shapes, energies and directions of orbitals

Answer 5

S Orbital:
- Spherical shape
- Non directional (electron density not concentrated in particular direction)

P Orbital (px, py, pz):
- Dumbbell shape
- Whatever axis it is named after cuts the dumbell in half (x-axis cuts through px)
- Orbitals in same subshell are degenerate (same energy)

D Orbital (dxz, dxy, dyz, dx2-y2, dz2):
- 4-lobed shape/ dumbell surrounded by small doughnut shaped ring
- For dxz. dxy, dyz, orbitals have lobes pointing between axis
- For dx2-y2, lobes are on the axis
- For z2, aligned along z axis

Question 6

Orbital energy change with increasing atomic number

Answer 6

1. As atomic number increases, nuclear charge increases
2. Electrostatic attraction between nucleus and electrons increases
3. Distance between electrons and nucleus increases
4. Energy released by electrons increases
5. Less energy required to be at that shell, lower orbital energy

Question 7

Aufbau Principle

Answer 7

Electrons fill orbitals from lowest energy orbital upwards, with the highest orbital energy first (1s -> 2s -> 2p -> 3s -> 3p -> 4s -> 3d -> 4p -> 5s -> 4d)

Electrons occupy 4s orbital first before 3d because 4s orbitals are at lower energy level than 3d orbitals

Question 8

Hund’s Rule

Answer 8

Orbitals of a subshell must be occupied singly by electrons of parallel spins before pairing can occur, minimising inter-electronic repulsion.

Question 9

Paul Exclusion Principle

Answer 9

Each orbital holds a maximum of 2 electrons and must be of opposite spins, so magnetic attraction resulting from opposite spins counterbalance electrical repulsion which results from identical charges

Question 10

Anomalous electronic configurations

Answer 10

Chromium: (3d5 4s1 instead of 3d4 4s2)
3d and 4s orbitals are about equal in energy, by having one electron each in 3d and 4s orbitals inter electronic repulsion is minimised

Copper: (3d10 4s1 instead of 3d0 4s2)
Fully filled 3d subshell is unusually stable due to symmetrical charge distribution around metal center

Question 11

Ground and excited state

Answer 11

Atom in ground state when electrons are in orbitals of lowest available energy level, atom in excited state when one or more electrons absorb energy and promoted to higher energy level, it is unstable and can emit energy to return to ground state

Question 12

Electronic configuration of ions

Answer 12

Anions: Electrons are added to next available orbital during formation of anion
Cations: Electrons removed from orbitals with highest energy

Note: Once electrons occupy inner 3d orbitals, provide some shielding for outermost 4s electrons, repelling 4s electrons to slightly higher energy level, so 4s electrons are lost before 3d electrons

Question 13

Atomic radius (definition, types)

Answer 13

Defined as half the shortest inter-nuclear distance found in structure of element

Metallic radius: half inter-nuclear distance between 2 neighbouring atoms in metal
Covalent radius: half inter-nuclear distance between 2 covalently bonded atoms
Van der Waals’ radius: Half inter-nuclear distance between atoms not chemically bonded (should not be taken into account in trends because its calculating something completely different)

Question 14

Ionic radius (definition, types)

Answer 14

Defined as radius of spherical ion in ionic compound

Cationic radius: smaller than radius of parent atom (less electronic shells, same nuclear charge, increase electrostatic attraction btw nucleus and valence electron, decrease electron cloud size)

Anionic radius: greater than radius of parent atom (same nuclear charge, more electrons, increased electron-electron repulsion, decreased electrostatic attratcion btw nucleus and valence electron, increase electron cloud size)

Question 15

Ionisation energy (definition)

Answer 15

First ionisation energy is energy required to remove 1 mole of electron from 1 mole of gaseous M atoms to form 1 mole of gaseous M+ ions. (gaseous because process is removing an electron that is not bonded together [due to intermolecular forces or other forces] and must be separate so ionisation energy is not distorted])

Question 16

Exceptions to ionisation energy trends

Answer 16

Group II and III:
First ionisation energy of Grp II is higher than that of Grp III
- P orbital electron to be removed from Grp III is at higher energy level than s orbital electron to be removed from Grp II
- Less energy required to remove p orbital electron than s orbital electron

Group V and VI:
First ionisation energy of Grp V is higher than that of Grp VI
- P electron to be removed from Grp VI is paired while that to be removed from V is unpaired
- Due to inter-electronic repulsion between paired electrons in the same orbital, less energy is required to remove the paired p electron from Grp V

Question 17

Deducing group number from successive ionisation data

Answer 17

If significantly more energy is required to remove the 2nd electron from an element, the 2nd electron is located in an electronic shell that is inner and nearer to the nucleus and hence, experiences a stronger electrostatic attraction to the nucleus. Hence, the element would have one valence electron.

Question 18

Electronegativity

Answer 18

Relative measure of an atom’s ability to attract bonding electrons

Question 19

Explaining Trends

Answer 19

Across the period/ down the group
1. No. of electronic shells {increase/ decrease/ remain constant} (if constant, distance between nucleus and {bonding/ valence} electrons {increase/ decreases})
2. Nuclear charge {increase/ decrease}, proton number {increase/ decrease} (if going down the group it is not significant because one entire shell is added [use the word despite nuclear charge increasing…])
3. Shielding effect experienced by {bonding/ valence} electrons {increase/ decrease/ constant} (if constant, because number of electrons increase but electrons are added to same valence shell)
4. Effective nuclear charge {increase/ decrease}
5. Electrostatic attraction between nucleus and {bonding/ valence} electrons {increases/ decreases}
6. LINK TO TOPIC

a. Atomic + ionic radii {increase/ decrease}
Electron cloud increases (down group) or electrons pulled closer to nucleus (across period)

b. Ionisation energy {increase/ decrease}
More/ less energy required to overcome electrostatic attraction to remove electron (decrease down group, increase across period)

c. Electronegativity {increase/ decrease}
Tendency to attract electrons increases/ decreases {decrease down group, increase across period)