Atomic Structure

Question 1

Protons

Answer 1

Charge: +1
Mass: 1

Question 2

Neutrons

Answer 2

Charge: 0
Mass: 1

Question 3

Electrons

Answer 3

Charge: -1
Mass: 1/1840, negligible

Question 4

Deflection of sub-atomic particles in an electric field

Answer 4

Angle of deflection = k(charge/mass)

Question 5

Atomic Symbols ^A_ZX

Answer 5

^{Mass no}_{Atomic no.}X

Question 6

Nucleons

Answer 6

Protons and neutrons

Question 7

Atomic number (Z)

Answer 7

• The number of protons in the nucleus
• Equal to no. of electrons present in an
  electrically neutral atom
• Unique to each element

Question 8

Mass number (A)

Answer 8

Total number of nucleons

Question 9

Isotopes

Answer 9

• Atoms of the same element with the same
  number of protons but different number of
  neutrons
• Same chemical properties
• Different physical properties due to different
  masses

Question 10

Orbitals

Answer 10

• Regions of space where there is a high
  probability of locating the electrons
• Each holds only 2 electrons
• Orbitals from different subshells are the same shape but different size

Question 11

S-orbital

Answer 11

• Spherical in shape
• Labelled ns

Question 12

P-orbital

Answer 12

• Dumbbell in shape
• Labelled np_x, np_y, np_z

Question 13

D-orbitals

Answer 13

• Shape is just diabolical
• Labelled ns_z2, ns_x2-y2, ns_xy, ns_xz, ns_zy

Question 14

Relative energies of orbitals

Answer 14

• Orbitals closer to the nucleus are lower in
  energy
• Orbitals of the same subshell have equal
  energy (degenerate orbitals)

Question 15

Subshells

Answer 15

• Labelled s, p, d or f with a principal quantum number
• The lower the principal quantum number,
  the closer to the shell is to the nucleus
• Electrons in the same subshell have the
  same energy level (degenerate)

Question 16

Aufbal Principle

Answer 16

Electrons always fill orbitals of lower energy first before proceeding to fill orbitals of higher energy

Question 17

Paui Exclusion Princple

Answer 17

• Each orbital can hold only 2 electrons and
  they must have opposite spins
• 2 electrons in the same orbital will
  experience repulsion

Question 18

Hund’s Rule

Answer 18

When a number of degenerate orbitals are available, electrons occupy them singly first before any pairing occurs

Question 19

Period

Answer 19

Horizontal row of element with the same number of core electrons

Question 20

Group

Answer 20

Vertical column of element with the same number of valence electrons and hence chemical properties

Question 21

First ionisation energy

Answer 21

The amount of energy required to remove one mole of electrons from one mole of gaseous atoms, producing one mole of gaseous ions with a single positive charge

X(g) → X⁺(g) + e^-

Successive energies become more endothermic

Question 22

Nuclear charge effect

Answer 22

• Total positive charge of protons in nucleus
• Arieses from the attraction between
  electrons and the positive nucleus
• Increase with increasing no. of protons

Question 23

Shielding/Screening effect

Answer 23

• Shielding electrons are the inner shell
  electrons found in between the nucleus and
  the valence electrons
• Reduces the strength of nuclear attraction
  experience by the valence electrons
• Increases with increasing number of inner
  shell electrons

Question 24

Effective Nuclear Charge

Answer 24

The effective nuclear attraction felt by the valence electrons after taking into account both the nuclear charge effect and the shielding effect

Question 25

First Ionisation energy trend across a period

Answer 25

• No. of protons increase, nuclear charge
  increases
• No. of inner shell electrons constant,
  shielding effect remains constant
• Hence effective nuclear charge increases
• Stronger attraction between nuclear and
  valence of electrons
• Hence atomic radius decreases and first
  ionisation energy increases

Question 26

First ionisation energy trend down the group

Answer 26

• No. of protons increase, nuclear charge
  increases
• No. of inner shell electrons increases,
  distance between the nucleus and the
  valence shell electrons increases
• Shielding effect increases
• Hence effective nuclear charge decreases
• Weaker attraction between nuclear and
  valence of electrons
• Hence atomic radius increases and first
  ionisation energy decreases

Question 27

Successive ionisation energy for same element

Answer 27

• Progressively more endothermic
• Extra energy needed to overcome the
  EFOA between leaving electrons and ions
  of increasing positive charge
• Large jumps in IE indicate removal of
  electrons from different electronic shells
• Small jumps in IE indicate removal of
  electrons from an inner subshell