Atomic Structure

Question 1

What is Bohr’s model?

Answer 1

For the first 20 elements in the periodic table, the first shell can hold 2 electrons, while the second and third can hold up to 8 electrons

Question 2

Define valence shell

Answer 2

The outermost electron shell that is furthest away from the nucleus

Question 3

How do you write the electronic configuration of an atom?

Answer 3

x,y, or 1s,2s,2p etc

Question 4

What is the definition of an isotope?

Answer 4

Isotopes are atoms of the same element with the same number of protons but different number of neutrons

Question 5

What is the difference in properties between isotopes and their element?

Answer 5

They have similar chemical properties but different physical properties

Question 6

Define

Relative atomic mass

Answer 6

Relative atomic mass of an element is defined as the average mass of the atom of an element to one-twelfth of the mass of one carbon-12 atom

Question 7

Define

Ions

Answer 7

A charged particle formed from an atom or a group of atoms by gaining or losing electrons

Question 8

What are the different orbitals for electrons, their shape and how many electrons can they hold?

Answer 8

s-orbital: sphere shaped; 2 electrons
p-orbital: dumbell shaped; 6 electrons
d-orbital: not needed to know; 10 electrons
f-orbital: not needed to know: 14 electrons

Question 9

What is Aufbau Principle?

Answer 9

The principle assumes that one “builds” an atom by starting with the nucleus then added electrons one by one to electron subshells, given designations like 1s, 2s, 2p…

Electrons are placed in orbitals from lowest to highest energy

Note that when filling electrons into orbitals, 4s is filled before 3d orbital, however, 3d is still written beofre 4s in writing electronic configuration

Question 10

What is Pauli Exclusion Principle?

Answer 10

Each orbital can only hold 2 electrons of opposite spin

Question 11

What is Hund’s Rule?

Answer 11

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

Question 12

Define

First ionisation energy and give its equation

Answer 12

Is the energy required to remove the most loosely held (outermost or highest energy) electron from one mole of gaseous atoms to form one mole of gaseous ions each with a charge of 1+

Equation: M(g) –> M+(g) +e-

Question 13

Factors affecting ionisation energy

Answer 13

1. Number of protons (more protons, more positive charge, electrons attracted to nucleus more strongly)
2. Distance of outermost electron from nucleus (further, less attractive forces)
3. Shielding effect (more shells, less attractive forces)
4. Paired electron repulsion

Question 14

What are some trends in first ionisation energy in the periodic table?

Answer 14

Energy increases across a period but decreases down a group

Question 15

Why does ionisation energy increase across the period?

Answer 15

• Nuclear charge increases as number of protons increases
• Electrons added to the same shell hence shielding effect remains constant
• Effective nuclear charge increases, electrostatic attractive forces increase
• More energy needed to remove outermost electron

Question 16

Why does ionisation energy decrease down the group?

Answer 16

• Down the group, nuclear charge increases as number of protons increase
• Increase in number of electron shells increases distance between outermost shell and nucleus
• Electrostatic forces of attraction becomes weaker
• Less energy needed to remove the outermost electron