Atomic Structure
Which subatomic particle determines the identity of an element?
The number of protons
How many electrons can an s subshell hold?
2
What is the first ionisation energy?
Energy needed to remove one mole of electrons from one mole of gaseous atoms.
What is the electron configuration of Mg (Z = 12)?
1s² 2s² 2p⁶ 3s²
What does the term “mole” represent?
The amount of substance containing 6.02 × 10²³ particles
What term refers to the number of protons in an atom?
Atomic number
What is the shape of a p orbital?
Dumbbell-shaped
Does ionisation energy increase or decrease down a group?
decreases
When three electrons are available to fill three empty 2p atomic orbitals, how will the electrons be distributed in the three orbitals?
one electron in each orbital
What is the formula to calculate number of moles from mass?
n = mass ÷ molar mass
Isotopes of the same element differ in which subatomic particle?
neutrons
How many orbitals are in the 3p subshell?
3
Why does ionisation energy increase across a period?
Increased nuclear charge and decreased atomic radius → stronger attraction to electrons
Write the electron configuration of the chloride ion, Cl⁻.
1s² 2s² 2p⁶ 3s² 3p⁶
What does relative atomic mass compare?
Average mass of an atom compared to 1/12 of carbon-12
Explain why the relative atomic mass is not a whole number.
It is a weighted average of the masses of all isotopes based on their abundance.
Electrons orbital must be filled singly first before pairing.
Hund's rule
Explain why the first ionisation energy of oxygen is lower than that of nitrogen.
Oxygen has paired electrons in a p orbital, causing repulsion and easier removal.
What is the region of high probability of finding an electron?
atomic orbital
What is the percentage composition formula?
(Mass of element in compound ÷ Molar mass of compound) × 100
What is the tendency of electrons to enter orbitals of lowest energy first?
aufbau principle
Why is the 4s subshell filled before the 3d subshell?
Because 4s has slightly lower energy than 3d when empty.
Why is the second ionisation energy of sodium much higher than the first?
After losing one electron, Na⁺ has a stable noble gas configuration; removing another requires breaking into a full shell.
Why do electrons in the same orbital have opposite spins?
Because the Pauli Exclusion Principle states that no two electrons in an atom can have the same set of quantum numbers.
What is the formula to calculate number of moles from mass?
n = mass ÷ molar mass