Atomic Structures and Configuration
What subatomic particle determines the atomic number of an element?
Protons
What analytical technique separates ions based on mass-to-charge ratio?
Mass spectrometry
What is the difference between a homogeneous and heterogeneous mixture?
Homogeneous mixtures are uniform throughout; heterogeneous mixtures are not
What type of reaction releases heat?
Exothermic
What is the value of Avogadro’s number?
6.02 × 10²³
How many electrons can occupy a single orbital?
2 electrons
In a flame test, what causes the coloured light?
Electrons falling to lower energy levels and releasing energy
Why can metals conduct electricity?
They contain delocalised electrons that can move freely
What is the sign of ΔH for an exothermic reaction?
Negative
How many moles are in 22 g of CO₂?
0.5 mol
What is the condensed electron configuration for chlorine?
[Ne]3s² 3p⁵
In Atomic Emission Spectroscopy (AES), why does each element produce a unique emission spectrum?
Each element has unique electron energy levels, so electrons release different wavelengths of light when falling to lower energy levels.
Explain why ionic compounds conduct electricity when molten but not when solid.
Molten ions are free to move and carry charge; solid ions are fixed in position
In an endothermic reaction, are products or reactants at a higher enthalpy?
Products
In the reaction:
2H₂ + O₂ → 2H₂O
How many moles of water are produced from 5 mol of oxygen?
10 mol H₂O
Why is the electron configuration of copper considered an exception?
Copper has a more stable configuration with a filled 3d subshell:
[Ar]3d¹⁰4s¹ instead of [Ar]3d⁹4s²
An element has isotopes:
75% X-35 and 25% X-37
Calculate the relative atomic mass.
35.5
Calculation:
(0.75 × 35) + (0.25 × 37)
Graphite and diamond are both allotropes of carbon. Why can graphite conduct electricity while diamond cannot?
Graphite contains delocalised electrons that can move between layers, while diamond has all electrons locked in covalent bonds
A reaction has:
Determine ΔH.
ΔH = +920 − 1050
ΔH = −130 kJ mol⁻¹
Exothermic
What is the empirical formula of a compound containing:
40% C, 6.7% H, 53.3% O?
CH₂O
Which law states that no two electrons in an atom can have the same set of four quantum numbers?
The Pauli Exclusion Principle
mass spectrometer is used to analyse a sample of naturally occurring magnesium. The spectrum shows three isotopes:
Mg-24 Mass: 23.99 Abundance: 78.70%
Mg-25 Mass: 24.99 Abundance: 10.13%
Mg-26 Mass: 25.98 Abundance: 11.17%
Calculate the relative atomic mass of magnesium.
Convert percentages to decimals:
Ar=∑(mass×abundance)Ar=∑(mass×abundance)
Calculation:
= (23.99 × 0.7870)
= 18.89 + 2.53 + 2.90
= 24.32 u
A substance:
Identify the type of bonding and explain your reasoning.
Ionic bonding
Reason:
A student adds 75.0 g of aluminium to excess hydrochloric acid in a calorimeter.
Reaction:
2Al + 6HCl → 2AlCl₃ + 3H₂
The temperature of 200 g of solution rises from 22.5°C to 38.0°C.
Determine the enthalpy of this reaction.
Q=mcΔT
Q = 12,958 J ≈ 12.96 kJ
n = 75.0 ÷ 27.0
n = 2.78 mol
ΔH = −12.96 ÷ 2.78
ΔH = −4.66 kJ mol⁻¹
In the reaction:
2Mg + O₂ → 2MgO
A student reacts 12.0 g of magnesium with excess oxygen and produces 16.0 g of magnesium oxide.
Determine the percentage yield
Percentage yield = 80.4%