Ionic bonding occurs when a metal and a non-metal ion, carrying opposite charges, are attracted to each other through electrostatic forces. For example, in sodium chloride (NaCl), a sodium atom (Na) loses an electron to become a positively charged ion (Na+), while a chlorine atom (Cl) gains that electron to become negatively charged (Cl-). The oppositely charged ions attract and form a giant ionic lattice.

Covalent bonding, on the other hand, involves two atoms sharing a pair of electrons. This sharing allows each atom to achieve a full outer electron shell. For instance, in a Cl₂ molecule, two chlorine atoms, each one electron short of a complete outer shell, share their last unpaired electrons to form a covalent bond.

Metallic bonding involves the attraction between metal ions and a 'sea' of delocalized electrons. In a sample of magnesium (Mg), each magnesium atom loses its two outer electrons, becoming Mg²⁺ ions. These electrons become part of the delocalized electron cloud, and the electrostatic attraction between the positively charged metal ions and the free-moving electrons creates metallic bonds, giving metals their unique properties.

Crude oil is a complex mixture of organic molecules containing carbon with varying chain lengths. These different chain lengths result in different boiling points: longer molecules, with stronger intermolecular forces, have higher boiling points and are less volatile compared to shorter molecules. This variation in boiling points allows the components of crude oil to be separated into fractions with similar boiling points through a process known as fractional distillation.

In fractional distillation, the column is designed with a temperature gradient, being hottest at the bottom and coolest at the top. The more volatile, less viscous fractions, such as gasoline (petrol), condense near the top of the column, while the less volatile, more viscous fractions, such as bitumen, remain liquid and separate at the bottom. Thus, the process effectively separates crude oil into fractions based on their volatility and viscosity.

A covalent bond forms between non-metal atoms when they share electrons from their outer electron shells. This electron sharing allows each atom to achieve a stable configuration, similar to that of an inert gas, by filling its outer shell.

A paramagnetic complex contains at least one unpaired electron. In the case of [Fe(H2O)6]²⁺, the complex is paramagnetic because water (H2O) is a weak field ligand. As a result, the energy gap between the t₂g and eₖ orbitals is small, making it energetically favourable for electrons to occupy the higher energy eₖ orbitals rather than pairing up in the t₂g orbitals. This leads to a high-spin configuration, with three electrons in the t₂g orbitals and two in the eₖ orbitals, resulting in five unpaired electrons. Therefore, [Fe(H2O)6]²⁺ is paramagnetic.

In contrast, [Fe(CN)6]²⁻ is diamagnetic because cyanide (CN⁻) is a strong field ligand, which creates a large energy gap between the t₂g and eₖ orbitals. This large gap forces the complex to adopt a low-spin configuration, filling all the t₂g orbitals with six electrons and leaving no unpaired electrons. As a result, [Fe(CN)6]²⁻ is diamagnetic.

There are two main factors that explain why it becomes easier to remove an electron as you move down a group: increasing atomic size and increasing shielding effect.

Increasing Atomic Size: As you move down a group, the atomic size increases, meaning the outermost electron is farther from the nucleus. This increased distance weakens the attraction between the positive nucleus and the outer electron, requiring less energy to remove the electron.

Increasing Shielding Effect: Electrons in the inner energy levels act as a shield for those in the outer levels. This shielding reduces the effective nuclear charge felt by the outer electron, further decreasing the attraction between the nucleus and the electron. As a result, it becomes easier to remove the outer electron.