Group 15 Elements and Molecular Orbitals

Flashcards providing vocabulary and definitions from the lecture notes on Molecular Orbitals and Group 15 Elements, focusing on phosphorus and nitrogen chemistry.

Molecular Orbitals (MOs) from p orbitals

Formed by combining atomic p orbitals, resulting in sigma (σ), pi (π) molecular orbitals, and their antibonding counterparts (σ, π).

Molecular Orbital Diagram

A diagram illustrating the relative energy levels of atomic orbitals and the molecular orbitals formed, showing electron occupancy.

Bond Order (from MO diagram)

Calculated as (number of electrons in bonding MOs - number of electrons in antibonding MOs) / 2; indicates bond strength.

HOMO

Highest Occupied Molecular Orbital; the highest energy molecular orbital containing electrons.

LUMO

Lowest Unoccupied Molecular Orbital; the lowest energy molecular orbital that does not contain electrons.

N₂ vs O₂ Orbital Order Change

A phenomenon observed in second-row diatomic molecules where the relative energies of σ₂p and π₂p orbitals change between N₂ and O₂.

Group 15 Elements

A chemical group including Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth, exhibiting varied properties from non-metal to metal.

Nitrogen (Group 15)

A colourless gas, forms acidic/neutral oxides.

Phosphorus (Group 15)

A waxy solid, forms acidic oxides.

Arsenic (Group 15)

A metallic solid, forms amphoteric oxides.

Antimony (Group 15)

A metallic solid, forms amphoteric oxides.

Bismuth (Group 15)

A metallic solid, forms basic oxides.

Molecular Nitrogen (N₂)

Constitutes 78% of Earth's atmosphere, is very unreactive, and essential for living organisms.

Nitrogen Fixation

The process of converting unreactive atmospheric nitrogen (N₂) into reactive nitrogen compounds usable by living organisms.

Liquid Nitrogen

A commonly used, effective, and cheap coolant in laboratories.

Nitrogen Oxides

Compounds of nitrogen and oxygen, such as N₂O, NO₂, N₂O₃, and N₂O₅, which generally follow the octet rule.

Nitrogen Oxyacids

Acids formed from nitrogen oxides, including HNO₃ (nitric acid) and HNO₂ (nitrous acid).

Phosphorus Oxides

Examples include P₂O₃ (P₄O₆) and P₂O₅ (P₄O₁₀), which can exhibit expanded octets.

Phosphate (PO₄³⁻)

A polyatomic ion crucial in biological systems (e.g., ADP, ATP) and industrial applications like fertilizers.

Allotropes of Phosphorus

Different structural forms of elemental phosphorus, predominantly white, red, and black phosphorus.

White Phosphorus

An allotrope of phosphorus with a tetrahedral P₄ structure, highly unstable, reactive, and glows in oxygen.

Red Phosphorus

An allotrope of phosphorus formed by connecting P₄ units into chains; less reactive than white phosphorus and used in safety matches.

Black Phosphorus

The most stable allotrope of phosphorus, forming a network of puckered sheets, with potential as a layered semiconductor.

Safety Matches

Matches containing an oxidising agent (e.g., potassium chlorate) in the head and red phosphorus on the striking surface, igniting via friction.

Potassium Chlorate (KClO₃)

A strong oxidizing agent, a main ingredient in the heads of safety matches.

White Phosphorus (Historical Matches)

Previously used in matches but replaced due to its toxicity, causing 'phossy jaw' and bone disorders.

Tripolyphosphate (TPP⁵⁻)

A sequestering agent used in water softening to bind hard water ions like Ca²⁺ and Mg²⁺.

Phosphates in Fertilizers

Phosphates are essential nutrients needed for plant growth, widely used in agricultural fertilizers.

Phosphates in Detergents

Historically used as chelating agents for hard water ions, but were banned due to environmental pollution.

Eutrophication

The process where excess nutrients, like non-biodegradable phosphates, contaminate water sources, leading to increased algae growth and harm to aquatic life.

Oxidation of Phosphorus

Phosphorus (P₄) can be oxidized to P₄O₆ (oxidation state +3) and P₄O₁₀ (oxidation state +5), forming acidic oxides.

Phosphoric Acid (H₃PO₄)

Often called orthophosphoric acid, it is a triprotic acid with phosphorus in the +5 oxidation state.