Covalent and Coordinate Bonding

This page delves into covalent bonding and coordinate $dative covalent$ bonding for AQA A Level Chemistry.

Covalent bonding is defined as a pair of electrons shared between two atoms. The strength of covalent bonds is generally high, with smaller atoms forming stronger bonds due to closer proximity of electrons to nuclei.

Coordinate bonding is introduced as a special type of covalent bond where both electrons come from the same species. The page explains when coordinate bonds are possible and provides an example with H₂O and H⁺.

Vocabulary: Coordinate $dative covalent$ bonding is a type of covalent bond where both electrons are donated by one atom.

The page also covers giant covalent structures, which form when bonds between atoms continue indefinitely to create a giant lattice.

Example: Diamond and graphite are examples of giant covalent structures with very different properties due to their structural differences.

Properties of giant covalent structures are discussed:

1. High melting and boiling points
2. Variable electrical conductivity
3. Hardness and brittleness

Highlight: The properties of giant covalent structures are directly related to their bonding and structural arrangements.

Giant Covalent Structures and Simple Molecular Structures

This page focuses on giant covalent structures and introduces simple molecular structures for AQA A Level Chemistry.

The page provides detailed information on diamond and graphite as examples of giant covalent structures:

Diamond:

• Tetrahedral structure
• Very high melting and boiling points
• Does not conduct electricity
• Extremely hard

Graphite:

• Layered structure
• Good electrical conductor due to delocalized electrons
• Lower density than diamond
• Soft and slippery

Example: Graphite is used in pencils and as an industrial lubricant due to its layered structure allowing planes to slip over each other.

The page also introduces simple molecular structures, which have weak intermolecular forces between molecules.

Highlight: The contrast between giant covalent structures and simple molecular structures is crucial for understanding their different properties.

Properties of simple molecular structures are briefly mentioned, including low melting and boiling points due to weak intermolecular forces.

Vocabulary: Intermolecular forces are the attractive forces between molecules, which are typically much weaker than covalent bonds within molecules.

Properties of Covalent Compounds

This page elaborates on the properties of covalent compounds for AQA A Level Chemistry, focusing on simple molecular structures.

The key properties discussed include:

1. Low melting and boiling points: Due to weak intermolecular forces between molecules, which require little energy to overcome.
2. Poor electrical conductivity: Covalent compounds generally do not conduct electricity as they lack free ions or delocalized electrons.
3. Solubility: Many covalent compounds are insoluble in water but may dissolve in organic solvents.
4. State at room temperature: Simple molecular substances can be gases, liquids, or soft solids depending on the strength of their intermolecular forces.

Highlight: The properties of simple molecular structures are primarily determined by the weak intermolecular forces between molecules, rather than the strong covalent bonds within molecules.

The page contrasts these properties with those of giant covalent structures and ionic compounds, emphasizing the importance of structure in determining physical properties.

Example: Water $H₂O$ is a simple molecular substance with relatively strong intermolecular hydrogen bonds, giving it unusually high melting and boiling points for its size.

The concept of polarity in covalent molecules is introduced, explaining how uneven electron distribution can lead to partial charges and affect properties like solubility and boiling point.

Vocabulary: Polarity refers to the uneven distribution of electron density in a molecule, resulting in partial positive and negative charges.

Bonding and Physical Properties

This final page summarizes the relationship between bonding and physical properties for AQA A Level Chemistry, tying together concepts from ionic, covalent, and metallic bonding.

The page presents a comparative overview of different types of structures and their properties:

1. Ionic compounds: High melting and boiling points Brittle when solid Conduct electricity when molten or dissolved
2. Simple molecular structures: Low melting and boiling points Soft or gaseous at room temperature Poor electrical conductors
3. Giant covalent structures: Very high melting and boiling points Hard and strong Variable electrical conductivity $e.g., diamond vs. graphite$
4. Metallic structures: Variable melting and boiling points Malleable and ductile Good electrical conductors

Highlight: Understanding the relationship between bonding type, structure, and physical properties is crucial for predicting and explaining the behavior of different substances.

The page emphasizes the importance of considering both the type of bonding within a substance and the forces between particles when explaining physical properties.

Example: The high melting point of sodium chloride $NaCl$ can be explained by the strong ionic bonds in its giant ionic lattice, while the low melting point of iodine $I₂$ is due to weak van der Waals forces between simple molecules.

The concept of structure-property relationships is reinforced, encouraging students to apply their knowledge of bonding to explain and predict the properties of various substances.

Vocabulary: Structure-property relationships refer to the way in which the microscopic structure and bonding of a substance determine its macroscopic physical and chemical properties.

Ionic Bonding and Properties

This page introduces ionic bonding and the properties of ionic compounds in AQA A Level Chemistry.

Ionic bonding is defined as the electrostatic force of attraction between oppositely charged ions in a lattice. Metals lose electrons to become positive ions, while non-metals gain electrons to become negative ions. Ionic compounds are formed between metals and non-metals, always having an overall charge of zero.

The page discusses giant ionic structures $lattices$ and their properties:

1. High melting and boiling points due to strong electrostatic forces
2. Brittle nature when stress is applied
3. Electrical conductivity only when molten or dissolved

Definition: Ionic bonding is the electrostatic force of attraction between oppositely charged ions in a lattice.

Factors affecting the strength of ionic bonds are explained:

• Charge on the ion: Higher charge leads to stronger bonding
• Size of the ion: Smaller ions create stronger bonds

Highlight: The properties of ionic compounds are directly related to their structure and the strength of the ionic bonds.