Structure and Bonding

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What is ionic bonding?

Ionic bonding is the electrostatic attraction between oppositely charged ions formed when electrons are transferred from a metal (which loses electrons) to a non-metal (which gains them).

Describe the structure of ionic compounds.

Ionic compounds form a three-dimensional lattice of alternating positive and negative ions. Each ion is surrounded by several oppositely charged ions, creating strong and extensive ionic bonding throughout the structure.

Why do ionic compounds have high melting and boiling points?

Ionic compounds have high melting and boiling points because a large amount of energy is needed to overcome the strong electrostatic attractions between oppositely charged ions in the lattice. The strength of these attractions depends on the charge and size of the ions; smaller ions or ions with higher charges produce stronger attractions and higher melting points.

Under what conditions do ionic compounds conduct electricity, and why?

Ionic compounds cannot conduct electricity when solid because ions are fixed in place within the lattice. When molten or dissolved in water, the lattice breaks apart and the ions are free to move, allowing them to carry charge and conduct electricity.

Explain the solubility of ionic compounds in polar solvents like water.

Ionic compounds are often soluble in polar solvents such as water. The polar water molecules are attracted to the ions (partially negative oxygen to cations, partially positive hydrogen to anions). These attractions overcome the ionic bonds, separating the ions and allowing them to dissolve.

What is ionic bonding, and how are ions formed in this process?

Ionic bonding is a strong chemical bond characterized by the electrostatic attraction between oppositely charged ions. These ions are typically formed when a metal atom (which has a tendency to lose electrons to achieve a stable electron configuration, becoming a positive cation) transfers one or more electrons to a non-metal atom (which gains these electrons to achieve a stable configuration, becoming a negative anion).

Describe the characteristic crystal lattice structure of ionic compounds.

Ionic compounds do not exist as discrete molecules but instead form a three-dimensional crystal lattice structure. In this lattice, alternating positive and negative ions are arranged in a highly ordered, repeating pattern. Each individual ion is surrounded by multiple ions of the opposite charge, leading to strong and extensive electrostatic attractions that extend throughout the entire solid.

What is covalent bonding in covalent molecular substances?

Covalent bonding is a type of chemical bond where two non-metal atoms share one or more pairs of electrons. This sharing allows both atoms to achieve a stable electron configuration, typically a full outer electron shell, leading to a strong internal bond within a discrete molecule.

Describe the structure of covalent molecular substances.

Covalent molecular substances consist of distinct, individual molecules. Within each molecule, atoms are strongly held together by covalent bonds. However, the forces of attraction between these separate molecules, known as intermolecular forces (IMFs), are relatively weak. These IMFs can include dispersion forces, dipole-dipole forces, or hydrogen bonds.

Why do covalent molecular substances have low melting and boiling points?

Covalent molecular substances exhibit low melting and boiling points because, during changes of state (melting or boiling), only the weak intermolecular forces (IMFs) between the molecules need to be overcome. The strong covalent bonds within the molecules remain intact. Since little energy is required to break these weak IMFs, the phase change occurs at lower temperatures.

What factors influence the strength of intermolecular forces (IMFs) in covalent molecular substances?

The strength of intermolecular forces depends on several factors:

1. Molecular Mass: Generally, larger molecules with more electrons have stronger dispersion forces, leading to higher melting/boiling points.

2. Polarity: Polar molecules possess a permanent dipole moment, leading to stronger dipole-dipole interactions compared to non-polar molecules of similar size.

3. Hydrogen Bonding: This is the strongest type of IMF, occurring when hydrogen is directly bonded to highly electronegative atoms like nitrogen (N), oxygen (O), or fluorine (F).

Why do covalent molecular substances not conduct electricity?

Covalent molecular substances do not conduct electricity in any state (solid, liquid, or gas) because they lack free-moving charged particles. All electrons are localized either within the strong covalent bonds between atoms or as non-bonding lone pairs on individual atoms, meaning there are no mobile ions or delocalized electrons available to carry an electrical charge.

How does solubility work for covalent molecular substances, particularly in polar and non-polar solvents?

The solubility of covalent molecular substances often follows the 'like dissolves like' principle:

1. Non-polar substances: These are typically soluble in non-polar solvents (e.g., oil in hexane) because weak dispersion forces can be established between solute and solvent molecules.

2. Polar substances: Polar covalent molecules (e.g., ethanol) tend to dissolve in polar solvents like water. This occurs

What is covalent bonding in covalent molecular substances?

Covalent bonding is a fundamental type of chemical bond formed when two non-metal atoms share one or more pairs of valence electrons. This electron sharing allows each atom to achieve a stable electron configuration, typically a full outer electron shell (like that of a noble gas), resulting in a strong intramolecular bond that holds the atoms together within a distinct, discrete molecule.

Describe the structure of covalent molecular substances.

Covalent molecular substances are characterized by their structure, which is comprised of distinct, individual molecules. Within each molecule, atoms are strongly linked by covalent bonds (intramolecular forces). However, the attractive forces between these separate molecules, known as intermolecular forces (IMFs), are comparatively weak. These IMFs encompass a range of interactions, including weak dispersion forces, dipole-dipole forces found in polar molecules, and the stronger hydrogen bonds.

Why do covalent molecular substances have low melting and boiling points?

Covalent molecular substances typically have relatively low melting and boiling points. This characteristic is observed because, during a phase change (melting or boiling), the strong covalent bonds within the individual molecules remain unbroken. Instead, it is only the weak intermolecular forces (IMFs) between these molecules that must be overcome. As significantly less energy is required to disrupt these weak intermolecular attractions compared to breaking strong covalent bonds, these substances transition between states at lower temperatures.

What factors influence the strength of intermolecular forces (IMFs) in covalent molecular substances?

The magnitude of intermolecular forces (IMFs) in covalent molecular substances is influenced by several key factors:

1. Molecular Mass/Size: Larger molecules generally possess a greater number of electrons. This leads to more significant instantaneous polarizations and, consequently, stronger London dispersion forces (a type of van der Waals force), resulting in higher melting and boiling points.

2. Molecular Polarity: Polar molecules have an uneven distribution of electron density, creating a permanent dipole moment. This allows for stronger dipole-dipole interactions between molecules, which are more significant than dispersion forces for molecules of comparable size.

3. Hydrogen Bonding: This is the strongest specific type of IMF. It occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (like nitrogen (N), oxygen (O), or fluorine (F)), creating a strong permanent dipole and allowing for a strong electrostatic attraction with a lone pair of electrons on an adjacent electronegative atom in another molecule.

Why do covalent molecular substances not conduct electricity?

Covalent molecular substances are electrical insulators, meaning they do not conduct electricity in their solid, liquid, or gaseous states. This is because they entirely lack free-moving charged particles. All of their electrons are either localized within the strong covalent bonds holding atoms together or are present as non-bonding lone pairs on specific atoms. Consequently, there are no mobile ions or delocalized electrons available to carry an electrical charge through the substance.

How does solubility work for covalent molecular substances, particularly in polar and non-polar solvents?

The solubility of covalent molecular substances largely adheres to the 'like dissolves like' principle, which dictates that substances with similar intermolecular forces tend to be soluble in each other.

1. Non-polar substances: These compounds are typically soluble in non-polar solvents (for example, oil in hexane). Solubility occurs because weak London dispersion forces can be established between the non-polar solute and non-polar solvent molecules, allowing them to mix.

2. Polar substances: Polar covalent molecules (such as ethanol) tend to dissolve readily in polar solvents like water. This dissolution occurs because the polar solute molecules can form strong intermolecular attractions (like dipole-dipole interactions or hydrogen bonds) with the polar solvent molecules. These new solute-solvent attractions are strong enough to overcome both the existing solute-solute attractions and solvent-solvent attractions.

What is metallic bonding, and how is it characterized?

Metallic bonding is a strong electrostatic force of attraction that exists between a lattice of positively charged metal ions (cations) and a 'sea' of delocalised valence electrons. These valence electrons are not bound to any single atom but are free to move throughout the entire metallic structure.

Describe the characteristic structure of metallic substances.

Metallic substances possess a unique crystal structure consisting of a regular, repeating lattice of positive metal ions. This lattice is immersed in a 'sea' of delocalised valence electrons, which are not associated with any particular ion but are free to move randomly throughout the entire metallic solid. This arrangement provides strong, non-directional bonding.

Why do metals typically have high melting and boiling points?

Metals generally exhibit high melting and boiling points because metallic bonds are strong and require a significant amount of thermal energy to overcome. This energy is needed to break the robust electrostatic attraction between the positively charged metal ions and the mobile 'sea' of delocalised electrons. The strength of this metallic bonding, and consequently the melting/boiling point, intensifies with an increased number of delocalised electrons per atom and a higher charge on the metal ions.

Explain the electrical conductivity of metals in both solid and liquid states.

Metals are excellent conductors of electricity in both their solid and molten (liquid) states. This high conductivity is directly attributable to the presence of delocalised valence electrons, which are not fixed to any atoms and are free to move throughout the entire metallic lattice. These mobile electrons can readily carry an electrical charge when a potential difference is applied, facilitating the flow of current.

What properties make metals malleable and ductile, and why?

Metals are characterized by their malleability (the ability to be hammered into sheets) and ductility (the ability to be drawn into wires). These properties arise because the layers of positive metal ions within the lattice can slide past one another when a force is applied. Crucially, the 'sea' of delocalised electrons is able to adjust its position to continuously maintain the strong electrostatic attraction between the ions, preventing the metallic bonds from breaking and thereby allowing the metal to deform without fracturing.