Chemistry Grade 10 Advanced - Metallic Bonds

EoT Term 3 2023-2024 Chemistry Grade 10 Advanced

• Course content is for Term 3, 2023-2024
• Subject is Chemistry
• Grade level is 10 Advanced

Metallic Bonds

• In a metallic lattice, the outer energy levels of the metal atoms overlap.
• The electron sea model suggests that all metal atoms in a metallic solid contribute their valence electrons to form a "sea" of electrons that surrounds the metal cations in the lattice.

Delocalized Electrons

• Electrons in the outer energy levels of bonding metallic atoms are called delocalized electrons. They move freely from one atom to the next.
• When an atom's outer electrons move freely, a metallic cation is formed.
• A metallic bond is the attraction of a metallic cation for delocalized electrons.

Physical Properties of Metals

• The physical properties of metals at the bulk scale can be explained by metallic bonding.
• These properties are evidence of the strength of metallic bonds.
  • Melting and boiling points
  • Thermal and electrical conductivity
  • Malleability, ductility, and durability
  • Hardness and strength

Melting and Boiling Points of Metals

• Melting points of metals are less extreme than boiling points.
• This is because cations and electrons are mobile in a metal.
• Less energy is needed for them to move past each other.
• During boiling, atoms must completely separate from the lattice, requiring more energy.

Metal Properties (Conductivity, Malleability, and Ductility)

• Movement of mobile electrons around positive metallic cations makes metals good conductors.
• Mobile electrons quickly transfer heat from one place to another.
• Mobile electrons easily move as part of an electrical current when an electric potential is applied to a metal.
• Metals are malleable (can be hammered into sheets).
• Metals are ductile (can be drawn into wire).
• Applied force causes metal ions to move through delocalized electrons, making metals malleable and ductile.

Metals Durability

• Metals are durable.
• Metallic cations are strongly attracted to electrons around them and are not easily removed from the metal.
• Hardness and strength increase with the number of delocalized electrons.

Metal Alloys

• An alloy is a mixture of elements with metallic properties. -Examples: stainless steel, brass, cast iron
• Alloy properties generally differ from the properties of the constituent elements. -Example: Steel (iron mixed with other elements) is stronger than iron.

Covalent Bonds

• A covalent bond is formed when atoms share electrons.
• Electronegativity (EN) measures an atom's ability to attract electrons in a covalent bond.
• Bond character describes the bond type (ionic, polar covalent, or nonpolar covalent) based on electronegativity difference.
• Polar bonds contain oppositely charged regions.
• Nonpolar bonds possess no difference charges.

Electronegativity and Bond Character

• Electronegativity decreases going down a group and increases going across a period.
• The difference in electronegativity between bonded atoms determines the bond character.
• Ionic bonds form when the EN difference is greater than 1.7, and polar covalent bonds form when the difference is between 0.4 and 1.7.
• Nonpolar covalent bonds form when the difference is less than 0.4.

Polar Covalent Bonds

• Shared electrons in a polar bond are more attracted to one atom than the other.
• Partial charges result on the ends of the bond (dipoles).
• The electronegativity difference between the atoms determines the extent of polarity.

Molecular Polarity

• Covalently bonded molecules can be polar or nonpolar.
• Nonpolar molecules are not attracted to electric fields.
• Polar molecules align with electric fields.
• Molecular shape influences polarity.

Intermolecular Forces

• Covalent bonds are strong, but intermolecular forces (van der Waals forces) between molecules are weak.
• Intermolecular forces are attractions between covalent molecules, not atoms.
• Types of intermolecular forces include: dispersion forces, dipole-dipole forces, and hydrogen bonds.

Kinetic Molecular Theory

• Gases are composed of small particles.
• Gas particles are in constant, random motion.
• Collisions between gas particles are elastic.

Particle Energy

• Kinetic energy depends on mass and velocity.
• Temperature is a measure of the average kinetic energy of particles.

Gas Density

• Gases have low density because of the large amount of empty space between their particles.

Gas Compression and Expansion

• Changing the volume of a gas in a closed container affects its density.

Diffusion and Effusion

• Gases will flow past each other due to their lack of significant attractive forces, resulting in diffusion.
• Effusion occurs when a gas escapes through a tiny opening.

Graham's Law

• The rate of effusion or diffusion is inversely proportional to the square root of the molar mass.

Dalton's Law of Partial Pressures

• The total pressure of a mixture of gases is the sum of the partial pressures of each gas in the mixture.
• Partial pressure is independent of the type of gas at a given temperature and pressure.

The Ideal Gas Law

• The ideal gas law relates pressure, volume, temperature, and the number of moles of a gas.
• The ideal gas law is PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature in Kelvin.

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