Metals and Their Properties

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Questions and Answers

What is primarily responsible for the efficient conduction of heat through metals?

Heavy metal atoms

Fixed atomic structure

Mobile electrons (correct)

Ionic bonds

Which type of alloy involves the substitution of host metal atoms with other metal atoms of similar size?

Substitutional alloy (correct)

Interstitial alloy

Covalent alloy

Heterogeneous alloy

Which property is characteristic of network solids?

High ductility

Very high melting points

Brittle nature (correct)

Good conductors of electricity

What is a significant characteristic of diamond's structure according to the localized electron model?

Tetrahedral arrangement of carbon atoms Signup and view all the answers

Which of the following statements about graphite is true?

It is slippery and can conduct heat and electricity. Signup and view all the answers

What are the components of a heterogeneous alloy?

Components not dispersed uniformly Signup and view all the answers

Which crystal structure does diamond adopt according to molecular orbital theory?

Large gaps between filled and empty levels Signup and view all the answers

What type of bonding is primarily responsible for the structure of network solids?

Directional covalent bonds Signup and view all the answers

What type of bonding is primarily responsible for the stability of graphite?

Covalent bonding Signup and view all the answers

Which characteristic distinguishes p-type semiconductors from n-type semiconductors?

They have positive charge carriers known as holes. Signup and view all the answers

What type of hybridization is present in the carbon atoms of graphite?

sp2 hybridization Signup and view all the answers

Which components in molecular solids contribute to their weak intermolecular forces?

London dispersion forces Signup and view all the answers

Which Group IVA element is known as an inorganic semiconductor?

Gallium Arsenide (GaAs) Signup and view all the answers

What type of structural arrangement is depicted in the localized electron model for graphite?

Trigonal planar arrangement Signup and view all the answers

What condition must be met for a material to be classified as an insulator in terms of band gaps?

Band gaps must exceed 3.5 eV. Signup and view all the answers

What is the primary role of delocalized electrons in graphite?

They provide good electrical conductivity. Signup and view all the answers

What type of bonding characterizes metallic solids?

Delocalized nondirectional covalent bonding Signup and view all the answers

Which characteristic is NOT associated with covalent network solids?

Metallic conductivity Signup and view all the answers

Which of the following best describes the structure of diamond?

Atoms bonded in a strong three-dimensional network Signup and view all the answers

What structure do graphite layers consist of?

Hexagonal planar arrangement Signup and view all the answers

Which type of solid consists of noble gas elements bonded through London dispersion forces?

Noble gas solids Signup and view all the answers

What is the main characteristic of atomic solids?

They have atoms at the lattice points Signup and view all the answers

Which property is associated with metals due to their closest packing arrangement?

High ductility Signup and view all the answers

When identifying an alloy, which classification would NOT apply?

Mixture of ionic and atomic solids Signup and view all the answers

Study Notes

Mobile Electrons in Metals

Mobile electrons are responsible for efficient heat conduction in metals.

Metal Alloys

Alloys are substances that contain a mixture of elements and exhibit metallic properties.
Substitutional alloys occur when some host metal atoms are replaced by atoms of similar size. (e.g., Brass - Cu is replaced by Zn, Sterling silver - 93% Ag, 7% Cu).
Interstitial alloys form when small atoms occupy the holes within the closely packed metal structure. (e.g., Steel - C atoms in Fe crystal).
Heterogeneous alloys have components that are not evenly dispersed.

Network Solids

Network solids are atomic solids with directional covalent bonds that form giant molecules.
Properties:
- Brittle
- Inefficient conductors of heat and electricity
- Hard
- Colorless
- Insulators
Key elements:
- Carbon - Examples include Diamond and Graphite.
- Silicon

Diamond

The hardest naturally occurring substance.
Each carbon atom is surrounded by a tetrahedral arrangement of other carbon atoms.
Localized electron model:
- Stable structure via covalent bonds.
- Formed by sp3 hybridized carbon atomic orbitals.
Molecular orbital theory:
- Large gaps between filled and empty levels.
- Electron transfer is difficult.

Graphite

Slippery, black, and conductive of heat and electricity.
Structure is based on layers of carbon atoms arranged in fused six-membered rings.
Localized electron model:
- Trigonal planar arrangement.
- 120-degree bond angles.
- sp2 hybridization - three sp2 orbitals on each carbon atom form σ bonds with three other carbon atoms. One unhybridized 2p orbital remains perpendicular to the plane.
Molecular orbital theory:
- All orbitals combine to form π MOs which contribute to graphite's stability.
- Delocalized electrons enable high electrical conductivity.

Semiconductors

Gap exists between occupied MOs (valence band) and unoccupied ones (conduction band).
Electrons must enter the conduction band for electron transfer.
Group IVA elements have band gaps ranging from 0.08 to 3.05 eV (7 to 300 kJ/mol).
Band gaps exceeding 3.5 eV result in an insulator.

Semiconductors (contd.)

Group IVA elements are semiconductors due to their 4 valence electrons.
Inorganic semiconductors (like GaAs) tend to have an average of 4 valence electrons.

Doping in Semiconductors

Doping manipulates the conductivity of semiconductors by introducing elements with different numbers of valence electrons.
n-type semiconductor: Conductivity is increased by doping with atoms that have more valence electrons than the host crystal. n-type have more electrons, allowing negative charge to travel in the conductance band.
p-type semiconductor: Conductivity is increased by doping with atoms having fewer valence electrons than the host crystal. p-type have fewer electrons, allowing “holes” to travel in the valence band.

Molecular Solids

Exhibit strong covalent bonding within molecules but weak forces between molecules.
Forces between molecules depend on the nature of the molecules.
- CO2, I2, P4 and S8: No dipole moment; they possess London dispersion forces.

Diffraction of X-rays

Bragg's Law: nλ = 2d sin θ
- n: Integer
- λ: Wavelength of X-rays
- d: Distance between atoms
- θ: Angle of incidence and reflection
Diffraction occurs due to:
- Constructive interference when parallel beam waves are in phase.
- Destructive interference when waves are out of phase.
The distance traveled by waves depends on the distance between atoms.
A diffractometer is used for X-ray analysis of crystals.

Example of X-ray Diffraction

X-rays with a wavelength of 1.54 Å were used to analyze an aluminum crystal.
A reflection was observed at θ = 19.3 degrees.
Assuming n = 1, the distance between the atomic planes (d) can be calculated using Bragg's Law.

Classification of Solids

Ionic solids: Ions occupy the lattice points defining their structure.
Molecular solids: Discrete covalently bonded molecules exist at each lattice point.
Atomic solids: Atoms occupy the lattice defining its structure.
- Metallic solids: Delocalized, nondirectional covalent bonding.
- Covalent network solids: Atoms are bonded to each other by strong, directional covalent bonds.
- Group 8A (18) solids: Noble gases, attracted by London dispersion forces.

Structures of Metals

Closest packing assumes metal atoms are hard, uniform spheres.
Spheres are packed in layers, with each successive layer occupying dimples formed by the previous layer.

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Description

This quiz covers the key concepts related to mobile electrons in metals, the formation and types of metal alloys, and the characteristics of network solids. Learn about the properties of materials such as diamond and how these properties influence their applications. Test your understanding of these fundamental concepts in materials science.