Structure and Properties of Metals
This is part of Year 11 HSC Chemistry course under the topic of Bonding.
HSC Chemistry Syllabus
- Investigate the different chemical structures of atoms and elements, including but not limited to:
– Metallic Structure
Structure of Metals
The properties of metals can be accounted by their structure: a meticulously arranged three-dimensional lattice of positive metal ions interlaced with a mobile 'sea' of delocalised electrons.
Positively charged metal ions arise when valence electrons dissociate from their parent atoms, leaving behind positive ions. The detached electrons, now 'free' are termed 'delocalised' as they no longer belong to any specific atom's valence shell. Instead, they can move through the lattice and are shared among a multitude of positive ions.
Types of Metal Lattice
Metals can adopt different types of lattice structures, such as body-centred cubic (BCC), face-centred cubic (FCC), and hexagonal close-packed (HCP) arrangements. These structures are determined by the way the metal atoms pack together in the most efficient way to minimise empty space.
While it is useful to be aware of the different types of metallic lattice, knowing which metals occupy each type of lattice and how they affect the metal's property is not required in the HSC Chemistry syllabus
Properties of Metals
Metals are predominantly solid under standard conditions (room temperature and 1 atmospheric pressure). Many metals are hard substances, although certain members of Groups 1 and 2, such as alkali and alkali earth metals including sodium and calcium, show softer properties, making them easily cut with a knife.
- Metallic Lustre: Metals are characterised by their shiny appearance, known as metallic lustre. This lustre is due to the ability of the free electrons within the metal to absorb and re-emit light, resulting in a surface that reflects light, producing the characteristic shine. While most metals are lustrous, they can become dull when oxidised or corroded, losing their shiny appearance due to surface reactions with oxygen or other chemicals in the environment.
- State of Matter: Most metals are solid at room temperature, known for their structural rigidity and high melting points, exceptions being mercury (Hg), which is liquid.
- High Density: Metals typically have high densities due to the close packing of their atoms and the presence of metallic bonding.
- Electrically Conductive: Metals are known for their excellent electrical conductivity. The metallic structure contains a sea of delocalised electrons surrounding metal atoms. These electrons are mobile and account for metals' relatively high electrical conductivity.
- Thermally Conductive: Metals typically exhibit high thermal conductivity, meaning they can transfer heat efficiently. This is due to the presence of free electrons within their structure, which can move freely and transfer heat rapidly across the material.
- Ductility and Malleability: Most metals are both ductile and malleable. This is because the structure of most metals (repeating atoms layered on top of each other) allows for relatively easy sliding movement between them without breaking the metallic bonds in between. Most metals deform well, whether being stretched (exhibiting ductility) or being compressed (which is malleability). Generally if a metal is ductile, it is also malleable (at the same temperature). However, lead is an example of a metal that is malleable (deforms under compressive stress), but not ductile (easily fractures under tensile stress).
- High Tensile Strength: Metals generally possess high tensile strength, attributable to the strong bonds between metal atoms and the ability of these atoms to slide past each other without losing cohesion. This property makes metals ideal for construction materials, cables, and tools. Steel, an alloy of iron (Fe), is renowned for its exceptional tensile strength and is widely used in construction and manufacturing.
Structure and Properties of Transition Metals
Transition metals, which occupy the d-block of the periodic table (Groups 3-12), are characterised by their unique electronic configurations, physical properties, and chemical behaviours. Their structure and properties are influenced by several key factors, including core charge, metallic bonding, delocalised electrons, melting points, and density.
- Electronic Configuration: Transition metals have an incomplete d subshell in their atoms or ions, which allows for a variety of oxidation states and contributes to their complex chemistry.
- Metallic Structure: Like other metals, transition metals have a crystalline structure where atoms are arranged in a closely packed pattern, either as face-centred cubic (FCC), body-centred cubic (BCC), or hexagonal close-packed (HCP) structures.
- Core Charge: In transition metals, the core charge increases across the period as protons are added to the nucleus. However, the added d-electrons provide only minimal shielding, which means the effective nuclear charge felt by the outermost electrons also increases. This increased core charge strengthens the metallic bond and affects various physical properties.
- Tensile Strength: Transition metals typically exhibit high tensile strength, which is the resistance of a material to breaking under tension. This is attributed to the strong metallic bonds and the ability of d-electrons to form localised bonds, in addition to the delocalised sea of electrons.
- The number of delocalised electrons in transition metals is higher than in s-block metals. This is because, in addition to the s-electrons, the d-electrons can also become delocalised and contribute to the metallic bond. This large number of delocalised electrons is responsible for the excellent electrical conductivity, malleability, and ductility observed in transition metals.
- Melting Point: Transition metals typically have higher melting points, attributed to the strength of their metallic bonds. The presence of d-electrons, along with s-electrons, in the bonding framework means that more energy is required to overcome these bonds during melting.
- Density: The density of transition metals is generally higher. This is due to their atomic masses and the close packing of atoms in their crystalline structure. The high density is also influenced by the presence of a larger number of electrons contributing to the mass per unit volume.