Metallic Bonding

Metallic Bonding

Define metallic bonding.

The strong electrostatic attraction between positive metal ions (cations) and delocalised electrons.

Describe the structure of a metal.

A giant lattice of positive metal ions surrounded by a sea of delocalised electrons.

What are delocalised electrons?

Electrons that are not associated with any single atom or covalent bond and are free to move throughout the metal structure.

Where do the delocalised electrons in a metal come from?

The outer-shell electrons of the metal atoms.

What holds a metallic lattice together?

Strong electrostatic attractions between the positive metal ions and the negatively charged delocalised electrons.

What particles are present in a metallic lattice?

Positive metal ions and delocalised electrons.

Are delocalised electrons fixed in position?

No, they are free to move throughout the metal structure.

What are the typical physical properties of metals?

High melting temperatures, good electrical conductivity, good thermal conductivity, malleability and ductility.

Why do metals generally have high melting temperatures?

There are strong electrostatic attractions between the metal cations and delocalised electrons in the giant lattice, requiring a large amount of energy to overcome.

What must happen for a metal to melt?

The attractions between the metal cations and delocalised electrons must be partially overcome so the cations can move through the structure.

Why does a giant metallic lattice require a lot of energy to melt?

Many strong electrostatic attractions between cations and delocalised electrons must be overcome.

What factors affect the strength of metallic bonding?

The charge of the metal cations, their ionic radius and the number of delocalised electrons per cation.

How does the number of delocalised electrons affect metallic bonding?

More delocalised electrons per cation produce stronger electrostatic attractions and generally stronger metallic bonding.

How does cation charge affect metallic bonding?

A higher positive charge produces a stronger electrostatic attraction between the cations and delocalised electrons.

How does cation size affect metallic bonding?

Smaller cations have a higher charge density and attract the delocalised electrons more strongly.

What is meant by the charge-to-radius ratio of a metal cation?

The charge of the cation relative to its ionic radius.

How does charge-to-radius ratio affect metallic bonding?

A greater charge-to-radius ratio gives stronger attraction between the cations and delocalised electrons.

How does charge-to-radius ratio affect melting temperature?

A greater charge-to-radius ratio generally strengthens metallic bonding and increases the melting temperature.

Why do Group 1 metals generally have relatively low melting temperatures?

Each atom contributes only one delocalised electron and forms a +1 cation, so metallic bonding is relatively weak.

Why do Group 2 metals generally have higher melting temperatures than Group 1 metals?

They form +2 cations and contribute more delocalised electrons, producing stronger electrostatic attractions.

Why do d-block metals typically have high melting temperatures?

They generally contribute more delocalised electrons per cation, producing strong metallic bonding.

Why does lithium have a higher melting temperature than sodium?

Li+ is smaller than Na+, so it has a greater charge-to-radius ratio and attracts the delocalised electrons more strongly.

Why is there not always a simple trend in metallic melting temperatures?

The arrangement of ions in the metallic lattice can also affect the melting temperature.

Why do metals conduct electricity?

They contain delocalised electrons that are free to move through the structure and carry electrical charge.

What happens to electrons when a potential difference is applied across a metal?

The delocalised electrons move towards the positive terminal.

What carries the electric current through a metal?

Mobile delocalised electrons.

Can solid metals conduct electricity?

Yes, because their delocalised electrons remain free to move even when the metal is solid.

Why does electrical conductivity generally increase when the number of delocalised electrons increases?

There are more mobile charge carriers available to carry electrical current.

Why are metals good thermal conductors?

Free-moving delocalised electrons rapidly transfer kinetic energy through the metal, and closely packed cations can also transfer kinetic energy to neighbouring cations.

What are the two ways thermal energy is transferred through a metal?

Delocalised electrons transfer kinetic energy through the structure, and closely packed cations transfer kinetic energy to neighbouring cations.

Which mechanism is more important for thermal conductivity in metals?

Energy transfer by the delocalised electrons.

Define malleability.

The ability of a material to be hammered or pressed into different shapes without breaking.

Define ductility.

The ability of a material to be drawn into a wire.

Why are metals malleable?

Layers of metal cations can slide over one another while the delocalised electrons move with them and maintain the metallic bonding.

Why are metals ductile?

The layers of cations can move relative to one another without the metallic bonding being destroyed because the delocalised electrons remain between the cations.

What happens to the layers of cations when stress is applied to a metal?

The layers can slide over one another.

Why doesn't a metal shatter when its layers of ions slide?

The delocalised electrons move with the cations and continue to provide electrostatic attraction, preventing strong repulsion between neighbouring positive ions.

Why are metals malleable whereas ionic crystals are brittle?

In metals, delocalised electrons maintain attraction as layers of cations slide. In ionic crystals, sliding can bring ions of the same charge next to each other, causing repulsion and the crystal to fracture.

Why are sodium, magnesium and aluminium expected to have increasingly strong metallic bonding in the order Na < Mg < Al?

The cation charge increases, cation radius decreases and the number of delocalised electrons per atom increases from Na to Al, strengthening the electrostatic attraction.

Why do the melting temperatures generally increase from Na to Mg to Al?

Metallic bonding becomes stronger because cation charge and the number of delocalised electrons increase while cation radius decreases.

Why does electrical conductivity generally increase from Na to Mg to Al?

The number of delocalised electrons available to carry charge increases from one per atom in Na to two in Mg and three in Al.

How many delocalised electrons does each sodium atom contribute?

One.

How many delocalised electrons does each magnesium atom contribute?

Two.

How many delocalised electrons does each aluminium atom contribute?

Three.

What should you include when drawing a diagram of metallic bonding?

A regular arrangement of positive metal ions surrounded by delocalised electrons, with a key identifying both.

What wording should you use in an exam definition of metallic bonding?

Strong electrostatic attraction between positive metal ions and delocalised electrons.