Metallic Bonding Flashcards
(32 cards)
Properties of metals
Lustrous-shiny surface when polished
Good conductors of electricity and heat
Malleable-can be hammered, bent, rolled into any shape
Ductile-can be drawn into wires
Generally have high densities
A range of melting points but most are quite high
Often hard and tough with high tensile strength (high resistance to the stresses of being stretched, therefore do not easily break)
-mostly non polar
What is metallic bonding?
Metallic bonding is the bond formed between positive ions surrounded by a sea of valance electrons. It only occurs in metals and holds metal atoms together very strongly.
Electronegativity
Metals have low electronegativities and so lose their valance electrons easily.
What is a model?
A representation or simplified version of something.
Doesn’t explain everything, but it explains a lot.
Structure of metals
The atoms in metals are arranged in a 3D lattice structure surrounded by a sea of electrons.
What are the sea of electrons known as?
Delocalised electrons.
What holds the metallic structure together?
The electrostatic forces of attraction between the positively charged cations and the negatively charged electrons. They hold the lattice structure together.
What does the lattice structure explain about metals?
Many of their properties.
How does the conduction of heat happen within a metal?
What does the heat in the metal cause?
The delocalised electrons are able to gain kinetic energy hotter in areas of the metal and are able to quickly transfer it to other parts of the metal lattice because of their freedom of movement.
The heat causes the electrons in the metal to move faster, and as they bump against each other and the protons, it transfers heat.
How does the conduction of energy happen within a metal?
When an electric field is applied to a metal, one end of the metal becomes positive and the other becomes negative.
All the electrons experience a force towards the positive end, as opposites attract. This movement of electrons is called an electric current.
The lustrous appearance of metals is due to?
The mobile electrons within the lattice being able to reflect light, causing the metal to shine light.
Malleability and ductility is due to?
The non-directional nature of metallic bonds. The attractive forces exerted by the metal cations for the electrons occur in all directions.
This means that layers of atoms can move past one another without disrupting the force between the cations and the delocalised electrons.
The nature of the metal does not change when the metal becomes thinner.
The generally high melting points and hardness of metals is due to?
The strong metallic bonding. Melting pints and hardness increase with an increase in the no. of valance electrons, since there is a greater attractive force between the cations and the electrons.
Why do most metals have relatively high densities?
Because metallic lattices are close-packed.
Unreactive metals can be used for….?
Jewellery and coins. Eg: gold, silver, copper
Reactive metals need to be…?
Placed in oils as they react violently with water. Eg: Li, Na, K
What is the disadvantage of the lattice model?
It does not explain ALLL of the properties of metals.
What doesn’t the lattice model explain about the properties of metals?
Which model does explain them though?
Why iron is magnetic and copper is not.
Why platinum is twenty times as dense as sodium.
Why lead is quite malleable whereas iron is tough.
The ball bearing model.
What does metal strength depend on?
Metal strength depends on the arrangement of atoms in their crystal grains.
Which type of metal will bend easily?
A metal with perfect rows of atoms will bend easily.
Metals with large grains have fewer dislocations and they bend easily.
Which type of metal will NOT bend easily?
A metal with rows of atoms that are distorted, as they will not be able to slide over each other as freely and the metal will not bend easily.
Metals with small grains have many dislocations and they do NOT been easily.
How can you modify metals?
By work hardening, heat treatment and alloying.
What is work hardening?
Toughening up a metal by bending or hammering cold metals which causes their crystal grains become smaller.
The metal will not bend back to the area in which it has been work hardened.
Work hardening makes metals more brittle.
What type of heat treatment modifications alter the metal’s properties?
Annealing
Quenching
Tempering