All the materials known to man are composed of 92 elementsMost substances are in the form of compounds, which means that they can be broken down into other substances. An element is a substance that cannot be broken down into anything else.E.g. Water is a compound because it can be broken down into Oxygen and Hydrogen. Oxygen and Hydrogen are both elements because they cant be broken down.

Atoms are the smallest particles of an elementAtoms join together to form molecules which are the ‘building blocks’ of all substances.For example each each molecule of water is composed of two hydrogen atoms and one oxygen atom.Atoms can be broken down into electrons, protons and neutrons.

Forces that hold atoms and molecules together are due to the charged particles in each atom.

Charged atoms are known as ions The forces are known as electrostatic forces and

there are several ways in which they cause ‘bonding forces’

States of matter The solid state – solids have fixed volume and

fixed shape. The liquid shape – Liquids have fixed volumes

but will take the shape of there container The gaseous state – gases have no fixed

volume and no fixed shape.

Structures of solidsCrystalline structure The arrangement of molecules are regular E.g salt, sugar and most metals

Amorphous Structures Random arrangements of molecules and has no

definite shape or form. E.g. many types of glass

Covalent Bonding Covalent bonds share

electrons in their outer orbitals, and they are the strongest type of bond. Covalent bonds are insoluble, have a high melting point, serve as an electrical insulator, and have a great stability

Metallic Bonding The properties of metals

suggest that their atoms possess strong bonds, yet the ease of conduction of heat and electricity suggest that electrons can move freely in all directions in a metal. The general observations give rise to a picture of "positive metal ions ‘fixed’ in a sea of electrons" to describe metallic bonding.

Ionic Bonding A bond in which one or

more electrons from one atom are removed and attached to another atom, resulting in positive and negative ions which attract each other.

Ionic Bonding (Salt) Common salt (I.e sodium chloride) Sodium chloride has one atom of sodium for each atom

of chlorine. The electrical forces between them the ions caused them to be regularly arranged.

The effect of water is to weaken the electrical forces between the ions. The ions break off and the crystal dissolves to form a solution. Most inorganic crystals are ionic

Sodium Chloride Free electron in outer shell

Chloride atom

Observation Explanation

Metals are dense

The particles present in metals are tightly packed in the lattice.

Metals have high melting and

boiling points.

Strong forces of attraction exist between particles. A Large amount of thermal energy is required to

overcome the strong electrical forces between the positive ions and the delocalised electrons. These

forces operate throughout the lattice.Metals are good

conductors of heat.

Delocalised electrons transmit the energy of vibrations of 1 positive ion to its neighbours.

Metals are good conductors of

electricity.

Mobile delocalised electrons within the lattice. Electrons flow in at one end, and the same number

flow out the other end.

Metals are malleable and

ductile.The distortion does not disrupt the metallic bonding.

Annealing Annealing is done to improve ductility (the ability to be

drawn and extruded) and reduce brittleness. Annealing consists of softening the metal by heating it

between 30 & 50 degrees C above it upper critical point and allowing it to cool slowly.

This can be done in either hot sand, ashes of a fire or by leaving the metal in an oven or furnace until cooled.

Tempering Tempering is done to remove some of the brittleness

and hardness of steel after hardening. Suitable temperatures for tempering vary considerably Tempering by colour still provides an accurate and

reliable method of dealing with plain carbon steels Hacksaws blades 220.C Pen knifes 250.C Light brown

Normalising The main purpose of normalising is to obtain a structure

that is uniform throughout the work piece and is free from any ‘locked up’ stresses.

Similar to annealing, but the cooling rate is accelerated by taking the work piece from the furnace and allowing it to cool in free air.

This more rapid cooling results in a finer grain structure which in turn leads to improved physical properties and improved finishes when machining.

Hardening Hardening of steels is done to increase the

strength and wear properties. Carbon steel is heated 30 & 50 degrees C

above the upper critical point and then quenched quickly

The quicker the steel is cooled the harder it will be.

Assignment- Heat Treatment and work hardening of metals Aim: The aim of this experiment is to test the

effects of hardening then tempering a piece of medium carbon steel to a level required for a punch

Hypothesis: I predict that after hardening…….. Method: Hardening……. Results/ Testing….After filing and hammering Conclusion: After the results

Key Terms you need to know Proportional limit Young’s Modulas? UTS Yield Stress elastic limit yield point Stress = ? / ? Strain = Change in ???? / ????