 All the materials known to man are composed of 92 elements  Most 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 element  Atoms 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 solids  Crystalline 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

ObservationExplanation 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 ???? / ????