What determines a materials physical, chemical and mechanical properties?

Atoms

Electrons

Neutrons

Protons

An atom is the smallest particle of an element that has the chemical properties of the element.

Negatively charged particle.

Neutral particle

Positively charged particle

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Elements

• Substances that cannot be broken down into other substances.

• Include metals and non-metals.

• Elements are composed of only 1 kind of atom.

Reading the Periodic Table

Molecule

The smallest particle of a compound that can exist independently & still have the properties of that substance.

Compounds – A substance that

contains 2 or more elements that are chemically combined in definite proportions.

Mixtures – made up of 2 or more elements or compounds that do not lose

their own physical or chemical properties.

Solutions – mixtures of 2 or more substances where the molecules of one

substance are spread out evenly between

the molecules of the other substances.

N 2 8 18 18

Number of Electrons Per Energy Level

Helium Atom

Helium2

He4.0026

• Some of the electrons in the outermost shell are called valence electrons.

• These are the electrons that can be gained or lost in a chemical reaction.

Valence

Atoms can attain a more stable arrangement of electrons in their outermost shell by interacting with one another.

An ionic bond is formed when electrons are transferred from one atom to the other.

A covalent, or molecular, bond is formed when electrons are shared between atoms.

Covalent (Molecular) BondSharing Electrons

Metallic Bond• In a metallic bond, the outer electrons of the

atoms form a common electron cloud. In a sense, the electrons become the property of ALL the atoms. These electrons are described as a "sea of electrons."

Solids

• Many solids are crystalline.

• Crystals are bounded by plane surfaces called ‘faces’.

• Crystals maintain their characteristic faces & angles.

Metals

• Metals:– Solid at room temperature– Opaque– Conductor of heat– Conductor of electricity– Reflects light like a mirror– Made of microscopic crystals– Expands when heated– Contracts when cooled

Metals

• Examples of pure metals:– Iron– Copper – Zinc– Tin – Aluminum – Magnesium – Manganese

– Vanadium– Molybdenum– Cobalt– Tungsten– Beryllium– Lithium– Zirconium– Titanium

Alloys

• Pure metals may not have the necessary physical properties

• Pure metals can be mixed with other metals and non-metals to form ALLOYS

• ALLOYS may have superior properties to pure metals

• What types of properties?

Alloys

• ALLOYS– Made of two or more metals, or– Made of one or more metals mixed with

one or more non-metals.– STEEL is an ALLOY of IRON and CARBON– CARBON improves the properties of IRON– Other elements make the properties of iron

worse.

Ferrous Alloys

• Ferrous metals:– Large percentage of IRON– IRON = Fe– Easily weldable– Carbon steel, tool steel, stainless steel,

cast iron, etc.

Ferrous Materials

• Iron

• Cast Iron

• Wrought Iron

• Steel– Carbon Steels

• Low Carbon Steels

• Medium Carbon Steels

• High and Very High Carbon Steels

– Alloy Steels

Non-Ferrous Alloys

• Non-Ferrous metals:– DO NOT contain IRON (Fe)– May contain small amounts of iron as an

ALLOYING agent– Aluminum, copper, tin, bronze, brass, zinc,

lead, nickel, etc.

Alloys

• Ionic and covalent bonding result in compounds.  • Metallic bonding between two (or more) different

metals always results in alloys, or mixtures, without fixed compositions. 

• There is not yet a systematic way of naming alloys like those for naming covalent and ionic compounds. In part, this is because alloys are not compounds, their composition is variable and their names need to reflect that. Generally, we use common names like brass, bronze, or steel or technical names like chromium steel or high carbon steel.