Metallic BondingMetallic Bonding

What are Metals?What are Metals?

A metal is an element that readily forms A metal is an element that readily forms positive ions (positive ions (cationscations) and has metallic ) and has metallic bonds.bonds.

What are Metals?What are Metals?

On the periodic table, a diagonal or stair step line On the periodic table, a diagonal or stair step line drawn from boron (B) to polonium (Po) separates the drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. Elements on this line are metals from the nonmetals. Elements on this line are metalloids, sometimes called semi-metals; elements metalloids, sometimes called semi-metals; elements to the lower left are metals; elements to the upper to the lower left are metals; elements to the upper right are nonmetals.right are nonmetals.

Almost 80% of the elements on the periodic table are Almost 80% of the elements on the periodic table are metals.metals.

Metallic BondsMetallic BondsThe valence electrons of metal atoms can The valence electrons of metal atoms can drift freely from one part of the metal to drift freely from one part of the metal to another- this is sometimes another- this is sometimes

called a “called a “sea of electronssea of electrons” ” Metallic bonds consist of Metallic bonds consist of

the attraction between these the attraction between these free floating electrons and the free floating electrons and the positively charged metal ions (cations). positively charged metal ions (cations).

This attraction is the “This attraction is the “bondbond” that holds ” that holds metals together.metals together.

Physical Properties of MetalsPhysical Properties of MetalsLusterous- they are shiny!Lusterous- they are shiny!

High density- atoms are tightly packed.High density- atoms are tightly packed.

Good Good conductorsconductors of electricity and heat. of electricity and heat. Reason- electrons can flow freely.Reason- electrons can flow freely.

Physical Properties of MetalsPhysical Properties of Metals

DuctileDuctile- they can be drawn into wires AND- they can be drawn into wires AND

MalleableMalleable- they can be hammered into - they can be hammered into shapesshapes Reason- cations can slide easily past each Reason- cations can slide easily past each

other because the sea of electrons insulates other because the sea of electrons insulates them and prevents strong repulsions.them and prevents strong repulsions.

……on the other handon the other hand

Ionic compounds are brittle and break Ionic compounds are brittle and break easily? Whyeasily? Why

Physical Properties of MetalsPhysical Properties of MetalsMetal ions are arranged in very compact Metal ions are arranged in very compact orderly patterns. orderly patterns.

––Similar to the way apples are stacked at Similar to the way apples are stacked at the grocery store.the grocery store.

Pure metals form the simplest kinds of Pure metals form the simplest kinds of crystalscrystals

Chemical Properties of MetalsChemical Properties of MetalsMost metals are chemically unstable and Most metals are chemically unstable and will react will oxygen in the air- that is they will react will oxygen in the air- that is they form form oxidesoxides- over varying timescales (for - over varying timescales (for example iron example iron rusts over years rusts over years and potassium and potassium burns in seconds). burns in seconds).

Chemical Properties of MetalsChemical Properties of Metals

-The alkali metals react quickest followed by the -The alkali metals react quickest followed by the alkaline earth metals. alkaline earth metals.

-The transition metals take much longer to oxidize -The transition metals take much longer to oxidize (such as iron, copper, zinc, nickel). Others, like (such as iron, copper, zinc, nickel). Others, like palladium, platinum and gold, do not react with palladium, platinum and gold, do not react with the atmosphere at all. the atmosphere at all.

-Some metals form a barrier layer of oxide on their -Some metals form a barrier layer of oxide on their surface which cannot be penetrated by further surface which cannot be penetrated by further oxygen molecules and thus retain their shiny oxygen molecules and thus retain their shiny appearance and good conductivity for many appearance and good conductivity for many decades (like aluminium, some steels, and decades (like aluminium, some steels, and titanium).titanium).

AlloysAlloysVery few metals that you encounter daily are pure Very few metals that you encounter daily are pure metals. Most metals are metals. Most metals are alloysalloys, a mixture of two or , a mixture of two or more elements of which at least one is a metal.more elements of which at least one is a metal. Examples:Examples:

BrassBrass is an alloy of copper and zinc is an alloy of copper and zincSterling silverSterling silver is an alloy of silver (92%) and copper (8%) is an alloy of silver (92%) and copper (8%)Stainless SteelStainless Steel is an alloy of iron (81%), chromium (18%), nickel is an alloy of iron (81%), chromium (18%), nickel (1%), and trace amounts of carbon.(1%), and trace amounts of carbon.

Alloys are important because their properties are Alloys are important because their properties are often superior to those of their component elements. often superior to those of their component elements. Examples: Examples:

Sterling silver is harder and more durable than pure silver, but still Sterling silver is harder and more durable than pure silver, but still soft enough to make jewelry and tableware.soft enough to make jewelry and tableware.Brass is harder and easier to shape than either copper or zincBrass is harder and easier to shape than either copper or zinc