Ionic Compounds 7.4 Metallic Bonds and the Properties of Metals.
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Transcript of Ionic Compounds 7.4 Metallic Bonds and the Properties of Metals.
Metallic BondsObjectives:
Describe a metallic bond Relate the electron sea model to the
physical properties of metals Define alloys and categorize them into two
basic types
Metallic BondsProperties of materials are based on
bonding, and the bonding in both metals and ionic compounds is based on the attraction of particles with unlike charges.
Metals are not ionic but share several properties with ionic compounds.
Metallic BondsAs solids, metal atoms form lattices,
similar to ionic crystal lattices.Each metal atom is surrounded by 8-12
other metal atoms.Although metal atoms have at least one
valence electron, they do not share these electrons with neighboring atoms nor do they lose electrons to form ions.
Metallic Bonds Instead, the outer energy levels of the
metal atoms overlap.The electron sea model proposes that
all metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons.
Metallic BondsThe electrons are not held by any
specific atom and can move easily from one atom to the next.
Because they are free to move they are often referred to as delocalized electrons, with the rest of the atom called a metallic cation.
Properties of MetalsIn general, metals have moderately high melting points.
Cations and electrons are mobile; it does not require extreme amounts of energy to move them past each other.
Melting points of metals do vary greatly, however.
high boiling points. Atoms must be separated from
the group of cations and electrons; requires a lot of energy.
Properties of MetalsMalleable, meaning they can be
hammered into sheets, and ductile, meaning they can be drawn into wire. Mobile particles can be pushed or pulled past
each other.Durable
Electrons even though mobile, are strongly attracted to the metallic cations. They are not easily removed from one another.
Properties of MetalsGood conductors
Delocalized electrons in metal are free to move, keeping metallic bonds intact.
Delocalized electrons move heat quickly from one place to another.
Electrons themselves move as part of an electric current when an electric potential is applied to the metal
Lustrous Delocalized electrons interact with light
Properties of MetalsThe mobile electrons in transition
metals consist of s and d electronsAs the number of delocalized
electrons increases, so do the properties of hardness and strength.
Metallic BondsWhereas alkali metals are considered
soft because they have only one delocalized electron.
Metal AlloysThe properties of alloys
differ somewhat from the properties of the elements they contain. Steel is iron mixed with at
least one other element. Properties of iron are
present but steel is much stronger than iron alone.
Metal AlloysAlloys most commonly form when the
elements involved are either similar in size or the atoms of one element are considerably smaller than the atoms of the other.
Two basic types of alloys exist.
Metal AlloysSubstitutional
Alloy: Atoms of the original metallic solid are replaced by other metal atoms of similar size.
Ex. sterling silver – Cu atoms replace some Ag atoms.
Metal AlloysAn interstitial alloy is formed when small
holes (interstices) in a metallic crystal are filled with smaller atoms. Carbon steel (see next slide)