metals
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Chapter 13: Properties of Metals. Metals. Physical Properties of Metals. Ductile Malleable Good conductors of electricity Good conductors of heat Shiny High melting points & boiling points High density Strength. Structure of Metals. Metals are generally solids. - PowerPoint PPT PresentationTRANSCRIPT
Physical Properties of Metals
1. Ductile 2. Malleable3. Good conductors of electricity 4. Good conductors of heat5. Shiny6. High melting points & boiling points7. High density8. Strength
Structure of Metals
Metals are generally solids. [Recall: Particulate Models of Matter]
Simplified diagram of a metal:
Structure of Metals: Explanation
Metals have high density because there is little empty space between the atoms.
Atoms are packed close together in a metal.
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Structure of Metals: Explanation
In pure metals, atoms of the same size are packed regularly in layers.
Metals are malleable and ductile because the layers of atoms can slide over each other easily when a force is applied.
Exceptions!
Group I metals: Low melting point Low density (it floats on water)
Mercury: Liquid at room temperature Low melting point
Alloys
Mixtures of a metal with another element For example,
Bronze: copper and tin Brass: copper and zinc Stainless steel: iron, chromium, nickel and carbon
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Alloys
The different sizes of the atoms disrupts the orderly layers of atoms, and makes it more difficult for the layers to slide over
each other.
Metals are often used in the form of alloys because..
2. They are more resistant to corrosion.E.g. Brass [copper, zinc] is more resistant to corrosion than pure copper.
3. It lowers the melting points of metals.E.g. Solder [tin, lead] has lower m.p. than pure tin or pure lead, and can be used to join metals.
3. It improves the appearance. E.g. Pewter [Tin, antimony, copper] looks more beautiful than pure tin.
Some alloys..
Decorative ornaments
Bright, shiny, looks like silver
Tin, antimony, copper
Pewter
For joining metals
Low melting pointTin, leadSolder
Cutlery, utensilsResistant to corrosion, strong
Iron, chromium, nickel, carbon
Stainless Steel
Coins, musical instruments
Does not corrode easily; looks like gold
Copper, zincBrass
UsesPropertiesCompositionAlloy
Metals
may react more or less violently than others the metal that reacts more vigorously is
said to be more reactive than the other metal
metals have different reactivities
An arrangement of metals in order of their ease of reaction, beginning with the most reactive
The position of a metal in the series determines Reactions of the metal with various reagents Displacement of one metal from its
compound by another metal Method of extraction of a metal from its ore.
Metal Reaction with water
Sodium Reacts very fast with cold water, sometimes with explosion, produces sodium hydroxide and H2(which may catch fire and explode)
Potassium Explodes with cold water, potassium hydroxide and H2 produced a lot of heat given off, H2 gas burns in air
Calcium Reacts readily with cold water, calcium hydroxide obtained together with lots of bubbles of H2
Zinc No reaction with cold water; hot zinc burns in steam to produce zinc oxide and H2
Iron No reaction with cold water, rusting occurs slowly in the presence of air. Red hot iron reacts slowly with steam to produce iron oxide and H2
Silver No reaction under any condition
Copper No reaction under any condition
Magnesium Reacts very slowly with cold water; a few bubbles of H2 gas produced; magnesium hydroxide solution obtained. Hot magnesium burns to produce magnesium oxide and hydrogen gas; H2 burns in air.
Write the Chemical Equation!
Reaction with water/steam
Metal + (cold) Water Metal hydroxide + Hydrogen Example:
Potassium + Water Potassium hydroxide + Hydrogen 2K(s) + 2H2O(l) 2KOH(aq) +H2(g)
Metal + Steam Metal oxide + Hydrogen Example:
Magnesium + Steam Magnesium oxide + Hydrogen Mg(s)+ H2O(g) MgO(s) + H2(g)
Write the Chemical Equation!
Reaction with dilute hydrochloric acid
Metal + Hydrochloric acid Metal chloride + Hydrogen Example:
Magnesium + Hydrochloric Acid Magnesium chloride + Hydrogen Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
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Potassium
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead
(Hydrogen)
Copper
Silver
Gold
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Reactivity increases
Most reactive
Least reactive
The Position of Aluminium
Aluminium does not appear to react with water or steam.
Shouldn’t it be lower in the reactivity series?
The Position of Aluminium
A thin layer of aluminium oxide protects the metal from reacting.
What happens when this layer of oxide is removed?
Aluminium will react with steam a little less vigorously than magnesium, according to the reactivity series.
Using the Reactivity Series
Predict chemical reactions of metals
E.g. Copper does not react with water under any condition. We can predict that gold will also have no reaction with water since it is less reactive than copper.
Reactivity Series: An explanation
When metals react with water/dilute acid, they lose electrons to become ions.
The more readily a metal gives up electrons to form ions, the more reactive it is.
Reactivity Series: A measure of how easily a metal gives up electrons to form positive ions.
Down a Group
Atom becomes bigger Increase in number of electron shells
Nucleus
Weaker attractive force between nucleus and valence electron
+
Valence electron (-)
Valence electron escapes easily
Valence electron (-)
+
Strong attractive force between nucleus and valence electron
Nucleus
Across a Period
Metals Non-metals Increase in tendency to lose electrons rather
than gain electrons
Sodium Chlorine
The higher the metal in the reactivity series, the more
reactive the metal The more reactive the metal, the more violent are the
reaction with HCl and water Reaction of metal with HCl
Metal + HCl Metal chloride + Hydrogen Reaction of metal with water/steam
Metal + Water Metal hydroxide + Hydrogen
Metal + Steam Metal oxide + Hydrogen