n(a) science (chem) chp 10 properties of metals

Properties of MetalsProperties of MetalsN-level Science (Chemistry)

Chapter 10

2Chp 10: Properties of Metals


Metals are Important!Metals are Important!

• Many things in our daily lives are made of metals.• Cars, trains, ships, bridges, pots, utensils and jewellery.


Metals –Metals –Physical PropertiesPhysical Properties

1. Good conductors of electricity2. Good conductors of heat3. Shiny4. High melting points and boiling points5. High density

– Little empty space between the closely packed atoms



6. Ductile – means can be stretched into wires

7. Malleable– means can be bent and beaten into shapes



• Metals are malleable and ductile because layers of atoms in a metal can slide over each other easily when a force is applied.

PUSH


Are there exceptions?Are there exceptions?

• Eg: Sodium – Low melting point– Low density (floats on water)

• Eg: Mercury– Low melting point– Liquid at room temperature

Yes

Just remember…Just remember… all metals all metals conduct conduct

electricityelectricity


AlloysAlloys

• An alloy is a mixture of metallic elements• Some also contain non-metallic elements• Pure metals are too soft and weak for most uses• Alloys are much stronger and harder than pure

metals


AlloysAlloys

In an alloy of 2 metals, the atoms have different sizes

• Orderly layers of atoms are disrupted

• Making it difficult for the layers to slide over each other

• Therefore, alloys are harder and stronger than pure metals Structure of an

Alloy

atoms of a different metal


Examples of AlloysExamples of Alloys

cutlery; pipes and tanks

iron + carbon + large amounts of chromium and nickel

stainless steel

musical instruments

copper + zincbrass

trophiescopper + tinbronze

car bodies; machinery

iron + carbon + a little manganese

mild steel

usescompositionname of alloy


Metals – Metals – Chemical propertiesChemical properties

1. Most metals react with water.

• Reactive metals can react with cold water

Metal + water metal hydroxide + hydrogen

• Less reactive metals react with steam

Metal + steam metal oxide + hydrogen


Metals with water!Metals with water!

unreactive

less reactive

more reactive

no reaction

steammetal + steam metal oxide + hydrogen

cold watermetal + water metal hydroxide + hydrogen

reactivity

copper and gold

lead

iron

zinc

magnesium

calcium

sodium

potassium

reaction with water / steammetal


calcium + water calcium hydroxide + hydrogenCa + 2H2O

Ca(OH) 2 + H2

Calcium reacts quickly with cold water.

sodium + water sodium hydroxide + hydrogen2Na + 2H2O 2NaOH + H2

Sodium reacts vigorously with cold water.

potassium + Water potassium hydroxide + hydrogen2K + 2H2O 2KOH + H2

Potassium reacts very vigorously with cold water.

calcium

sodium

potassium

reaction with water equationmetal

Reactive metals with waterReactive metals with water


iron + steam iron oxide + hydrogen3Fe + 4H2O Fe3O4 + 4H2

Hot iron reacts slowly with steam to produce iron (II, III) oxide.

zinc + steam zinc oxide + hydrogenZn + H2O ZnO + H2

Hot zinc reacts quickly with steam.

• Magnesium reacts very slowly with cold water.

• Hot magnesium reacts vigorously with steam.

iron

zinc

magnesium

reaction with water equationmetal

Less Reactive metals with Less Reactive metals with waterwater

magnesium + steam magnesium oxide + hydrogenMg + H2O MgO + H2


Metals –Metals –Chemical PropertiesChemical Properties

2. Most metals react with dilute hydrochloric acid.

metal + hydrochloric acid metal chloride + hydrogen


Reactive metals with Reactive metals with hydrochloric acidhydrochloric acid

calcium + hydrochloric acid calcium chloride + hydrogenCa + 2HCl CaCl2 + H2

Calcium reacts very fast with dilute hydrochloric acid.

sodium + hydrochloric acid sodium chloride + hydrogen2Na + 2HCl 2NaCl + H2

Sodium explodes with dilute hydrochloric acid.

potassium + hydrochloric acid potassium chloride + hydrogen2K + 2HCl 2KCl + H2

Potassium explodes with dilute hydrochloric acid.

calcium

sodium

potassium

reaction with HCl equationmetal


iron + hydrochloric acid iron chloride + hydrogenFe + 2HCl FeCl2 + H2

Iron reacts slowly with dilute hydrochloric acid.

zinc + hydrochloric acid zinc chloride + hydrogenZn + 2HCl ZnCl2 + H2

Zinc reacts moderately fast with dilute hydrochloric acid.

magnesium + hydrochloric acid magnesium chloride + hydrogenMg + 2HCl MgCl2 + H2

Magnesium reacts fast with dilute hydrochloric acid.

iron

zinc

magnesium

reaction with HCl equationmetal

Less Reactive metals Less Reactive metals Hydrochloric acidHydrochloric acid


Test for Hydrogen gasTest for Hydrogen gas

Hydrogen burns with a ‘pop’ sound when tested with

lighted splint.

lighted splint

metal + acid


Question!Question!

The diagram shows the reaction of 4 metals with hydrochloric acid. Arrange the metals in order of reactivity, starting from the most reactive.

1 234


The Reactivity SeriesThe Reactivity Series

Metals can be listed in order of their chemical reactivity


The Reactivity SeriesThe Reactivity SeriesMost

reactive

Least reactiv

e

Forms positive ion more

easily

Forms positive ion less easily

Reacts more vigorously

with chemicals

Reacts less vigorously

with chemicals

Corrodes more easily

Corrodes less

easily

PPotassiumotassium

SSodiumodium

CCalciumalcium

MMagnesiumagnesium

AAluminiumluminium

ZZincinc

IIronron

TTinin

LLeadead

(Hydrogen)(Hydrogen)

CCopperopper

SSilverilver

GGoldold


The Reactivity SeriesThe Reactivity Series

A metal ‘high up’ in the reactivity series:

• Reacts vigorously with chemical

• Readily gives up electrons in reactions to form positive ions

• Corrodes easily

A metal ‘low down’ in the reactivity series:

• Does not react vigorously with chemicals

• Does not readily give up electrons to form positive ions

• Does not corrode easily


Reactivity of AluminiumReactivity of Aluminium

• Although aluminium is quite high up in the reactivity series, it appears unreactive

• It is because the metal is covered with a thin layer of oxide that protects the metal from reacting.

• This explains why aluminium is corrosion-resistant.

Why?


Hydrogen in the Hydrogen in the Reactivity SeriesReactivity Series

• Hydrogen is a non-metal.

• It is placed in the Reactivity Series as a reference point.

• Metals above hydrogen react with acids to produce hydrogen gas

• Metals below hydrogen do not react with acids


Using the Reactivity SeriesUsing the Reactivity Series

• The reactivity series can be used to predict what chemical reactions will happen

Eg: Lead is below Zinc– Lead must be less reactive than Zinc– If Zinc does not react with cold water, Lead will not

react with cold water

• The position of metal is also helpful when we want to extract them.


RustingRusting

• Rusting is the corrosion of iron and steel.• The brown solid product formed during rusting is

called rust; iron (III) oxide Fe2O3


Conditions for rustingConditions for rusting

Presence of:

• air• water


Preventing Rusting…Preventing Rusting…

Surface protection• The surface of an object is covered with a layer of

substance to stop air and water from reaching the iron and steel underneath.

• The layer of substance can be:– paint– oil or grease– plastic– metal plating

• Iron or steel objects are covered with a thin layer of another metal eg tin, chromium or silver.


Will our things still rust?Will our things still rust?

If the layer is broken, air and water can reach the iron and steel.

Yes


Magnesium + WaterMagnesium + Water

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n(a) science (chem) chp 10 properties of metals

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