METAL AND NON-METALS notes part2

METALS AND NON-METALS

On the properties of their properties, all the elements can be divided into two main groups: metals and non-metals.

METALS

Metals are the elements that conduct heat and electricity, and are malleable and ductile. Some of the examples are: Iron, Aluminum, Copper, Silver, Gold, Platinum, Zinc, Tin, Lead, Potassium, Calcium and Magnesium.

Metals are the elements (except hydrogen) which form positive ions by losing electrons (or donating electrons). Metals are known as electropositive ions losing electrons.

METAL AND NON-METALS

Non-metals are the elements that do not conduct heat and electricity, and are neither malleable for ductile. They are brittle. Some of the examples of non-metals are: Carbon, Sulphur, Phosphorus, Silicon, Hydrogen, Oxygen Nitrogen Chlorine, Bromine, Neon and Argon. The two allotropic forms of carbon element, diamond and graphite, are non-metals.

Non-metals are the elements which negative ions by gaining electrons (or accepting electrons). Non-metals are known as electronegative elements because they can form negative ions by gaining electrons.

Through non-metals are small in number a compound to metals, but they play a very important role in our daily life. The most abundant non-metal in the earth’s crust is oxygen.

PHYSICAL PROPERTIES OF METALS

1. Metals are malleable, that is, metals can be beaten into thin sheets with a hammer (without breaking).
2. Metals are ductile, that is, metals can be drawn (or stretched) into thin wires.
3. Metals are good conductor of heat.
4. Metals are good conductors of electricity.
5. Metals are lustrous (or shine) and can be polished. The metals lose their shine or brightness on keeping in air for a long time and acquire a dull appearance due to the formation of a thin layer of oxide, carbonate or sulphide on their surface (by the slow action of the various gases present in air).
6. Metals are generally hard (except sodium and potassium which are soft metals).
7. Metals are strong (except sodium and potassium metals which are not strong).
8. Metals are solids at room temperature (except mercury which is a liquid metal).
9. Metals have high melting points and boiling points (except sodium and potassium metals which have low melting and boiling points).
10. Metals have high densities (except sodium and potassium metals which have low densities).
11. Metals are sonorous. That is, metals make sound when heat with an objects.
12. Metals usually have a silvery or gray color (except copper and gold).

PHYSICAL PROPERTIES OF NON-METALS

The physical properties of non-metals are just the opposite of physical properties of metals.

1. Non-metals are neither malleable nor ductile. Non-metals are brittle (break easily).
2. Non-metals do not conduct heat and electricity. Carbon (in the form of graphite) is the non-metal which is a good conductor of electricity.
3. Non-metals are not lustrous (not shiny). They are dull. Iodine is non-metals having lustrous appearance.
4. Non-metals are generally soft (except diamond which is extremely hard non-metal).
5. Non-metals are not strong. They are easily broken.
6. Non-metals may be solid, liquid or gases at the room temperature.
7. Non-metals have comparatively low melting points and boiling points (except diamond which is a non-metal having a high melting point and boiling point).
8. Non-metals have low densities, that is, non-metals are light substances.
9. Non-metals are non-sonorous. They do not product sound when hit with an object
10. Non-metals have many different colors.

Exception in Physical Properties

1. Electrical conductivity—Carbon in the form of graphite is non-metal which conducts electricity.
2. Luster—Iodine is a non-metal which is lustrous having a shining surface.
3. Hardness and Softness—Alkali metals (Lithium, Sodium and Potassium) are soft. Carbon in the form of diamond is anon-metal which is extremely hard.
4. Physical State—Mercury metal is a liquid at room temperature.
5. Melting Point and Boiling Points—Sodium, Potassium, cesium and gallium metals have low melting points (just like non-metals). Diamond is a non-metal which has a very high melting point and boiling point.
6. Density—Alkali metals (lithium, sodium, potassium) are low density.

CHMICAL PROPERTIES OF METALS

1. Reaction of Metals with Oxygen (of air)

Metals react with oxygen to form metal oxides. Metal oxides are basic in nature. Metal oxides, being basic, turn red litmus solution blue.

Metal + Oxygen  Metal Oxide

The vigor of reaction with oxygen depends on the chemical reactivity of metals.

1. Sodium metal—

Sodium metal reacts with oxygen to form a basic oxide called sodium oxide.

4Na(s) + O₂(g)  2Na₂O(s)

Potassium metal also reacts with oxygen to form basic oxide called potassium oxide.

Potassium metal and sodium metal are stored under kerosene oil to prevent their reaction with the oxygen, moisture and carbon dioxide of air (so as to protect them).

Most of the metal oxides are insoluble in water. But some of the metal oxide dissolves in water to form alkalis.

Na₂O(s) + H₂O  2NaOH(aq)

2. Magnesium Metal—

On heating magnesium metal burns giving heat and light to form a basic oxide called magnesium oxide

2Mg(s) + O₂(g)  2MgO(s)

Magnesium oxide dissolves in water partially ti form magnesium hydroxide solution

MgO(s) + H₂O(l)  Mg(OH₎₂

3. Aluminum Metals—

On heating aluminum metal burns in air to form aluminum oxide

4Al(s) + 3O₂(g)  2Al₂O₃(s)

Those metal oxides which show basic as well as acidic behavior are known as amphoteric oxides. Aluminum oxide and zinc oxide are amphoteric in nature. Amphoteric oxides react with both, acids as well as bases to form salts and water.

1. Aluminum oxide reacts with hydrochloric acid to form aluminum chloride and water

Al₂O₃(s) + 6HCl(aq)  2AlCl₃₍aq) + 3H₂O(l)

2. Aluminum oxide reacts with sodium hydroxide to form sodium aluminate

Al2O3(s) + 2NaOH(aq)  2NaAlO2(aq) + H2O(l)

4. Zinc metal—

Zinc metal burns in air only on strong heating to form zinc oxide:

2Zn(s) + O₂(g)  2ZnO(s)

Zinc oxide is amphoteric in nature

1. Zinc oxide reacts with hydrochloric acid to form zinc chloride and water.

ZnO(s) + 2HCl(aq)  ZnCl₂(aq) + H₂O(l)

2. Zinc oxide reacts with sodium hydroxide to form sodium zincate and water

ZnO(s) + 2NaOH(aq)  Na₂ZnO₂ + H₂O(l)

5. Iron metal—

Iron metal does not burn in air even on strong heating. Iron rects with oxygen to form iron (I,II) oxide

3Fe(s) + O₂(g)  Fe₂O₄(s)

6. Copper metal—

Copper metal does not burn in air even on strong heating. Copper reacts with oxygen air to form copper(II) oxide:

2Cu(s0 + O₂(g)  2CuO(s)

2. Reaction of Metal with Water

Metals reacts with water to form z metal hydroxide (or metal oxide) and hydrogen gas.

1. When a metal reacts with ,then the products formed are metal hydroxide and hydrogen gas:

Metal + Water  Metal hydroxide + Hydrogen

2. When a metal reacts with steam, then the products formed are metal oxide and hydrogen gas:

Metal + Steam  metal oxide + Hydrogen

9. Potassium reacts violently with water to form potassium hydroxide and hydrogen gas.

2K(s) + 2H₂O(l)  2KOH(aq) + H₂(g) + heat

(ii) Sodium reacts vigorously with cold water forming sodium hydroxide and hydrogen gas.

2Na(s) + 2H₂O(l)  2NaOH(aq) + H₂(g) + heat

(iii) Calcium reacts with cold water to form calcium hydroxide and hydrogen gas.

Ca(s) + 2H₂O(l)  Ca(OH)₂(aq) + H₂(g)

(iv) Magnesium metal does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen

Mg(s) + 2H₂O  Mg(OH)₂(aq) + H₂(g)

Magnesium reacts rapidly with steam to form magnesium oxide and hydrogen

Mg(s) + 2H₂O(l)  MgO(s) + H₂(g)

(v) Aluminum reacts with steam to form aluminum oxide and hydrogen gas:

2Al9s) + 3H₂O(g)  Al₂O₃(s) + 3H₂(g)

(vi) Zinc reacts with fsteam to form zinc oxide and hydrogen

Zn(s) + H₂O(g)  ZnO(s) + H₂(g)

(vii) Red-hot iron reacts with steam to form iron (I,II) oxide and hydrogen

3Fe(s) + 2H₂O(g)  Fe₃O₄(s) + 4H₂(g)

Metals like lead, copper, silver and gold do not reacts with water (or even steam).

Only those metals displace hydrogen from water (or steam) which are above hydrogen in the reactivity series.

3. Reaction of Metals with Dilute Acids

Metals usually displace hydrogen from dilute acids.

Metal + Dilute acid  Metal salt + Hydrogen

Metals react with dilute hydrochloric acid to give metal chlorides and hydrogen gas.

(i) Sodium metal reacts violently with dilute hydrochloric acid to form sodium chloride and hydrogen.

2Na(s) + 2HCl(aq)  2NaCl(aq) + _H2(g)

(ii) Magnesium reacts quite rapidly with dilute hydrochloric acid forming magnesium chloride and hydrogen gas

Mg(s)

(iii) Aluminum metals react rapidly with dilute hydrochloric acid to form aluminum chloride and hydrogen gas:

2Al(s) + 6HCl(aq)  2AlCl₃(aq) + 3H₂(g)

(iv) Zinc reacts with dilute hydrochloric acid to zinc chloride and hydrogen gas

Zn(s) + 2HCl(aq)  ZnCl₂(aq) + H₂(g)

(v) Iron reacts slowly with dilute hydrochloric acid to give iron(II) chloride and hydrogen gas

(vi) Copper does not reacts with hydrochloric acid at all.

Cu(s) + HCl(aq)  No reaction

Silver and gold metals also do not react with dilute acids.

The metals like copper and silver which are less reactive than hydrogen do not displace hydrogen from dilute acids. All the metals which are above hydrogen in activity series displace hydrogen from hydrochloric acids. Metals react with dilute sulphuric acid to give metal sulphates and hydrogen gas.

Metals react with sulphuric acid to give metal sulphates and hydrogen gas.

2Na(s) + H₂SO₄(aq)  Na₂SO₄(aq) + H₂(g)

Mg(s) + H₂SO₄(aq)  MgSO₄(aq) + H₂(g)

2Al(s) + 3H₂SO(aq)  Al₂(SO)₃ + 3H₂(g)

Zn(s) + H₂SO₄(aq)  ZnSO₄(aq) + H₂₍g)

Cu(s) + H₂SO₄(aq)  No reaction

When hydrogen dilute nitric acid, then hydrogen gas is not evolved. As soon as hydrogen gas is formed in the reaction between a metal and dilute nitric acid, the nitric acid oxidizes this hydrogen to water. Very dilute acid, however, reacts with magnesium and manganese metals to evolve hydrogen gas.

1. Magnesium reacts with very dilute nitric acid to form magnesium nitrate and hydrogen gas.

Mg(s) + 2HNO₃(aq)  Mg(NO₃)₂(aq) + H₂(g)

2. Manganese reacts with very dilute acid to form manganese nitrate and hydrogen gas.

Mn(s) + 2HNO₃(aq)  Mn(NO₃)₂(aq) + H₂(g)

Agua-Regia

Aqua-regia is freshly prepared mixture of concentrated nitric acid and 3 parts of concentrated hydrochloric acid. Aqua-regia can dissolve even gold and platinum metals.

The Reactivity Series of Metals (or Acidity Series of Metals)

The arrangement of metals in a vertical column in the order of decreasing reactivates is called reactivity series of metals (or activity series of metals).

Metals which are More Reactive They hydrogen

The metals which are more reactive than hydrogen are potassium, Sodium, Calcium, Magnesium, Aluminum, Zinc, Iron, Tin and Lead.

Metals which are Less Reactive than Hydrogen

The metals are less reactive than hydrogen are Copper, Mercury, Silver and gold.

4. Reaction of Metals with Salt Solutions

A more reactive metal displaces a less reactive metal from its salt solution.

Salt solution of metal B + Metal A  Salt solution of a metal A + Metal B

1. The Reaction of Zinc with Copper Sulphate Solution.

CuSO₄(aq) + Zn(s)  ZnSO₄(aq) + Cu(s)

2. Reaction of Iron with Copper Sulphate Solution.

CuSO₄(aq) + Fe(s)  CuSO₄(aq) + Cu(s)

3. Reaction of Copper with silver nitrate solution.

2AgNO₃(aq) + Cu(s)  Cu(NO₃)₂(aq) + 2Ag(s)

4. Reaction of metals with Chlorine

Metals react with chlorine to form ionic chlorides

1. Sodium is a metal. So sodium readily reacts with chlorine to form an ionic chloride called sodium chloride.

2Na(s) + Cl₂(g)  2NaCl(s)

2. Calcium is a metal which reacts vigorously with chlorine to form an ionic chloride called calcium chloride.

Ca(s) + Cl₂(g)  CaCl₂(s)

3. Magnesium on heating with chlorine readily forms magnesium chloride, which is an ionic chloride

Mg(s) + Cl₂(g)  MgCl₂(s)

4. Aluminum reacts with chlorine, on heating, to form aluminum chloride

2Al(s) + Cl₂(g)  2AlCl₃(s)

5. Zinc combines directly with chlorine to form zinc chloride

Zn(s) + C_l2(g)  ZnCl₂(s)

6. Iron combines with chlorine, when heated, to form iron(III) chloride

2Fe(s) + 3Cl₂(g)  2FeCl₃(s)

7. Copper reacts with chlorine on heating to form copper (II) chloride

Cu(s) + Cl₂(g)  CuCl₂(s)

5. Reaction of Metals with Hydrogen

Most of the metals do not combine with hydrogen. Only a few reactive metals like sodium, potassium, calcium and magnesium react with hydrogen to form metal hydrides.

9. When hydrogen gas is passed over heated sodium, then sodium hydride is formed

2Na(s) + H₂(g)  2NaH(s)

2. When hydrogen gas is passed over heated calcium, then calcium hydride is formed

Ca(s) + H₂(g)  CaH₂(s)

CHEMICAL PROPERTIES OF NON-METALS

1. Reaction of Non-Metals with Oxygen

Non-metals react with oxygen to form acidic oxides pr neutral oxides. The acidic oxides of non-metals dissolve in water to form acids.

1. Carbon reacts with oxygen of air to form an acidic oxide called carbon oxide

C(s) + O₂(g)  CO₂(g)

2. Sulphu reacts with the oxygen to form an acid called sulphurous acid

S(s) + O₂(g)  SO₂(g)

2. Reaction of Non-Metals with Water

Non-metals do not react with water (or steam) to evolve hydrogen gas.

3. Reaction of Non-metals with Dilute Acids

Non-metals do not react with dilute acids.

4. Reaction of Non-Metals with Salt solutions

A more reactive non-metal displace a less reactive non-metal form its salt solution.

2NaBr(aq) + Cl₂(g)  2NaCl(aq) + Br₂(aq)

5. Reaction of Non-Metals with Chlorine

Non-metals reacts with chlorine to form covalent chlorides which are non-electrolytes (do not conduct electricity).

1. Hydrogen reacts with chlorine to form a covalent chloride called hydrogen chloride

H₂(g) + Cl(g)  2HCl(g)

2. Phosphorus reacts with chlorine to form a covalent chloride called phosphorous trichloride

P₄(s) + 6Cl(g)  4PCl₃(l)

Non-metals form covalent chlorides because they cannot give electrons to chlorine atom to form chloride ions.

6. Reaction of Non-Metals with Hydrogen

Non-metals react with hydrogen to form covalent hydrides

1. Sulphur combines with hydrogen to form a covalent hydrogen called hydrogen sulphide, H₂S

H₂(g) + S(l)  H₂S(g)

2. Nitrogen combines with hydrogen in the presence of ironcatalyst to form a covalent hydride called ammonia, NH3

N₂(g) + 3H₂(g)  2NH₃(g)

Non-metals form covalent hydrides because non-metal atoms connot give electrons to hydrogen atoms to form hydride ions.

When metals react with non-metals, they form ionic compounds, when non-metals reacts with other non-metals, they form covalent compounds. The force which links the atoms (or ions) in a molecule is called a chemical bond.

Inertness of Noble Gases

Though 8 electrons in the outermost shell always impact stability to an atom, but 2 electrons in the outermost shell impact stability to an atom, but 2 electrons in the outermost shell impart stability only when the outermost shell is the first shell (K shell), and no other shells are present in the atom.

The usual number of electrons in the outermost shell of the atom of a noble gas is 8. Only in the case of one noble gas helium, the number of outermost electrons is 2.

The reactivity of elements as a tendency of their atoms to achieve a completely filled outermost shell or valence shell (just like those of noble gases) and become stable.

Cause of Chemical Bonding (or Chemical Combination)

The atoms combine with one another to achieve the inert gas electron arrangement and become more stable. Atoms form chemical bonds to achieve stability by acquiring the inert gas electron configuration.

IONS

An ion is an electrically charged atom (or group of atoms). An ion is formed by the loss or gain of electrons by an atom, so it contains an unequal number of electrons and protons.

1. A positively charged ion is known as cation. A cation is formed by the loss of one or more electrons by an atom. A cation contains less electrons than a normal atom. A cation contains less electrons than protons.
2. A negatively charged ion is known as anion. An anion is formed by the gain of one more electrons by an atom. An anion contains more electrons than a normal atom. An anion contains more electron then protons.

FORMATION OF POSITIVE IONS (OR CATIONS)

If an electron has 1, 2 or 3 electrons in the outermost shell of its atoms, then it loses these electrons to achieve the inert gas electron arrangement of eight valence electrons and forms positively charged ion or cation. The metal atoms lose electrons to form positively charged ions or cations.

FORMATION OF NEGATIVE INS ( OR ANIONS)

If an element has 5, 6 or 7 electrons in the outermost shell of its atom, then it gains (accepts) electrons to achieve the stable, inert gas electron configuration of 8 valence electrons, and forms negatively charged ion called anion. The non-metal atoms accept electrons to form negative ions or anions.

Types of Chemical Bonds

There are two types of chemical bonds

1. Ionic bond, and
2. Covalent bond.

Ionic bonds are formed by the transfer of electrons from one atom to another. Covalent bonds are formed by the sharing of electrons between two atoms. Ionic bond is also called electrovalent bond.

IONIC BOND

The chemical bond formed by the transfer of electrons from one to another is known as an ionic bond.

An ionic bond is formed when one of the atoms can donate electrons to achieve the inert gas electron configuration, and the other atom needs electrons to achieve the inert gas electron configuration.

When a metal reacts with a non-metal, transfer of electrons takes place from metal atoms to the non-metal atoms, and an ionic bond is formed. The ionic bonds are formed between metals and non-metals. The strong force of attraction developed between the positively charged ions is known as an ionic bond. Ionic compounds are made up of ions.

COVALENT BOND

The chemical bond formed by the sharing of electrons between two atoms is known as a covalent bond. A covalent bond is formed when both the reacting atoms need electrons to achieve the inert gas electron arrangement. Whenever a non-metal combines with another non-metal, sharing of electrons takes place between their atoms and a covalent bond is formed. A covalent bond can also be formed between two atoms of the same non-metal. The bond formed between the atoms of the same element is a covalent bond. The shared electrons are counted with both the atoms due to which each atom in the resulting molecule gets an inert gas electron arrangement of 8 electrons (or 2 electrons) in the outermost shell.

Covalent bonds are of two types:

1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond

Single Bond

A single bond is formed by the sharing of one pair of electrons between two atoms. A single covalent bond is formed by the sharing of 2 electrons between the atoms, each atom contributing one electron for sharing.

Double Bond

A double bond is formed by the sharing of two pairs of electrons between two atoms, each atom contributing two electrons for sharing.

Triple Bond

A triple bond is formed by the sharing of three pairs of electrons between two atoms. A triple bond is formed by the sharing of six electrons between two atoms, each atom contributing three electrons for sharing.

PROPERTIES OF IONIC COMPOUDS

1. Ionic compounds are usually crystalline solids. The ionic compounds are solid because their oppositely charged ions attract one another strongly and formed a regular crystalline structure.
2. Ionic compounds have high melting points and high boiling points.
3. Ionic compounds are usually soluble in water but insoluble in organic solvents (like ether, acetone, alcohol, benzene, carbon disulphide and carbon tetrachloride).
4. Ionic compounds conduct electricity when dissolved in water or when melted.

PROPERTIES OF COVALENT COMPOUNDS

1. Covalent compounds are usually liquids or gases. Only some of them are solids.
2. Covalent compounds have usually low melting points and low boiling points.
3. Covalent compounds are usually insoluble in water but they are soluble in organic solvents.
4. Covalent compounds do not conduct electricity

OCCURRENCE OF METALS

The earth’s crust is the major source of metals. Most of the metals are quite reactive and hence they do not occur as free elements in nature. Only a few less reactive metals (like copper, silver, gold and platinum) are found in the ’free state’ as metals. Copper and silver metals occur in free (native state) as well as in the combined state (in the form of compounds). All the metals which are placed above copper in the reactivity series are found in nature only in the form of their compounds.

Minerals and Ores

The natural materials in which the metals or their compounds are found in earth are called minerals. Those minerals from which the metals can be extracted conveniently and profitably are called ores. All the ores are minerals, but all the minerals are not ores.

EXTRACTION OF METALS

To obtain a metal from its ores is called the extraction of metal. The various process involved in the extraction of metals from their ores, and refining are known as metallurgy.

The three major steps involved in the extraction of a metal from its ore are:

1. Concentration of ores (or enrichment of ores)
2. Conversion of concentrated ore into metal, and
3. Refining (purification) of impure metal.

1. Concentration of ore ( or Enrichment of Ore)

The unwanted impurities like sand, rocky material, earthly particles, limestone, mica, etc., present in an ore called gangue.

2. Conversion of Concentrated Ore into Metal

The extraction of a metal from its concentrated ore is essential a process of reduction of the metal compound present in the ore.

For the propose of extracting metals from the concentrated ores, we can group the metals in three categories:

1. Metals of high reactivity
2. Metals of medium reactivity
3. Metals of low reactivity

Extraction of Highly Reactive Metals

The highly reactive metals such as potassium, sodium, calcium, magnesium aluminum are placed high up in the reactivity series in its upper part. The highly reactive metals (which are placed high up in the reactivity series) are extracted by the electrolysis of their molten chlorides or oxides. The highly reactive metals potassium, sodium, calcium, and magnesium are extracted by the electrolysis of their molten chlorides whereas aluminum metal is extracted by the electrolysis of its molten oxide.

Extraction of Moderately Reactive Metals

The moderately reactive metals which are in the middle of reactivity series are extracted by the reduction of their oxides with carbon, aluminum, sodium or calcium. It is easier to obtain metals from their oxides (by reduction) than from carbonates and sulphides. The concentration ores can be converted into metal oxide by the process of calcination and roasting.

1. Calcination is the process in which a carbonate ore is heated strongly in the absence of air to convert it into metal oxide.
2. Roasting is the process in which a sulphide ore is strongly heated in the presence of air to convert it into metal oxide.

The metal oxides (obtain by calination or roasting of ores) are converted to the free metal by using reducing agents like carbon, aluminum, sodium or calcium.

Extraction of less Reactive Metals

The less reactive metals which are quite low in the activity series are extracted by the reduction of their oxides by heat alone.

3. Refining of Metals

The process of purifying impure metals is called refining of metals. The most important and most widely used method for refining impure metals is electrolytic reefing.

CORROSION

The eating up of metal by the action of air, moisture and chemical 9such as an acid) on their surface is called corrosion. Corrosion of irons is a continuous process which ultimately eats up the whole iron object. The corrosion of iron is called rusting.

Rusting of iron

When an iron is left in damp air (or water) for a considerable time, it gets covered with a red-brown flaky substance called rusting. This is called rusting of iron. Rust is mainly iron (III) oxide, Fe2O3.xH2O

Condition Necessary for the Rusting of Iron

1. presence o air
2. presence of water

Damp air alone supplies both the things air and water required for the rusting of iron. Ordinary water alone also supplies both the things air and water needed for rusting.

Prevention of Rusting

1. Rusting of iron can be prevented by painting
2. Rusting of iron can be prevented by applying grease or oil
3. Rusting of iron can be prevented by galvanization
4. Rusting of iron can be prevented by tin-planting and chromium-plating
5. Rusting of iron can be prevented by alloying it to make stainless steel

Corrosion of Aluminum

Due to the formation of a dull layer of aluminum oxide on exposure to moist air, the aluminum vessel loses its shine very soon after use. A thin aluminum oxide layer formed on the surface of aluminum objects protects them from further corrosion. A common metal which is highly resistance to corrosion is aluminum.

Anodizing is a process of forming a thick layer of aluminum oxide on an aluminum objects by making it anode during the electrolysis of dilute sulphuric acid.

Corrosion of Copper

When a copper objects remains in damp air for a considerable time, then copper reacts slowly with the carbon dioxide and water of air to form a green coating of basic copper carbonate on the surface of the objects. The formation of this green coating on the surface of object corrodes it.

Corrosion of silver

Silver ornaments (and other silver articles) gradually turn black due to the formation of a thin silver layer on their surface by the action of hydrogen sulphide gas present in air. Silver metal is used to make jewelry and silverware because of its bright shiny surface and resistance to corrosive.

The Case of Gold and Platinum

Since gold does not corrode, therefore, gold ornaments look new even after several years of use. Gold is used to make jewelry because of its bright shiny surface and high resistance to corrosion. Platinum is another metal which is highly resistance to corrosion. Platinum is used to make jewelry because of it bright shiny surface and high resistance to corrosion.

ALLOYS

The mixture of two or more metals is called an alloy.

Aluminum metal is light but not strong, but an alloy of aluminum with copper, magnesium, and manganese (called duralumin) is light as well as strong.

Aluminum metal is light but not hard, but an alloy of aluminum with magnesium (called magnalium) is light as well as hard.

When a small amount of carbon (varying from about 0.1 percent to 1.5 percent) is mixed with iron, we get an alloy called steel. Steel is hard and strong. It also rusts less readily than iron. When iron metal is alloyed with other metals such as chromium and nickel, we get an alloy called stainless steel which is strong, tough and does not rust at all.

An alloy is a homogenous mixture of two or more metals (or metal and small amount non-metals). An alloy is prepared by mixing the various metals in molten state in required proportions, and then cooling their mixture to the room temperature.

The properties of an alloy are different from the properties of the constituent metals (from which it is made).

1. Alloys are stronger than the metals from which they are made.
2. Alloys are harder than the constituent metals.
3. Alloys are more resistance to corrosion.
4. Alloys are more resistance to corrosion.
5. Alloys are lower melting points than the constituent metals.
6. Alloys have lower electrical conductivity than the pure metals.

Some of the common alloys are : Duralumin or Duralium, Magnalium, Steel, Stainless steel, Brass, Bronze, Solder and Amalgams.

1. Brass. Brass is an alloy of copper and zinc (Cu and Zn). It contains 80% copper and 20% zinc.
2. Bronze. Bronze is an alloy of copper and tin (Cu and Sn). It contains 90% copper and 10% tin.
3. Solder. Solder is an alloy of lead and tin (Pb and Sn). It contains 50% lead and 50% tin.
4. Amalgam. An alloy of mercury metal with one and other metals is known as an amalgam. A solution of sodium metal in liquid mercury is called sodium amalgam.
5. Alloys of gold. Pure gold is said to be of 24 carats. Gold is alloyed with a small amount of silver or copper to make it hard.

QUESTIONS FOR PRACTICE

1. What are metals and non-metals? Give examples.
2. Name one metal and one non-metal which exist in liquid state at room temperature.
3. Why are metals called electropositive elements where as non-metals are electronegative elements?
4. Name one metal which has a low melting point.
5. Name a metal which is so soft that it can be cut with a knife
6. Name the metal which is the best conductor of heat and electricity.
7. Name the metal is the poorest conductor of heat.
8. Which metal foil is used for packing of some of the medicine tablets?
9. Metals are said to be shiny. Why do metals generally appear to be dull? How can their brightness be stored?
10. Name a non-metal which conducts electricity.
11. Name a non-metal which is extremely hard.
12. Name anon-metal having a very high melting point.
13. Which property of graphite is utilized in making electrodes?
14. Name two metals whose melting points are so low that they melt when held in the hard.
15. In nature, metal A is found in free state while metal B is found in the form of its compounds. Which of these two will be nearer to the top of the reactivity series of metal?
16. What is meant by the reactivity series of metals? Arrange the following metals in an increasing order of their relativities towards water:

Zinc, Iron, magnesium, Sodium

17. Give reasons for the following:

Hydrogen is not a metal but it has been assigned a place in the reactivity series of metals.

18. Arrange the following metals in order of their chemical reactivity, placing the most reactive first:

Magnesium, Copper, Iron, Sodium, Zinc, Lead, Calcium.

19. Which of the metals is more reactive: copper and silver?
20. What happens when a rod of zinc metal is dipped into a solution of copper sulphate? Give chemical equation of the reaction involved.
21. What will happens if a strip of zinc is immersed in a solution of copper sulphate?
22. What will happen if a strip of copper is kept immersed in a solution of silver nitrate (AgNO3)?
23. Complete the following chemical equation:

Cu(NO3)2(aq) + Zn(s) 

24. What happens when iron nails are put into copper sulphate solution?
25. State the reaction, if any, of the following metals with a solution of copper sulphate:

(i) Gold (ii) Copper (iii) Zinc

26. Name one metal which displaces copper from copper sulphate solution and one which does not.
27. In a solution of lead acetate, a strip of metal M was dipped. After some time, lead from the solution was deposited on the metal strip. Which is more reactive, M or lead?
28. What are amphoteric oxides? Give examples two amphoteric oxides.
29. Describe the reaction of potassium with water. Write the equation of the reaction involved.
30. Write an equation for the reaction of iron with steam.
31. Why does aluminum not react with water under ordinary condition?
32. What is the action of water on : (i) Sodium, (ii) Magnesium, and (iii) aluminum?
33. Write the equations for the reaction of:

1. Magnesium with dilute hydrochloric acid
2. Aluminum with dilute hydrochloric acid
3. Zinc with dilute hydrochloric acid
4. Iron with dilute hydrochloric acid

Name the products formed in each in each case. Also indicate the physical states of all the substances involved.

34. What happens when calcium reacts with chlorine? Write the equation for the reaction.
35. What types of oxides are formed when metals combine with oxygen? Explain with the help of an example.
36. What types of oxides are formed when non-metals combine with oxygen? Explain with examples.
37. Name two metals which can liberate hydrogen gas from very dilute nitric acid.
38. an element X forms two oxides: XO and XO₂. The oxide XO neutral where as XO₂ is acidic in nature. Would you call element X a metal or a non-metal? Give reasons for your answer.
39. Which of the following elements would yield: (i) an acidic oxide, (ii) a basic oxide, and (iii) a neutral oxide?

Na, S, C, K, H

40. (a) Write the formula of metal hydride

(b) Write the formula of non-metal hydride

41. State the reasons (of which at least one must be chemical) for believing that sodium is a metal.
42. How can you explain the reactivity of elements?
43. What is the difference between a cation and an anion? How are they formed? Give the names and symbols of one cation and one anion.
44. The atomic number of an element X is 12.
    1. What must an atom of X do to attain the nearest inert gas electron configuration?

(b) Which inert gas is nearer to X?

45. What is a covalent bond? What types of bond exist in: (i) CCl₄? (ii)CaCl₂?
46. What is an ionic bond? What type of bond is present in oxygen molecule?
47. What types of bonds are present in the following molecules? Draw the electron-dot structure. (i) H₂ (ii) CH₄ (iii) Cl₂ (iv) O₂
48. Name the cations and anions present in MgCl₂?
49. Name one ionic compound containing chlorine and one covalent compound containing chlorine.
50. Explain why ionic compounds have high melting points and covalent compounds have low melting points.
51. Explain why, a solution of cane sugar does not conduct electricity but a solution of sodium chloride is a conductor.
52. Explain why, a salt which does not conduct electricity because in the solid state becomes a good conductor in molten state.
53. Which of the following will conduct electricity and which not?

MgCl₂, CCl₄, NaCl, CS₂, Na₂S

54. You can bye solid air-fresheners in shops. Do you think these substances are ionic or covalent? Why?
55. Define the terms: (i) minerals, (ii) ore, and (iii) gangue
56. What is meant by ‘concentration of ore’?
57. A zinc ore gave CO2 on treatment with a dilute acid. Identified the ore.
58. Give reason for the following :

Carbonate and sulphide ores usually converted into oxides during the process of extraction.

59. How does the method used for extracted a metal from its ore depend on the metal’s position in the reactivity series?
60. What is corrosion? Name any two metals which do not corrode easily.
61. In one method of rust prevention, the iron is not coated with anything. Which method is this?
62. How can a layer a aluminum oxide on an aluminum oxide make thicker? What is this process called?
63. Give the reason why copper is used to make hot water tanks but not steel (an alloy of iron) is not.
64. What is an alloy? Give two examples of alloys.
65. How the properties of an alloy are different from those of constitute methods?
66. Write the composition of an alloy called bronze? Give two uses of bronze.
67. Name an alloy of lead and tin.

Chemistry for class 10....
acids-and-alkalis
carbon-and-its-compound-notes
periodic-classification-of-elements
unsaturated-hydrocarbon
metal-and-non-metals-notes
chemical-reaction-and-equations-notes-2
periodic-classification-of-elements

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