Science [3 Mark Questions]

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

Since nitrogen has 5 electrons in its outermost shell so, to achieve the 8-electron structure of an inert gas, it needs 3 more electrons and hence combines with another nitrogen atom to form a molecule of nitrogen gas.

This type of bonding is called covalent bonding.

1. Minerals: The natural materials in which the metals or their compounds are found in earth are called minerals.
2. Ores: Those minerals from which the metals can be extracted conveniently and profitably are called ores.
3. Gangue:The unwanted impurities like sand, rocky material, earthy particles etc. present in an ore are called gangue.

1. A is a metal.
2. B and C are non-metals.
3. A and B combines to form an ionic bond.
4. B and C combines to form a covalent bond.
5. B will form an anion with valency 1 since it needs only 1 electron to complete its octet.

Metals lose their shine or brightness on keeping in air for a long time and acquire a dull appearence due to the formation of a thin layer of oxide, carbonate or sulphide on their surface by the slow action of various gases present in air.
Brightness of metals can be restored by rubbing the dull surface of the metal object with a sand paper, then the outer corroded layer is removed and the metal object becomes shiny and bright once again.

Different methods are used for extracting metals belonging to category of highly reactive metals, moderately reactive metals and less reactive metals. This is because the extraction of a metal from its concentrated ore is essentially a process of reduction of the metal compound present in the ore.
For example: Manganese metal is obtained by the reduction of its oxide with aluminium powder and not carbon. This is because carbon is less reactive than manganese. Carbon, which is a non-metal, is more reactive than zinc and it can be placed just above Zn in the reactivity series.
Hence, carbon can reduce the oxides of zinc and all other metals below zinc to form metals.

There are some elements in group 18 of the periodic table which do not combine with other elements. These elements are helium, neon, argon, krypton, xenon and radon . They are known as noble gases or inert gases because they are unreactive.
If we look at the electronic configuration of noble gases, we would notice that except helium, all other inert gases have 8 electrons (helium has 2) in their outermost shells. This is considered to be the most stable arrangement of electrons.

Aluminium begins to corrode quickly when it comes in contact with moist air. The action of moist air on aluminium metal forms a thin layer of aluminium oxide all over the metal. This aluminium oxide is very tough and prevents the metal underneath from further corrosion. Therefore, aluminium is used for making utensils irrespective of its highly reactive property as its corrosion leads to the non-corrosion of the metal in the longer run.

We cannot use an aqueous solution of sodium chloride to obtain sodium metal because if we electrolyse an aqueous solution of sodium chloride, then as soon as sodium metal is produced at cathode, it will react with water present in the aqueous solution to form sodium hydroxide. Hence, electrolysis of an aqueous solution of sodium chloride will produce sodium hydroxide and not sodium metal.

We would create an apparatus using dry cell, a torch bulb fitted in a holder and some connecting wires with crocodile clips and connect them to make an electric circuit. Then insert a piece of sulphur between the crocodile clips and the bulb does not light up at all. This means that sulphur does not allow the electric current to pass through it. Now insert a piece of copper between the crocodile clips and the bulb will light up. This observation shows that non metals (ex- sulphur) do not conduct electricity and metals (ex- copper) conduct electricity.

The atomic number of chlorine is 17, so its electronic configuration is 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and needs 1 more electron to complete its octet and become stable.
It gets this electron by sharing with another chlorine atom. So, two chlorine atoms share one electron each to form a chlorine molecule. Because the two chlorine atoms share electrons, there is a strong force of attraction between them which holds them together. This force is called covalent bond.
Now, each chlorine atom in the chlorine molecule has the electronic configuration 2, 8, 8 resembling its nearest inert gas argon. Since the chlorine atoms in a chlorine molecule have inert gas electron arrangements, therefore, a chlorine molecule is more stable than two separate chlorine atoms.

Common salt is an ionic compound containing ionic bonds whereas cane sugar is a covalent compound containing covalent bonds. Since, ionic compounds conduct electricity and covalent compounds do not, hence common salt is a good conductor of electricity and cane sugar is a non-conductor of electricity.

Since an oxygen atom has 6 electrons in its outermost shell so, it needs 2 more electrons to achieve the stable 8-electron inert gas configuration. Hence, it combines with another oxygen atom and forms a molecule of oxygen.
This type of bonding is called a double covalent bond.

The moderately reactive metals are extracted by the reduction of their oxides with carbon,
aluminium, sodium or calcium.
Example: When zinc sulphide (zinc blende ore) is strongly heated in air (roasted), it forms zinc oxide and sulphur dioxide. This process is called roasting. Then, zinc oxide is heated with carbon to form zinc metal. This process is termed as reduction.

1. Ionic bond.
2. High melting point and boiling point.
3. Yes.
4. No.

1.  

1. Aluminium does not react with cold or hot water but it reacts with steam.
2. Gold does not react with any physical state of water.

2. Sodium is more reactive than calcium. The reaction between sodium and water produces a large amount of heat, which causes the evolved hydrogen to burn and catch fire. But in the reaction between calcium and water, no heat is produced and hence the evolved hydrogen does not catch fire.

1. B : Magnesium atom (At. no. = 12)
2. C : Oxygen atom (At. no. = 8)
3. D : Sodium ion (E.C = 2, 8)
4. A : Chloride ion (E.C = 2, 8, 8)

1. Ionic bonding.
2. Covalent bonding.
3. Covalent bonding.

Difference between metals and non-metals:Metals

1. Metals form basic oxides.
2. Metals displace hydrogen from water.
3. Metals displace hydrogen from dilute acids.

Non-metals

1. Non-metals form acidic or neutral oxides.
2. Non-metals do not react with water.
3. Non-metals do not react with dilute acids.

1. Basic oxide.
2. Metal.
3. Sodium,Na.

Difference between metals and non-metals:Metals

1. Metals are malleable i.e. they can be beaten into thin sheets with a hammer.
2. Metals are ductile i.e. they can be drawn into thin wires.
3. Metals are good conductors of heat and electricity.

Non-metals

1. Non-metals are non-malleable i.e. they cannot be beaten into thin sheets with a hammer.
2. Non-metals are non-ductile i.e. they cannot be drawn into thin wires.
3. Non-metals are bad conductors of heat and electricity.

1. Y and Z will form an ionic compound because an ionic bond is formed when one of the atoms can donate electrons to achieve the inert gas configuration, and the other atom needs electrons to achieve the inert gas configuration. Since Y has 7 and Z has 1 electron in their outermost shell, they would form an ionic bond.
2. X and Y will react to form a covalent compound because a covalent bond is formed when both the reacting atoms need electrons to achieve the inert gas electron arrangement.

Sodium and potassium metals react violently with cold water Observations:

1. Metal starts moving over the surface of water making a hissing sound.
2. Metal starts reacting with water causing little explosions.
3. Soon the metal catches fire and starts burning.

1. Sodium chloride is a metal chloride and its formula is NaCl.
   Hydrogen chloride is a non-metal chloride and its formula is HCl.
2. Metal chlorides are ionic chlorides, which are electrolytes that can conduct electricity. However, non-metal chlorides are covalent chlorides, which are non-electrolytes that do not conduct electricity.
3. They differ in this property because of the bonding in the chlorides. Metal chlorides have ionic bonds but non-metal chlorides have covalent bonds.