Chemistry

Physical Properties Of Metals And Nonmetals

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Physical Properties Of Metals And Nonmetals

Different elements have different properties. These properties can make these elements suitable for various purposes. Elements can be classified into two broad categories: metals and non-metals. Aluminium and mercury are examples of metals. Diamond and oxygen are examples of non-metals.
Let us learn about physical and chemical properties of metals and non-metals.
Physical properties include physical state, lustre, colour, hardness, malleability, ductility, thermal conductivity, electrical conductivity, and sonority.

Physical State

Metals: Almost all metals are solids at room temperature. Mercury, gallium, francium, caesium, and rubidium are the only metals known to occur in a liquid state at or near room temperature.
Non-metals: Almost all non-metals are solids or gases at room temperature. Bromine is the only non-metal that exists as a liquid at room temperature.

Lustre

Metals: ‘Glitter’ or a shiny surface is a property of most metals. This is because metals can be polished. This property is called lustre. Because of their ability to shine and reflect light, metals like gold, silver, and platinum are used for making jewellery and other decorative articles.
Non-metals: Almost all non-metals have a dull surface. As most of them occur as powders and gases, they cannot be polished like metals. Graphite and iodine do show some lustre.

Physical Properties Of Metals And Nonmetals 1
metals with lustre

Colour

Metals: Most metals are white or silvery-grey. There are, however, a few exceptions. For example, gold is yellow and copper is reddish-brown.
Non-metals: Some non-metals are colourless while some are coloured. For example, chlorine is a greenish-yellow gas, bromine is a brown liquid, iodine is a violet solid, and oxygen and nitrogen are colourless gases.

Hardness

Metals: Most metals are hard but some (e.g., sodium and potassium) are so soft that they can be cut with a knife.
Non-metals: Non-metals are generally soft. Diamond is an exception. It is the hardest substance known.

Malleability

Metals: Most metals can be beaten into thin sheets or foils. The property by virtue of which metals can be beaten into thin sheets is called malleability. Gold and silver are the most malleable metals known. This is what helps jewellery designers create intricately carved bangles, chains, and decorative articles in gold and silver. Other metals that can be beaten into sheets include aluminium, iron, copper, and tin.
Non-metals: Non-metals are brittle and cannot be beaten into sheets or foils.

Physical Properties Of Metals And Nonmetals 2Physical Properties Of Metals And Nonmetals 2

Activity

Aim: To show that metals are malleable and non-metals are brittle.
Materials needed: Small samples of easily available metals (e.g., aluminium wire, iron nail, copper wire, etc.) and non-metals (e.g., graphite and charcoal) and a hammer.
Method: Pound the objects one by one with the help of the hammer.
Observation: Metal objects get flattened upon hammering while non-metals break.
Conclusion: Metals are malleable whereas non-metals are brittle.
Note: Adult supervision required.

Ductility

Metals: Most metals can easily be drawn into thin wires, which have a wide range of applications. The property by virtue of which metals can be drawn into thin wires is called ductility. Gold and silver are two of the most ductile metals known. Other metals that can be drawn into wires include copper, aluminium, and tungsten.
Non-metals: Non-metals are brittle and cannot be drawn into wires.

Thermal Conductivity

Metals: Metals are good conductors of heat and are, therefore, used for making cooking utensils. Silver is the best conductor of heat followed by copper.
Non-metals: Non-metals are generally poor conductors of heat. Diamond, which is a good conductor of heat, is an exception.

Electrical Conductivity

Metals: Metals are good conductors of electricity and are, therefore, used for making electrical wires and cables.
Non-metals: Non-metals are generally poor conductors of electricity. Graphite, which is a good conductor of electricity, is an exception.

Activity

Aim: To show that metals and graphite are good conductors of electricity and other non-metals are poor conductors.
Materials needed: Small samples of easily available metals (e.g., aluminium wire, iron nail, copper wire, etc.) and non-metals (e.g., graphite and charcoal), a copper wire cut into three pieces, a pencil cell, and a 1.5-volt bulb.
Method:
1. Set up the apparatus as shown in the figure.
2. Connect the two free ends (A and B) of the copper wire to the objects, one by one.
Physical Properties Of Metals And Nonmetals 3
Observation: The bulb glows when metals and graphite are connected to the free ends of the copper wire, but not for other non-metals.
Conclusion: Metals and graphite are good conductors of electricity whereas non-metals are poor conductors.

Sonority

Metals: When metal pipes strike each other, they produce a ringing sound. The property by virtue of which metal objects produce a ringing sound when struck with a hard object is called sonority. Objects like wind chimes and bells make use of this property of metals.
Non-metals: Non-metals produce a dull sound when struck with a hard object.

Which acid is used for coagulating rubber from latex?

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Which acid is used for coagulating rubber from latex?

 

Coagulation process of latex:

  • The milky fluid obtained from tapped rubber trees is called latex.
  • It consists of an aqueous suspension of colloidal rubber particles.
  • Each rubber particle is made up of rubber polymers covered by a layer of protein membrane.
  • Negative charges are found on the surface of the membrane, making each rubber particle negatively charged. The negatively-charged rubber particles repel each other, preventing themselves from combining and coagulating.
  • Acids such as methanoic acid (forfnic acid) are added to make the latex coagulate.
  • Hydrogen ions from the acid neutralise the negative charges on the surface of the membrane. A neutral rubber particle is formed.
  • When these neutral particles collide with each other, their outer membrane layers break up. The rubber polymers are set free.
  • The rubber polymers start to coagulate by combining together to form large lumps of rubber polymers which then precipitate out of the latex solution.
  • Latex can still coagulate if acids are not added. Normally, the latex will coagulate if left overnight.
  • Bacteria from the air slowly attack the protein on the membrane to produce lactic acid. Ionisation of the lactic acid produces hydrogen ions. The hydrogen ions neutralise the negative charges to form neutral rubber particles, allowing coagulation to occur.
  • Alkalis such as ammonia solution are added to latex to prevent coagulation.
  • The hydroxide ions from alkali neutralise hydrogen ions produced by lactic acid as a result of bacterial attack on protein.
  • Because there are no hydrogen ions to neutralise the negative charges on the rubber particles, they remain negatively charged and hence cannot combine and coagulate.

Coagulation of latex experiment

Aim: To investigate the coagulation of latex.
Materials: Latex, 2 mol dm-3 ethanoic acid, 2 mol dm-3 ammonia solution, red and blue litmus paper.
Apparatus: Beakers, dropper, glass rod.
Procedure:

  1. About 20 cm of latex is poured into each of the three beakers labelled A, B and C.
  2. Ethanoic acid is added drop by drop into beaker A until the latex becomes acidic (blue litmus paper turns red). The mixture is stirred after each addition of acid.
  3. Ammonia solution is added drop by drop into beaker B until the latex becomes alkaline (red litmus paper turns blue). The mixture is stirred after each addition of alkali.
  4. The three beakers are left overnight. Any changes that occur are noted.

Observations:

BeakerObservation
AThe latex coagulates very quickly.
BThe latex does not coagulate.
CThe latex coagulates slowly.

Discussion:

  1. Ethanoic acid is an organic acid. It ionises in water to produce hydrogen ions. The positive hydrogen ions help to neutralise the negatively-charged rubber particles, allowing the latex to coagulate.
  2. Ammonia solution neutralises lactic acid secreted by bacteria when they attack the protein membrane. This keeps the rubber particles negatively charged and prevents coagulation.
  3. When latex is exposed to air, bacteria from the air slowly attack the protein membrane to produce lactic acid. The lactic acid helps to coagulate the latex.

Conclusion:
Acids speed up the coagulation of latex, whereas alkalis prevent the coagulation of latex.

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Describe how to write a formula for a covalent compound

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Describe how to write a formula for a covalent compound

Method to deduce the formulae of covalent compounds

Non-metals combine with non-metals to form covalent compounds.
Table shows the number of electrons needed by an atom of a non-metal to achieve a stable noble gas electron arrangement. The number of electrons needed is a measure of the combining power of the non-metal.

 

ElementNumber of valence electronsNumber of electrons needed to achieve a stable noble gas electron arrangement
Group 1771
Group 1662
Group 1553
Carbon and Silicon in Group 1444
Hydrogen11

The molecular formulae of covalent molecules formed from non-metals of Group 14, Group 15, Group 16, Group 17 and hydrogen can be deduced as shown in Table.

Non-metalsMolecular formula
XY
Group 14Group 17XY4
Group 14Group 16XY2
Group 15Group 17XY3
Group 16Group 17XY2
HydrogenGroup 17XY (HY)
HydrogenGroup 16X2Y( H2Y)
Group 15HydrogenXY3 (XH3)

The information in above Tables can be used to determine the formulae of covalent compounds as shown in the examples below.

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Writing formulas for covalent compounds examples

1. Atom T has a proton number of 6. Atom W has 10 neutrons and a nucleon number of 19. Atoms T and W combine to form a compound. Determine the molecular formula of the compound.
Solution:
Describe how to write a formula for a covalent compound
One atom of T combines with 4 atoms of W to form a compound.
∴ Molecular formula = TW4

2. Element R is located in Group 16 and Period 3 of the Periodic Table. Element R reacts with hydrogen to form a compound. Determine the molecular formula of the compound formed. (Proton number : H = 1)
Solution:
Atom R has 6 valence electrons because it is situated in Group 16 of the Periodic Table.
Proton number of a hydrogen atom = 1
∴ Electron arrangement of a hydrogen atom = 1.
∴ A hydrogen atom has one valence electron.
Describe how to write a formula for a covalent compound 2
Two hydrogen atoms combine with one R atom
∴ Molecular formula = H2R

3. Non-metal J reacts with non-metal Q to form a molecule with the molecular formula JQ3. Which groups of the Periodic Table do J and Q belong to?
Solution:
Simplest whole number ratio of the number of atoms of J : Q = 1 : 3.
Describe how to write a formula for a covalent compound 3
Hence, J is from Group 15 because it has 5 valence electrons.
Q is from Group 17 because it has 7 valence electrons.

What is the difference between ionic and covalent bonds?

Comparison between the formation of ionic and covalent bonds:

The structural changes during the formation of ionic and covalent bonds from their respective atoms are different.
Table compares and contrasts the structural changes during the formation of ionic and covalent bonds.

Ionic bondCovalent bond
1. It is formed when metal atoms combine with non­metal atoms.1. It is formed when non­metal atoms combine with non-metal atoms.
2. It involves the transfer of electrons from metal atoms to non-metal atoms.2. It involves the sharing of electrons between atoms of non-metals.
3. Metal atoms lose electrons to form positive ions, whereas non-metal atoms gain electrons to form negative ions.3. Each non-metal atom contributes an equal number of electrons to each other for sharing.
4. Formation of positive and negative ions enables the ions to achieve stable noble gas electron arrangements.4. Two atoms share 1,2 or 3 pairs of electrons to enable each atom to achieve a stable noble gas electron arrangement.
5. Oppositely-charged ions are held together by strong electrostatic forces of attraction, Known as ionic bonds.5. Atoms in a molecule are bonded together by covalent bonds, whereas molecules are held together by weak forces of attraction.

How Acid rain is formed equations?

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How Acid rain is formed equations?

Formation of acid rain:

  1. Sulphur dioxide accounts for most of the acid rain problems.
    (a) When sulphur dioxide dissolves in water, sulphurous acid is formed.
    SO2(g) + H2O(l) → H2SO3(aq)
    (b) Sulphur dioxide can react with oxygen and water to form sulphuric acid.
    2SO2(g) + O2(g) + 2H2O(I) → 2H2SO4(aq)
  2. Acid rain occurs when the pH of rain water falls between 2.0 to 5.5. This is due to the presence of sulphurous acid, sulphuric acid and nitric acid in rain water.

Sources of SO2

  1. Almost all the sulphur dioxide in the air comes from
    (a) vehicles (vehicles release SO2 by burning of fossil fuels)
    (b) industrial sources (SO2 released from the factories causes air pollution)
  2. Other sources that release sulphur dioxide in the atmosphere are:
    (a) Volcanic eruption
    (b) Extraction of metals from their sulphide ores
    (c) Burning of fossil fuels such as coal and petroleum with high sulphur content
    (d) Burning of waste products manufactured from sulphuric acid such as rayon

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Effects of Acid Rain on the Environment

Air pollution

  • Acid rain pollutes the air and corrodes buildings, monuments and statues made of metals and marble.
  • Metals like iron and calcium carbonate react with the acid in the rain slowly as follows:
    Fe(s) + H2SO4(aq) FeSO4(aq) + H2(g)
    CaCO3(s) + H2SO4(aq) CaSO4(s) + CO2(g) + H2O(l)

Water pollution

  • Acid rain increases the acidity in rivers and lakes.
  • The acidic water kills aquatic and organisms like planktons and fishes, disturbing ecosystem.

Soil pollution
Acid rain:

  • (a) increases the acidity of soil
    The reaction of sulphuric acid with aluminium compounds forms aluminium sulphate which can damage the roots of trees. The damage roots are easily attacked by viruses and bacteria.
  • (b) leaches minerals and nutrients in the soil
    The acid reacts with the minerals in the soil forming soluble salts and they are carried away by rain water.
  • (c) destroys plants and trees in the forests
    Apart from the acidic soil, the trees die of combination of malnutrition and diseases.

How can we reduce the effects of acid rain?

Ways to control the effects of acid rain:

  • Use low-sulphur fuels to reduce the amount of sulphur dioxide released into the air.
  • Remove sulphur dioxide from the waste gas before it is emitted into the atmosphere.
    (a) Powdered limestone is blown into the combustion chamber. It decomposes into calcium oxide.
    CaCO3(s) CaO(s) + CO2(g)
    (b) Calcium oxide reacts with sulphur dioxide to form calcium sulphite.
    CaO(s) + SO2(g) CaSO3(s)
    (c) Calcium sulphite is then oxidised to calcium sulphate to be used in the building industry.
  • Neutralise the acidic soil and water by treating them with calcium oxide (lime), calcium hydroxide and calcium carbonate.

Physical and Chemical Properties of Group 18 Elements

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Physical and Chemical Properties of Group 18 Elements

Elements in Group 18 of the Periodic Table are:
Helium, Neon, Argon, Krypton, Xenon, Radon
These elements are known as noble gases.

Physical properties of noble gases

1. Table shows some physical properties of Group 18 elements.

ElementHeliumNeonArgonKryptonXenonRadon
Proton number21018365486
Atomic radius (nm)0.0500.0700.0940.1090.130–
Melting point (°C)-272-249-189-157-112-71
Boiling point (°C)-269-246-185-152-107-62
Physical stateGasGasGasGasGasGas
Density (g dm-3)0,180.841.663.735.899.73

2. Atomic radius (atomic size)

  • The atomic radii (atomic sizes) of noble gases increase when going down Group 18 from helium to radon.
  • This is because the number of shells occupied with electrons increases when going down the group.

3. Melting and boiling points

  • All noble gases have very low melting and boiling points. They exist as gases at room temperature and pressure.
  • Explanation:
    • This is because noble gases consist of single atoms (monoatomic molecules) held together by weak van der Waals forces of attraction.
    • Only a small amount of heat energy is required to overcome the weak interatomic forces of attraction during melting and boiling.

Trend of change down the group

  • The melting and boiling points of noble gases increase when going down Group 18.
  • Explanation:
    • This is because the atomic sizes of the noble gases increase when going down the group from helium to radon, thus the van der Waals forces of attraction between the atoms become stronger.
    • Hence, more heat energy is required to overcome the stronger interatomic forces of attraction during melting and boiling.

4. Density

  • All noble gases have very low densities.
  • The densites of noble gases increase when going down Group 18.

5. Solubility

All noble gases are colourless gases which are insoluble in water.

6. Electrical and heat conductivity

  • All noble gases cannot conduct electricity.
  • All noble gases are poor conductors of heat.

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Unreactive (Inert) properties of noble gases

Table shows the electron arrangements of the atoms of noble gases.

ElementElectron arrangement
Helium2
Neon2.8
Argon2.8.8
Krypton2.8.18.8
Xenon2.8.18.18.8
Radon2.8.18.32.18.8
  • Each helium atom has only 2 electrons in one filled electron shell.
    This electron arrangement is known as the duplet electron arrangement.
  • The outermost shells of the atoms of the other noble gases have 8 electrons.
    This electron arrangement is known as the octet electron arrangement.
  • The duplet electron arrangement of helium and the octet electron arrangement of the other noble gases are very stable.
  • Hence, atoms of noble gases do not release electrons, accept electrons or share electrons among each other or with atoms of other elements.
  • Thus, noble gases exist as monatomic molecules and do not react with the other elements or compounds. This means that noble gases are inert chemically or chemically unreactive.

Uses of Group 18 elements

  1. The inert property of noble gases enable them to be used in various fields in our daily life.
  2. Helium, neon and argon are the most commonly used noble gases.

Helium

  • To fill weather balloons and airships.
    Reasons:
    This is because helium gas is very light and non-flammable (unreactive).
    Hydrogen, the lightest gas, is not used for the above purposes because it is flammable.
  • A mixture of 80% helium and 20% oxygen is used as an artificial atmosphere for divers.
    Reasons:
    Helium is used in preference to nitrogen because helium is less soluble than nitrogen in the blood. Nitrogen can cause a decompression sickness called bends’.
  • Used in thermometers to measure very low temperatures
  • Used as a protective atmosphere for growing crystals of silicon and germanium.
    Silicon and germanium are used to make microchips.

Neon

  • Used to fill advertising light bulbs. These bulbs can light up advertisement boards with a reddish-orange colour.
  • Small neon lamps are widely used as indicator lights to show that a circuit is ‘on’.

Argon

  • Used to fill electric bulbs.
    Reasons:
    This is because argon is chemically inert. Thus, the hot tungsten filament in the bulb does not react with it. As a result, argon gas prevents the tungsten filament from being oxidised.
  • Used to provide an inert atmosphere for welding.
    Reasons:
    This is because argon gas prevents the hot metals from reacting with oxygen in the air.
  • Argon is used as a carrier gas in liquid-gas chromatography because it is unreactive.

Krypton

  • Used to fill high speed photographic flash lamps.
  • Used in lasers to repair the retina of the eye.

Xenon

  • Used in electron tubes and stroboscopic lamps.
  • Used in bubble chambers.

Radon

  • Used to treat cancer because it is radioactive.