composition of matter-8

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General Science: Physics and Chemistry

2. The numbers of compounds are unlimited in nature.3. The smallest particles of compound are called molecule.4. Every day new compounds are formed. As a result the number of

compound is increasing everyday.

5. compounds are of two types :(i) Organic compound and (ii) Inorganic compound.

(d) Classify the following substances into element and compound:Edible salt, Gold, Sulphur, Tin, Sugar, Water, Copper, Coal, UreaMercury, Nitrogen.

Ans.:Element Compound

1. Gold 1. Edible salt2. Sulphur 2. Sugar 3. Tin 3. Water 4. Cupper 4. Fertilizer 5. Mercury7. Nitrogen

(e) What is intermolecular space?

Ans.: Intermolecular space :Substances are the combination of molecules.Molecules are arranged side by side in thesubstance. There are certain spaces in

between the molecules. The space betweentwo molecules is called intermolecular space.Because of intermolecular spaces a spike can

be penetrated into the wood.

(f) What happens when a liquid is heated in a closed condition?

Ans.:The molecules of a liquid start vibrating when itis heated in closed condition and thus moleculesobtained kinetic energy. As a result inter molecular energy decreases and intermolecular space increases.

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Fig.: Aggregation of solid molecules

Fig.: Molecules in the liquid stat



Structure of Matter: Atom, Molecule

But the volume of the container is constant, so the molecules struck the surfaceof the container with a very high speed. As a result the container can be brokendue the extra heat.

(a) What are atoms and molecules? Define them.

Ans.: Atoms: The smallest particle of the elements which participate in thechemical reaction and on further division loses its own identity totally is calledatom.But there are atoms of some elements which can exist freely. For examplehelium, neon, argon etc. As 109 elements have been so far invented, there are109 types of atoms remain in this world.

Example :Iron, hydrogen etc. are composed with their very small particles.

Molecules:Molecule is the smallest particle of element or compound. Atoms are

obtained by split up molecule. That is, molecules are the smallest particles of substance which can exist freely, can be divided into atoms and which can not participate into chemical reaction without dividing into atoms, is calledmolecules. Molecules are composed with two or more atoms.

Example : O2 – is a molecule of oxygen which contains two atoms of oxygen. N 2 – is a molecule of nitrogen which contains two atoms of nitrogen.CO 2 – is a molecule of carbon dioxide which contains two atoms of oxygen andone atom of carbon.

(b) How many types of molecules are there? What is the difference betwethe molecule of hydrogen and water?

Ans.:There are two types of molecules. These are as follows:

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Answer to the Essay type Questions




(1) Elementary molecules:When the atoms of the same elements combinetogether to form a molecule then it is called elementary or simple molecule. For example----

H + H = H 2

Hydrogen atom hydrogen atom hydrogen moleculeO + O = O 2

Oxygen atom Oxygen atom Oxygen molecule

But there are some elementary molecules which are composed of only one atom.For example the inert gases are elementary molecules.

(2) Compound molecules:When two or more atoms of different elementcombine together to form a molecule, it is then called compound molecule. For example---

2Na + 2Cl = 2NaClSodium atom chlorine atom sodium chloride molecule

2H + O = H 2OHydrogen atom oxygen atom water molecule

Difference between the molecule of hydrogen and water are as follows:

Hydrogen molecule Water molecule1.The formula of hydrogen is H 2 1. The formula of water is H 2O2. Two atoms of hydrogen remain inhydrogen molecule

2. There are two hydrogen and oneoxygen atoms in water molecule

3. Two hydrogen atoms will beobtained by splitting up a hydrogen

molecule4. One molecule of hydrogen iscomposed of two atoms of hydrogen

5.Hydrogen is an elementary molecule

3. Two hydrogen atoms and oneoxygen atoms will be obtained by

splitting up a water molecule4. One molecule of water is composedof one atom of oxygen and two atomsof hydrogen

5. Water is compound molecule

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(c) What are the ideas of Dalton about atom?

Ans.: In 1880 British Mathematician and natural scientist John Dalton gave newidea of atom. The idea of Dalton about atom is known as atomic theory. Thetheory can be described as follows:

(i) Element is made up of indivisible particles called atom.(ii)The atoms of the same element are same in nature, property and mass. Sothe atoms of hydrogen are all alike in mass and property and so the case withthe atoms of all elements.(iii) The atoms of the different elements are different from one another inmass and properties. So the atoms of hydrogen, oxygen, carbon, sulphur etcare different from each other in mass and properties.(iv) The atoms of different elements combine with one another in simplenumerical proportions to form a compound.

(d) What are the states of matter? What influences these changes? Describhow these changes occur in case of water.

Ans.:There are three kinds of the states of matter. These are as follows:(i) Solid (ii)Liquid (iii)GasHeat influences these changes.

How these changes occur in case of water:Generally water remains in three physical states. These are –ice, water andvapour.If we heat solid ice slightly, the vibration of the molecules of ice increases. As aresult the molecules move away from one another. On the application of moreheat intermolecular spaces increase further resulting in reduction of intermolecular forces and allowing free movement of molecules. At this stage icetransforms into water. If more heat is applied to liquid the kinetic energy of the

molecules increase to a great extent and some of the molecules leave the liquidsurface after overcoming the intermolecular force of attraction. Thus the water isconverted to a vapour state.Again when the gaseous substances are cooled the velocity of the moleculesdecrease and the molecules come closer to each other. As a result intermolecular space decreases and intermolecular force increases. If cooling is continued astage is reached when the intermolecular force brings the molecules together andconverts them into water. When the liquid is cooled further the molecules come

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closer to each other and the intermolecular space decreases to a great extent. Asthe temperature falls down the kinetic energy of the molecules also decreasesresulting in the increase of inter molecular force of attraction and the water isfinally converted to the solid state. Thus with the change of temperature, state of

substance is changed.

Increased temperature Rising temperatureSolid Liquid Gas

Decreased temperature Lowering temperature

(e) How the molecules of solid, liquid and gas exist? Describe with figure

Ans.: Arrangements of the molecules of solid substances :

(i) In the case of solid their have great intermolecular attraction force between themolecules. The force holds together the molecules of the solid substances.So these make solid very strong. The solid substances like brick, wood, chair,table etc have fixed size, shape and volume.

Arrangements of the molecules of liquid substances :

(ii) In the case of liquid the molecules areloosely held together leaving some space

between the molecules. For that reasonliquid possesses the definite shape andvolume. But they have lack of definite size.

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Fig.: Molecules of solid

Fig.: Molecules of liquid




Arrangements of the molecules of gaseous substances :

(iii) In case of gas theintermolecular force arenegligibly small. As a result theymove freely. The moleculesremain far apart. So gas has nodefinite size, shape and volume.

(f) Why the condition of substance changes due to the application of heat?

Ans.:At normal temperature the molecules of a solid continue to vibrate in their own position. After application of heat it gains additional energy causing rapidvibration among the molecules. As a result the molecules move away from oneanother. On application of more heat intermolecular spaces increase further resulting in reduction of the intermolecular forces and allowing free movementof molecules. At this stage solid transforms into liquid. If more heat is applied tothe liquid the kinetic energy of the molecules increase to a great extent and some

of the molecules leave liquid surface after overcoming the intermolecular forceof attraction. Thus a liquid is converted to a vapour state.

Conversely, when the gaseous substances are cooled, the velocity of themolecules decrease and the molecules come closer to each other. As a resultintermolecular space decreases and intermolecular force increases. If cooling iscontinued a stage is reached when the intermolecular forces brings the moleculestogether and convert them into liquid. When the liquid is cooled further themolecules come closer to each other and the intermolecular space decreases to a

great extent. As a result the liquid finally is converted to solid.

(g) What happens when equal pressure is applied to solid, liquid and gas?

Ans.: Solid substances :Every substance is made with molecules of its own.These molecules are held together in the solid substances very strongly for their attraction force. There is no space between the molecules. For that reason,change of volume is not occurred applying strong force on solid substances.

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Fig.: Molecules of gases




Liquid substances :Like solid substances the molecules of liquid substances arealso combined together. But in this case the molecules are held together loosely.That is, there are spaces between the molecules of liquid substances. For thatreason there is short of attraction force between the molecules of liquid

substances. So change of volume is occurred in the case of liquid substance, if the equal pressure is applied in it.

Gaseous substances :Gaseous substances are also composed of molecules. Incase of gas the intermolecular force is negligibly small. As a result they movefreely. The molecules remain far apart. The molecules of gas scatter all around.For that reason gaseous substances are kept in container by closing the conver. If the cover is opened a little, all the gases are escaped away. But the molecules of gaseous substances come closer, if pressure is applied on these. So, theconditions are changed. Therefore, if pressure is increased successively of gaseous substances, the substances will be converted to liquids and solidrespectively.

1. What is substance? How many types of substances are there and what athose? What are the differences between element and compound?

Ans.: Substance :The matter which has weight, occupies space and opposeswhen any force is applied on it is called substance. Substances are of two types;(1)Element (2)Compound.

The differences between element and compound are as follows :

Subject of differences Element Compound1. Definition 1. A substance which isnot be split up or decomposed intodifferent chemicalsubstance is calledelement.

1. A substance which iscomposed of differentsubstances is calledcompound.

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Answer to the Extra Questions




2. Numbers 2. The numbers of element are 109 in thisworld.

2. The numbers of compound are unlimited.

3. Characteristics 3. After dividing anelement all the atomsfound are same.

3. The properties of compound arecompletely different thanits constituent elements.

4. Name of smallest particles

4. The smallest particlesof element are calledatoms.

4. The smallest particlesof compound are calledmolecules.

2. Write down the differences between atoms and molecules.

Ans.: The differences between atoms and molecules are as follows :

Subjects of differences

Atoms Molecules

1. structure 1. Atoms are composed of the smallest particles of element.

1. Molecules are composedof the smallest particles of element or compound.

2. Independence 2. Maximum atom can not

exist freely.

2. All molecules can exist

freely.3.Chemicalreaction

3. Atoms can participate inthe chemical reactiondirectly.

3. Before participating in thechemical reaction themolecules have to be dividedinto atoms.

4. Number 4. The number of atoms islimited; so far 109 atomshave been discovered.

4. Unlimited amount of molecules have beendiscovered, still discovering.

5. Decomposition 5. Electrons and protons arefound by decomposingatoms.

5. Atoms are found bydecomposing molecules.

6.Dividingcharacter

6. The characteristics of atoms do not exist if theseare further divided.

6. Atoms are obtained bydividing the molecules.

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3. What is elementary molecule and compound molecule?

Ans.: Elementary molecules:When the atoms of the same elements combinetogether to form a molecule, it is called elementary or simple molecule. For

example----

H + H = H 2

Hydrogen atom hydrogen atom hydrogen molecule

O + O = O 2

Oxygen atom Oxygen atom Oxygen molecule

But there are some elementary molecules which are composed with only oneatom. For example the inert gases are elementary molecules. Compound molecules:When two or more atoms of different elements combinetogether to form a molecule, it is called compound molecule. For example---

2Na + 2Cl = 2NaClSodium atom chlorine atom sodium chloride molecule2H + O = H 2OHydrogen atom oxygen atom water molecule

4. What is intermolecular force? Why different conditions are shown by object at different temperatures?

Ans.: Intermolecular force :There is anattractive force within the molecules of asubstance whereby the molecules are heldtogether closely; at the same time there exists

a repulsive force within the molecules due towhich they tend to move apart. The resultantof these two opposing forces is called theintermolecular force.

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Fig.: Intermolecular force




Causes of different conditions of the same substances at differetemperatures :

At normal temperature the molecules of a solidcontinue to vibrate in their own position. After application of heat it gains additional energycausing rapid vibration among the molecules.

As a result the molecules move away from oneanother. On application of more heat intermolecular spaces increase further resulting in reduction of theintermolecular forces and allowing free movementof molecules. At this stage solid transforms intoliquid.

If more heat is applied to the liquid the kineticenergy of the molecules increase to a great extentand some molecules leave the liquid surface after overcoming the intermolecular force of attraction.Thus a liquid is converted to a vapour state.

5. Why solid substances have definite size and shape?

Ans.: Causes for having definite sizeand shape of solid substances :In thecase of solid there is greatintermolecular attraction force betweenthe molecules. The force holds themolecules of the solid substancestogether. At normal temperature themolecules of a solid continue to vibrate

in their own position. So these makesolid very strong.For this reason, the solid substanceslike brick, wood chair, table etc havefixed size, shape and volume.

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Fig.: Solid condition

Liquid condition Gaseous condition

Fig.: Molecules of solid



Fig.: Molecules of gases


6. Why liquid substances have no definite size?

Ans.: Causes for having no definite size of liquidsubstances: In the case of liquid the molecules are loosely

held together leaving some space between the molecules.For that reason they have lack of definite size.

7. Why gaseous substances have no definite size, shape and volume?

Ans.: Causes for having no definite size of gaseous substances :In case of gas theintermolecular force are negligibly small.As a result they move freely. The moleculesremain far apart.So, gaseous substances have no definitesize, shape and volume.

Multiple Choice Questions :

1. Tick (√) the correct Answer :

(1) What is the number of elementary gases in the universe?

(a) 13 (b) 12√ (b) 11 (d) 9(2) What are there in one molecule of carbon dioxide molecule?

(a) One Carbon and two Oxygen molecules(b) One Carbon atom and one Oxygen molecule

√ (c) One Carbon atom and two Oxygen atoms(d) Carbon dioxide has two atoms.

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Fig.: Molecules of liquid

Answer to the Objective Questions




(3) What is the distinction between oxygen and carbon dioxide molecule?√ (a) The molecule of oxygen is elementary molecule and the molecule of

carbon dioxide is a compound molecule(b) Both the molecule of oxygen and carbon dioxide are compoundmolecule(c) Both the molecules of oxygen and carbon dioxide are elementarymolecule.(d) The molecule of oxygen is compound molecule and the molecule of carbon dioxide is elementary molecule.

(4) Why it is easy to push spike into wood?√ (a) Because of space in between the molecules

(b) Because of rapid vibration of molecules(c) Because of Intermolecular force(d) Because of attractive forces of the molecules.

(5) Which substance has least intermolecular force?(a) Solid (b) Liquid

√ (c) Gas (d) Ice(6) What is the reason of change in a substance into three states?√ (a) By the influence of heat the speed of molecules changes and thus the

state of the substance is changed.(b) Due to rearrangement of molecules

(c) Due to rearrangement of atoms(d) Due to chemical change(7) Why the tube of a cycle is punctured some times in the summer?

(a) The volume of the rubber tube increases(b) The number of molecules of air inside the tube increases

√ (c) The molecules of air inside tube move faster due to heat and strikewall of the tube strongly.(d) The molecules of the air inside become heavier.

(8) What happens when steam in a closed air container is cooled atransformed into water?(a) The speed of the molecules increase√ (b) The speed of the molecules reduce

(c) The number of molecules decreases(d) The total weight of the container increases.

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2. Fill in the blanks :

(a) Carbon dioxide is ……………molecule(b) Hydrogen consists of ………atoms

(c) Solid substance has fixed …………..(d) Liquid has only fixed………….(e) The idea of the molecules was put forward by …..(f) …………is liquid(g) The space between two molecules is called…….(h) Intermolecular force is minimum ……….(i) When a liquid is cooled the speed of the molecules……….

Ans.: (a) a compound (b) the combination of two (c) shape, size and volume(d)volume (e) Avogadro (f) Mercury (g) intermolecular space (h) in gaseoussubstances (i)decreases.

3. Match the left side sentence with that on the right side

Left Right(a) Modern idea about atom wasgiven by

(a) Solid

(b) Gaseous elements (b) Atoms(c) Intermolecular force isgreatest in

(c) Scientist Dalton

(d) Take part in a chemicalreaction

(d) Consist of elementarymolecule

(e) Element loses its identity (e) when atoms are split up(f) In liquid.

Ans.:1. Modern idea about atom was given by Scientist Dalton.2. Gaseous elements consist of elementary molecule.3. Intermolecular force is greatest in Solid.4. Atomstake part in a chemical reaction.5. Element loses its identity when atoms are split up

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Structure of Matter: Atom, Molecule 15

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