IMPORTANT FOR CLASS X CBSE (TERM II)

What are the main symbols of an independent nation? 3

Ans. The main symbols of an independent nation are:(i) The National Flag(ii) The National Anthem(iii) The National Language(iv) The National SealEvery country is identified through these symbols which are distinct from others.

Choose three examples to show the contribution of culture to the growth of nationalism in Europe.

Ans. Culture of the people plays a significant role in strengthening nationalistic feelings. The idea of a nation

can be created through stories, poems or painting. Music often helped in expressing and shaping the nationalist feelings.

Romanticism , a cultural movement in Europe made effort to create a sense of shared collective heritage , a common cultural past as the basis of a nation.

Folk culture such as folk songs , folk poetry and folk dances displays the true sprit of the nation and unites common people. Pride in folk culture and promotion of Vernacular language help in nation building.

Explain the most important achievements of the French Revolution of 1789.

Important achievements of the French Revolution of !789 werea) Led to drastic political and constitutional changes ,transfer of sovereignty from monarchy to National

Assembly , an elected body of French citizens.b) The revolution proclaimed that henceforth the French people would constitute the nation and shape its

destiny.c) The new constitution guaranteed equality before law. Uniform laws were made.d) The royal standard was replaced by the National Flag-the French tricolour.e) The French Parliament , the Estates General , was renamed as the National Assembly.f) A centralised administrative system was put in place.

Explain any three measures introduced by the French Revolutionaries to create a sense of collective identity amongst the French people.

Three measures introduced by the French Revolutionaries to create a sense of collective identity amongst the French people were:

a) The idea of a fatherland and citizen emphasised a notion of a united community enjoying equal rights under a constitution.

b) A new French flag, the tricolour was chosen to replace the former royal standard.c) The estates General was elected by the active citizens and was renamed as the national assembly.

How did the French revolutionary ideas spread to other countries?

The French revolutionary ideas spread to other countries and inspired the oppressed people, with liberal ideas.a) The French revolutionaries clearly said that it was their mission to liberate not all the French people but

people of all the parts of the Europe from despotism and help them to become nations.b) Jacobin clubs were set up to spread these ideas.

c) With the outbreak of revolutionary wars the French armies began to carry the idea of nationalism to other countries.

UNIFICATION OF ITALY :

1) During the 1830s Giuseppe Mazzini decided to make a programme to unite Italy. He formed Young Italy for the purpose.

2) After revolutionary wars King Victor II took power to unify the Italian states through wars.3) Through a tactful diplomatic alliance Cavour succeeded in defeating the Austrian forces in 1859.4) Under the leadership of Garibaldi armed Volunteers marched into South Italy.5) With the help of the Kingdoms of the two Sicilies and the peasants drove away the Spanish rulers.6) In 1861 Victor Emmanuel II was proclaimed the King of united Italy.

Economic Impact of first world war

1) It led to huge increase in defense expenditure.2) Increased taxes.3) Custom duties were raised.4) Income tax introduced.5) Prices increased.6) It led to extreme hardships for the common people.7) Crops failed in many parts of India resulting acute shortage of food.

Rowlatt act

1. Decided to launch a nationwide Satyagraha.2. Rallies were organised.3. Workers went on strike in railway workshops.4. Shops closed down.

Difference between Metallic and Non- Metallic minerals

1) Metallic minerals contain metal. Non-metallic minerals do not contain metals.2) Metallic minerals found in igneous rocks whereas sedimentary rocks may contain both metallic & non metallic minerals.3) Iron-ore, Manganese, Copper, lead, Bauxite etc. are the example of Metallic minerals. Mica, Salt, Potash, granite marble sandstone etc. are the example of non metallic minerals.

Manganese: Orissa is the largest producer

Uses: (1)1) Mainly used in manufacturing of steel.2) It is also used in manufacturing Ferro-manganese alloy.

3) It is used in manufacturing bleaching powder, insecticides and paints.4) It is used in manufacturing insecticides.5) It is also used in preparing paints.

Agriculture and Industry go hand to hand1) Agro based industries give a major boost to agricultural productivity.2) Industries provide irrigation pumps, fertilizers, insecticides, pesticides, plastic and PVC pipes to agriculture.3) They also provide different types of machines and tools to the farmers.4) Agriculture provides different types of the raw materials to the industries such as Cotton, Jute,Sugarcane, etc.

National political party which gets inspiration from Indian ancient cultural & values:Bharatiya Janata Party (1)Features1) Believes in Cultural nationalism.2) It wants full territorial and political integration of Jammu and Kashmir with India.3) It stresses a uniform Civil code for all.4) It supports a ban on religious conversions.

Multi - National Companies1) Setting up units in a region where raw materials is available in abundance.2) Availability of cheap skilled and unskilled labour.3) Nearness to the market.4) Favourable Government policies.5) Regular supply of power.6) Safety

Legal- Constitutional changes1) Laws play an important role in political reforms.2) Laws can help to discourage wrong political practices and encourage good ones.3) But Laws are not much meaningful without cooperation of masses.4) Democratic reforms are to be carried out mainly by political activists, parties , movements and politically conscious citizens.5) Example LBW rules of Cricket.

Money as a medium of exchange1) A person holding money can easily exchange it for any commodity or service that he or she wants.2) Every one prefers to receive payments in money.3) Money acts as an intermediate in the exchange process.4) Money eliminates the need for double coincidence of wants. For example, a farmer can sell his cropsto anyone who wants to purchase it and earn money. With the earned money he can purchase anything.

Values of an ideal government1) Honesty and integrity2) Justice3) Truthfulness4) Transparency

5) Accountability6) Patriotism

Producers and Consumers1) As producers of goods and services, we wouldbe working in any of the economic sectors - Primary, secondary and tertiary like agriculture and industry services.2) Produce different goods and supply them to the market.3) As consumers we participate in the market as and when goods and services are required.

Role of Culture in Europe1) Art and poetry helped to express and shape of nationalist feelings.2) Stories and music also helped to express and creating the idea of the nation.3) Romanticism, a cultural movement sought to develop a particular form of nationalist sentiment.4) Romantic artists and poets generally criticized the glorification of reason and science.5) They focused on emotions, intuition and mystical feelings.6) Their efforts was to create a sense of shared collective heritage, a common cultural past as the basis of a nation.

Participation of Dalit in the Civil Disobedient Movement.1) For a long time the congress had ignored the dalits.2) Gandhiji organised Satyagraha in favour of Harijans.3) Many Dalit leaders were keen on a different political solution.4) They began organizing themselves demanding reserved seats.5) They demanded separate electorate.6) They believed in political empowerment.

Measures to control industrial pollution1) Smoke emitted by industries can be reduced by using mineral oil, natural gas instead of coal.2) Pollutants in the air can be reduced by fitting smoke stacks.3) Treating hot water and effluents before releasing them in water bodies.4) Dumping and disposing the waste material by land filling.5) Pollution norms should be followed.6) Noise producing machineries and equipments should be fitted with silencers.

Problems faced by road transport1) The road network is inadequate.2) About half of the roads are unmettaled.3) They limit their usage during the rainy season.4) National Highways are inadequate.5) Roads are highly congested in cities.6) Most of the bridges and culverts are old and narrow.7) Lack of amenities along the road sites.

Struggle of Nepali people1) Refusal by King Gyanendra to accept democracy.

2) Seven party alliances (SPA) formed by major political parties demanding democracy.3) Support given by Maoist and other organization to the demand.4) Defying curfew people took to streets.5) Rejection of half hearted concession made by the King.6) The Parliament was restored and passed Laws taking away most of the powers of king.

Democracy in Principle and Practice1) The expectations of the people in a democracy are too high. If they are fulfilled in time, newexpectations arise.2) It is not possible to fulfill all the expectations of all people.3) Some of them would be satisfied others would not.4) Those who are not satisfied, start blaming democracy and appreciate other forms of Government.5) Democracy is just a form of government. It can create conditions for achieving something.6) The citizens have to take advantage of those conditions and achieve those goals.

Transformation of markets1) In the past two or three decades, more and more MNCs have been looking for locations aroundthe world.2) Foreign investment has been rising, foreign trade has also been rising rapidly.3) There is greater integration of production and markets across countries today.4) We have a wide choice of goods and services before us.5) The latest models of digital cameras, mobile phones and T.V.’s made by the leading manufacturers of the world are within our reach.6) Every season new models of automobiles can be seen on Indian roads.7) A similar explosion of brands can be seen for many other goods.

Need for rules and regulations:1) Individual customers often find themselves in weak positions.2) The sellers try to shift all the responsibility on to the buyers.3) Sometimes traders indulge in unfair trade practices.4) Adulterated goods are sold.5) False information is passed by advertisements.

Unification of Germany:1) National feelings were spread among middle class people.2) They tried to unify Germany in 1848.3) Their feelings were repressed by the combined forces of the monarchy and military4) Prussia took on the leadership of the movement.5) Otto von Bismarck with the help of military and bureaucracy was the architect of this process.6) Three wars over seven years ended in Prussian victory and completed the process of unification.

Multi - National Companies1) Setting up units in a region where raw materials is available in abundance.2) Availability of cheap skilled and unskilled labour.3) Nearness to the market.4) Favourable Government policies.

5) Regular supply of power.6) Safety

Producers and Consumers1) As producers of goods and services, we would be working in any of the economic sectors - Primary, secondary and tertiary like agriculture and industry services.2) Produce different goods and supply them to the market.3) As consumers we participate in the market as and when goods and services are required.4) Any other relevant point like agriculture, industry or services.

Nationalist political party which espouses secularism is Indian National Congress (1)Features of the Party1) A centrist party in its ideological orientation 2) Supports new economic reforms with a human face.3) One of the oldest parties of the world .4) Played a dominant role in Indian Politics at the National and State Level for several decades afterindependence.5) Sought to build a modern secular democratic republic in India.

Economic Impact of first world war1) It led to huge increase in defense expenditure.2) Increased taxes.3) Custom duties were raised.4) Income tax introduced5) Prices increased.6) It led to extreme hardships for the common people.7) Crops failed in many parts of India resulting acute shortage of food.

Rowlatt act1. Decided to launch a nationwide Satyagraha.2. Rallies were organised.3. Workers went on strike in railways workshop.4. Shops closed down.

Modern forms of moneyCurrency -paper notes and coins. (1)Reasons for acceptance of ‘rupee’1) The currency is authorized by the government of the country.2) As per Indian Law no one can refuse to accept a payment made in rupees3) The Reserve Bank of India issues currency note on behalf of the Central Government.4) No other individual or any organization is allowed to issue currency.

Values of an ideal government1) Honesty and integrity2) Justice3) Truthfulness

4) Transparency5) Accountability6) Patriotism

Democracy in Principle and Practice1) The expectations of the people in a democracy are too high. If they are fulfilled in time, new expectations arise.2) It is not possible to fulfill all the expectations of all people.3) Some of them would be satisfied others would not.4) Those who are not satisfied, start blaming democracy and appreciate other forms of Government.5) Democracy is just a form of government. It can create conditions for achieving something.6) The citizens have to take advantage of those conditions and achieve those goals.

Lukewarm response of the Muslims in Civil Disobedient Movement1) After the decline of the Non-Cooperation-Khilafat movement, a large of Muslims felt alienated from the Congress.2) From the mid-1920 the Congress came to be visibly associated with openly Hindu religious nationalist groups.3) As relations between Hindus and Muslims worsened, it resulted in clashes.4) Even riots widened the gaps between the two communities.5) In 1927 it appeared to unite but failed due to differences over future representatives in the assemblies.

Industries create different type of pollutions:1) Industries emit smoke which pollutes air and water.2) Air pollution caused by the presence of higher proportion of undesirable gasses.3) Water pollution is caused by the Industrial effluents that are discharged into rivers.4) Industrial waste containing toxic metal pollutes land and soil.5) Surface mining also leads to land degradation.6) Noise pollution results in irritation, anger and hearing impairment.

Transformation of markets1) In the past two or three decades, more and more MNCs have been looking for locations aroundthe world.2) Foreign investment has been rising, foreign trade has also been rising rapidly.3) There is greater integration of production and markets across countries today.4) We have a wide choice of goods and services before us.5) The latest models of digital cameras, mobile phones and T.V.’s made by the leading manufacturers of the world are within our reach.6) Every season new models of automobiles can be seen on Indian roads.7) A similar explosion of brands can be seen for many other goods.

Comparison between the struggles of Nepal and Bolivia1) The movement in Nepal was to establish democracy while the struggle in Bolivia involved to ensure the working of democracy as a elected democratic government2) Bolivia struggle about one specific policy of the government while the struggle in Nepal was about the foundations of the country’s politics.3) Both the struggles were successful 4) The impacts of the both struggles were different.

5) Both are the examples of political conflicts that led to popular struggles.6) In both cases the struggles involved mass mobilization.7) Both examples involved critical role of political organizations.

Need for rules and regulations:1) Individual customers often find themselves in weak positions.2) The sellers try to shift all the responsibility on to the buyers.3) Sometimes traders indulge in unfair trade practices.4) Adulterated goods are sold.5) False information is passed by advertisements.

Role of Culture in Europe1) Art and poetry helped to express and shape of nationalist feelings.2) Stories and music also helped to express and creating the idea of the nation.3) Romanticism, a cultural movement sought to develop a particular form of nationalist sentiment.4) Romantic artists and poets generally criticized the glorification of reason and science.5) They focused on emotions, intuition and mystical feelings.6) Their efforts was to create a sense of shared collective heritage, a common cultural past as the basis of a nation.

Road Problems1) The road network is inadequate.2) About half of the roads are unmettaled.3) They limit their usage during the rainy season.4) National Highways are inadequate.5) Roads are highly congested in cities.6) Most of the bridges and culverts are old and narrow.7) Lack of amenities along the road sites.

Q. 15. How do the political parties help in the formation of public opinion? Explain.

Ans. 1. Political parties shape the public opinion. They raise the highlight issues. Parties have lakh of members and activists spread all over the country.2. Many of the pressure groups are the extensions of political parties among different sections of the society. 3. Parties sometimes also launch movements for the solution of problems faced by the people. Often opinions in the society crystallize on the lies parties take.

Q. 17. Distinguish between a political party and a pressure group.

Ans .Political Party1. It is a group of people, who come together to contest elections.2. Political parties are generally of two types (National Party and regional party).3. Political parties contest elections.4. Example. BJP, Congress etc.

Pressure Group 1. It is group of people, who seek to promote the interests of a particular section or society.2. Pressure groups are also of two types (Sectional and public interest groups).3. They do not contest elections.4. Example, The Trade Unions and All Indian Sikh Students Federations.

Q. 18. What are the various challenges faced by political parties?

Ans. 1. Lack of Internal Democracy:- Party do not hold organizational meetings and do not conduct internal elections regularly. They do not have the means or the connections needed to influence the decisions.2. Unfair Advantage and dynastic succession:- Since most political parties do not practice open and transparent procedures for their functions, there are very few ways for an ordinary worker to rise to the top in a party.3. Money and Muscle Power:- Growing role of money and muscle power in parties especially during the elections. Since parties are focused only on winning elections, they tend to use shortcuts to win elections.4. Absence of Meaningful Choice:- Very often parties do not seen to offer a meaningful choice to the voters. In order to offer meaningful choice, parties must be significantly different.

Q. 1. Why democracy preferred as the better form of government than dictatorship?

Ans. Democracy is better than dictatorship because:1. Promotes equality among citizens.2. Enhances the dignity among citizens.3. Improves the quality of decision making.4. Provides a method to resolve conflicts5. Allows room to correct mistakes.

Q. 2.  Why is democracy better than other forms of government?

Ans. Promotes the dignity of the individual.1. Improves the quality of decision making.2. Provides a method to resolve conflicts.3. Allows a room to correct mistakes.

Q. 3. ‘Democratic government is a legitimate government.’ Explain.

Ans. 1. A democratic government is people’s own government elected by the people.2. People all over the world wish to be ruled by representatives elected by them.

3. Various surveys conducted by various agencies show that most of the people favour democracy as the government.4. Democracy provides people the option to choose their own rulers.

Q. 4.  What should be the basic outcome of democracy?

Ans.  It produces a government that is accountable and representative to the citizensIt is responsive and legitimate to the needs and expectations of the citizens.

Q. 5.  What is the importance of costs of time in decision making?

Ans. The cost of time that democracy pays in decision making is perhaps worth it. As, democracy is based on the idea of deliberations and negotiations so, some delay is bound to take place.

Water Pollution:1) Water pollution is caused by organic and inorganic industrial wastes and effluents discharged into rivers.2) Some pollutants are dyes, detergents, acids, salts and heavy metals.3) Pesticides, fertilizers, synthetic chemicals with carbon, plastics, rubber, etc. are discharged by different industries into water bodies.4) Hot water from factories and thermal plants is drained into rivers and ponds, affect adversely adequately aquatic life.5) Every litre of waste water discharged into rivers/water bodies pollutes the quality of fresh water.

Methods to control water pollution :1) Minimizing use of water for processing by reusing and recycling it in two or more successive stages.2) Treating hot water and effluents before releasing them in rivers and ponds.3) Use of ground water resources also needs to be regulates legally.4) Strict legal laws to be passed against water pollution

NationalismThe sense of collective belonging came partly through the experience of united strength. But there were also a variety of cultural processes through which Nationalism captured people’s imagination. History and fiction, folklore and songs, popular prints and symbols, all played a part in the making of Nationalism. The identity of the nation is most often symbolized in a figure. This helps to create an image with which people can identify the nature.

CollateralCollaterals are an asset that the borrower owns and uses. This is a guarantee to a lender until the loan is rapid.Reasons for lenders asking for collateral :1) Collateral ensures the repayment.2) If the borrower fails to repay his loan, the lender has the right to sell the asset.3) It prevents the loss to the lender. Any other relevant point.

National Political Party: Bahujan Samaj Party(BSP)Features;1) Founded in 1984 under the leadership of Kansi Ram2) Draws inspiration from the ideas and teachings of Sahu Maharaj, Mahatma Phule, PeriarRamaswami and Ambedkar.3) Stands for the cause of securing the interests and welfare of the Dalit sang oppressed class.4) It had been the ruling party in U.P.,Mayawati as the Chief Minister.5) Seeks to represent secure power for the Bahujan Samaj which include the dalits, adiwasies, OBC and religious minorities.

Differences between conventional and non-conventional energy Conventional source:1) Coal, oil natural gas, hydro-electricity and nuclear energy are the conventional sources of energy2) The sources of thermal electricity are exhaustible and cannot be replenished.3) Hydro-electricity is renewable source of energy.4) They are much expensive sources of energy.Non-conventional source:1) Solar, Wind, Tidal, Geothermal etc.2) They have a great advantage over the conventional sources.3) These are renewable and inexhaustible.4) They are inexpensive in nature.

Britain coming into existence:1) There was no British Nation prior to eighteenth century. There were several different ethnic groups like English, Welsh, Scots and Irish.2) All these groups had their own cultural and political traditions

3) Gradually the English nation grew in wealth, importance and power. It was able to extend its influence over the other nations of the islands.4) The English parliament had seized power from the monarch in 16885) The Act of Union between England and Scotland resulted in the formation of United Kingdom of Great Britain.6) The English helped the Protestant of Ireland to establish their dominance over a large Catholic country.7) Ireland was forcibly incorporated with the U.K. and a new British Nation was formed

Periodic Classification of Elements

Dobereiner's triads According to Dobereiner's triads - 'when three elements in a triad are arranged in order of increasing atomic masses, the atomic mass of the middle element is roughly the average of the atoms of the other two elements.' E.g. Li (6.9), Na (23), K (39). Avg at mass of Na = (6.9+39)/2 = 22.95.

Limitations of Dobereiner's triads . Dobereiner could identify only three triads from the elements known at that time. So, all the elements could not be arranged in triads.

Newlands' Law of octaves According to the Newlands' Law of octaves - when the elements are arranged according to increasing atomic mass, the properties of every eighth element are similar to that of first.

E.g. elements with atomic mass up to 40 are

HFCl

LiNaK

BeMgCa

BAl

CSi

NP

OS

Limitations of Newlands’ Law of octaves

1. This law was applicable only to lighter elements (up to atomic mass 40).2. Newlands assumed that only 56 elements existed in nature. But, later on many new elements were

discovered whose properties did not fit into law of octaves.3. To fit the elements in his table, he adjusted two elements in the same slot. He also put some unlike

elements under same note.

Mendeleev’s Periodic Law According to Mendeleev’s Periodic Law – ‘The physical and chemical properties of elements are the periodic function of their atomic masses.’

Achievement of Mendeleev’s Periodic Table.            

1. Mendeleev placed an element with slightly larger atomic mass before an element with slightly lower atomic mass so that the elements with same properties fell in the same group. E.g. Co (58.93) was placed before Ni (58.71).

2. Mendeleev left some gaps for the elements to be discovered.3. Correction of doubtful atomic mass.

Limitations of Mendeleev’s Periodic Table

1. Correct position of hydrogen could not be assigned.2. Anomalous position of isotopes.3. Uncertainty in discovery of new elements.4. Wrong order of atomic masses.

Modern Periodic Law. According to Modern Periodic Law - ‘The physical and chemical properties of elements are the periodic function of their atomic numbers.’

Explanation of limitations of Mendeleev’s Periodic Table.

i. Position of isotopes. Since all isotopes of an element have same atomic number, they can be placed in same group. E.g. C-12 and C-13 both have atomic number 6.

ii. Anomalous position of some elements. Co (58.93) and Ni (58.71)Cobalt with higher atomic mass is placed before nickel because the atomic numbers of cobalt and nickel are 27 and 28.

iii. Uncertainty in prediction of new elements. Atomic masses do not increase in regular manner i.e. they may be in decimals. But, atomic numbers increase in regular manner i.e. increase by 1 in going from one element to the next.

Groups. The vertical columns in the Modern Periodic Table are called groups. There are 18 groups in the Modern Periodic Table.

Periods. The horizontal rows in the Modern Periodic Table are called periods. There are 7 periods in the Modern Periodic Table.

Period no 1 2 3 4 5 6 7No of elements 2 8 8 18 18 32 incompleteName of period Very short Short Short Long Long Very long incomplete

Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.

The repetition of properties of elements after certain regular intervals is called periodicity in elements.

The cause of periodicity in properties of the elements is the repetition of similar outer electronic configuration after certain regular intervals.

The elements in the first group (Li, Na, K, …) are called alkali metals because they all react with water to form alkalis. Water soluble bases are called alkalis. All alkalis are the bases but all bases are not the alkalis.

The elements in the second group (Ca, Sr, Ba, …) are called alkaline earth metals because their oxides are alkaline in nature and exist in earth.

The elements in the 17th group (F, Cl, Br, …) are called halogens because they reacts with metals to form  salts. (halo means salt, gene means producer)

Isotopes :The atoms of same element having same atomic numbers but different atomic masses are called isotopes. Isotopes of some elements are –

Hydrogen (At No = 1)

Carbon (At No = 6) Oxygen (At No= 8)Chlorine (At No=

17)H1, H2, H3 C12, C14 O16, O17 Cl35, Cl37

Valence electrons The electrons present in the outermost shell of an atom are called valence electrons. Valency The number of electrons lost or gained by an atom to complete its octet or duplet is called its

valency. Valency of an element can be calculated from electronic configuration in two ways –

i. Valency = number of valence electrons (if they are 1, 2, 3 or 4).ii. Valency = 8 – number of valence electrons (if they are 5, 6, 7 or 8).

Electropositive elements. The elements which lose electrons and form positive ions are called electropositive elements. All the metals are electropositive in nature.

The tendency to lose electrons by metals to form positive ions is called metallic character or electropositive character .

Electronegative elements. The elements which gain electrons and form negative ions are called electronegative elements. All the nonmetals are electronegative in nature.

The tendency to gain electrons by nonmetals to form negative ions is called nonmetallic character or electronegative character.

Metalloids or semimetals. The elements which show the properties of both metals and nonmetals are called metalloids or semimetals. E.g. boron, silicon, germanium, arsenic, antimony, tellurium and polonium.

Periodic Classification of Elements

In the Modern Periodic Table, a zigzag line separates the metals from the nonmetals.

Metals are found on left hand side of the periodic table while nonmetals are found on the right hand side of the periodic table

Oxides of metals are basic while oxides of nonmetals are acidic in nature. Maximum number of electrons that can be accommodated in a shell are calculated using the formula 2n2

where n is number of shell. The position of an element in the periodic table tells us about its reactivity.

Need for classification of elements. It is very difficult to study the properties of all the elements and their compounds. So, to study the properties of elements and their compounds easily and conveniently scientists classified them.

Besides gallium, germanium (Ge) of group IV A, polonium (Po) of group VI A and astatine (At) of group VII A have been discovered that fill the gaps left by Mendeleev in his periodic table.

Out of all the elements known, noble gases are most unreactive. They are present in atmosphere in very low concentration. So, they are grouped together in separate group (zero group) in Mendeleev’s periodic table.

Atomic number of helium is 2. Its first shell is the last shell which can accommodate only 2 electrons. So, outermost shell of helium is completely filled. This is why helium is placed in the 18th group of the periodic table.

Trends in the Modern Periodic Table

Characteristics In Period (Left to Right) In Group ( Top to Bottom)

Valence electronsIncrease due to the increase in atomic number

Remains the same

ValencyFirst increases from 1 to 4 then decreases to 0

Remains the same

Atomic size or atomic radius

Decreases due to increase in nuclear charge which tends to pull the electrons closer to the nucleus

Increases due to the increase in the new shells. This increases the distance between the nucleus and the outermost shell. So the atomic size increases in spite of increase in nuclear charge.

Metallic character

Decreases. When the effective nuclear charge acting on the valence electrons increases, the tendency to lose electrons decreases.

Increases because the effective nuclear charge on valence electrons decreases due to increase in atomic size.

Nonmetallic character

Increases. When the effective nuclear charge acting on the valence electrons increases, the tendency to gain electrons increases.

Decreases because the effective nuclear charge on valence electrons decreases due to increase in atomic size.

Reactivity First decreases and then increases

Reactivity of metals increases because the tendency to lose electrons increases but the reactivity of nonmetals decrease because the tendency to gain electrons decreases.

 

Mendeleev’s Periodic Table Modern Periodic Table

1. Elements are arranged in increasing order of their atomic masses.

1. Elements are arranged in increasing order of their atomic numbers.

2. There are no separate positions for isotopes of an element as their atomic masses are different.

2. Separate positions are not required as they have same atomic numbers.

3. Some elements of higher atomic masses have been placed before elements of lower atomic masses.

3. No such problems occur in this table. All elements are in proper order.

4. Some dissimilar elements are grouped together while some similar elements are not grouped together.

4. All similar elements are grouped together.

5. Electronic configuration of an element cannot be calculated from its position.

5. Electronic configuration of an element can be easily calculated from its position.