Class 10 Science Chapter 5 Important Questions

Class 10 Science Chapter 5 Important Questions of Periodic Classification of Elements. All the extra questions are prepared form NCERT textbook, Exemplar book and from the famous publisher’s books for the academic session 2020-21.

It will provide a complete revision for chapter 5 of class 10 science. All the questions are confined to NCERT only based on latest CBSE Syllabus 2020-2021.

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Class 10 Science Chapter 5 Important Questions 2020-21

Class: 10Science
Contents:Chapter 5 Important Questions

Class 10 Science Chapter 5 Important Questions for Exams

Class 10 Science Chapter 5 Important Questions with answers and explanation are given in the forms of sets of questions. We have prepared these questions by extracting the questions from each page of NCERT Books of Class 10 Science Chapter 5.

10th Science Chapter 5 Important Questions Set – 1

What is the need to classify elements?

There are one hundred and elements and each elements forms a large number of compounds. It is therefore necessary to understand the basis of their properties and the rules according to which these react. This is possible if the element is classified and grouped together based on their properties.

Write an account of early attempt made for the classification of elements.

(i) About more than one hundred years ago Lavosier discovered that some elements resemble in their properties. He classified the thirty then known element into metal and non-metals to study their acid and basic properties. But his classification could not account for those elements which had the properties of both metal and non-metal.

(ii) Dobereiner’s triads: Dobereiner in 1829 observed that there were certain group of three similar elements called triads. The elements of a triad had similar properties and when arranged in order of increasing atomic masses, the atomic mass and the properties of other element were roughly the arithmetic mean of the other two. For example, lithium (atomic mass 7), Sodium (atomic mass 23), and potassium (atomic mass 39) formed such a triad. The atomic mass of sodium is equal to the average of the atomic mass of lithium and potassium {(7+39)/2 = 23}.

(iii) Newland’s Law of octaves: Newland in 1864 found that if the elements were arranged in the order of increasing masses, every eighth element starting from a given one would to be the repetition of the first with regard to its properties. Therefore, Newlands’ law came to be known as law of octave.
However, this law was applicable to a few elements only. It cannot be applicable to element of higher atomic masses. With the discovery of noble gases, it became the ninth element and not the eighth element that will be similar to first one.

Lithium, sodium and potassium were put in one group or triad on the basis of their similar properties. What is the name of the group? State their properties.

Lithium, sodium and potassium formed a group called alkali metal group. Their similar properties are:
(i) All these elements are metals.
(ii) All these react readily with water to form alkalis and hydrogen gas.
(iii) All of them have a valency of 1.

Consider the following elements: K, I, Li, Sr, Cl, Mg, Br, Ca, Na. Separate these elements in three group or triads having similar properties. State one property in each case on the basis of which group are separated.

These elements can be separated into three groups as given below:
(a) K, Li, Na – have valency of 1+.
(b) Sr, Mg, Ca – have valency of 2+.
(c) I, Cl, Br- have valency of 1-.

Mendeleev Periodic Law

In 1869 Mendeleev found that if all 63 elements known at that time were arranged in the increasing order of their atomic masses the properties of the element and also formulae of compounds like oxides, hydrides, etc., formed by those elements gradually changed from element to element and at certain interval they suddenly started almost repeating. This relationship was expressed by Mendeleev as Periodic law.




10th Science Chapter 5 Important Questions Set – 2

How did Mendeleev construct his periodic table?

Mendeleev started his work with 63 elements known at that time. He examined the relationship between atomic mass of the element and their physical and chemical properties. Among chemical properties, he concentrated on the compounds formed by elements with oxygen and hydrogen which were known to react with most elements were known react with most elements. The formulae of oxide and hydrides of the elements were treated as basis he observed that most of the elements could be placed in a table in the order of their increasing atomic masses.

What are the discrepancies in Mendeleev’s periodic table?

(i) Position of isotopes: Isotopes of various elements cannot be filled into Mendeleev’s table. Isotopes are the elements having similar chemical properties but different atomic masses.

(ii) Anomalies of atomic weights and properties of elements: If arranged according to gradation in chemical properties element of higher atomic weight are to be placed before those of lower atomic weight at some place. This is contrary to Mendeleev’s law. For example, argon with atomic mass of 40 comes before potassium with atomic mass 39. Iodine (at mass = 127) comes after tellurium (at mass 127.8).

(iii) Falling of dissimilar elements in same group: Some chemically similar elements fall in different group while some chemically dissimilar element is placed together. For example, copper, silver, and gold are placed in the same group alkali metals. Mercury, lead and barium which possess similar properties fall into different groups.
(iv) Hydrogen resembles both alkali metals (group I) and halogen (group VII) and thus no fixed position could be given to hydrogen in the periodic table.

What were the two factor by which Mendeleev was guided while classifying the then known elements?

In increasing of then known elements Mendeleev was guided by:
(i) In increasing atomic mass and
(ii) grouping of elements with similar properties together.

Name one element that could be discovered on the basis of Mendeleev prediction.

Mendeleev kept one gap in the third group below Aluminium and predicted that the element should have properties similar to boron and its atomic masses should be lesser than 48. His prediction came to be true and scandium(Sc) was discovered on the basis of prediction.

Feature of Mendeleev Periodic Law

    • Basis of classification: Elements were grouped on a more fundamental basis than earlier attempt.
    • Prediction of properties of new elements: Because of their placement in the periodic table properties of several yet to be discovered elements like scandium, gallium and germanium could be predicted.
    • Correction of atomic weight/masses: Mendeleev gave more weightage to similarities in properties of elements rather than atomic masses. So atomic masses of some element got corrected. Atomic weights of elements like gold and platinum could thus be corrected.
    • Inert gases: The discovery of the new elements, inert gases did not disturb the arrangement and they found their place as a new group.

10th Science Chapter 5 Important Questions Set – 3

How did Mendeleev periodic law has been changed afterward?

Owing to defect in Mendeleev classification of elements it was considered that atomic mass cannot be the suitable basis for the classification. After Moseley’s works it was proved that atomic number is more fundamental than atomic mass and it formed the basis of periodic classification. It increases by one from element to element. This has also eliminated anomalies in Mendeleev Periodic table.

Why did Mendeleev leave gaps in the periodic table?

Mendeleev gave due importance to the chemical properties of the elements. Therefore, he placed elements with similar properties one below the other and therefore ignored his own law at many places. This led him to leave gaps in the table. He left proper gaps in the periodic table for the then undiscovered elements like titanium(Ti), gallium(Ga), Scandium (Sc) and Germanium (Ge). When these elements were discovered later on they were placed in those gaps without disturbing the existing arrangement.

Write a short note on the position of hydrogen in the periodic table.

The position of hydrogen in the periodic table is unique. Its properties resemble with both alkali metals and halogens because it can loss one electron like alkali metals as well as gain one electron like halogens. It is therefore to be placed at the top of both alkali metals and halogens.

Mention the position of (i) hydrogen and (ii) isotopes of same element in the Modern Periodic Table.

(i) Hydrogen is placed at the top of group IA.
(ii) Isotopes of the same element are placed in the same slot.

The Modern Periodic Law

Modern Periodic Law: The physical and chemical properties of elements are the periodic function of their atomic numbers. The Modern Periodic Table is called “long form: of the periodic table.




10th Science Chapter 5 Important Questions Set – 4

State modern periodic law. Where are (i) metals, (ii) non-metals (iii) metalloids located in the periodic table?

The physical and chemical properties of elements are the periodic function of their atomic numbers.
(i) Metals are located toward left in the periodic table.
(ii) Non-metals are located toward right in the periodic table.
(iii) Metalloids are located in the middle toward right in the periodic table.
Q16. What is the cause of periodic repetition of properties of elements?
Ans. On examination of electronic configuration of element it can be seen that the electronic configuration of the outermost shell of the elements repeat after a certain interval. As the chemical properties of elements depend on the valency of electrons (electrons in the outermost shells of the atom) it seems that the periodic properties of elements due to similar valences after a regular interval. For example, if we start with lithium which has one electron in its outermost shell, then its comes sodium which has the configuration 2,8,1 and then it repeats at potassium which has the configuration 2, 8, 8, 1.

Describe Modern Periodic Table or long form of periodic table.

Modern periodic table was prepared by Bohr and other chemical. As shown in the table, modern periodic table is based on the electronic configuration of elements. Elements are arranged in the order of increasing atomic number in periods and in groups the elements are placed having similar electronic configuration or having similar number of electrons in their outermost shells.
Description of Periods:
On the basis of electronic configuration first shell or period complete up to He (atomic number 2). So first period contains two elements H and He.
In second shell, electron start to fill from Li ad it gets 8 electrons up to Ne (atomic number 10). So second period contain 8 elements Li, Be, B C, N, O, F and Ne.
In third shell, electron start to fill from Na and gets 8 electrons up to Ar (atomic number 18) and contain eight elements Na, Mg, Al, Si, P, S, Cl, and Ar.
Similarly, 4th, 5th, 6th, and 7th, periods are completed with different number of electrons.

Description of Groups:
1. First group contain seven elements: Hydrogen, lithium, Sodium, Potassium, Rubidium, Cesium, and Francium that’s why H, Li, Na, K, Rb, Cs and Fr. These elements are called as alkali metal and this group is also called an alkali metal group, because the element of 1st group easily from alkalis (strong bases) on reaction with water.
2. 2nd group contain 6 elements- Beryllium, Magnesium, Calcium, Strontium, Barium and Radium that’s why Be, Mg, Ca, Sr, Ba and Ra. These elements are called as “Alkaline earth metal” and this group is called “Alkaline earth metal group” because their oxide are alkaline in nature and present on earth.
3. 13th and 17th all the groups contain 5 – 5 elements each. 17th group contains 5 elements- Fluorine, Chlorine, Bromine, Iodine, Astatine or F, Cl, Br, I and At. These elements are called as Halogens and this group is called halogen group because the element react with metals to form salts (halo= salt, gene= producer).
4. 18th group or 0 group contain 6 elements, Helium, Neon, Argon, Krypton, Xenon and Radan or He, Ne, Ar, Kr, Xe and Rn. The elements are gases and do not react with any other elements in normal conditions so they are called as Inert gases or noble gases, with other element in normal conditions so they are called as Inert gases or noble gases.
5. Between 2nd and 13th groups there are 10 elements each in periodic 4 to 6. These elements are called Transitional elements.
6. In groups 3rd and 6th period there are 14 elements. They are called Lanthanides. In the same group with 7th period also there are 14 elements. They are called as Actinides.

How is Modern Periodic Table or long form of Periodic table superior to Mendeleev’s Table?

(i) Long form of the periodic table is based upon atomic number which is a more fundamental property of the atom.
(ii) It relates the position of an element in the periodic table with its electronic configuration.
(iii) It remove the anomaly about the position of isotopes in the Mendeleev’s Table.
(iv) It removes the anomaly of inversions in the Mendeleev Table thus Ar and K in the periodic table because it has a lower atomic number through its atomic mass is more than that of potassium.
(v) It also removes the other anomalies found in Mendeleev periodic table (like grouping of chemically dissimilar elements and separation of chemically similar elements etc.)
(vi) It reflects more clearly the changes in the properties of various elements while moving across a periodic or down a group.
(vii) Typical (representative) and transition elements have been separated in this form of the periodic table.
(viii) It also separates metals and non-metals.

Give two typical feature of a group in terms of electronic configuration of elements.

(i) Elements show similar chemical properties owing to similar electronic configuration.
(ii) In a group there is gradual change of properties owing to gradual variation in the attraction of the nucleus and the outer valence electrons.

These all questions are prepared from NCERT Textbook of Class 10 Science Chapter 5 for UP Board, CBSE, Gujrat, MP Board and all other users who are using NCERT Books for session 2020-21.

10th Science Chapter 5 Important Questions Set – 5
The electronic configuration of an element X is 2,8,8,2. To which (a) period and (b) group of the Modern Periodic Table does X belong? State its valency. Justify your answer in each case.

(a) Element belongs to periods 4 since it occupies four shell K, L, M and N.
(b) It belong to group 2 since it has 2 electrons in the outermost shell.

Discuss the merits and defects of the long form of the periodic table.

Merits of the long form of the periodic table:
(i) Fundamental property as basis of classification: It is based on the atomic number of elements which is the most fundamental property of elements.
(ii) Similarity between structure and properties of element in placement: The elements are arranged according their electronic configurations. All the elements will similar electronic configuration are put in the same group. Thus it gives the relationship between atomic structure and properties of elements.
(iii) Periodicity explained: It explains the reason for the periodicity in properties of elements. The electronic configuration of the elements are repeated as regular intervals.

Defect of the long term of periodic table:
(i) The position of the hydrogen is still not clear although it is generally grouped with alkali metals.
(ii) There is no place for lanthanides and actinides in the main body of the table.

An element has atomic number 12. In which period and group it should be placed? Explain.

3rd period and group 2. Elements from atomic number 1 and 2 are placed in 1st period. Elements with atomic number 3-10 are placed in 2nd period. Then thirds periods start and element with atomic number 12 find a place in group 2.

Why is atomic number of an element more important to a chemist than its atomic mass?

The properties of elements depends upon the number of electrons present in the valence shell which are related to atomic number. Thus properties of different elements can be compared if we know their atomic number. On the other hand, atomic mass can in no way determine the chemical properties of elements, because it does not vary regularly with gradation in the chemical properties of elements.



10th Science Chapter 5 Important Questions Set – 6
What are the basic difference between a group and a period in terms of electronic configuration?

In a group through the number shells increases as we move downward, but the number of electrons in the outermost shell remains the same.
In a period as we move from left to right the outermost or valence shell gets progressively filled from group 1 to 18 and the shell does not change.

How many electrons can be representing in the valence shells of metal atoms and non-metal atoms?

Metals have 1, 2, or 3 electrons in their valence shells whereas non-metal atoms have 4 to 7 electrons in their valence shells.

What do you mean by atomic size of an atom?

The atomic size refers to radius of an atom. For metals it is taken as half of the intermolecular distance between the two metal ions whereas for non-metallic substance it is equal to half distance between radii of the two binding atoms. For an isolated it is considered as the distance between the center of nucleus and the outermost shell. It is expressed in picometres (pm).

Define electron affinity.

Whenever an atom gains electron energy is released. Thus electron affinity is the energy released when an electron is gained by a neutral gaseous atom to became negatively charged ion.

Ionisation Energy

Ionisation energy is the energy required to remove an electron completely from an isolated gaseous atom or ion of an element. When more than one electron is to be removed more energy is required because in this case electron is to be removed from the unipositive ion. Similarly, subsequent ionization energy will be still greater, that’s why 1st ionisation energy < 2nd ionisation energy < 3rd ionisation energy.

10th Science Chapter 5 Important Questions Set – 7
What are the important characteristic of a period in periodic table?

(i) Valence electrons: On moving from left to right in a period the number of valence electron increases from one to eight (expect first period where the increase is from one to two only)
(ii) Valency: The valency of elements increases from one to four then decreases to one and became zero in the case of inert gases. For example, in compound LiCl, BeCl2, BCl3 and CCl4 the valency of Li, Be, B and C are 1,2,3 and 4 respectively whereas in compounds NH3, H2O, HF the valency of N, O, F are 3, 2 and 1 respectively.
(iii) Zero group: At the end of each period is the zero group elements the inert gas.
(iv) Size of the atoms: Atomic radii of the element decreases gradually from left to right in a period because the nuclear charges increase but no extra shell is added.
(v) Metallic character: Metallic character decreases from left to right across a period and non-metallic character increases.
(vi) Ionisation energy: Ionisation energy increases across a period from left to right. Ionisation energy is the energy required to remove the most loosely bound electron from a neutral gaseous atom.
(vii) Chemical reactivity: On moving from left to right in a period the chemical reactivity of elements first decreases and then increases. For example, in third period, Na is very reactive Mg, Al are less reactive Si is least reactive and the reactivity increases from P, S, to Cl.
(viii) Oxides: The basis character of the oxide of the elements decreases and the acidic nature of the oxides of the elements increases. For example, in the 3rd period starting with sodium oxide, it is highly basic in nature, the next magnesium oxide is less basic. Then comes Aluminium and silicon which give amphoteric oxides. Then are oxide of phosphorous and sulphur which are acidic. And the last chlorine oxide is highly acidic.
(ix) Electronegativity: Electronegativity increases on moving across a period from left to right. It is measure of the tendency of the element to attract electrons towards itself.

What is a group in periodic table? What are the characteristic of a group?

The vertical table in the periodic table is called a group.
Characteristic of a group:
(i) Valency: In a group all the elements have the same valency. For example, group I elements: Li, Na, K etc., all have a valency of +1. Elements of group 17: Cl, Br, I etc., all have valency of -1.
(ii) Size of atoms: Atomic radii or the size of atoms of the elements increases on given going down a group. This is due to the addition of new electronic shells.
(iii) Metallic character: On descending a group the metallic character increases. For example, groups 14 and 15 begin with carbon and nitrogen which are non-metals. The oxides of the elements also became increasingly basic.
(iv) Melting and boiling point: The melting and boiling point of metals decreases on going down in a group. For example, the melting and boiling point of alkali metals group 1 decreases gradually on going down the group. Li (melting point 180.5oC and boiling point 1347oC), K (melting point 63.4oC and boiling point 774 oC) The melting point and boiling point of non-metal increases on going down in group. For example, the melting points of the group 17 increases gradually on going down in group F (melting point 219.6 oC) Iodine (melting point 113.6 oC).
(v) Ionisation energy: Ionisation energy decreases on moving down a group with the increases in atomic number. This is because the size of the atom increases and the valency electron are farther removed from the attractive effect of the nucleus.
(vi) Chemical reactivity: The chemical reactivity of metals increases on going down a group. For example, in group 1 of alkali metals the chemical reactivity increases from lithium to francium. On the other hand, the chemical reactivity of non-metal decreases on going down in a group. For example, in group 17 of halogen elements (non-metals), fluorine is most reactive and iodine is least reactive.

What are metalloids? Write any two example?

Metalloids have properties between those of metals and non-metals. Example are silicon, arsenic.

An element X belong to 13th group of periodic table. Find its valency. What will be the formula of its sulphate?

Elements X belonging to group 13th has 3 valence electron and so its valency is 3. Sulphate of X = X2(SO4)3.



10th Science Chapter 5 Important Questions Set – 8
The atomic number of an element X is 20. Write (a) its valency, (b) whether it is a metal or non-metal. (c) the formula of compound formed when the elements X react with an element Y of atomic number 8.

(a) Electronic configuration of X is 2, 8, 8, 2. Its valency is 2.
(b) It is a metal. It belongs to group 2 and can lose 2 electrons easily.
(c) Formula of compound of X and Y is XY. Since valency of Y is – 2(2, 6).

What is a group in a periodic table? In what part of a group would you separately expect the element to have (i) the greatest metallic character (ii) the largest atomic size?

Group is a vertical column in the periodic table. The elements placed in a vertical column in the periodic table are said to belong to the same group.
(i) As the metallic character increases on going down a group the greatest metallic character is expected to be shown by the elements in the lowest part of a group.
(ii) Atomic size increases on moving down a group. So element at bottom of a group would be of largest size in that group.

In the following set of elements, one element does not belong to the set: Select this element and explain why it does not belong. Sodium, Potassium, Calcium, Rubidium.

Calcium, because it has two electrons in the outermost shell and belongs to group 2 while other elements have one electron each in their outermost shells and belong to group 1.

Two elements X and Y belong to group 1 and 2 respectively in the same period of periodic table. Compare these elements with respect to (i) number of electrons in the outermost orbit. (ii) their valences (iii) metallic character (iv) their atomic size (v) formula of their chlorides (vi) formula of their sulphates.

(i) X has one electron and Y has 2 electrons in their outermost orbit.
(ii) X has valency 1 and Y has valency 2.
(iii) X is more metallic than Y.
(iv) X is bigger in size than Y.
(v) XCl, YCl2.
(vi) X2SO4, YSO4.

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10th Science Chapter 5 Important Questions Set – 9
Why is argon bigger in size than Chlorine, when argon is next to chlorine in 3rd period and the size of elements decreases when moving from left to right in a period?

The size of chlorine is less than that of argon because electronegativity of chlorine is quite high that’s why it has a tendency to attract an electron to attain inert gas (stable) configuration (with eight electrons in the outermost shell). On the other hand, argon with already complete outermost shell is bigger in size because it is stable and the positive nucleus does not have so much attractive pull on the outermost shell.

What were the achievement of Mendeleev’s Periodic Table?

While framing the periodic table, Mendeleev placed an element with slightly greater atomic mass before an element with slightly lower atomic mass. For example, Co (58.9) appear before Ni (58.71). This was done to arrange similar elements together in the same vertical column. Another such anomaly in the table is that of Al and Si.
Mendeleev predicted the existence of some elements that had not been discovered till then and he left some gaps in the table for such elements. Such undiscovered elements were named by prefixing Sanskrit numeral Eka to the name of the predicting elements.
For example, Scandium, gallium and germanium, discovered later have the properties similar to Eka-boron, Eka-aluminium and Eka-silicon. This provided convincing evidence for the correctness and usefulness of Mendeleev periodic table. Noble gases which were discovered much later were placed in a separate group without disturbing Mendeleev’s Table.

Explain How modern periodic table could remove various anomalies of Mendeleev’s Periodic Table?

Henry Moseley in 1931 showed that atomic number of an elements is a more fundamental property than its atomic mass. Thus the Mendeleev’s Periodic Law was modified. The modern periodic law may be stated as:
Properties of elements are a periodic function of their atomic number.
It was found that properties of elements could be predicted with greater accuracy when the elements were arranged on the basis of increasing atomic number.
(i) Position of cobalt and nickel was resolved in the light of new classification of elements based on atomic number. Cobalt and nickel have atomic number 27 and 28 respectively. Naturally cobalt with atomic number 27 has to be placed first followed by nickel.
(ii) As the isotopes possess the same atomic number according to Modern Periodic Law, they have to be given the same position in the Periodic Table.
(iii) Unlike atomic mass atomic number is always a whole number. Hence we cannot have an element with fractional number 1.5 placed between hydrogen and helium.
(iv) Although hydrogen has resemblance both with elements of alkali metals and halogen, it has been decided to place it over lithium in the alkali metal group.

Properties of some elements are given below. Identify in each case the element and group in the periodic table to which it belongs. (a) A soft metal stored under kerosene. (b) An element with variable valency stored under water. (c) An element which is tetravalent and forms the basis of organic chemistry. (d) An element which is an inert gas with atomic number 2. (e) An element which burns with brilliant light when ignited. (f) An element which is yellow solid at room temperature that shows catenation and allotropy.

(a) Sodium Group1
(b) Phosphorous Group 15
(c) Carbon Group 14
(d) Helium Group 18
(e) Magnesium Group 2
(f) Sulphur Group16

The Limitation of Mendeleev’s Classification

Mendeleev’s classification suffers from some limitation:
(i) One limitation of Mendeleev’s classification is that it could not assign a position to hydrogen. Hydrogen resembles alkali metals in the combination with halogens oxygen and sulphur. On the other hand hydrogen resembles halogens in that it exists as a diatomic molecule and it combines with metals and non-metals to form covalent compounds.
(ii) Mendeleev’s classification cannot assign position to isotopes. Isotopes are atoms of an elements having similar chemical properties but different atomic masses.

10th Science Chapter 5 Important Questions Set – 10
Explain how, the tendency to lose/gain electron change in a period and in a group?

As the effective nuclear charge acting on the valence shells electrons increases across a period the tendency to lose electrons decreases. Down the group the effective nuclear charge on the valence electron decreases because outermost electrons or valence electron are farther away from the nucleus and the tendency to lose electron increases. Reserves will happen if it is required that electrons are gained.

Give reason for the following: (a) Metals have tendency to form cations. (b) Fluorine atom is smaller than chlorine atom. (c) Non-metals have tendency to gain electrons.

(a) As the effective nuclear charges on the valence electrons in metals is comparatively less, they have tendency to form cations.
(b) Fluorine atom is smaller than chlorine atom as it has less number 2 of shells compared to that in chlorine (shells 3).
(c) Non-metals have higher nuclear attraction on the outermost shells and thus these have tendency to attract/gain electrons.

Given below are some elements of the modern periodic table: 4Be, 26Fe, 14Si, 19K, 20Ca (i) Select the elements that has one electron in the outermost shell and write its electronic configuration. (ii) Select two elements that belong to the same period. Give reason for your answer. (iii) Select two elements that belong to the same period. Which one of the two has bigger atomic mass?

The electronic configuration are:
Be (2,2), Fe (2, 8, 8, 5, 3), Si (2, 8, 4), K (2, 8, 8, 1) and Ca (2, 8, 8, 2).
(i) K(2, 8, 8, 1).
(ii) Be and Ca. These have two electrons in the outermost shell.
(iii) K and Ca belong to the same period that’s why 4th period K(potassium) is beggar than Ca(Calcium).

An element X is liquid, non-metallic. Can you predict its position in the periodic table?

As the elements X is non-metallic it may be belonging to group 17. In a group 17, the first two elements are gases. Melting point and metallic character of elements (non-metals) increases on moving down a group. Therefore, the elements X may be located in group 17 and 3rd or 4th period of the periodic table.

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10th Science Chapter 5 Important Questions Set – 11
An elements X belong to group 17 and third period of the periodic table. (a) Write electronic configuration of the element. What is its valency? (b) Predict its nature, whether it is a metal or a non-metal. (c) Give the formula of the compound formed when it combines with an element Y having valence three.

(a) 2,8,7 valency is -1.
(b) It is a non-metal.
(c) YX3.

What are the elements belonging to group 3 to 12 called? What is their special characteristic?

They 3 to 12 elements are called transition elements. In these elements outermost shell as well as the next to outermost shell are incomplete and are in the process of being filled with electrons. For example Cu, Ag, Au belong to group 11.

What are metalloids? How many electrons can be present in the valency shell of their atoms? In what part of the periodic table these are located? What type of oxide are formed by these elements?

Metalloids are elements which resembles both metals and non-metals. The valency shell of metalloids contain 3,4,5,6 elements starting from period 2 to 5 respectively. These are found on the right side of the table in the zig-zag column, example boron, silicon, germanium, arsenic etc. These form amphoteric oxides.

(a) How many elements are known till date? (b) List the triads that Dobereiner could identifying? (c) Which scientist believed that no more elements will be discovered in future? (d) What was the nationality of Mendeleev? In which year was his periodic Table published? (e) How many periods and groups are there in the Modern Periodic Table?

(a) 118 elements are known till date.
(b) Triads identified by Dobereiner are:
Li Ca Cl
Na Sr Br
K Ba I
(c) John Newlands.
(d) Mendeleev was Russian. His periodic Table was published in the year 1872.
(e) There are 7 periods and 18 groups in the Modern Periodic Table.

The Limitation of Newlands Law of Octaves

The limitation of Newlands’ Law of Octave were:
(i) It was found that law of Octaves was applicable only upto calcium. After calcium, every eight elements did not possess properties similar to that of first.
(ii) To fit the elements into his table, Newlands adjusted two elements in the same slot but also put some unlike elements in the same slot but also put some unlike elements under the same note.
(iii) Newlands assumed that only 56 elements existed in nature and no more elements would be discovered in future. But later several new elements were discovered.



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