State Dobereiner's law of triads.

What is Newlands' law of octaves? Why is it called so?

On what basis Mendeleev classify the elements?

Why did Mendeleev left some gaps in his periodic table?

Why was the position of hydrogen not fixed in Mendeleev's periodic table?

How many groups and periods are present in the modem periodic table?

What is the main difference between Mendeleev's and modern periodic law?

Elements of the same group have similar properties. Why?

In which period and group would you place the elements with the following electronic configurations.

(i) 2,8 (ii) 2,5

How does the atomic size of the elements very along a period?

A metal M forms an oxide having the formula M₂O₃. It belongs to the third period in the modern periodic table. Write the atomic number and valency of the metal.

Among the following elements F, Cl, Br and I, which does not fit in Dobereiner’s triad.

What Is the basis for the classification of modem periodic table?

Name the two elements whose valencies are equal to their group number.

Which element comes after (right) lithium in the periodic table?

Calcium is element with atomic number = 20. Is it more reactive or less reactive than Mg.

Why does carbon has valency 4 and chlorine 1?

A metal M belongs to 13th group in the modern periodic table. Write the valency of the metal.

X is an element with Atomic number = 20. What will be the formula of its chloride?

Out of the three elements Ca, Mg. Sr which one will have atom of biggest size?

Out of Li, C and N, which element form the most basic oxide and which form the most acidic oxide?

Initially It was believed that atomic mass of beryllium was 13. But Mendeleev suggested that its atomic mass should be 9.

(i) was Mendeleev suggestion correct?

(ii) How had he reached to this Conclusion?

An element X belongs to the second period and group 15 of the periodic table. Find out

(i) the number of valence electrons in its atoms.

(ii) valency of the elements.

Identify the similarity in the atoms of pairs of elements given below:

(i) Na (atomic number=11) and

K (atomic number=19)

(ii) B (atomic number=5) and

C (atomic number=6)

Write the trend of atomic size along a group and a period in the modem periodic table.

An atom of some element has electronic configuration 2,8,6.

(i) What is the atomic number of this element?

(ii) Name the element that shows chemical similarity with it.

The order of metallic character of elements A, B, C and D is

D>A>C>B

(i) What is the order of their electronegative character?

(ii) What is the nature of oxide of B If oxide of A is amphoteric?

Write the reason for the following (number in parenthesis is atomic number of the substance)

(i) Lithium (3) and sodium (11) are considered as active metals.

(ii) Fluorine (9) is more reactive than chlorine (17).

The elements of second and third period of the periodic table are given below:

(i) Which atom is bigger in size Li or Be? Why?

(ii) Which one element out of those given above is the most metallic and why?

The atomic number of elements A, B, C, D and E are given below.

From the above table, answer the following questions.

(i) Which two elements are chemically similar?

(ii) Which element is an innert gas?

(iii) Which element belongs to 3rd period of periodic table?

(iv) Which element among these is a non-metal?

What are valence electrons? Does the number of valence electrons increase or decrees on moving from left to right in a period. How does valency of elements vary in the period?

The atomic number of three elements A, B and C are 11, 14 and 17 respectively.

(i) State the group to which these elements belong in the modern periodic table.

(ii) Write the formula of the compound formed when the elements B reacts with C.

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.

Arrange the following elements according to the instructions written in paranthesis.

(i) Cu, Mn, Ge, Sc (increasing atomic size)

(ii) Fe, Hs, Ru, Os (increasing number of valence shells)

(iii) Hf, Cs, Ba, Tl (increasing valency)

Four elements P, Q, R, and S have atomic numbers 12, 13, 14 and 15 respectively. Answer the following questions giving reasons.

(i) What is the valency of Q?

(ii) Classify these elements as metals and non-metals.

(iii) Which of these elements will form the most basic oxide?

Name

(i) two elements having valency 2 with respect to oxygen.

(ii) two elements forming oxides of the types XO₃.

(iii) an element having number of electrons double in its L-shell than that present in its M-shell.

X is an element with atomic number 20.

(i) Is it a metal or a non-metal?

(ii) Among X or Mg, which one is more reactive?

(iii) What is the valency of X?

X is an element of modern periodic table. It is surrounded by elements having atomic number 17, 34, 36 and 53.

(i) What is the atomic number of X?

(ii) Predict its position in the periodic table.

(iii) Which among these do not belong the same period?

The position of five elements in the periodic table are shown below:

What are the number of valence electrons in B?

Identify the element(s) which

(i) will have the smallest atomic radius?

(ii) will be the most metallic?

(iii) will form basic oxide?

(iv) will show valency three?

(v) will show greatest tendency to gain electron?

A non-metal A which is the largest constituent of air combines with hydrogen on heating in the presence of Fe (as catalyst) and forms a gas

B. When this gas B is treated with H₂SO₄, compound C is formed which is broadly used as chemical fertiliser.

(i) Identify A, B and C.

(ii) Locate the position of A in the modern periodic table.

(iii) Which elements are present before and after the element A?

(iv) Write the electronic configuration of element A.

A teacher of Xth class, during teaching explains the importance of the music in our daily life. She was telling to her students that in the Indian system of music, there are seven musical notes in a scale sa, re, ga, ma, pa, da, ni. And in the west notations used are do, re, mi, fa, so, la, ti. The notes in a scale are separated by whole frequency intervals of tones. Every eighth note is similar to the first one and it is first note of next scale. A musician use these notes for composing music of a song.

Read the above passage carefully and answer the following questions accordingly.

(i) Is the situation discussed above is similar to something in chemistry? Explain.

(ii) What are the limitations of the above principle in case of chemistry?

(iii) What are the values you will infer from above passage?

Every school has assembly Students stand in rows which should be straight, horizontally as well vertical. Each class stands in a single line, with schools. Each class has a name, e.g. class 1, 2, 3... etc. In general, height of students of class 1st is smallest and 12th is biggest. Everyone sings the prayer at the same time.

Read the above passage carefully and answer the following questions given below.

(i) Do you find similarity between rows of assembly with periodic table? Explain two points.

(ii) How can you compare qualities of students with elements of periodic table?

(iii) What values are inculcated during assembly of school?

Consider the section of the periodic table:

Identify A, B, C and D.

The correct order of increasing acidic nature of SO₂, SiO₂ <P₂O₃ and Al₂O₃ is

An element X combines with hydrogen to form a compound XH₃. The element Xis placed on the right side of the periodic table. Which of the following statement is correct for element X?

I. Has two valence electrons.

II. Is a metal and is solid.

III. Is a non-metal and is a gas.

IV. Has five valence electrons.

V. XH₃ reacts with water to forma basic compound.

Listed below are the locations of certain elements in groups and periods of the periodic table. Arrange these elements in the expected order of increasing non-metallic character:

I. Element in the fourth period and group IV A

II. Element in the third period and group VI A

III. Element in the fourth period and group VI A

IV. Element in the six period and group III A

V. Element in the second period and group VII A

The correct order is:

An element X belongs to group 2 and period 3 of the periodic table. The chemical formulae of its nitrate, sulphate and phosphate respectively will be

An element belongs to group 17. It is present in third period and its atomic number is 17. What is the atomic number of the element belonging to same group and present in fifth period?

Consider the following figure:

Here, p, q, r and s respectively are: