9th Class Chemistry Chapter 3 Short Questions with Answers Solved

Question: 1

Why noble gases are not reactive?

Answer: 1

1-40

Nobel gases are not reactive because they do have 2 or 8 electrons in their valence shell Mean all nobel gases have completely filled valence shell. Their atoms do not have vacant space to accommodate extra electrons. Therefore, nobel gases do not gain, lose or share electrons.

Question: 2

Define Periods?

Answer: 2

2-40

Seven horizontal rows present in periodic table are called periods. Numbered from 1 to 7.

Question: 3

Why the size of atom does not decrease regularly in periods?

Answer: 3

3-40

The atomic size does not decrease regularly in periods due to presence of transition elements. The size of atom first decreases then increases.

Question: 4

What do you mean by group and periods in the periodic table?

Answer: 4

4-40

The Horizontal rows in periodic table called periods and vertical columns in the periodic table are called group.

Question: 5

Waht are Dobereiner's Triads?

Answer: 5

5-40

A German chemist Dobereiner observed relationship between atomic masses of several groups of three elements called Triads. In triads the central and middle element had atomic mass average of the other two elements.

Question: 6

Define Mendeleev's Periodic law.

Answer: 6

6-40

A Russian chemist arranged elements (63) discovered at that time according to increasing atomic mass. "Properties of elements are periodic function of their atomic masses".

Question: 7

Why shielding effect of electron makes action formation easy?

Answer: 7

7-40

As we move down in a group more and more shells come between valence shell and the nucleus of atom, additional shell reduce the electrostatic force of attraction felt by teh electron present in the outermost shell, and the shielding effect increases resultantly, and electrons can be taken away, easily and cations form.

Question: 8

What are blocks. How many blocks are present in periodic table?

Answer: 8

8-40

On the basis of completion of a particular sub shell, elements with similar sub-shell electronic configuration are referred as a block of elements. Four blocks are present in periodic table.s.p.d.f

Question: 9

Define Modern Periodic law.

Answer: 9

9-40

In 1913 H.Moseley give modern periodic law "Properties of elements are periodic function of their atomic number".

Question: 10

Define groups?

Answer: 10

10-40

Seven horizontal rows present in periodic table are called periods. Numbered from 1 to 7.

Question: 11

What are Lanthanide and Actinide series?

Answer: 11

11-40

Due to space problem two series of elements are placed below periodic table. Lanthanide: Series of elements starts from Lanthanum(Z=57) Called Lanthanide series. Actinide: Sereis of element starts from Actinium(Z-89) called actinide series.

Question: 12

Why Cesium requires little energy to release its one electron present in the their outermost shell?

Answer: 12

12-40

Cesium is the 2nd last element of 1st group . It has large size and less force of attraction between the nucleus and valence electron, as a result small amount of energy is required to remove electron from the valence shell

Question: 13

Give the trend of ionization energy in a period?

Answer: 13

13-40

If we move from left to right in a period the value of ionization energy increases. Because the size of atom reduce and valence electrons are held strongly by the electrons are held strongly by the electrostatic force of nucleus. Therefore elements on left side of the periodic table have low ionization energies as compared to those on right side of the periodic table.

Question: 14

Why do the bigger size atoms have more shielding effect?

Answer: 14

14-40

In bigger size atoms the number of inner shells and inner shell electrons increases hence the shielding effect in bigger size molecules also increases.

Question: 15

What are SI units of atomic radius?

Answer: 15

15-40

Pico meter

Question: 16

Describe Newland of octaves

Answer: 16

16-40

According to Newland law of octaves when the elements are arranged in order go increasing atomic weight, then every eight elements Has properties similar to that of the first element

Question: 17

Define Mendleev's periodic law

Answer: 17

17-40

Mendleev's periodic law states that "The physical and chemical properties of the elements are periodic functions of their atomic weights

Question: 18

Define Atomic Radius.

Answer: 18

18-40

"The half of the distance between the nuclei of the two bonded atoms referred as atomic radius". Example: Distance between the nuclei of two carbon atoms in elemental form is 154 pm its half is 77 pm. Which is atomic radius of Carbon.

Question: 19

Define atomic size and atomic radius

Answer: 19

19-40

Atomic size is the distance between a nucleus of an atom and its valence or outermost shell . and half of the distance between the nuclei of the two bonded atom is known as atomic radius

Question: 20

Define electron affinity.

Answer: 20

20-40

Amount of energy releases when an electron is added up in the outer most shell of an isolated gaseous atom is called electron affinity.

Question: 21

Describe Ionization energy.

Answer: 21

21-40

The ionization energy is the amount of energy required to remove the most loosely bound electron from the valence shell of an isolated gaseous atom.

Question: 22

Why do atoms react?

Answer: 22

22-40

Those elements which do not have complete octel and duplet. They react with other element to complete valence shell by losing or gaining of electrons.

Question: 23

Define Periodicity.

Answer: 23

23-40

Properties of elements were found repeating after regular after regular intervals in periodic tabel it is the periodicity.

Question: 24

Write any four properties of the long form periodictable.

Answer: 24

24-40

1-It shows arrangement of elements based on modern periodic law.

2- There are 18 vertical columns known as groups

3- There are 7 horizontal row known as periods Elements having similar outer electronic configurations

Question: 25

How many elements are placed in first period and what are their names and symbols.

Answer: 25

25-40

There are two elements in first period, Hydrogen (H), Helium(He)

Question: 26

Distinguish between period and group in periodictable.

Answer: 26

26-40

Groups and periods are two way of categorizing elements on the periodic table. Periodic table. Periods are horizontal rows in the periodic table while groups are vertical columns in the table.

Question: 27

Who introduced the name periodic table?

Answer: 27

27-40

Mendeleev introduced name of periodic table.

Question: 28

Define electron affinity with an example.

Answer: 28

28-40

Electron affinity is defined as the amount of energy released when an electron is added in the outermost shell of an isolated gaseous atom.

Example:

The first electron affinity of chlorine is -349kJmole-²

Question: 29

Define Ionization Energy.

Answer: 29

29-40

"The ionization energy is the amount of energy required to remove the most loosely bond electron from the valence shell of an isolated gaseous atom.

Question: 30

How many elements are placed in 4th period?

Answer: 30

30-40

Eighteen elements are present

Question: 31

What is meant by periodic function?

Answer: 31

31-40

When any property, whether its chemical or physical of all periodic table elements repeats after a fixed number of elements in increasing atomic number it is referred as periodic function.

Question: 32

How many elements are there in 4period?

Answer: 32

32-40

The fourth period contains 18 elements, beginning with potassium and ending with krypton.

Question: 33

Write down the names of clements of groups I with their symbols.

Answer: 33

33-40

1st group elements are called alkali metals. It consists of hydrogen , (H). Lithium(Li), Sodium (Na) , Potassium(K), Rubidium (Rb) and Cesium(Cs) and Francium(Fr)

Question: 34

Write down drawbacks of Mendeleev's periodic table?

Answer: 34

34-40

1-In some cases element of higheratomic masses are placed before those having lower atomic masses.

2- No attempt has been made to place metals and non-metals separately in it.

Question: 35

What is effective nuclear charge?

Answer: 35

35-40

The valence electron of an atom experiences less nuclear change than that of actual charge . It is called effective nuclear charges of Z

Question: 36

What are the elements arranged in group 3 to 12 called?

Answer: 36

36-40

Elementof group 3 to 12 in a modern periodic table are called d-block elements

Question: 37

Why the elements are called s and p block elements?

Answer: 37

37-40

The elements having their valence electrons in s and p sub shell called s and p blocks elements.

Question: 38

Explain Dobereiner's triads

Answer: 38

38-40

A German chemist Dobereiner observed relationship between atomic masses of several groups of three elements called triads. In these groups, the central or middle element had atomic mass average of the other two elements

Question: 39

How many periods are considered normal periods?

Answer: 39

39-40

2nd and 3rd periods are normal periods.

Question: 40

Why ionization energy of Na is less than Ma?

Answer: 40

40-40

Ionization energy is the energy required to remove the most loosely bound electron from an atom. As the nuclear charge of an atom increases as more energy is required to remove an electron. Mg atom has a smaller rediusand higher nuclear charge than Na atom, thus more energy will requireto remove the electron from the same orbital (3s), making the first ionization energy of Mg higher than that of Na.

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9th Class Chapter 3 Chemistry Short Questions

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