Class 9 Chemistry Chapter 3 Question Answer
Important Notes of Class 9 Chemistry Chapter 3 Question Answer English Medium written by Professor M. Shahid Suib. These notes are very helpful in the preparation of Periodic Table and Periodicity of Properties Class 9 for students of the 9th class Chemistry English Medium and these are according to the paper patterns of all Punjab boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Here are the detailed Class 9 Chemistry Chapter 3 Question Answer to help you prepare for your exams.
- Complete Exercise MCQs of Chapter No.3 Periodic Table and Periodicity of Properties
- Complete Exercise Short Questions with Answers of Chapter No.3 Periodic Table and Periodicity of Properties.
- Why are noble gases not reactive?
- State periodic law.
- Write down the demerits of Mendeleev’s periodic table.
- Write down any two salient features of the long form of the periodic table. (Also a long question).
- What is the difference between Mendeleev's periodic law and modern periodic law?
- Define groups and periods in the periodic table.
- How many elements are present in 1st, 2nd, 3rd, 4th, 5th, 6th, and 7th period? Also, write the names of the periods.
- Why the elements are called s or p or d or f block elements?
- What are Dobereiner’s triads? Give example.
- Describe Newlands Law of octaves.
- Define atomic radius. Write its trend in groups and periods. Write its unit.
- Define ionization energy. ? Write its trend in groups and periods.
- Define electron affinity. Write its trend in groups and periods.
- Define electronegativity. Write its trend in groups and periods.
- What is the shielding effect? Write its trend in groups and periods.
- Define effective nuclear charge (Zeff).
- Write the names of any four elements or symbols of the first group (Alkali metals) of the periodic table.
- Write the symbols of any four elements of the halogen 17th group.
- Write the symbols of any four elements of the second group (Alkaline Earth metals).
- PERIODICITY OF PROPERTIES: Atomic Size and Atomic Radius: As we know that atoms are very small and don't have defined boundaries that fix their size. So it is difficult to measure the size of an atom. Therefore, the common method to determine the size of an atom is to assume that atoms are spheres. When they lie close to each other, they touch each other. Half of the distance between the nuclei of the two bonded atoms is referred as the atomic radius of the atom. For example, the distance between the nuclei of two carbon atoms in its elemental form is 154 pm, its means its half 77 pm is radius of carbon atom.
- When we move from left to right in a period although atomic number increases, yet the size of atoms decreases gradually. It is because with the increase of atomic number, the effective nuclear charge increases gradually because of addition of more and more protons in the nucleus. But on the other hand addition of electrons takes place in the same valence shell i.e. shells do not increase. There is gradual increase of effective nuclear charge which increases due to addition of protons. This force pulls down or contracts the outermost shell towards the nucleus. For example, atomic size in period 2 decreases from Li (152 pm) to Ne (69 pm).
- The size of atoms or their radii increases from top to bottom in a group. It is because a new shell of electrons is added up in the successive period, which decreases the effective nuclear charge.
- The trend of atomic size of transition elements has slight variation when we consider this series in a period. The atomic size of the elements first reduces or atom contracts and then there is increase in it when we move from left to right in 4th period.