Periodic Table & Periodicity of Properties|CH#3 chemistry|tutoronlines

Chapter # 3

Periodic Table and Periodicity of Properties

Table of contact:

Sr. no Topic name
1 Periodic Table
2 Mendleev’s periodic
3 Group
4 Newland’s Law
5 Electron Configuration
6 Periodic Law
7 Periodicity of Properties
8 Atomic Radius
9 Electron Affinity
10 Ionization Energy
11 Shielding Effect
12 Electronegativity

Give the short answer to the following questions.

Q.N.o.1. Define Mendeleev’s periodic law?

Ans. The law states that ” the characteristics of elements are periodic function of their atomic masses.

Q.No.2. Define periods and group in the periodic table?

Ans. In periodic table the horizontal rows are called period while vertical column are called group.

Q.No.3. Write names of any four elements of group 17?

Ans. Chlorine, Bromine, Fluorine, Iodine.

Q.No.4. Write down the name or symbol of the elements of first period?

Ans. In first period only two elements are present Hydrogen (H) Helium (He).

Q.No.5. Write down name of any four elements in Group 1st?

Ans. Hydrogen, Lithium, Sodium, Potassium.

F + e → F  ∆H = -328kj/mole

Q.No.6. Define Newland’s Law of Octaves?

Ans. In 1864 an English chemist Newland gave law of Octaves. According to him if elements are arrange in order of their increasing atomic masses, the properties of every 8th element, starting from any point are similar to one from.

Na → Na+ + e ∆H = +496kj/mole

Q.No.7. Define period with one example?

Ans. The horizontal rows of element in periodic table called period. For example, those elements having one electron in their valence shell called alkali metals.

Q.No.8. Define Mosely’s periodic law?

Ans. He states that, “Properties of elements are periodic function of their atomic numbers.

Q.No.9. What is contribution of Doberiener towards classification of elements?

Ans. A German chemist Doberiener observed the relation between atomic masses of triads (group of three element ). In triad, the atomic mass of the middle element is approximately the average of atomic masses of the other two elements. For example group of triad consists of calcium, stronsium and Barium. The atomic mass of stronsium is the average of atomic masses of calcium and Barium. Since few element could be classified, so this type of classification did not get wide acceptance.

Q.No.10. Differentiate between periods and group?

Ans. In periodic table the horizontal rows are called period while vertical column are called group.

Q.No.11. Write down general electronic configuration of carbon family?

Ans. ns2, np2.

Q.No.12. What are the element arranged in group 3 to 12 called?

Ans. From third (3rd) to twelvth (12th) group element are known transition element.

Q.No.13. From which element lanthanide series starts? What is its atomic number?

Ans. Lanthanide series starts with lanthanum atomic number of 57.

Q.No.14. Write the name of element arranged in the group first of periodic table?

Ans. The first group of periodic table consists of hydrogen, lithium, sodium, potassium, Rubidium, cesium and francium.

Q.No.15. How Newland arranged the element?

Ans. Newland arranged element, according to their increasing number of atomic masses. He observed that if elements arranged in Octaves manner, the chemical properties of every 8th element resemble the first one. His law did not get wide acceptance.

Q.No.16. Write the name of any four P-block elements?

Ans. Boron, Carbon, Nitrogen, Oxygen.

Q.No.17. Give reason that element of group 13 to 18 are called P-block elements?

Ans. The element from group 13 to 18 are known as P-block elements, because their valance electrons are found in P-block shell.

Q.No.18. Write down demerit of Mendeleev’s periodic table?

Ans.

  1. Mendeleev’s periodic table does not explain the position of isotope.
  2. And when the element are arranged according to their increasing atomic masses, the order of certain element become reversed.
Q.No.19. Define periodic law and modern periodic table?
Ans. Periodic law:

Properties of elements are periodic function of their atomic masses.

Periodic table:

Properties of elements are periodic function of their atomic number.

Q.No.20. Atomic number is a more fundamental property than atomic mass? Give reason.

Ans. Atomic number is the basic property, instead of atomic mass, because it is specific for every element while atomic mass may be same of two elements due to their isotopes.

Q.No.21. How many blocks are present in periodic table?

Ans. In periodic table, there are four blocks s, p, d, f are present.

Q.No.22. How many elements are found in the first period and what are their names?

Ans. In first period, only two elements are found hydrogen and helium.

Q.No.23. Write down the number of group and period in the long form of periodic table?

Ans. Long periodic table consists of 18 group and 7 period.

Q.No.24. Why size of atom increase from top to bottom in periodic table?

Ans. The size of atom increase down the group due to increase in number of shells of electron. Due to this, the effective unclear change become decreased.

Q.No.25. Why noble gases are not reactive?

Ans. Noble gases have 2 or 8 electrons in their valance shell. It means their valance shell are complete and there is no space for more electrons. Due to this stability they neither gain or loss electron, nor they share electrons. That is why they are non reactive.

Q.No.26. State about the trend of ionization energy in a period?

Ans. In period, ionization energy increases from left to right. The reason is reduced size of atom due to more electrostatic force of nucleus on valance electrons.

Q.No.27. Define atomic radius?

Ans. The half of the distance between nuclei of two bonded atoms is called atomic radius. It is measure in peco meter (pm=10-12m)

Q.No.28. Define electron affinity with an example?

Ans. The amount of energy released when an electron is added to an isolated gaseous atom is called electron affinity.

Q.No.29. Define ionization energy with an example?

Ans. The amount of energy required to remove the outer most electron from an isolated gaseous atom is called ionization energy.

Q.No.30. Write trend of electronegativity in a group?

Ans. Electronegativity decreases down the group. Because atomic size increases resulting in less forec of attraction of nucleus toward valence electrons.

Q.No.31. What is meant by periodic function?

Ans. Those properties which are repeated after specific interval of time, known as periodic function. e.g chemical properties, electronic configuration.

Q.No.32. What is shielding effect?

Ans. The decrease in attractive force exerted but nucleus on valance electron due to presence of electrons lying between nucleus and valence shell electron is called shielding effect.

Q.No.33. What is the trend of electronegativity in period?

Ans. Along the period, electronegativity increase. In period, the number of proton in nucleus increased, resulting in more attraction of nucleus toward valence electron, so the size of atom become small.

Q.No.34. Why shielding effect of electron make cation formation easy?

Ans. When the shielding effect of electron increases, it decreases the attractive force between valence electron and nucleus, which make the removal of electron easy.

Q.No.35. How is periodicity of properties dependent upon the number of protons in an atom?

Ans. The properties of atom depend upon its size. And the size of atom depend the Z effect or nuclear charge, which is due to number of protons. Greater the number of protons, greater will be nuclear charge, and result in small size of atom.

Q.No.36. What is the trend of ionization energy in a group and period?

Ans. Along the period, from left to right ionization energy increases. While along group, from top to bottom ionization energy decreased.

Q.No.37. Why the size of atom decrease in a period?

Ans. The reason is along the period, number of protons in nucleus due to increase in atomic number increase, resulting in more nuclear charge towards revolving electrons. But the number of shells do not increase. So there is more attraction of nucleus towards valence shell electrons that’s why atomic size reduced.

Q.No.38. Why the size of atom does not decrease regularly so in period?

Ans. Due to weak shielding effect, the size of atom do not regularly reduced. Along the period firstly the atomic size of decrease than increase.

Q.No.39. Why the second ionization energy of an element is higher than first one?

Ans. The second ionization is greater because when an electron is removed, the number of electrons become decreased while number of protons will remain same, so the size of atom decrease, which increased the ionization energy.

Q.No.40. Define shielding effect. Describe its trend along the period?

Ans. The decrease in attractive force of nucleus towards valence electrons due to presence of electrons in inner shells. This is known as shielding effect.

Trend:

Along the period it is decreased.

Q.No.41. Give the trend of electrons affinity in period?

Ans. The value of electrons affinity increase along the period. The reason is that, the atomic size get reduced along period, resulting in attraction of nucleus towards valence electron. It means, more the attraction will be, the greater is energy released, by adding electrons.

Q.No.42. Define Electronegativity?

Ans. Ability of atom to attract shared pair of electrons towards itself is known as Electronegativity.

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