Sindh and Karachi All board Class 9 Chemistry Notes Chapter 4 Periodicity of Elements, short, long question, MCQs, multiple-choice question and, fals true.
Table of Contents
Sindh Class 9 Chemistry Chapter 4 Periodicity of Elements
Read more: Long Questions Sindh Class 9 Chemistry Notes Chapter 3 Atomic Structure
MCQ: Both elements of 1st period contain valence electrons in
- M shell
- N shell
- K shell
- S shell
Answer: 3
MCQ: In the periodic table, helium is placed at
- top left corner
- bottom right corner
- bottom left corner
- top right corner
Answer: 4
MCQ: Across the period the atomic size decreases due to
- shielding effect
- photoelectric effect
- increase in nuclear force of attraction
- decrease in nuclear force of attraction
Answer: 3
MCQ: The first three periods are
- long periods
- short periods
- moderate periods
- all of above
Answer: 2
MCQ: On basis of electronic configuration the group and period of 95B is
- 2 and IIIA
- 3 and IIA
- 4 and VIA
- 5 and VIIA
Answer: 1
MCQ: Chemical properties depend upon
- electronic configuration
- valence shell electronic configuration
- atomic mass
- atomic size
Answer: 2
MCQ: Nobel gases are present in
- VIIA group
- VIA group
- VA group
- VIIIA group
Answer: 4
MCQ: The energy required to remove an electron from the outermost shell is called
- potential energy
- kinetic energy
- mechanical energy
- ionization energy
Answer: 4
MCQ: As we go from top to bottom in a group the shielding effect
- doesn’t change
- decreases
- increases
- remains constant
Answer 3
MCQ: Group A elements are called
- metals
- alkali metals
- representative elements
- transition elements
Answer 3
Fill in the Blanks
- The rule of triad was introduced by __________ .
- The repetition of properties after regular intervals is called _______ .
- The longest period_____ is period and contains total ________ elements.
- The longest period is period and contains total _____________ elements.
- The long form of periodic table contains _____ groups and _______ periods.
- According to Mendeleev the properties of the elements are the periodic functions of their _____ .
Fill in the blanks Correct Answer
- Dobereiner
- periodicity
- 6th, 32
- metalloids
- 8, 7
- mass number
Part 1
Part 2 Chemistry Class IX |Chapter 4 Part-2 PERIODICITY OF ELEMENTS
Multiple Choice Questions class 9 Chemistry Notes Chapter 4 (Periodicity of Elements)
Mendeleev’s periodic table contained_____ periods
A. 7
B. 8
C. 12
D. 10
The incomplete period in the periodic table is _____ .
A. 7
B. 6
C. 3
D. 1
The most reactive metal is_____ .
A. Na
B. Cu
C. Fe
D. Ca
The only liquid metal is___________ .
A. Molybdenum
B. Gold
C. Mercury
D. Bromine
Lothar Meyer’s curve included about _____ elements.
A. Thirty
B. Forty
C. Fifty Six
D. Sixty two
True or False Chemistry Class 9 Notes Chapter 4 Sindh and Karachi board
- Mendeleev put forward his periodic law in 1856. False
- The first period contains two elements, hydrogen, and helium . True
- The longest period in the periodic table is 7th period. False
- Lanthanides and Actinides are d-block elements. False
- Down the group the electronegativity increases with increasing atomic number. False
- The law of octaves was introduced by John Newland. True
- Li7, Na23 and K39 form a triad. True
Q.1 Define the followings:
a) Doberneir’s rule of triad
b) Periodicity
c) Modern periodic law
d) Electronegativity
Answer:
a) Doberneir’s rule of triad:
It states that central atom of each set of triad had an atomic mass almost equal to the arithmetical mean of the atomic masses of other two elements.
For example, Lithium 7, Sodium 23, and Potassium 39 are the group of triad. The average atomic mass of this triad is 23.
b) Periodicity:
The repetition of chemical and physical properties at regular intervals in the periodic table according to their atomic number is called periodicity.
c) Modern periodic law:
It states that the physical and chemical properties of all elements are periodic functions of their atomic numbers. In periodic table, elements are arranged in order of their increasing atomic number.
d) Electronegativity:
Electronegativity is the relative tendency of an atom in a molecule to attract shared pair of electrons to itself. For example, in case of HCl, Cl is more electronegative than hydrogen then it will attract shared pair electrons more to itself.
Q.2) If an element contains two shells only and its outershell contains five electrons then to which group the element belongs in the periodic table. Name the element. Predict its period.
Answer:
Data:
No. of shells = 2
Valence shell electrons = 5
Solution:
Electronic configuration of element = 1s2, 2s2, 2p3
Valence shell has configuration = 2s2, 2p3
Period number = 2
Group number = 2 + 3 = 5
Total number of electrons in both shells = 7
Thus this element is nitrogen (N) with atomic number 7. It belongs to 2nd period and 5th group of the periodic table.
Q.3) State Mendeleev’s periodic law. Describe Mendeleev’s periodic table. Write down the advantages and disadvantages of Mendeleev’s periodic table.
Answer:
Mendeleev’s periodic Law:
It states that “the physical and chemical properties of elements are the periodic function of their atomic masses”.
Mendeleev’s Periodic table:
He classified elements in 1869. His periodic table was based on the increasing order of atomic masses of elements. He divided periodic table into eight vertical columns called groups and horizontal rows called periods. He also left spaces for the unknown elements with atomic masses.
Advantages of Mendeleev’s periodic table:
i) There was a regular gradation in physical and chemical properties of elements.
ii) The group number of an element indicates highest oxidation state that it can attain.
iii) There were many vacant spaces in Mendeleev’s periodic table for the elements to be discovered. He named them Eka-Boron, Eka-Aluminium and Eka-silicone He also predicted the properties of these undiscovered elements including atomic masses. These elements were discovered as Sc, Ga and Ge with same features as he predicted.
iv) Mendeleev’s arrangement helped to correct atomic masses of a number of elements.
Disadvantages of Mendeleeve’s periodic table:
i) There are three pairs of elements i.e. elements of higher atomic masses placed before elements of lower atomic masses i.e.
a) Argon (40) placed before potassium (39)
b) Cobalt (59.9) placed before nickle (58.6)
c) Tellurium (127.6) placed before iodine (126.9)
2) No place for isotopes of elements.
3) Dissimilar elements placed in same group i.e. Alkali metals (Li, Na, K, Rb, Cs, Fr) were placed with coinage metals (Ag, Cu, Au).
4) Similar elements placed in different groups for example Barium (Ba) and lead (Pb) resemble in many properties but they are placed in separate groups.
5) It failed to give the idea of atomic structure.
Explain Newland’s law of Octave. How this law provided a larger scope for the classification of the elements?
In 1863 John Newland, a London industrial chemist proposed Newland’s law of octave, which states that: “If elements are arranged in the order of increasing atomic masses, the eighth element starting from a given one, has similar properties as first one i.e. its properties are a kind of repetition of the first, as the eighth note in an octave of music.”
For example, Na is the eighth element from Li and has similar properties, Mg is the eighth element from Be and has similar properties, etc.
This arrangement of elements for the first time brought to light the existence of periodicity i.e. recurrence of chemical and physical properties at regular intervals and provided a great idea towards the development of the modern periodic table.
This law failed because it held good for the first sixteen elements but did not work after the seventeenth element. Moreover, hydrogen was not included in this sequence.
Which pair of elements are chemically similar?
a) K, Cr
b) Cu, Ca
c) F, Cl
d) N, O
Answer:
c) This pair is similar because it belongs to the same group halogens. Elements of group halogens possess the same chemical properties.
What do you understand by the long form of the periodic table? Explain some of its applications?
The present form of the periodic table is called the long form of the periodic table because it contains eighteen groups instead of eight and seven periods instead of twelve.
Applications:
i) Group number of an element represents the number of valence electrons found in its outermost shell. For example, nitrogen belongs to group 5A because it has five electrons in its valence shell.
ii) Period number shows the total number of shells of an element. For example, sodium has three shells because it has three electronic shells in its atoms.
iii) The periodic table tells the physical state of the element whether it is solid, liquid or gas.
iv) The periodic table is divided into four blocks, s-block, p-block, d-block, and f-block depending upon whether the valance electron is present in s, p, d, and f orbitals.
Discuss some of the physical properties of the elements which exhibit periodicity.
Periodic properties of atoms
Atomic Radius:
The atomic size or atomic radius is the distance from the center of the nucleus to the outer most shell of electrons in the atom of any element.
Trend of Atomic radii in a period:
The atomic radii decrease while going from left to right in a period because the number of electrons increases in the same shell. This shows the strong attraction of nucleus on the outermost electrons toward itself causes the decrease in size.
Trend of Atomic radii in a group:
The atomic radii increase in moving from top to bottom in a group. This is because the addition of electron takes place in the new energy shell. The nuclear charge does not hold its influence on the increased size of an atom.
Ionization Energy:
The ionization energy is the energy required to completely remove an electron from a gaseous atom or ion. The closer and more tightly bound an electron is to the nucleus, the more difficult it will be to remove, and the higher its ionization energy will be.
Trend of ionization energy along the groups
Ionization energy decreases moving down a group. This is because the shielding effect in atoms increases from top to bottom. Greater shielding effects results in a weaker attraction of the nucleus for the valence electrons. So, they are easier to remove. This leads to decrease in ionization energy from top to bottom in a group.
Trend of ionization energy along the periods
As we move from left to right in a period, the shielding effect remains constant. But progressively nuclear charge increases. A stronger force of attraction between nucleus and the valence electron increases. This leads to an increase in ionization energy from left to right in a period.
Electron Affinity
Electron affinity is the energy required when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.
Trends of electron affinity in a period
In a period, the electron affinity increases from left to right because successive atoms have higher nuclear charge and attract the incoming electron more towards itself.
Trends of electron affinity in a group
Down a group in the periodic table, electron affinity decreases because the addition of a new shell to each atom decreases its force of attraction.
Electronegativity:
Electronegativity is the tendency of an atom in a molecule to attract shared pair of electrons to itself.
Trends of electronegativity in a period
In a period from left to right, it increases due to increase in nuclear charge.
Trends of electronegativity in a group
Down a group electronegativity decreases as due to addition of new shell, the power of a nucleus to attract electron decreases.
How does the modern periodic law differ from Mendeleev’s periodic law? Explain clearly groups and periods in the modern periodic table.
Answer:
| Mendeleev’s periodic table | Modern periodic table |
| Mendeleev’s periodic table is based on a law that states that the physical and chemical properties of the elements are the periodic functions of their atomic masses. | The modern periodic table is based on a law that states that the physical and chemical properties of the elements are the periodic functions of their atomic number. |
Periods
A period is a horizontal row in the periodic table. There are seven periods in the periodic table. Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity.
Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an addition of electrons, which causes the electron to be much closer to the nucleus.
This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bounded element required more energy to remove an electron.
Electronegativity increases in the same manner as ionization energy because of the attraction exerted on the electrons by the nucleus.
Electron affinity also increases. Metals generally have a lower electron affinity than nonmetals.
Groups
A group is a vertical column in the periodic table. Groups usually have more significant periodic trends than periods. Elements within the same group generally have the same electron configurations in their valence shell.
The groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases).
Elements in the same group show patterns in atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more shells, valence electrons are found farther from the nucleus.
From the top, each successive element has low ionization energy because it is easier to remove an electron since the atoms are less tightly bound.
Similarly, in a group from top to bottom decrease in electronegativity due to an increasing distance between valence electrons and nucleus.
What do you understand by the periodic classification of elements? What are the merits and demerits of the classification of the elements in the periodic tabular form?
Answer:
According to the periodic law, properties of the elements are the periodic function of their atomic numbers. Elements with the same properties repeat at regular intervals so that the elements having similar properties have been placed in the same groups. They come one above the other in the periodic table.
Merits:
i) The classification of elements is based on the atomic number, which is more fundamental property.
ii) The reason for placing isotopes at one place is justified as the classification is based on atomic number.
iii) It explains the periodicity of the properties of the elements and relates them to their electronic configurations.
iv) The position of the elements that were misfit on the basis of mass number (like argon and potassium) could be justified on the basis of atomic number.
v) The lanthanides and actinides are placed separately at the bottom of the periodic table.
vi) The table is simple, systematic and easy for remembering the properties of various elements as it is based on the electronic configuration.
Demerits:
i) Hydrogen resembles both the alkali metals and halogens. But it has been placed with the alkalis.
ii) The lanthanides and actinides have not been placed in the main body of the table.
Q.11) What do you understand by representative and transition elements?
Answer:
Representative elements:
Groups are divided into sub-groups A and B. Elements with similar valence shell configuration are placed in the same group in the periodic table. Group A elements are called normal or representative elements. They are also called main group elements. These elements include both metals and non-metals. Their outermost s or p orbitals are partially filled.
Transition elements:
The group B elements are called transition elements because their properties show gradual change or transition between the two sets of representative elements. Transition elements are metals and they form colored compounds. They have similar valence shell configuration. They have high densities and high melting and boiling points.
Q.12) Discuss the following physical properties of the elements.
a) Ionization energy
b) Electron affinity
c) Electronegativity
d) Atomic Radii
Answer:
a) Ionization Energy:
The ionization energy is the energy required to completely remove an electron from a gaseous atom or ion. The closer and more tightly bound an electron is to the nucleus, the more difficult it will be to remove, and the higher its ionization energy will be.
Trend of ionization energy along the groups
Ionization energy decreases moving down a group. This is because the shielding effect in atoms increases from top to bottom. Greater shielding effects results in a weaker attraction of the nucleus for the valence electrons. So, they are easier to remove. This leads to decrease in ionization energy from top to bottom in a group.
Trend of ionization energy along the periods
As we move from left to right in a period, the shielding effect remains constant. But progressively nuclear charge increases. A stronger force of attraction between nucleus and the valence electron increases. This leads to an increase in ionization energy from left to right in a period.
b) Electron Affinity
Electron affinity is the energy required when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.
Trends of electron affinity in a period
In a period, the electron affinity increases from left to right because successive atoms have higher nuclear charge and attract the incoming electron more towards itself.
Trends of electron affinity in a group
Down a group in the periodic table, electron affinity decreases because the addition of a new shell to each atom decreases its force of attraction.
c) Electronegativity:
Electronegativity is the tendency of an atom in a molecule to attract shared pair of electrons to itself.
Trends of electronegativity in a period
In a period from left to right, it increases due to increase in nuclear charge.
Trends of electronegativity in a group
Down a group electronegativity decreases as due to addition of new shell, the power of a nucleus to attract electron decreases.
d) Atomic Radius
The atomic size or atomic radius is the distance from the center of the nucleus to the outer most shell of electrons in the atom of any element.
Trend of Atomic radii in a period:
The atomic radii decrease while going from left to right in a period because the number of electrons increases in the same shell. This shows the strong attraction of nucleus on the outermost electrons toward itself causes the decrease in size.
Trend of Atomic radii in a group:
The atomic radii increase in moving from top to bottom in a group. This is because the addition of electron takes place in the new energy shell. The nuclear charge does not hold its influence on the increased size of an atom.
What are lanthanides and actinides? Are they d or f-block elements?
The lanthanides and actinides form a group that appears almost disconnected from the rest of the periodic table. This is the f block of elements, known as the inner transition series. This is due to the proper numerical position between Groups 2 and 3 of the transition metals.
The lanthanide series includes elements 58 to 71, which fill their 4f sublevel progressively.
The actinides are elements 89 to 103 and fill their 5f sublevel progressively. Actinides are typical metals and have properties of both the d-block and the f-block elements, but they are also radioactive.
Lanthanides have different chemistry from transition metals because their 4f orbitals are shielded from the atom’s environment. They are also called d-block and f-block elements because their valence electrons come in these orbitals.
lanthanides block
actinides
