Frank Brothers Solutions for ICSE Class 9 Chemistry Chapter 8 The Periodic Table

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Question 1:
Answer: The present form of periodic table has eighteen vertical columns called ‘groups’. These groups are numbered from 1 to 18.
Groups are like vertical families where all the members have similar characteristics and behaviors. In the modern table, knowing the group number helps you predict how an element will react with others.
Teacher's Tip: Think of "Groups" as "G" for "Ground-to-Sky" to remember they are the vertical columns.
Exam Tip: Always specify that there are exactly 18 groups in the modern long form of the periodic table.

Question 2:
Answer: Seven horizontal rows in periodic table are called periods. These are numbered as 1, 2, 3, 4, 5, 6 and 7 from top to bottom.
Periods represent the rows that you read from left to right, just like a line of text in a book. As you move across a period, the elements change from being very metallic to being non-metallic.
Teacher's Tip: Remember "Periods" are like the "Period" at the end of a horizontal sentence.
Exam Tip: Note that the period number corresponds to the number of electron shells an atom has.

Question 3:
Answer: Certain chemically similar elements are arranged into set of three elements are called triads. When these elements are arranged in order of their atomic mass, the atomic mass of the middle element is approximately average of the atomic masses of the other two. For Example - Lithium, Sodium, Potassium
This was an early scientific attempt to show that the weights of elements were not random but followed a mathematical pattern. Scientists like Dobereiner noticed that nature grouped elements in "threes" with very similar personalities.
Teacher's Tip: Think of a "Triad" as a "Trio" of musical notes or a group of three best friends.
Exam Tip: Be ready to calculate the middle mass by adding the first and third masses and dividing by two.

Question 4:
Answer: According to Dobereiner’s law of Triad, When certain elements are arranged in order of their atomic mass, the atomic mass of the middle element is approximately average of the atomic masses of the other two.
i.e. {A+C}/{2} = B
{40+137}/{2} = 88.5
This formula provides a way to predict the weight of an unknown middle element if you know its neighbors in the triad. In the example shown, the calculation helps identify Strontium by its approximate atomic mass of 88.5.
Teacher's Tip: Always write the generic formula A+C/2 before doing the actual math to show your steps.
Exam Tip: Ensure your final calculated value includes the decimal point for better accuracy.

Question 5:
Answer: 1. (a) When elements are arranged in increasing order of their atomic masses, the eighth element resembles the first in physical and chemical properties just like the eighth note on a musical scale resembles the first note.
2. (b) It is based on the notes of the musical scale.
3. (c) No, the law of octaves was not valid beyond calcium i.e. not valid for heavier elements having atomic no. greater than ’40’.
4. (d) There are 6 elements in between A and B.
This law compared the world of chemistry to the world of music, showing that properties repeat in cycles. It was a brilliant observation for light elements, even though it did not work for the much heavier ones discovered later.
Teacher's Tip: Think of the "Octaves" in music: Do, Re, Mi, Fa, So, La, Ti... and then back to Do!
Exam Tip: Remember the limit of this law is the element Calcium; it does not work for elements after it.

Question 6:
Answer: Important conclusions of Newland’s law of octaves are-
1. It was the first logical attempt to classify elements on the basis of atomic masses.
2. Periodicity of elements was recognized for the first time.
Periodicity is the idea that certain traits in elements appear again and again at regular intervals. Newland's work was the foundation that later helped other scientists build the perfect periodic table we use today.
Teacher's Tip: Periodicity is like a "pattern that repeats," just like days of the week or months of the year.
Exam Tip: Use the word "logical attempt" to describe early classification systems for higher marks.

Question 7:
Answer: The physical and chemical properties of elements are the periodic functions of their atomic masses.
This rule was the original "Periodic Law" used by Mendeleev to organize his version of the table. It suggested that if you know the weight of an element, you can guess what its physical and chemical "personality" will be.
Teacher's Tip: Mendeleev's table was like a puzzle where weight was the most important clue to where the piece fits.
Exam Tip: Note the difference: Mendeleev used "Atomic Mass," but the modern table uses "Atomic Number."

Question 8:
Answer: 1. It helps to understand that the properties of elements are related with some fundamental unit of all elements.
2. It simplifies and systemizes the study of the properties of various elements and their compounds.
3. It helps to understand the relationship between the different types of elements.
4. It helps to understand the cause of gradual change in properties from one element to another.
Organizing elements makes chemistry much easier because you don't have to memorize every element separately. Instead, you can learn the rules of a group or period and apply them to all the elements found there.
Teacher's Tip: The periodic table is like a "map" for chemists; it tells you exactly where to find metals, gases, and liquids.
Exam Tip: Mention "systemization" to explain how the table turns a mess of facts into an organized system.

Question 9:
Answer: The number of elements in various periods are-
Period 1 - 2
Period 2 - 8
Period 3 - 8
The first period is very short because it only contains the two simplest gases in the universe. As we go down to periods 2 and 3, the "shells" of the atoms get bigger, allowing them to hold exactly eight elements each.
Teacher's Tip: Think of the periods as "shelves" in a cupboard, with the top shelf being the smallest.
Exam Tip: Memorize the sequence 2, 8, 8 for the first three periods as they are frequently tested.

Question 10:
Answer: Hydrogen and Helium are the elements of period 1.
These two elements are unique because they only have one electron shell. Hydrogen is the lightest element known, and Helium is a very stable gas that does not like to react with anything.
Teacher's Tip: Remember "H" and "He" are the two "Heads" of the periodic table at the very top.
Exam Tip: If asked for the smallest period, identify Period 1 and name its two elements.

Question 11:
Answer: At the end of the period 2 and period 3 the outer shell of the elements are fully filled i.e. they have complete octet.
Having a full outer shell makes an element very "satisfied" and chemically lazy, which is why these elements don't form bonds. This stable state is called an "octet" because it usually involves eight electrons in the outer shell.
Teacher's Tip: An "Octet" is like a "Full House" in a card game; the atom doesn't need to trade any more cards.
Exam Tip: Use the term "complete octet" to explain the stability of the noble gases at the end of periods.

Question 12:
Answer: The element of group II (2) is likely to be metallic in character.
Elements in the first and second groups are almost all metals that are good at conducting heat and electricity. They have a shiny appearance and usually exist as solids at room temperature.
Teacher's Tip: Groups 1 and 2 are the "Strong Metals" found on the far left side of the table.
Exam Tip: Associate the left side of the periodic table with "Metallic character."

Question 13:
Answer: Metallic character increases on moving down the group. Therefore, the element that is placed at the end of the group will have the greatest metallic character.
As you go down a column, the atoms get larger and find it easier to lose electrons, which is a key trait of metals. This means the elements at the bottom of a group are usually much more "metallic" than those at the top.
Teacher's Tip: Think of it as "The lower you go, the more metallic you grow!"
Exam Tip: When comparing two elements in the same group, the one lower down will always be more metallic.

Question 14:
Answer: 1. (a) Two alkali metals and their groups and period are-
Lithium - First group and second period.
Sodium - First group and third period.
2. (b) Two alkaline earth metals with their groups and periods are-
Beryllium - Second group and Second period
Magnesium - Second group and Third period
3. (c) Halogens belong to Group 17.
4. (d) Elements of groups from 3 to 12 are called as transition elements.
5. (e) Helium gas has duplet arrangement of electrons.
6. (f) Germanium is a metalloid of group 14.
7. (g) The bond formed between the atoms of an element of group 2 and group 16 is called as electrovalent or ionic bond.
8. (h) The bond formed between the atoms an element of group 14 and group 17 is called as covalent bond.
9. (i) Lithium and Magnesium are the elements which are showing a diagonal relationship.
10. (j) In Group 18 all elements are gases.
This list identifies the major families and bonds that make up the world of chemistry. Each group has a unique name and specific rules for how they like to share or swap electrons with their neighbors.
Teacher's Tip: Alkali metals (Group 1) are super reactive, while Noble gases (Group 18) are completely calm.
Exam Tip: Be careful with the spelling of "electrovalent" and "covalent" as they are different types of chemical bonds.

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Question 15:
Answer: 1. (a) Newland, Newland law of Octaves
2. (b) atomic masses
3. (c) 18, 7
4. (d) unstable
5. (e) Atomic number, Moseley
6. (f) similar outer electronic configuration at certain regular intervals
7. (g) decreases
8. (h) 2 electrons
9. (i) different
These filled-in blanks summarize the history of how scientists discovered the rules of the periodic table. From early ideas about atomic mass to modern atomic numbers, each discovery helped complete the scientific picture.
Teacher's Tip: Focus on the scientist names like Newland and Moseley to keep their specific theories straight.
Exam Tip: Always double-check if the question asks for the number of groups (18) or periods (7).

Question 16:
Answer: 1. (a) False
2. (b) True
3. (c) True
4. (d) False
5. (e) False
6. (f) False
7. (g) False
True and False questions are excellent for checking if you understand the small details of periodic trends. For example, knowing that atomic size increases down a group but decreases across a period is a very important fact.
Teacher's Tip: If a statement says something "decreases" when it actually "increases," it is a classic False trap!
Exam Tip: Read every word of the statement carefully; sometimes one small word like "not" can change the entire answer.

Question 17:
Answer: 1. (a) A - 2, 1
B - 2, 3
C - 2, 8, 2
D - 2, 8, 8
E - 2, 8, 8, 2
2. (b) B is placed right to A.
3. (c) C and E belongs to same group.
4. (d) The formula for sulphate of C is CSO₄.
5. (e) C has a smaller size atom.
6. (f) Sodium is placed below A.
7. (g) Helium is the first element of the group to which D belongs.
8. (h) The formula for chloride of B is BCl₃.
9. (i) A₂O is the formula of oxide of A.
10. (j) Fluorine is the non-metallic element which belongs to the same period as A.
By looking at electron configurations, we can tell exactly where an element "lives" in the periodic table. Elements with the same number of electrons in their outer shell (like C and E) are "roommates" in the same vertical group.
Teacher's Tip: The number of digits in the configuration (like 2, 1) tells you the Period Number (Period 2).
Exam Tip: Practice building chemical formulas like A₂O by swapping the valencies of the two elements.

Question 18:
Answer: 1. (a) Properties of Germanium i.e. also called as eka-silicon were predicted on the basis of its position in Mendeleev’s periodic table.
2. (b) Beryllium and Gold are the two elements whose atomic weights were corrected on the basis of their positions in Mendeleev’s periodic table.
3. (c) There were 63 elements known at the time of Mendeleev’s classification of elements.
Mendeleev was so confident in his table that he predicted elements that hadn't even been discovered yet! When these elements like Germanium were finally found, they matched his predictions perfectly, proving he was a genius.
Teacher's Tip: "Eka" is a Sanskrit word meaning "one," which Mendeleev used to mean "the one below."
Exam Tip: Remember the count of "63" elements as the starting point for Mendeleev's work.

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Question 19:
Answer: Merits of Mendeleev’s classification of elements are:-
1. Systematic study of the element: Elements could now be studied as groups or families rather than individuals. The Mendeleev’s periodic table simplified and systemized the study of the elements and their compounds.
2. Prediction of new elements: While arranging the elements, in increasing order of atomic mass, Mendeleev left some blanks for the elements that were not discovered at that time. Though unknown, he was able to predict their properties more or less accurately. He named 3 of such elements as eka-boron, eka-aluminium, eka-silicon. He named them, as they were below boron, aluminium and silicon in the respective sub-groups. Eka-boron was later named as scandium, eka-aluminium as gallium and eka-silicon as germanium.
3. Correction of atomic masses: The Mendeleev’s periodic table helped in correcting the atomic masses of elements based on their position in periodic table. Example- Atomic masses of Be was corrected from 13.5 to 9.
Mendeleev's table was not just a list; it was a powerful scientific tool that could fix old mistakes and find new truths. His ability to leave "blank spaces" for future discoveries is what made his table world-famous.
Teacher's Tip: Think of Mendeleev's table as a completed jigsaw puzzle with a few pieces missing that he described before they were found.
Exam Tip: Be ready to name the three "Eka" elements and their modern names like Scandium and Gallium.

Question 20:
Answer: Mendeleev left some gaps in his periodic table of elements for the elements that were not discovered at that time. Though they were unknown, he was able to predict their properties more or less accurately at that time. Example - He named eka-boron, eka- aluminium and eka-silicon to some elements as they were just below boron, aluminium and silicon in the respective sub-groups. Eka-boron was later named as scandium, eka-aluminium as gallium and eka-silicon as germanium.
By leaving these gaps, Mendeleev showed that science is always growing and that there was more to learn about the universe. This prediction is considered one of the greatest moments in the history of chemistry.
Teacher's Tip: A "gap" in the table was not an error; it was a prediction of a future discovery!
Exam Tip: Mention that Mendeleev predicted "properties" not just the existence of the elements.

Question 21:
Answer: The main characteristic of the last elements in the periodic table are-
1. Their octet is attained.
2. They are inert in nature.
The general name of such elements is noble gas or inert elements.
These elements are found in the very last group (Group 18) and are very stable because their outer electron shells are completely full. Because they have everything they need, they don't react with other atoms and exist as single gases.
Teacher's Tip: "Inert" means "chemically inactive" - these gases are the "couch potatoes" of the periodic table!
Exam Tip: Use both names "Noble gas" and "Inert elements" to show you know both standard terms.

Question 22:
Answer: 1. (a) The physical and chemical properties of elements are the periodic functions of their atomic numbers.
2. (b) There are 7 periods and 18 groups in the long form of the periodic table.
3. (c) The number of elements in each period is-
1 period-2
2 period-8
3 period-8
4 period-18
5 period-18
6 period-32
7 period-Incomplete
This is the modern rule of chemistry that fixed the small problems in Mendeleev's older version. By using "Atomic Number" (the number of protons) instead of mass, everything in the table falls into a perfectly logical order.
Teacher's Tip: Atomic Number is like a student's Roll Number; it's the most accurate way to identify an element.
Exam Tip: Memorize the specific count of elements for the first six periods as they are frequently asked.

Question 23:
Answer: 1. (a) X belongs to 17th group.
2. (b) The period number of X is 3.
3. (c) In atom of X there are 7 valence electrons.
4. (d) Valency of X is 1.
5. (e) It is non-metal.
6. (f) The element right to it is Argon and the element left to it is Sulphur.
7. (g) The atomic number of the elements above to it is 9 and below to it is 35 in the periodic table.
Based on this information, we can identify element X as Chlorine, which is a very reactive non-metal gas. Its 7 valence electrons mean it only needs one more to be happy, which is why its valency is 1.
Teacher's Tip: Elements in Group 17 are the "Halogens" and they are all very reactive non-metals.
Exam Tip: Be careful: Valency (1) is different from the number of valence electrons (7).

Question 24:
Answer: 1. (a) The nature of bond will be ionic in the compound XY.
2. (b)
1. Y and Z will form covalent bond.
2. X and Z will form ionic compound.
Ionic bonds are formed when a metal "gives" an electron to a non-metal, creating a strong attraction. Covalent bonds happen between two non-metals who decide to "share" their electrons to become stable together.
Teacher's Tip: Ionic = Giving/Taking. Covalent = Sharing.
Exam Tip: Identify the group of the elements first to determine if they are metals or non-metals before deciding the bond type.

Question 25:
Answer: 1. (a) There would be 2 electrons in the outermost shell of the element X.
2. (b) Element X belong to second group of the periodic table.
3. (c) When X reacts with chlorine, the compound formed of the formula XCl₂.
Because element X has two electrons to give away, it needs two Chlorine atoms (which each take one) to balance the reaction. This results in a stable compound where everyone has a full outer shell.
Teacher's Tip: Group 2 elements always have a valency of 2 and form formulas like XCl₂ or XO.
Exam Tip: Use the "criss-cross method" of valencies to write the final chemical formula correctly.