Periodic Classification of Elements
Multiple Choice Questions
- Mendeleev’s periodic table is based on
(a) Atomic mass
(c) Atomic radius
(b) Atomic number
(d) Atomic volume.
- Group 18 elements are also called
(a) Alkali metals (c) Halogens
(b) Alkaline Earth metals. (d) Noble gases.
- As we move from top to bottom in a group in modern periodic table, generally atomic size of elements
(a) increases (c) remains same
(b) decreases (d) approaches zero.
- Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic table?
(a) The elements become less metallic in nature
(b) The number of valence electrons increases
(c) The atoms lose their electrons more easily
(d) The oxides become more acidic..
- Element X forms a Chloride with the formula XCh₂, which is a solid with a high
melting point. X would most likely be in the same group of the Periodic Table as
(a) Na. (c) Al
(b) Mg (d) Si.
- Which among the following is not a metalloid ?
(a) Silicon. (b) Germanium
(c) Boron . (d) Sodium.
Ans. 1. (a), 2. (d), 3. (a), 4. (c), 5. (b), 6. (d)
Fill in the Blanks
- Elements are classified on the basis of ………… in their properties.
- Dobereiner grouped the elements into……………
- Atomic size refers to the ………… of an atom.
- Mendeleev could not assign a correct position to………….. in his table.
- In Modern Periodic Law, the properties of elements are a periodic function of their
6…………. group consisting of rare gases was not known when Mendeleev preparedhis periodic table.
- There are …………. groups in modern periodic table.
- Horizontal rows are known as …….
Ans. 1. similarities, 2. triads, 3. radius, 4. hydrogen, 5. atomic number, 6. Zero,7. 18, 8. periods.
- In the Modern Periodic Table, metallic character decreases from left to right in a period.
- It was assumed by Newland that only 56 elements existed in nature.
- According to Mendeleev’s Periodic Law, the properties of elements are the periodicfunction of their atomic number.
- Non-metals are electropositive.
- In Modern Periodic Table, the atomic size increases down the group.
- Newland found that every eighth element had properties similar to that of first.
Ans. 1. True, 2. True, 3. False, 4. False, 5. True, 6. True.
Match the Columns
Column ‘A’. Column ‘B’
- Helium. (a) Modern Periodic Table
- Mendeleev. (b) Newland
- Law of Octaves. (c) Noble gas
- Silicon. (d) Group 15
- Nitrogen. (e) Metalloid
Ans. 1. → (c), 2. (a), 3. → (b), 4. → (e), 5. → (d).
Answer in one Word/Sentence
- How many elements have been discovered so far?
- X and Y are the two elements having similar properties which obey Newland’s law of octaves. How many elements are in between X and Y ?
- Besides Gallium, which other elements have since been discoveredleft by Mendeleev in his Periodic Table (any two) ?
Ans. Scandium (Sc) and Germanium (Ge).
- On what basis did Mendeleev arrange the elements ?
Ans. Atomic masses. 5. Which is the longest period in Modern Periodic Table?
Ans. Sixth Period.
- Which is the shortest period in the Modern Periodic Table?
Ans. First Period.
Very Short Answer Type Questions
- 1. Write Dobereiner’s Triads Rule.
Ans. Dobereiner’s Triads Rule: Dobereiner arranged the elements of similar properties in the groups of three elements each in ascending order of their atomic masses (weights) these groups are called Dobereiner’s triads. He stated, “If the elements of similar properties are grouped in triads in asscending order. their atomic weights then the atomic weight of middle element will be the mean of atomic weights of the rest two elements.” This is called Dobereiner’s Triads Rule.
- 2. Write the Mendeleev’s Periodic Law.
Ans. Mendeleev’s Periodic Law”The physical and chemical properties of elements are periodic function of their atomic weight (or mass numbers or atomic masses).
- 3. Did Dobereiner’s triads also exist in the columns of Newland’s octaves ?
Ans. Yes, Dobereiner’s triads also exist in the columns of Newland’s octaves. One such column is Li, K, Na..
- 4. What are the limitations of Dobereiner’s classification?
Ans. Limitation of Dobereiner’s classifi was that, all known elements could not be classified into groups of triads on the basis of their properties. He couldthree triads from the elements known at that time.
- 5. Why do you think that the noble gases are placed in a separate group? (2021) Ans. Noble gases are inert elements. Their properties are different from all other elements. Therefore, they are placed in a separate group.
- 6. In the Modern Periodic Table, Calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling Calcium ?
Ans. The element with atomic number 12 has same chemical properties as that of Calcium. This is because both of them have same number of valence electrons, i.e. 2.
- 7. An atom has electronic configuration 2, 8, 7
(a) What is the atomic number of this element ?
(b) To which of the following elements would it be chemically similar ?
N (7), F (9), P (15), Ar (18).
Ans. (a) The atomic number of this element is 17.
(b) It would be chemically similar to F(9) with configuration 2, 7.
- 8. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic fluorine have in common?
Ans.(a) Valency equal to 3.
(b) Valency equal to 1, as number of electrons in outermost shell is 7.
- 9. Which element has
(a) two shells, both of which are completely filled with electrons ?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell ?
(e) twice as many electrons in its second shell as in its first shell?
Ans. (a) Neon Q. 10. Define valency.
(d) Boron Table as
Ans. Valency of an element is its combining capacity with other atoms when it forms chemical compounds or molecules..
- 11. What do you understand by isotopes ?
Ans. Atoms of some elements having same atomic number but different mass number are called isotopes.
- 12. Write the limitations of Newland’s law of octaves.
Ans. Newland’s law of octaves has the following limitations: T
(1) This law was applicable only upto calcium. (2) This law was not applicable on heavy elements.
(3) Newland adjusted some unlike elements under the same slot.orgANISE
Short Answer Type Questions
- 1. What were the criteria used by Mendeleev in creating his periodic table ?
Ans. Mendeleev used atomic mass of the elements as the unique criteria of the classification of elements. He proposed that the chemical properties of elements are the periodic function of their atomic masses. And thus, he arranged the elements in the increasing order of their atomic masses.
- 2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis of your choice?
Ans. Calcium (Ca) and Strontium (Sr) are expected to show chemical reactions similar
to Magnesium (Mg). This is because the number of valence electrons (2) is same in all these
three elements and since chemical properties are due to valence electrons, they show same
- 3. Name
(a) Three elements that have a single electron in their outermost shells
(b) Two elements that have two electrons in their outermost shells.
(c) Three elements with filled outermost shells.
Ans. (a) Lithium (Li), sodium (Na) and potassium (K), have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar) and xenon (Xe) have filled outermost shells.
Q.4. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements? (b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What,
if anything, do their atoms have in common? Ans. (a) Yes, the atoms of all the three elements lithium, sodium and potassium have one electron in their outermost shells.
(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duple! in its K-shell, while neon has an octed in its L-shell.
Q.5. The position of three elements A, B, C in the Periodic Table are shown below
(a) State whether A is a metal or non-metal?
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
Ans. (a) A is a non-metal.
(b) C is less reactive than A, as reactivity decreases down the group in halogens.
(c) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore electrons come closer to the nucleus.
(d) A will form an anion or it accepts an electron to complete its octet.
- 6. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative ? Why?
Ans. Nitrogen (7)-2,5 SEO
Phosphorus (15)-2, 8, 5
Since electronegativity decreases on moving from top to bottom in a group, thus nitrogen will be more electronegative.
- 7. An element ‘X’ has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’.
Ans. Mass Number =No. of neutrons + No. of protons or electrons
35= 18+ No. of protons
No. of protons or electrons = 35-18
Atomic No. of X = 17
Electronic configuration of X = 2, 8, 7
Valency of X = 7
Group No. of X = 17
Period of X 3rd
:: X belongs to 17th Group and 3rd period in Periodic Table.
Long Answer Type / Analytical Questions
- 1. Write the number of periods and groups in the Modern Periodic Table. How does the metallic character of elements vary on moving (i) from left to right in a period and (ii) down a group ? Give reasons to justify your answer.
Ans. The Modern Periodic Table has 18 vertical columns known as groups and 7 horizontal rows known as periods. In the Modern Periodic Table, the metallic character of elements decreases on moving from left to right in a period and increases down a group. This is so because metals tend to lose electrons while forming bonds, that is, they are electropositive in nature. As the effective nuclear charge acting on the valence shell electrons increases along a period, the tendency to lose electrons will decrease. Hence, metallic character, decreases across a period. Down the group, the effective nuclear charge experienced by valence electrons decreases because the outermost electrons are further away from the nucleus. Therefore, these can be lost easily. Hence, metallic character increases down the group.
- 2. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and Modern Periodic Table.
Q3. Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic radius and (c) maximum chemical reactivity? Justify your answer stating the reason for each.
Atomic No. of Na. =11
Atomic No. of Mg. =12
Atomic no. of Al. =13
Electronic configuration of Na=2, 8, 14
Electronic configuration of Mg -2, 8, 2
Electronic configuration of Al = 2,8, 3
(a) Al has the highest valency as the no. of electrons in its outermost shell is 3 which
is greater than that of Na and Mg.
(b) Atomic radius of Na will be the largest because atomic radius decreases while moving from left to right along a period. This is due to the increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom. Na, Mg, and Al belong to the 3rd period in Periodic table.
(c) Chemical reactivity of Na is maximum (Na > Mg > Al) as chemical reactivity decreases in moving from left to right in a period.
- 4. What are the salient features of Modern Periodic Table?
Ans. Salient features of Modern Periodic Table wil (1) In a period of the periodic table, the number of valence electrons increases as atomic number increases. As a result, elements change from metal to metalloid and to non-metal
to noble gas.
(2) Atomic size is a periodic property. As atomic number increases in a period, atomic radius decreases. As atomic number increases in a group, atomic radius increases.
(3) Positive ions in the group increase in size down the group.
(4) In a group, each element has the same number of valence electrons. As a result, the elements in a group show similar chemical behaviour.
(5) Metallic character decreases from left to right in a period because of the increase in the effective nuclear charge.
(6) Non-metallic character increases from left to right in a period because of increase in effective nuclear charge. Non-metallic character decreases down the group because of increase in the size of the atom.