The Periodic Table - Questions & Answers

1. State the number of elements in - Period 1, Period 2, and Period 3 of the Periodic Table.
Period 1 has 2 elements, Period 2 has 8 elements, and Period 3 has 8 elements.

2. Name the elements in - Period 1.
Hydrogen (H) and Helium (He).

1. State the common feature - of the electronic configuration of the elements at the end of Period 2 & Period 3.
The common feature is that they both have completely filled outermost electron shells (a stable octet of 8 electrons).

2. Supply the missing word - from those in brackets: If an element has one electron in its outermost energy level [shell] then it is likely to be ________________ [metallic/non-metallic].
metallic

3. Copy and complete the following sentences choosing the correct word or words from those given in brackets at the end of each sentence :- The similarities in the properties of a group of elements is because they have the same ________________ (electronic configurations, number of outer electrons, atomic numbers.)
The similarities in the properties of a group of elements is because they have the same number of outer electrons.

4. What is meant by - a Group in the Periodic Table.
A Group is one of the eighteen vertical columns in the periodic table, consisting of elements with similar outer electronic configurations and the same number of valence electrons.

5. If an element - is in Group 17 [Group 7A] is it likely to be metallic or non-metallic. Give reasons
It is likely to be non-metallic. Elements in Group 17 have seven valence electrons, making them highly electronegative electron acceptors, which is a characteristic property of non-metals.

1. Name or state the following - with reference to the elements of the first three periods of the periodic table.
(a) The noble gas having duplet arrangement of electrons.
Helium (He)
(b) The noble gas having an electronic configuration 2, 8, 8.
Argon (Ar)
(c) A metalloid in period 2 and in period 3.
Boron (B) in period 2 and Silicon (Si) in period 3
(d) The number of electron shells in elements of period 1, period 2 and period 3.
Period 1 has 1 shell; Period 2 has 2 shells; Period 3 has 3 shells
(e) The valency of elements in group 1 [IA].
1
(f) The group whose elements have zero valency.
Group 18 (Noble Gases)
(g) An alkaline earth metal in period 3.
Magnesium (Mg)
(h) The non-metallic element present in period 3 other than sulphur and chlorine.
Phosphorus (P)
(i) A non-metal in period 2 having electronic configuration 2, 6.
Oxygen (O)
(j) An electrovalent compound formed between an alkali metal and a halogen.
Sodium chloride (NaCl)
(k) A covalent compound formed between an element in period 1 and a halogen.
Hydrogen chloride (HCl)
(l) An alkali metal in period 3 which dissolves in water giving a strong alkali.
Sodium (Na)
(m) A metal in period 3 having valency 3.
Aluminium (Al)
(n) The bridge elements of period 3 of group 1 [IA], 2 [IIA] and 13 [IIIA].
Magnesium (Mg), Aluminium (Al), and Silicon (Si)
(o) The periods which contain the inner transition elements.
Period 6 and Period 7
(p) The formula of the hydroxide of the element having electronic configuration 2, 8, 2
Mg(OH)2
(q) The valency of the element in period 3 having atomic number 17.
1 (The element is Chlorine)
(r) A non-metal in period 2 which is tetravalent
Carbon (C)

1. Give a reason why - elements need to be properly classified.
Elements need to be properly classified to make their study simpler and systematic by putting together elements with maximum resemblances and separating the others.

2. State why - the basis of classification by early chemists was discarded for future classification of elements.
It was discarded because elements behave as both metals and non-metals, show dual nature, and have variable valencies, making properties and valencies an inconsistent basis for classification.

3. State what - was Dobereiner's basis of classification of elements. State Dobereiner's Law - of Triads with suitable examples.
His basis of classification was the increasing order of atomic weights. Dobereiner's Law of Triads states that chemically analogous elements arranged in increasing order of their atomic weights form well-marked groups of three called 'triads', in which the atomic weight of the middle element is generally the average arithmetic mean of the atomic weights of the other two. Example: Lithium (7.0), Sodium (23.0), Potassium (39.0).

4. Give a reason why - Dobereiner's method of classification did not hold much weightage for future classification.
It did not hold much weightage because it resulted in a disordered collection of elements, the rule did not hold true for all elements, and the properties of some elements grouped in triads were found not to be similar.

5. State the basis - of classification proposed by Newland. State Newland's Law of Octaves with a suitable example.
Newland's basis of classification was arranging elements in series of eight in increasing order of their atomic weights. His Law of Octaves states that elements arranged in increasing order of atomic weights show resemblance in physical and chemical properties between the eighth element and the first element. Example: The eighth element from Lithium (Li) is Sodium (Na), which shows similarity in properties.

6. In which way - was Newland's Law of Octaves comparable to a musical note.
Just as the eighth note on a musical scale is a repetition of the first note, in Newland's arrangement, every eighth element showed a repetition of the physical and chemical properties of the first element.

7. State how - Mendeleeff arranged the elements in the periodic table. What was the basis of his classification.
Mendeleeff arranged elements in horizontal rows called 'periods' and vertical columns called 'groups'. The basis of his classification was the increasing order of their atomic weights.

8. State Mendeleeff's Periodic Law. How did Mendeleeff's arrangement - of elements correlate with periodicity of properties of elements.
Mendeleeff's Periodic Law states: "The physical and chemical properties of elements are periodic functions of their atomic weights." By arranging elements in increasing order of atomic weights, he observed that elements with similar properties appeared at regular intervals, which correlated perfectly with the concept of periodicity.

9. State the contributions - made by Mendeleeff towards the periodic table.
He methodically grouped elements, left gaps for undiscovered elements while predicting their existence and properties correctly (e.g., eka-boron, eka-aluminium), and corrected the incorrect atomic weights of certain arranged elements using the atomic weights of adjacent elements.

10. State - the defects & anomalies in Mendeleeff's Periodic Table and how are they resolved by Moseley.
Defects included anomalous pairs (elements with higher atomic weights placed before lower ones, like Cobalt before Nickel) and no justifiable positions for rare earths, actinides, and isotopes based on atomic weights. Moseley resolved these by changing the fundamental basis of classification from atomic weights to atomic numbers.

11. How were elements - arranged in the long form of the periodic table or the Modern Periodic Table. State the Modern Periodic Law - and compare it with Mendeleeff's Periodic Law.
Elements are arranged in increasing order of their atomic numbers in seven horizontal rows (periods) and eighteen vertical columns (groups). The Modern Periodic Law states: "The physical and chemical properties of elements are periodic functions of their atomic numbers." This compares to Mendeleeff's Law, which was based on atomic weights rather than atomic numbers.

12. State what are - periods in a periodic table. What is 'period number'. What does it signify.
Periods are the seven horizontal rows of elements arranged in increasing order of atomic numbers. The 'period number' (1 to 7) signifies the total number of electron shells an element possesses.

13. Name the period - which is the shortest period and state the number of elements present in it.
Period 1 is the shortest period. It contains 2 elements.

14. Name the elements - in the correct order of their increasing atomic numbers present in the first, second and third short periods of the periodic table.
First period: Hydrogen, Helium. Second period: Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon. Third period: Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Chlorine, Argon.

State which - of the elements are - a] metallic b] non-metallic c] noble gases in each of the periods 2 & 3.
Period 2: a] Metallic: Li, Be. b] Non-metallic: B, C, N, O, F. c] Noble gases: Ne.
Period 3: a] Metallic: Na, Mg, Al. b] Non-metallic: Si, P, S, Cl. c] Noble gases: Ar.

15. State the property trends - in general of elements on moving from left to right in a period of the periodic table.
On moving from left to right, the number of electron shells remains the same, valence electrons increase progressively by one, electronegativity increases, and there is a transition from metallic character to non-metallic character.

16. State what are - i] groups in a periodic table. ii] property trends - in general of elements on moving down in a group of the periodic table. iii] the characteristics - which remain similar on moving down in a group of the periodic table.
i] Groups are the eighteen vertical columns in the periodic table. ii] Property trends moving down: the number of electron shells increases by one at each step, metallic character increases, and electronegativity decreases. iii] Characteristics that remain similar: the number of valence electrons remains the same, resulting in the same valency and similar chemical properties.

17. Write short notes on the following types of elements -
(a) alkali metals (b) alkaline earth metals (c) halogens (d) noble gases (e) transition and inner transition elements (f) normal elements.
(a) Alkali metals (Group 1): Light, highly reactive electropositive metals with one valence electron that form strong alkalis.
(b) Alkaline earth metals (Group 2): Light metals with two valence electrons, similar to alkali metals but slightly less reactive.
(c) Halogens (Group 17): Highly reactive, electronegative non-metals with seven valence electrons that act as salt producers and strong oxidizing agents.
(d) Noble gases (Group 18): Unreactive, inert, monoatomic gases with stable, fully filled outermost electron shells.
(e) Transition and inner transition elements: Transition elements are heavy metals placed in the center of the table (Groups 3-12). Inner transition elements include Lanthanides and Actinides, placed at the bottom in two horizontal rows, and are highly reactive metals.
(f) Normal elements: Elements of Groups 1, 2, 13-17 whose atoms have all inner shells complete but the outermost shell is incomplete. They consist of metals, metalloids, and non-metals.

1. The element which is univalent & a strong reducing agent, present in the same period as the element having two electron shells with eight electrons in valence shell.
(a) F (b) Li (c) Na (d) Cl
(b) Li

2. A solid univalent element which is a strong oxidising agent & present in the group 'X' which means - salt producer.
(a) F (b) I (c) Si (d) B
(b) I

3. Assertion (A): Valency or combining capacity of noble gas is - zero.
Reason (R): Noble gases are monoatomic gases.
(a) Both A & R are true - and R is the correct explanation of A. (b) Both A & R are true - but R is not the correct explanation of A. (c) A is true - but R is false (d) A is false - but R is true.
(b) Both A & R are true - but R is not the correct explanation of A.

4. Select the incorrect statement.
(a) A defect in Mendeleeff's periodic table was the position of hydrogen - isotopes had to be placed in the same position according to - atomic numbers.
(b) Aluminium is a weak post transition element.
(c) Chlorine is more electronegative than fluorine, but less electronegative than bromine.
(d) Elements in period-2 have two electron shells & in group 2 - have two valence electrons.
(c) Chlorine is more electronegative than fluorine, but less electronegative than bromine.

5.

1. State the non-metallic element in the period having the metalloid with three valence electrons - which is diatomic & unreactive at ordinary temperatures.
Nitrogen (N2)

2. State the most electronegative element - from the elements chlorine, bromine & iodine in group 17 [VIIA] and the least non-metallic element from carbon, oxygen & fluorine in period 2.
Most electronegative: Chlorine (Cl). Least non-metallic: Carbon (C).

Q.1 Select the correct answer from the words in bracket.
1. He arranged elements in increasing order of atomic numbers. [Dobereiner/Moseley/Mendeleeff]
Moseley
2. Is a metal in period 2 having electronic configuration 2,1. [Beryllium/Lithium/Sodium]
Lithium
3. Is a period having elements from atomic no. 11 to 18. [period - 1/2/3]
period - 3
4. The most reactive halogen from group 17. [chlorine/fluorine/bromine]
fluorine
5. Is the group number of the element whose atomic number is 4. [ group - 1/group - 2/group - 18].
group - 2

Q.2 Fill in the blanks from the words A to F given below.
A: Decreases B: Increases C: Remains same D: Increases by one E: Electropositive F: Electronegative
1. Across a period from left to right in the Modern Periodic Table.
No. of electron shells ________________; No. of valence electrons ________________; Electronegativity ________________. Character of elements changes from ________________ to ________________.
No. of electron shells Remains same; No. of valence electrons Increases by one; Electronegativity Increases. Character of elements changes from Electropositive to Electronegative.

2. Down a group in the Modern Periodic Table.
No. of electron shells ________________; No. of valence electrons ________________; Electronegativity ________________. Character of elements changes from ________________ to ________________.
No. of electron shells Increases by one; No. of valence electrons Remains same; Electronegativity Decreases. Character of elements changes from Electronegative to Electropositive.

Q.3 Give reasons for the following.
1. Mendeleeff's contributions to the periodic table, laid the foundation for the Modern Periodic Table.
He was the first to systematically group elements into periods and groups based on similarities in their properties, leaving strategic gaps for undiscovered elements, which became the structural blueprint for the Modern Periodic Table.

2. Properties of elements are periodic functions of their atomic numbers and not atomic weights.
Atomic number defines the fundamental electronic configuration of an atom. Periodicity in properties results from a recurrence of similar valence electron configurations at regular intervals, which depends strictly on atomic numbers.

3. A transition from metallic to non-metallic elements is seen on moving from left to right in a period of the periodic table.
As one moves across a period, valence electrons increase, increasing the atom's electronegativity and its tendency to accept electrons, thereby transitioning its chemical character from metallic to non-metallic.

4. Noble gases do not form compounds readily.
Noble gases have entirely stable electronic configurations with completely filled outermost shells, possessing zero valency, meaning they do not need to lose, gain, or share electrons.

5. Group 1 [IA] elements are called alkali metals.
They readily react with water to form highly soluble and strong alkalis.

Q.4 State the following.
1. The group to which the element with electronic configuration of 2, 8, 2 belongs.
Group 2
2. The group from the groups 1 [IA], 2 [IIA], 16 [VIA] and 17 [VIIA] whose elements are most electronegative.
Group 17 [VIIA]
3. The group which contains highly electropositive metals including sodium.
Group 1 [IA]
4. The group whose elements are unreactive or inert.
Group 18
5. The group which contains highly reactive electronegative non-metals including chlorine.
Group 17 [VIIA]

Q.5 Match the elements of List-I with their type from List-II.
List-I
1. Highly reactive, univalent metals.
2. Highly reactive, univalent non-metals
3. Unreactive, inert elements
4. Elements of group 3 to 12 [IB to VIIB & VIII]
5. Radioactive elements
List-II
A: Halogens
B: Transition elements
C: Alkali metals
D: Lanthanide series
E: Noble gases
F: Actinide series
1 - C, 2 - A, 3 - E, 4 - B, 5 - F

Q.6 Complete the table pertaining to the following elements given in Column I.