1). Which of the following is correct about the modern periodic law?
i. It is based on atomic size.
ii. It is based on atomic number.
iii. It is based on valence electron.
iv. It is based on atomic mass.
Ans: ii. It is based on atomic number.
2). Which of the following do alkali metals belong to?
i. S-block elements
ii. P-block elements
iii. D-block elements
iv. F-block elements
Ans: i. S-block elements
3). Which of the following is a highly reactive element?
i. Beryllium
ii. Magnesium
iii. Sodium
iv. Aluminium
Ans: iii. Sodium
4). Which one of the given elements is the least reactive?
i. Fluorine
ii. Chlorine
iii. Iodine
iv. Bromine
Ans: iii. Iodine
5). Which are called the d-block elements?
i. Halogens
ii. Representative elements
iii. Transition elements
iv. Alkaline earth metals
Ans: iii. Transition elements
6). How many groups are there in the modern periodic table?
i. 7
ii. 8
iii. 14
iv. 18
Ans: iv. 18
7). Which of the following is the orbital configuration of chlorine?
i. 1s², 2s², 2p6, 3s2, 3p6
ii. 1s2, 2s2, 2p6, 3s2, 3p4
iii. 1s2, 2s2, 2p6, 3s2, 3p5
iv. 1s2, 2s2, 2p6, 3s2, 3p3
Ans: ii. 1s², 2s², 2p⁶, 3s², 3p⁶
8). Which of the following do inert elements belong to?
i. group 4
ii. group 6
iii. Group 18
iv. Group 8
Ans: iii. Group 18
a. Group and Period
| Group | Period |
| A group is a vertical column on the periodic table. | A period is a horizontal row on the periodic table. |
| There are 18 groups in the modern periodic table, numbered from 1 to 18. | The period number indicates the number of electron shells (energy levels) the elements in that row have. |
| Elements in a group may have different numbers of electron shells. | There are 7 periods in the modern periodic table, labeled from 1 to 7. |
b. Short period and Long period
| Short period | Long period |
| A short period in the periodic table refers to a series of elements that fit within a single row horizontally. | A long period, on the other hand, includes elements that span multiple rows or several horizontal rows in the periodic table. |
| In a short period, elements share the same principal energy level for their outermost electrons. | In a long period, as you move across the period from left to right, the outermost electrons are in different principal energy levels, making the period longer. |
| A short period is typically the first two rows, periods 1 and 2, as they can only accommodate a small number of elements due to the limited space available in those rows. | A long period includes periods 3 and beyond, where there is more space for elements to fit in multiple rows. |
c. s-block elements and p-block elements
| s-block elements | p-block elements |
| Found on the left side of the periodic table. | Found on the right side of the periodic table. |
| Have 1 or 2 valence electrons in the s subshell. | Have 3 to 6 valence electrons in the p subshell. |
| Highly reactive and form ionic compounds. | Show diverse chemical properties, including metals, non-metals, and metalloids. |
d. Mendeleev’s periodic table and Modern periodic table
| Mendeleev’s periodic table | Modern periodic table |
| Mendeleev’s based on atomic mass and similar properties with gaps for undiscovered elements. | Modern based on atomic number for accuracy without gaps. |
| Mendeleev predicted missing elements and placed hydrogen with reactive metals. | Modern doesn’t predict and positions hydrogen separately due to its unique behavior. |
| Mendeleev arranged elements by weight and chemical behavior | Modern arranges elements by atomic number for better alignment with properties. |
e. Metals and non-metals
| Metals | Non-metals |
| Metals are usually solid and have a shiny or lustrous appearance. | Non-metals can be solid, liquid, or gas at room temperature and lack a shiny appearance. |
| Metals are good conductors of heat and electricity. | Non-metals are generally poor conductors of heat and electricity. |
| Metals are malleable and ductile. | Non-metals are generally not malleable or ductile. |
10). What is the periodic table?
Ans:The periodic table is like a big chart that shows all the different types of elements.
11). Introduce Mendeleev’s periodic law.
Ans: In mendeleev’s periodic law elements are arranged on based of increasing atomic mass and similar chemical properties, leaving gaps for undiscovered elements.
12). Introduce modern periodic table.
Ans: In modern periodic law elements are arranged on based of increasing atomic number, which is the count of protons in the nucleus, ensuring a more accurate ordering according to properties.
13). Name two alkaline earth metals.
Ans: Two alkaline earth metals are:
1. Beryllium (Be)
2. Magnesium (Mg)
14). Define group and period.
Ans: A group is a vertical column on the periodic table. A period is a horizontal row on the periodic table.
15). What are isotopes?
Ans: Isotopes are versions of an element with the same type of atoms (same atomic number) but different weights (different number of neutrons).
16). What factors do the valencies of elements depend upon?
Ans: Here are the factors on which the valencies of elements depend:
1. Number of Valence Electrons
2. Group Number (or Family) in the Periodic Table
3. Valence Shell Configuration
4. Desire for Stability
17). Which important property did Mendeleev use to classify elements in his periodic table?
Ans: Mendeleev used the atomic mass of elements as the important property to classify them in his periodic table. He arranged elements based on increasing atomic mass, which helped in organizing them into groups with similar properties and predicting the existence and properties of undiscovered elements.
19). In which group, period and block will the element with atomic number 20 be present?
Ans:The element with atomic number 20 will be present in the following:
Group: It will be in Group 2, also known as the alkaline earth metals group.
Period: It will be in Period 4.
Block: It will be in the s-block.
20. Write the atomic number of the element present in the third period and Seventeenth group of the periodic table.
Ans: The atomic number of the element present in the third period and Seventeenth group of the periodic table is 35.
22). Use the periodic table to answer the following questions.
i. Identify an element with six electrons in the outer subshell.
Ans: Oxygen (O), which has 6 electrons in its outer subshell.
ii. Identify an element that would tend to lose one electron.
Ans: Sodium (Na) is likely to lose one electron as it is in Group 1 (alkali metals), and losing one electron would give it a stable configuration.
iii. Identify an element that would tend to gain two electrons.
Ans: Oxygen (O) is likely to gain two electrons to achieve a stable configuration, forming the oxide ion (O2-).
23).The Increasing order of reactivity among group 1 elements is Li <Na <K. Explain.
Ans: The reactivity increases from lithium (Li) to potassium (K) in Group 1 due to the larger atomic size as you move down the group. Lithium has the smallest atomic size and the tightest hold on its outer electron, making it the least reactive. Potassium, with the largest atomic size, can easily lose its outer electron, making it the most reactive in the group. Sodium falls in between in terms of reactivity.
24). Write the general outer electronic configuration of s-, p-, d- and f-block elements.
Ans:
| Element | General outer electronic configuration |
| s–block | ns1–2, where n = 2 – 7 |
| p–block | ns2np1–6, where n = 2 – 6 |
| d–block | (n–1) d1–10 ns0–2, where n = 4 – 7 |
| f–block | (n–2)f1–14(n–1)d0–10ns2, where n = 6 – 7 |
25). What are the merits of Mendeleev’s periodic table?
Ans: The merits of Mendeleev’s periodic table are:
1. Predicting Undiscovered Elements
2. Pattern Identification
3. Organization and Classification
4. Facilitating Further Research
26). What are the features of the modern periodic table?
Ans: The features of the modern periodic table are:
1. Elements are ordered by atomic number for accurate arrangement.
2. Elements are organized in periods (rows) and groups (columns) based on similar properties.
3. Elements are grouped into blocks (s, p, d, f) according to their last electron’s subshell.
4. Electronic configurations are presented for each element.
27). How is the modern periodic table superior to Mendeleev’s table?
Ans: The modern periodic table is superior to Mendeleev’s table because:
Accurate Atomic Ordering:
The modern table arranges elements by atomic number, ensuring precise ordering, unlike Mendeleev’s reliance on atomic mass.
Enhanced Predictive Ability:
With atomic number-based arrangement, the modern table predicts element properties more accurately compared to Mendeleev’s method.
Consistent Group Characteristics:
Groups in the modern table exhibit consistent properties due to the atomic number-based arrangement, addressing variations present in Mendeleev’s table.
Incorporation of Subshell Structure:
The modern table incorporates subshell structure (s, p, d, f blocks), providing deeper insights into electron configurations and element behaviors.
28). Why are Li, Na and K placed in the same group of the periodic table?
Ans: Li (Lithium), Na (Sodium), and K (Potassium) are placed in the same group of the periodic table because they share similar outermost electron configurations. They all have one valence electron in their outermost shell, specifically in the “s” sublevel. This similarity in electronic configuration leads to comparable chemical properties and reactivity, hence grouping them together in the same group.
29).What do you mean by p-block elements? Write any five examples of this block.
Ans: P-block elements are a group of elements in the periodic table characterized by the filling of electrons in the p orbitals of their outermost energy level.
Here are five examples of p-block elements:
1. Oxygen (O)
2. Oxygen (C)
3. Silicon (Si)
4. Chlorine (Cl)
5. Neon (Ne)
30. Name:
i. Three elements that have a single electron in their valence shell
Ans:
- Hydrogen (H)
- Lithium (Li)
- Sodium (Na)
ii. Two elements that have seven electrons in their valence shell
Ans:
- Fluorine (F)
- Chlorine (Cl)
iii. Three elements with filled valence shell
Ans:
- Helium (He)
- Neon (Ne)
- Argon (Ar)
31. Argon is an inert gas.
Ans: Argon is an inert gas because its electron arrangement in the outermost shell is stable and doesn’t easily react with other elements
32. The valency of nitrogen is 3.
Ans: The valency of nitrogen is 3 because it needs to gain three electrons to complete its outermost energy level. Nitrogen has five electrons in its outermost shell, but to achieve stability like the noble gas neon, it seeks to gain three more electrons.
33. Chlorine is an active non-metal.
Ans: Chlorine is an active non-metal because it easily gains one electron to complete its outermost energy level. It has seven electrons in its outer shell, making it highly reactive.
34). Fluorine is more reactive than chlorine.
Ans: Fluorine is more reactive than chlorine because fluorine has a smaller atomic size and a stronger pull on electrons due to its higher electronegativity.
35). Sodium is less reactive than potassium.
Ans: Sodium is less reactive than potassium because sodium has a larger atomic size compared to potassium.
36). The members of group IA are called alkali metals.
Ans: The members of Group IA are called alkali metals because when they react with water, they form alkaline solutions.
37). Group I elements are very active.
Ans: Group I elements are very active because they have only one electron in their outermost energy level.
38). Lanthanides and actinides are kept separately in the modern periodic table.
Ans: Lanthanides and actinides are kept separately in the modern periodic table because they are a distinct group of elements with unique properties and behaviors.
39). Transition elements have variable valency.
Ans: Transition elements have variable valency because they have electrons in both their outermost and the second-to-last energy level.
40). Halogens are active non-metals.
Ans:Halogens are active non-metals because they readily gain one electron to achieve a stable configuration in their outermost energy level.
41). The elements in the same group have similar physical and chemical properties.
Ans: The elements in the same group have similar physical and chemical properties because they have the same number of electrons in their outermost energy level.
