Explore the periodic table and periodicity with this SLO-based solved exercise for 9th class students. Aligned with the new 2025 syllabus, ideal for Lahore Board and all Punjab Boards.
Multiple choice questions
1. In which period and group will you place the element which is an important part of the solar cell?
Options:
(a) Third period and fourth group
(b) Second period and fourth group
(c) Third period and sixth group
(d) Third period and fifth group
Correct Answer: (c) Third period and sixth group
Explanation: The element used in solar cells is silicon, which is in the third period and sixth group of the periodic table.
2. Identify the electronic configuration of the outermost shell of a transition metal.
Options:
(a) ns²np⁴
(b) nd⁵ns²
(c) ns⁴np²
(d) ns³np³
Correct Answer: (b) nd⁵ns²
Explanation: Transition metals typically have electrons in the (n-1)d and ns orbitals, such as nd⁵ns² for a partially filled d-subshell.
3. Which is the softest metal?
Options:
(a) Na
(b) Ca
(c) Al
(d) Zn
Correct Answer: (a) Na
Explanation: Sodium (Na) is an alkali metal, and its softness is due to its relatively large atomic size and weak metallic bonds.
4. A yellow solid element exists in allotropic forms, which is also present in fossil fuel. Name the element.
Options:
(a) Carbon
(b) Iodine
(c) Aluminium
(d) Sulphur
Correct Answer: (d) Sulphur
Explanation: Sulphur is a yellow solid, has various allotropes, and is found in fossil fuels like coal.
5. How many electrons can nitrogen accept in its outermost shell?
Options:
(a) 2
(b) 3
(c) 4
(d) 5
Correct Answer: (b) 3
Explanation: Nitrogen has 5 electrons in its outer shell and needs 3 more to complete its octet.
6. Which element is the most reactive element?
Options:
(a) Oxygen
(b) Chlorine
(c) Fluorine
(d) Nitrogen
Correct Answer: (c) Fluorine
Explanation: Fluorine is the most reactive due to its high electronegativity and small atomic size.
7. Which element has the highest melting point?
Options:
(a) Na
(b) Ca
(c) Rb
(d) Cs
Correct Answer: (b) Ca
Explanation: Calcium has stronger metallic bonds compared to other alkali or alkaline earth metals listed.
8. In what order does the metallic character change in the second group?
Options:
(a) Mg > Ca > Ba > Sr
(b) Sr > Ba > Ca > Mg
(c) Mg > Sr > Ba > Ca
(d) Ba > Sr > Mg > Ca
Correct Answer: (d) Ba > Sr > Mg > Ca
Explanation: Metallic character increases down the group in the periodic table.
9. Which of the following best describes the correct order of oxygen, fluorine, and nitrogen’s atomic radii?
Options:
(a) O < F < N
(b) N < F < O
(c) F < O < N
(d) O < N < F
Correct Answer: (c) F < O < N
Explanation: Atomic radius decreases across a period. Nitrogen > Oxygen > Fluorine.
10. Which of the following elements has d-electrons filled completely?
Options:
(a) Zn
(b) Ca
(c) Al
(d) Fe
Correct Answer: (a) Zn
Explanation: Zinc has a completely filled d-subshell (3d¹⁰).
Q2 Short Questions
i. Why was atomic number chosen to arrange the elements in the periodic table?
Answer: Atomic number represents the number of protons in an atom, which determines its identity and chemical properties. Arranging elements by atomic number ensures that elements with similar properties are grouped together systematically.
ii. What is the significance of the word “periodic”?
Answer: The word “periodic” signifies the repeating pattern of chemical properties of elements when they are arranged in order of increasing atomic number.
iii. Why does the size of a period increase as we move down the periodic table?
Answer: As we move down the periodic table, new electron shells are added, increasing the distance between the outermost electrons and the nucleus, which results in a larger atomic size.
iv. In a group, the elements have the same number of electrons in the outermost shell. Why is it so?
Answer: Elements in the same group have the same number of valence electrons because they share the same electron configuration in their outermost shell. This gives them similar chemical properties.
v. Do you expect calcium to be more reactive than sodium? Give the reason for your answer.
Answer: No, sodium is more reactive than calcium. Sodium is an alkali metal in Group 1, and it loses its single valence electron more easily than calcium, which belongs to Group 2 and has two valence electrons to lose.
vi. Which element has the maximum atomic radius and which element has the minimum atomic radius in the third period?
Answer: In the third period, sodium (Na) has the maximum atomic radius, and chlorine (Cl) has the minimum atomic radius because atomic size decreases across a period due to increasing nuclear charge.
vii. Why are the most electronegative elements present in the sixth and seventh groups?
Answer: Groups 6 and 7 contain nonmetals like oxygen, sulfur, fluorine, and chlorine, which have a strong tendency to attract electrons to complete their octet. This high attraction makes them highly electronegative.
viii. The first ionization energy value of magnesium is less than the second one. Give reason.
Answer: The first ionization energy removes one valence electron, which is loosely held. The second ionization energy requires removing an electron from a stable, fully filled orbital, requiring significantly more energy.
ix. Is it possible for two metals or two non-metals to form an ionic bond?
Answer: No, ionic bonds are typically formed between a metal and a non-metal due to the transfer of electrons. Two metals or two non-metals cannot easily transfer electrons in this way.
x. Which element has the least value of ionization energy and which element has the highest value of electronegativity?
Answer:
- Least ionization energy: Cesium (Cs), as it is a large alkali metal with loosely held valence electrons.
- Highest electronegativity: Fluorine (F), due to its small size and high nuclear charge, which strongly attracts electrons.
Constructed Response Questions
i. Suppose a new element is discovered. Where would you like to accommodate this element in the periodic table?
Answer: To place a new element in the periodic table, we must first determine its atomic number and electronic configuration. These will help identify the group and period it belongs to. For example:
- Group: The number of valence electrons will indicate the group.
- Period: The number of electron shells will determine the period.
By knowing these properties, the new element can be placed in the correct position in the periodic table to match its chemical and physical properties with similar elements.
ii. What is the first element of the periodic table? Will it lose or gain an electron?
Answer: The first element of the periodic table is hydrogen. It has one electron in its outer shell and can lose this electron to form H⁺ (like metals) or gain one electron to form H⁻ (like non-metals), depending on the chemical environment.
iii. Atomic radii of boron and aluminum are 88 pm and 125 pm, respectively. Which element is expected to lose electrons more easily?
Answer: Aluminum is expected to lose electrons more easily because it has a larger atomic radius (125 pm). The larger the atomic radius, the weaker the attraction between the nucleus and the outer electrons, making it easier to lose electrons.
iv. How would you find the atomic radius of an atom?
Answer: The atomic radius is measured as half the distance between the nuclei of two identical atoms that are bonded together. Scientists use techniques like X-ray diffraction or spectroscopy to measure this distance accurately.
v. Why is it not possible for an oxygen atom to accept three electrons to form O³⁻, unlike nitrogen which can accept electrons to form N³⁻?
Answer: Oxygen has 6 valence electrons, so accepting three electrons would result in 9 electrons in the outer shell, exceeding the stable octet rule. This would create too much electron-electron repulsion, making O³⁻ unstable. Nitrogen, with 5 valence electrons, can accept 3 electrons to form a stable N³⁻ ion.
Descriptive Questions
i. Which information is needed to locate elements in the periodic table if you do not know its atomic number? Is atomic mass helpful for this purpose?
Answer:
To locate an element:
- Atomic Number: This is the most accurate way to locate an element, as it directly determines its position.
- Atomic Mass: It can provide a clue, but it is not always reliable because elements with similar masses may belong to different groups (e.g., isotopes).
In summary, atomic number is more helpful than atomic mass for identifying an element’s position.
ii. How many blocks of elements are present in the periodic table? Are these blocks helpful in studying the properties of elements?
Answer:
There are four blocks in the periodic table: s-block, p-block, d-block, and f-block. These blocks are very helpful because they group elements based on their valence electron configuration, which determines chemical properties. For example:
- s-block elements are highly reactive metals.
- p-block contains both metals and non-metals.
- d-block elements are transition metals with variable oxidation states.
- f-block elements include lanthanides and actinides.
iii. Explain the variation in the following properties in the periods giving reasons:
(a) Atomic Radius:
- Atomic radius decreases across a period because of increasing nuclear charge, which pulls the electrons closer to the nucleus.
(b) Ionization Energy:
- Ionization energy increases across a period because the electrons are held more tightly due to increasing nuclear charge, requiring more energy to remove them.
iv. Which physical properties of elements may lead us to know what type of bond it will form?
Answer:
Physical properties like ionization energy, electronegativity, and atomic radius help predict bond type:
- Elements with low ionization energy and large atomic radius form ionic bonds.
- Elements with high electronegativity form covalent bonds.
v. Write down the names of four non-metals which exist in solid state at normal temperature.
Answer:
- Carbon
- Sulfur
- Phosphorus
- Iodine
vi. Why do second and third periods have equal numbers of elements while all other periods contain different numbers?
Answer:
The second and third periods have 8 elements each because their outermost electron shell can hold a maximum of 8 electrons. In contrast, higher periods (4th and beyond) involve d and f orbitals, which allow for more elements.
Investigative Questions
i. Why is the periodic table considered a remarkable achievement?
Answer:
The periodic table organizes elements systematically based on their properties and atomic number. Its benefits include:
- Predicting chemical behavior of elements.
- Identifying trends in properties like atomic radius, electronegativity, etc.
- Helping discover new elements by identifying gaps in the table.
ii. Why do lithium and beryllium behave differently from other alkali and alkaline earth metals?
Answer:
Lithium and beryllium have smaller atomic sizes and higher ionization energies compared to other elements in their groups. For example:
- Lithium forms a strong bond with water, unlike sodium.
- Beryllium shows covalent bonding, unlike other alkaline earth metals that form ionic bonds.
iii. How is the modern periodic table different from Mendeleev’s periodic table?
Answer:
- Mendeleev’s Table: Organized by atomic mass, had gaps for undiscovered elements, and grouped some elements with different properties.
- Modern Table: Organized by atomic number, includes all discovered elements, and uses a clear block structure (s, p, d, f).
