Q1: What is the basis for arranging elements in the modern periodic table? (a) Increasing order of atomic mass (b) Increasing order of atomic number (c) Decreasing order of atomic mass (d) Decreasing order of atomic number
Solution:
Ans: (b) Explanation: The modern periodic table arranges elements according to their increasing atomic number, which is based on the modern periodic law stating properties are periodic functions of atomic numbers.
Q2: How many elements are present in the longest period of the periodic table? (a) 2 elements (b) 8 elements (c) 18 elements (d) 32 elements
Solution:
Ans: (d) Explanation: The sixth period is the longest period in the periodic table and consists of 32 elements, whilst other periods contain fewer elements like 2, 8 or 18.
Q3: What determines the group number of an element in the periodic table? (a) Number of protons in the nucleus (b) Number of neutrons in the nucleus (c) Number of electrons in the outermost shell (d) Total number of shells in the atom
Solution:
Ans: (c) Explanation: A group in the periodic table is determined by the number of electrons present in the outermost shell, which influences the chemical properties and reactivity of elements.
Q4: According to Dobereiner's Law of Triads, what relationship exists between the atomic masses of elements in a triad? (a) The lightest element has half the mass of the heaviest (b) The middle element's mass is the arithmetic mean of the other two (c) All three elements have equal atomic masses (d) The masses are in geometric progression
Solution:
Ans: (b) Explanation: Dobereiner noted that the atomic mass of the middle element in a triad is the arithmetic mean of the other two elements with similar chemical properties.
Q5: Which property describes the energy required to remove an electron from a neutral gaseous atom? (a) Electron affinity (b) Electronegativity (c) Ionisation energy (d) Atomic radius
Solution:
Ans: (c) Explanation: Ionisation energy is defined as the energy required to remove an electron from a neutral isolated gaseous atom and convert it into a positively charged gaseous ion.
Fill in the Blanks
Q1: The vertical columns in the periodic table are called _____.
Solution:
Ans: groups
Q2: The atomic number of an element is equal to the number of _____ in the nucleus.
Solution:
Ans: protons
Q3: Elements in groups 3 to 12 are called _____ elements.
Solution:
Ans: transition
Q4: The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is called _____.
Solution:
Ans: electronegativity
Q5: Newlands arranged elements in increasing order of atomic mass and noticed that every _____ element had similar properties.
Solution:
Ans: eighth
True or False
Q1: The first period of the periodic table consists of 8 elements.
Solution:
Ans: False Explanation: The first period consists of only 2 elements and is called the shortest period in the periodic table.
Q2: The mass number of an element is the sum of protons and neutrons in the nucleus.
Solution:
Ans: True Explanation: The mass number is defined as the sum of the number of protons and neutrons in the nucleus of an atom.
Q3: On moving down a group, the valency of elements changes continuously.
Solution:
Ans: False Explanation: On moving down a group, the valence electrons and valency of all elements in that group remain the same throughout.
Q4: Noble gases are placed in Group 18 at the extreme right of the periodic table.
Solution:
Ans: True Explanation: Group 18 at the extreme right contains noble or inert gases, which are chemically unreactive due to complete outer shells.
Q5: Mendeleev arranged elements in order of their increasing atomic numbers.
Solution:
Ans: False Explanation: Mendeleev arranged elements in increasing order of their atomic masses, not atomic numbers, as the modern periodic law was developed later.
Match the Following
Column A
Column B
1. Dobereiner's classification
A. Periodic function of atomic number
2. Newlands' Law
B. 18 elements each
3. Modern Periodic Law
C. Groups of three elements
4. Fourth and fifth periods
D. Distance from nucleus to outermost shell
5. Atomic size
E. Law of Octaves
Solution:
Ans:
1 - C: Dobereiner classified elements with similar chemical properties into groups of three called triads based on atomic mass relationships.
2 - E: Newlands noticed that every eighth element had similar properties when arranged by increasing atomic mass, like musical octaves.
3 - A: The modern periodic law states that physical and chemical properties of elements are periodic functions of their atomic numbers.
4 - B: The fourth and fifth periods are called long periods because they contain 18 elements each in the periodic table.
5 - D: Atomic size or atomic radii is defined as the distance between the centre of the nucleus and the outermost shell.
Short Answer Questions
Q1: What is valency and how does it vary across a period in the periodic table?
Solution:
Ans: Valency denotes the combining capacity of the atom of an element. It is equal to the number of electrons an atom can donate, accept or share. On moving from left to right in a period, the number of valence electrons increases from 1 to 8. Some elements like copper, iron, silver and gold lose electrons in steps and hence show variable valency.
Q2: State Mendeleev's Periodic Law and explain its basis for classification.
Solution:
Ans: Mendeleev stated the law of chemical periodicity in 1869. The physical and chemical properties of elements are a periodic function of their atomic masses. When elements are arranged in increasing order of their atomic masses, elements with similar properties are repeated after certain regular intervals. This is called Mendeleev's Periodic Law and it formed the basis for his periodic table classification.
Q3: Distinguish between metallic character and non-metallic character of elements.
Solution:
Ans: Metallic character refers to elements which have a tendency to lose their valence electrons and form positive ions, such as sodium losing an electron to form sodium ion. Non-metallic character refers to elements which have a tendency to gain electrons in order to attain an octet in their outermost orbit. In metals, greater tendency to lose electrons means greater reactivity, whilst in non-metals, greater tendency to gain electrons means greater reactivity.
Q4: What is electron affinity and how is it different from ionisation energy?
Solution:
Ans: Electron affinity or electron gain enthalpy is the amount of energy released while converting a neutral gaseous isolated atom into a negatively charged gaseous ion by the addition of electrons. Ionisation energy is the energy required to remove an electron from a neutral isolated gaseous atom and convert it into a positively charged gaseous ion. Electron affinity involves energy release whilst ionisation energy involves energy requirement.
Q5: Describe the structure and organisation of the modern periodic table in terms of periods and groups.
Solution:
Ans: The modern periodic table has seven horizontal rows called periods and eighteen vertical columns called groups. The first period has 2 elements, second and third have 8 elements each, fourth and fifth have 18 elements each, sixth has 32 elements, and seventh is incomplete. Groups are arranged from left to right as IA, IIA, IIIB to VIIB, VIII, IB, IIB, IIIA to VIIA and Zero group containing noble gases.
Long Answer Questions
Q1: Analyse the development of periodic classification from Dobereiner to the modern periodic table. Compare the basis of classification used by different scientists and justify why the modern periodic law is considered superior.
Solution:
Ans: The periodic classification evolved through several stages. Dobereiner grouped elements into triads based on atomic mass relationships. Newlands proposed the Law of Octaves where every eighth element showed similar properties. Lother Meyer classified elements based on atomic volume as a periodic function. Mendeleev arranged elements by increasing atomic mass and noted periodic repetition of properties. However, Mendeleev's table had anomalies like isotope positions and anomalous pairs. The modern periodic law, based on atomic number instead of atomic mass, resolved these issues. Atomic number is unique for each element and directly relates to electronic configuration, making it the most logical basis for classification and explaining periodicity accurately.
Q2: Evaluate how chemical reactivity varies across periods and down groups for both metals and non-metals. Analyse the underlying reasons for these variations in terms of atomic structure.
Solution:
Ans: Chemical reactivity depends on the tendency to lose or gain electrons. In metals, greater tendency to lose electrons means greater reactivity. Across a period from left to right, metallic character decreases as valence electrons increase, making electron loss harder. Down a group, metallic reactivity increases as atomic size increases and outermost electrons are farther from nucleus, making them easier to lose. For non-metals, greater tendency to gain electrons means greater reactivity. Across a period, non-metallic character increases as atoms need fewer electrons to complete their octet. Down a group, non-metallic reactivity decreases as atomic size increases, making it harder to attract additional electrons to the larger atom.
Q3: Compare and contrast the various periodic properties, including atomic size, ionisation energy, electron affinity and electronegativity. Justify how these properties show periodicity and their practical significance in understanding chemical behaviour.
Solution:
Ans: Atomic size is the distance from nucleus to outermost shell and increases down a group whilst decreasing across a period. Ionisation energy is energy required to remove an electron and shows opposite trends to atomic size. Electron affinity is energy released when gaining an electron and generally increases across periods. Electronegativity is the tendency to attract shared electrons in molecules and also increases across periods whilst decreasing down groups. These properties are interconnected through atomic structure and electron configuration. Periodicity occurs because valence electrons increase across periods whilst shells increase down groups. Understanding these properties helps predict chemical bonding, reactivity patterns, compound formation and behaviour of elements in chemical reactions, making them fundamental to chemistry.
The document Worksheet with Solutions: Periodic Table - Periodic Properties and Variations of Properties is a part of the Class 10 Course Chemistry Class 10 ICSE.
FAQs on Worksheet with Solutions: Periodic Table - Periodic Properties and Variations of Properties
1. What are the main periodic properties of elements?
Ans. The main periodic properties of elements include atomic radius, ionisation energy, electron affinity, and electronegativity. These properties exhibit trends across periods and down groups in the periodic table.
2. How does atomic radius change across a period and down a group?
Ans. Atomic radius decreases across a period from left to right due to increased nuclear charge pulling electrons closer to the nucleus. Conversely, atomic radius increases down a group as additional electron shells are added, which outweighs the increase in nuclear charge.
3. What is ionisation energy, and how does it vary in the periodic table?
Ans. Ionisation energy is the energy required to remove an electron from a gaseous atom. It typically increases across a period due to increasing nuclear charge and decreases down a group because the outermost electrons are farther from the nucleus and experience greater shielding.
4. Explain the concept of electronegativity and its trend in the periodic table.
Ans. Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. It generally increases across a period due to higher nuclear charge and decreases down a group due to increased distance of the valence electrons from the nucleus and increased shielding effect.
5. What is the significance of the periodic law in chemistry?
Ans. The periodic law states that the properties of elements are periodic functions of their atomic numbers. This is significant as it helps in predicting the properties of elements, understanding chemical behaviour, and guiding the arrangement of elements in the periodic table for systematic study.
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