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ICSE Selina Concise Solutions for Grade 10 Chemistry Chapter 1. – Periodic Table, Periodic Properties and variations of Properties 1. (i) State modern periodic law. Ans: "The properties of elements are periodic functions of their atomic number," according to the modern periodic law. (ii) Name the scientist who stated the law. Ans: The periodic law was proposed by Henry Moseley. (iii) How many groups and periods does modern periodic table have? Ans: Modern Periodic table has 7 periods and 18 groups. 2. What are horizontal rows and vertical columns in a periodic table known as? Ans: In the periodic table, the horizontal rows are known as periods, while the vertical columns are known as groups. 3. Periodicity is observed due to the similar............. (number of valence electrons/ atomic number/ electronic configuration) Ans: Periodicity is observed due to the similar electronic configuration. 4. How does electronic configuration in atoms change (i) In a period from left to right? Ans: While the number of shells remains constant, the number of valence electrons rises by one as we move from left to right over any given period. (ii) In a group top to bottom? Ans: The number of shells rises sequentially, one by one, from top to bottom in a group, but the number of valence electrons remains constant. Class X Chemistry www.vedantu.com 1 5. Name 2 elements in each case: (i) Alkali metals Ans: Sodium and Potassium (ii) Alkaline earth metals Ans: Calcium and Magnesium (iii) Halogens Ans: Chlorine and Bromine (iv) Inert gas Ans: Neon and Argon 6. Elements of group 1 and elements of group 17 both have valency1. Explain. Ans: The combining capability of an element's atom is known as valency. It's the number of electrons that an atom can provide, take, or share. It's merely a number with no positive or negative sign attached to it. The outermost orbital of Group 1 elements has one electron, while the outermost orbital of Group 7 elements has seven electrons. The number of electrons in the outermost shell determines the valency (i.e. valence shell). If the outermost shell has only one electron, it can contribute one electron while interacting with other elements to form a stable electronic configuration. If the outermost shell has seven electrons, its valency is one (8 - 7 = 1) since it may accept one electron from the combining atom. The number of electrons in the valence (outermost) shell rises from left to right in a given period. However, the valency grows only until Group 14, when it becomes 4, and then drops, becoming 1 in Group 17. 7. Correct the statements. (i) Elements in the same period have equal valency. Ans: Elements in the same group have equal valency. (ii) Valency depends upon the number of shells in an atom. Ans: Valency depends upon the number of valence electrons in an atom. (iii) Copper and zinc are representative elements. Ans: Copper and zinc are transition elements. Class X Chemistry www.vedantu.com 2 (iv) Transition elements are placed at the extreme right of the periodic table. Ans: Noble gases are placed at the extreme right of the periodic table. 8. What do you understand by? (i) Periodicity Ans:Periodic qualities are properties that return at regular intervals or have a progressive variation at regular intervals, and the phenomenon is known as periodicity of elements. (ii) Typical elements Ans: The third-period elements Na, Mg, Al, Si, P, and Cl are known as typical elements because they summarise the features of their respective groups. (iii) Orbits Ans: The orbits or shells in which elements circle around the nucleus are known as orbits or shells. 9. Name 2 elements you would expect to show chemical reactions similar to calcium. What is the basis of your choice? Ans: Beryllium and magnesium will have chemical interactions that are similar to those of calcium. Because these elements, like calcium, belong to the same group 2 and have two electrons in their outermost shell. 10. Name the (i) metals, (ii) metalloids and (iii) non-metals in the first twenty elements. Ans: Metals: Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, Calcium Metalloids: Boron, Silicon Non-metals: Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Phosphorous, Sulphur, Chlorine, Argon 11. Fluorine, Chlorine and Bromine are put in one group on the basis of their similar properties. Class X Chemistry www.vedantu.com 3 (i) What are those similar properties? Ans: Non-metallic, highest electronegativity, highest ionisation potentials, and maximum electron affinity in respective periods. (ii) What is the common name of this group or family? Ans: The common name is halogens, as they are salt forming elements. 12. What is the main characteristic of the last element in each period of the Periodic Table? What is the general name of such elements? Ans: The last element in each period of the periodic table has the property of being inert or chemically unreactive. These elements are referred to as "Noble gases" in general. 13. According to atomic structure, what determines which element will be the first and which will be the last in a period? Ans: The quantity of valence electrons defines the first and final element in a period, according to atomic structure. 14. How does the number of: i. Valence electrons and ii. Valency vary on moving from left to right in the third period of the periodic table? Ans: i. In the third period of the periodic table, the valence electrons grow from 1 to 8. ii. The valency climbs from 1 to 4 and then lowers from 4 to 0 as you move from left to right. 15. Name the type of elements, which have their (i) Outermost shell complete Ans: Noble gases (ii) Outermost shell incomplete Class X Chemistry www.vedantu.com 4
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