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# ICSE Notes 2018 : Chemistry (Seventh Day Adventist Higher Secondary School, Chennai)

29 pages, 2 questions, 1 questions with responses, 1 total responses,    1    0
 Balaaji Balu Seventh-Day Adventist Higher Secondary School, Chennai
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Class X Chapter 1 Periodic Table Chemistry ______________________________________________________________________________ Book Name: Selina Concise INTEXT - QUESTION - 1 Question 1: a) State modern periodic law. Name the scientist who stated the law. b) What is a periodic table? How many groups and periods does modern periodic table have? Solution 1: a) The modern periodic law states that "The properties of elements are the periodic functions of their atomic number." Henry Moseley put forward the modern periodic law. b) A tabular arrangement of the elements in groups (vertical columns) and periods (horizontal rows) highlighting the regular trends in properties of elements is called a Periodic Table. Modern Periodic table has 7 periods and 18 groups. Question 2: Why sodium element of group 1 and chlorine element of group 17 both have valency 1? Solution 2: Valency is the combining capacity of the atom of an element. It is equal to the number of electrons an atom can donate or accept or share. It is just a number and does not have a positive or negative sign. Group 1 elements have 1 electron in their outermost orbital, while Group 7 elements have 7 electrons in their outermost orbital. Valency depends on the number of electrons in the outermost shell (i.e. valence shell). If the number of electrons present in the outermost shell is 1, then it can donate one electron while combining with other elements to obtain a stable electronic configuration. If the number of electrons present in the outermost shell is 7, then its valency is again 1 (8 - 7 = 1) as it can accept 1 electron from the combining atom. In a given period, the number of electrons in the valence (outermost) shell increases from left to right. But the valency increases only up to Group 14, where it becomes 4, and then it decreases, that is, it becomes 1 in Group 17. Question 3: What are horizontal rows and vertical columns in a periodic table known as? Solution 3: The horizontal rows are known as periods and vertical columns in the periodic table are known as groups Printed from Vedantu.com. Register now to book a Free LIVE Online trial session with a Top tutor.

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