3. He placed them in a new group. Its electronic configuration is 1s 1, which means either it requires one more electron to completely fulfill the s orbital or it can lose one electron. * Dihydrogen *It resembles both alkali metals and halogens and therefore, its position is anomalous. NCERT Solutions for Class 10 Science Chapter 5- Periodic Classification Of Elements. (iii) Limitations: Dobereiner could identify only three triads. (c) No regular trend in atomic mass: Position of some elements with lower atomic masses before with higher atomic mass. property of elements, ‘atomic number’ and this was I adopted as the basis of Modem Periodic Table. There were three gaps left by Mendeleev in his Periodic Table. Hydrogen’s position was not justified in the very old Mendeleev’s periodic table. Example: First group element : Li < Na < K < Rb < Cs In Mendeleev’s Periodic Table the position of hydrogen could not be explained, while in Modern Periodic table hydrogen is placed above alkali metals. The modem periodic table consists of 18 groups and 7 periods. H + I – Iodine. Mendeleev left some gaps in his periodic table. The position of isotopes could not be explained because isotopes have the same chemical properties but different atomic masses. Class 10 Chemistry Periodic Classification of Elements: Position of elements in the modern periodic table : Position of elements in the modern periodic table. It increases with increase of nuclear charge or decrease in atomic size. Its electronic configuration resembles that of alkali metals. (i) Valency: Elements belonging to the same group have the same number of valence electrons and thus the same valency. Mendeleev arranged all the 63 known elements in increasing order of their atomic masses. The placement of hydrogen in the Periodic Table is still a cause of dissention. Form of Newland’s octaves is given in the following table: Present attempts for the classification of elements: Mendeleev’s Periodic Table, the Modern Periodic Table. Valency of elements in a particular group is same. The Modern Periodic Table consists of 18 vertical columns termed as ‘groups’. is done on EduRev Study Group by Class 10 Students. Horizontal rows of the periodic table of elements are the periods. They show a regular gradation in their physical properties and chemical reactivities. According to new CBSE Exam Pattern, MCQ Questions for Class 10 Science pdf Carries 20 Marks. Several attempts have recently been made to point to ‘the proper place’ for hydrogen (sometimes also helium) in the Periodic Table of the elements. Need for classification of elements: Metals like Na and Mg occupy the left-hand side whereas the non-metals like sulphur and chlorine occupy the right-hand side of the Periodic Table. (iii) A correct position could not be assigned to Hydrogen in the periodic table. In Group: Metallic character, when moving from top to bottom increases because the atomic size and tendency to lose electrons increases. Hydrogen Class 11 Notes Chemistry Chapter 9 • Electronic Configuration of Hydrogen 1s 1 Position of hydrogen in the periodic table: Position of hydrogen in periodic table is not justified because it resembles both alkali metals as well as halogens. Need for classification of elements III.Dobereiner’s Triads IV.Newland’s Law of Octaves V. Mendeleev’s Periodic Table VI.Modern Periodic Table VII.Trends in Modern Periodic Table CONTENTS 2. Hydrogen 1s 1. Limitations: Position of hydrogen – Hydrogen resembles both, the alkali metals and halogens in properties so Mendeleev could not decide where to place it. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. K – Potassium, 2nd Triad Na2O, MgO etc. Also, with increase in atomic number by one unit on moving from left to right, the valence shell electrons increases by one unit. For example, aluminium appeared before silicon, cobalt appeared before nickel. 5. The Modern Periodic Table consists of 18 vertical columns termed as ‘groups’. Groups and periods in the Modem (long form) Periodic Table: There are 18 groups (vertical columns) and 7 periods (horizontal lines) in the Modern (or long form) Periodic Table. There is an increase in distance between the outermost shell electrons and the nucleus of the atom. Example: Metallic character of second period elements: Li > Be > B > C >> N > O > F 17th group elements: F < Cl < Br < I, (iv) Non-metallic character: It is tendency of an atom to gain electrons. Example ; Li < Na < K < Rb < Cs (1st group) In non-metals: Chemical reactivity of non-metals decreases down the group because tendency to gain electrons decreases. Later on the elements were discovered, for example, gallium replaced Eka-aluminium and it showed properties similar to that of aluminium. Na – Sodium Achievements of Mendeleevs periodic table, Class 10 Chemistry Periodic Classification of Elements. (i) Characteristics of Newlands’ Law of Octaves: (ii) Table showing Newlands’ Octaves: Inert gases were not known at the time of Mendeleev. Here, the different proposed locations will be described and contrasted. For Example Li (6.9), Na (23), K (39). Position of elements in the modern periodic table. Modern Periodic Table; Trends in the Modern Periodic Table; Periods. Example: Cl-35 and Cl-37. In Mendeléev’s periodic table only 63 elements were arranged that were examined on the basis of the relationship between the atomic masses of elements and their physical and chemical properties. CBSE Class 10 Science Notes Chapter 5 Periodic Classification of Elements Pdf free download is part of Class 10 Science Notes for Quick Revision. Example: Cl-35 and Cl-37. It contained the elements from hydrogen to thorium. Properties of every eighth element were similar to that of the first element. The periodic table, also known as the periodic table of elements, arranges the chemical elements such as hydrogen, silicon, iron, and uranium according to their recurring properties. There are 18 groups and 7 (seven) periods in the Modern Periodic Table. Metallic characters decrease from left to right in a period and increase while going down in a group. This is possible only when you have the best CBSE Class 10 Science study material and a smart preparation plan. However, its actual position is always has been a matter of discussion in science. According to this, when elements are arranged in order of increasing atomic masses, groups of three elements, having similar properties are obtained. As atomic number determines the distribution of electrons in the orbits, and electrons of the outermost orbit determine the properties of an element. Trends in Modem Periodic Table 2) Electropositive character: Like alkali metals ,hydrogen also loses its only electron to form hydrogen ion i.e. The Modern Periodic Table: In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass. The placement of elements in the periodic table is based on their electronic configuration. What is Periodic table II. It is by far the most abundant element in the universe and makes up about about 90% of the universe by weight. In a group, atomic size and radii increases from top to bottom. Co and Ni), having different properties. The elements with similar physical and chemical properties came under the same groups. Sodium 1s 2 2s 2 2p 6 3s 1. Example: Atomic mass of Na is 23 in the triad Li, Na and K. This atomic mass is the average of the atomic masses of Li and K which have atomic masses 7 and 39 respectively. Atomic size increases down a group due to the increase in the number of shells. Modern periodic table contains 18 vertical column known as group and seven horizontal rows known as periods. There are seven such periods in the table, each numbered from 1 to 7. (iii) Metallic and Non-Metallic properties: In the modern periodic table metals are on the left side and non-metals on the right side of the table. Hydrogen has the atomic number 1 and so it should occupy the first position in the first group of the modern periodic table.But due to its chemical similarities with the elements of group 17, its position is still being debated.so,the position of the hydrogen is not fixed in the modern periodic table.. hope this helps u. thumbs up plsss.. Group: The vertical columns in Mendeleev’s, as well as in Modern Periodic Table, are called groups. * In modern periodic table it is located separately 3. Properties of hydrogen do not completely match any one of the above-mentioned groups. CBSE Class 10 Chemistry By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics. complete octet). To study a large number of elements with ease, various attempts were made. In Period: Along the period from left to right, metallic characters decreases because a tendency to lose electron decreases due to the increase in nuclear charge. He did so because hydrogen and alkali metals have similar properties. Candidates who are ambitious to qualify the Class 10 with good score can check this article for Notes. Classification of Isotopes : Elements having same atomic number but different Mass Number are called Isotopes. So if you glance at the periodic table, you will see hydrogen is the first element in the table. For example; Co and Ni with Fluorine, Chlorine, Bromine and Iodine. In fact, Hydrogen has only one shell. Earlier attempts of the classification of elements: Dobereiner’s Triads, Newland’s law of octaves. Properties of elements in each triad were similar. This unit, on the whole, comprises 25 marks in the board exam, most compared to any chapter in the syllabus, hence all chapters in Unit Chemical Substances … Atomic size decreases along a period due to an increase in the nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom. (i) Characteristics of Triads: (ii) Examples of Triads: Example: Size of second period elements: Li > Be > B > C > N > O > F (ii) The position of elements in Modem Periodic Table: (iii) Table showing Electronic Configuration of First 20 Elements: (b) No place for isotopes: Position of isotopes were not decided. (i) Mendeleev left a number of gaps in his table to accommodate the new elements which would be discovered later on. CBSE 10 Science Periodic Classification of Clements. Since hydrogen can either gain or lose an electron it can find a place in Group 1 or 17. The atomic mass of middle element of the triad being nearly equal to the average of the atomic masses of the other two elements. Write the name and formula of a molecule made up of three atoms of oxygen. Therefore, some of the properties of hydrogen are similar to those of alkali metals and hence, it can be placed in group along with alkali metals. added in spite of the increase in nuclear charge. The atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. Modern periodic table is based on atomic number of elements. It also consists of 7 horizontal rows termed as ‘periods’. The position of isotopes should be separated according to Mendeleev’s periodic rule but they were kept within the same group. are solved by group of students and teacher of Class 10, which is also the largest student community of Class 10. He positioned hydrogen in the first column above alkali metals. Trends in Modern Periodic Table: Valency, Atomic size, metallic and non-metallic characters, and Electronegativity. It also consists of 7 horizontal rows termed as ‘periods’. Limitation: It fails to arrange all the known elements in the form of triads, even having similar properties. (i) Modem Periodic Law: Properties of elements are a periodic function of i their atomic number. The trend of atomic size (radius) in moving from left to right in a period: On moving from left to right along a period, the size of atoms decreases because on moving from left to right, the atomic number of elements increases which means that the number of protons and electrons in the atoms increases. Defects in the Mendeleev’s Periodic Table. If you have any query regarding NCERT Class 10 Science Notes Chapter 5 Periodic Classification of Elements, drop a comment below and we will get back to you at the earliest. (i) Valency: The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom (i.e. It is usually placed in Period 1 and Group 1 of the periodic table. Hydrogen resembles alkali metals i.e. If the elements are arranged according to atomic masses, the isotopes should be placed in different groups of the Periodic Table. The attempts resulted in the classification of elements into metals and non-metals. A zig-zag line of metalloids separates metals from non-metals. 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It has atomic number one, which means it has only one electron orbiting it its shell. The table consists of eight vertical column called ‘groups’ and horizontal rows called ‘periods’ Limitations of mendeleev’s classification : (i) He could not assign a correct position of hydrogen in his periodic table, as the properties of hydrogen resembles both with alkali metals as well as with halogens. Although it can also combine with metals and non-metals forming covalent bonds like Halogens. Non-metal oxides are acidic in nature. Position of Hydrogen in Periodic Table *Lightest element known having atomic number 1. Example: Eka-boron, Eka-aluminium and Eka-silicon. (c) Hydrogen had no fixed position in Mendeleev’s Periodic table because it resembles alkali metals by forming positive ions and resembles halogens by forming diatomic molecule. (ii) Wrong order of atomic masses of some elements could not be explained. Br – Bromine Valency in a particular period from left to right first increases as positive valency and then decreases as negative valency. For example, hydrogen reacts with halogens, oxygen, and sulphur to form compounds whose formulae are similar to those of alkali metals. There is an irregularity with the position of hydrogen as it can be placed either in group 1 or group 17 in the first period. 1)Anomalous position of hydrogen: Hydrogen is placed in group A .It resembles the elements of both group A and group A .The position of hydrogen in periodic table is not fixed but is anomalous. Dobereiner. Hydrogen is the lightest element. (c) Hydrogen is placed at the topmost of periodic table because it resembles both alkali metals and halogens some of the properties so the position in the periodic table is unclear. Example: Position of hydrogen with alkali metals and halogens (17th group). 2. All the elements in the period have the same number of shells. Limitations of Mendeleev’s classification: Modem Periodic Law: This law was proposed by Henry Moseley, a scientist in 1913. Mendeleev’s Periodic Table: Dmitri Ivanovich – 5 ’ Mendeleev, a Russian demist, was the most important contributor to the early development of a periodic table of elements wherein the elements were arranged on the basis of their atomic mass and chemical properties. In Period: On moving from left to right in a period, the valency first increases from 1 to 4 and then decreases to zero (0). 1) Electronic configuration : Like alkali metals, hydrogen also contains 1 electron in its outermost shell. No distinction was made between metals and non-metals. In a period, atomic size and radii decreases from left to right. Mendeleev’s left vacant places in his table which provided an idea for the discovery of new elements. Ex. Example ; Non-metallic character of 2nd period elements : Li < Be < B < C < N < O < F In Group: On moving from top to bottom in a group, non-metallic character decreases because atomic size increases and tendency to gain electrons decreases. Atomic masses did not increase in a regular manner in going from one element to the next. Position of Hydrogen in the Periodic Table. Modem Periodic Table: Henry Moseley, gave a new ! According to Newland, only 56 elements existed in nature and no more elements would be discovered in future. Sr – Strontium F > Cl > Br > I. Point to know: The atomic size of noble gases in corresponding period is largest Example: Ni-58.7 before Co-58.9. So Mendeleev boldly predicted the existence of some more elements. No place could be assigned to isotopes of an element. Note that while hydrogen is normally shown at the top of the Group 1 elements in the periodic table, the term "alkaline metal" refers to the Group 1 elements from lithium downwards and not hydrogen. It is also the lightest element on the periodic table. Cl – Chlorine Example: F > Cl > Br > I (17th group), (vi) Electronegativity: It is tendency of an element to attract the shared pair of electrons towards it in a covalently bonded molecule. Hydrogen is the first element of the periodic table as its atomic number is one, which means it has only one electron in its atom and thus only one electron is present in its outermost shell. There is an irregularity with the position of hydrogen as it can be placed either in group 1 or group 17 in the first period. Ca – Calcium Example: In elements of 2nd period: Example ; Atomic size of first group element : Li < Na < K < Rb < Cs < Fr As outermost shell can have only 8 electrons, so the third period also has only 8 elements. Elements present in any one group have the same number of valence electrons. Periodicity of Properties: The repetition of properties of elements after certain regular intervals is known as Periodicity of Properties. Atomic size: The atomic size may be visualised as the distance between the centre of the nucleus and the outermost shell of an isolated atom. Mendeleev’s Periodic Law: It states that “the properties of elements are the periodic functions of their atomic masses.” It means the properties of the elements depend on their atomic masses and the elements are given a position in the periodic table on the basis of their increasing atomic masses. Hydrogen occupies a unique position in the modern periodic table due to the following reasons (i) Both hydrogen and alkali metals have similar outer electronic configuration as both have one electron in the valence shell. Hydrogen is the chemical element with the symbol H and atomic number 1. Here we have given NCERT Class 10 Science Notes Chapter 5 Periodic Classification of Elements. Positions of Isotopes of all elements was not certain according to Mendeleev’s periodic table. The properties of elements are periodic functions of their atomic mass. Valency of elements in a period first increases from one to four and then decreases to zero. The tendency to gain electrons from the outermost shell of an atom, is called non-metallic character of an element. In order to fit elements into the table, Newlands’ adjusted two elements like cobalt and nickel in die the same slot and also put some unlike elements under the same note. On the basis of the table of Mendeleev’s Periodic Table (a) Name the element which is in (i) I group and 3rd period. Hydrogen is a chemical element with atomic number 1 which means there are 1 protons and 1 electrons in the atomic structure.The chemical symbol for Hydrogen is H. With a standard atomic weight of circa 1.008, hydrogen is the lightest element on the periodic table. Limitations of Mendeleev’s Periodic Table (a) No fixed position for hydrogen: No correct position of the hydrogen atom was in Mendeleev’s periodic table. Atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. Non-metallic character of 17th period element: F > Cl > Br > I, (v) Chemical Reactivity Forget 10 Downing Street or 1600 Pennsylvania Avenue, the most prestigious address in the universe is number one in the periodic table, hydrogen. (ii) The atomic size or atomic radius increases: as we move down in a group and it decreases as we move from left to right in a period. Atomic size of 17th group elements : F < Cl < Br < I, (iii) Metallic character: It is the tendency of an atom to lose electrons. the combining capacity of an element is known as its valency). The elements present in any one group have the same number of valence electrons. Ex. Merits of Mendeleev’s Periodic Table He could not assign a correct position to hydrogen in his table because hydrogen has some properties similar to alkali metals and some properties similar to halogens. Hydrogen (Z = 1) is placed at the top of the alkali metal family because it resembles alkali metals in its properties. NCERT Class 10 Science Chapter 5- Periodic Classification of Elements is categorized under Unit Chemical Substances – Nature and behavior. 1. The elements present in any one group have the same number of valence electrons. 1st Triad In metals: Chemical reactivity of metals increases down the group because tendency to lose electrons increases. Mendeleev’s Periodic Table: Mendeleev’s periodic table is based on the physical and chemical properties of elements and their atomic masses. (d) Silicon and Germanium. Example: Valency of first group elements = 1 Valency of second group elements = 2. The number of each element corresponds to the number of protons in its nucleus (which is the same as the number of electrons orbiting that nucleus). (e) Noble gases were missing from Mendeleev's original periodic table. Along the period electronegativity increases. The position of Hydrogen in the periodic table: Hydrogen is placed in the first position of the periodic table. Li – Lithium Actually, the question’s premise is only half true, insofar as its traditional placement with the alkali metals is only half wrong. For instance, elements like fluorine (F) and chlorine (Cl), belong to group 17. (ii) He gave the proper position to the noble gases which were discovered later on, without disturbing the existing order of elements. Class 10 Chemistry Periodic Classification of Elements Limitations of Mendeleevs classification Limitations of Mendeléev’s classification No fixed position could be assigned to hydrogen … 3)Correction of doubtful atomic weights:Mendeleev periodic table has helped in correcting the doubtful atomic weights of some elements.. Hydrogen resembles the elements of group I-A, IV-A and VII-A in some respects. Trends in the Modern Periodic Table: We hope the given CBSE Class 10 Science Notes Chapter 5 Periodic Classification of Elements Pdf free download will help you. Periodic Classification of Elements Class 10 Important Questions Very Short Answer Type. 2. (ii) Atomic size: Atomic size refers to radius of an atom. The Questions and Answers of Why hydrogen does not given fix place in mendeleevs periodic table? Position of Hydrogen. No fixed position was given to hydrogen in this Periodic Table. This discussion on Why hydrogen does not given fix place in mendeleevs periodic table? (2013 D, 2014 D) Answer: Example ;Li < Be < B < C < N < O < F. Down the group electronegativity decreases. Noble gases could accommodate in the Mendeleev’s periodic table without disturbing the periodic table after discovery. (b) No place for isotopes: Position … Li , K , Na , K, Rb ,Cs and Fr of group 1 of the periodic table. Characteristics of triads of J.W. It is the smallest element on the table. Increase in the discovery of different elements made it difficult to organise all that was known about the elements. No fixed positions were given to hydrogen in the Mendeleev’s periodic table. Elements present in any one period, contain the same number of shells. The maximum number of electrons that can be filled in a shell can be calculated by the formula 2n. The defects of Mendeleev’s periodic table are: 1. due to presence of fully filled electronic configuration (i.e. NCERT Solutions for Class 6, 7, 8, 9, 10, 11 and 12, CBSE NotesCBSE Notes ScienceNCERT Solutions Science. Silicon or some other metals exhibiting the properties of both metals and non-metals termed as semi-metal or metalloid are positioned in the middle of periodic table. Li has 1+ valency, then Be2+, B3+, C4+ covalency, N3- valency, then O2- and F(-) valency. Also, the number of shells increases as we go down the group. (2012 OD) Answer: O 3 → Ozone. Triads as formed by Dobereiner. Since isotopes have different masses hence there should be dedicated position to each isotope in Mendeleev’s periodic table. The trend of atomic size (radius) in moving down a group: Ongoing down in a group of the Periodic Table, the atomic size increases because a new shell of electrons is added to the atoms at every step. The atomic masses do not increase in a regular manner in going from one element to the next. Non-metallic characters increase from left to right in a period due to increase in the electronegativity and these characters decrease from top to bottom in a group due to the decrease in the electronegativity of atoms while going down in a group. The other two elements F ) and chlorine occupy the left-hand side whereas the non-metals like sulphur and occupy. Is by far the most abundant chemical substance in the first element 6.9 ), Na 23!: it fails to arrange all the 63 known elements Mendeleev ’ s periodic ;. Ion i.e ease, various attempts were made is known as periodicity of properties isotopes of all the elements. Noble gases were missing from Mendeleev 's original periodic table the above-mentioned groups from left right! Consists of 18 vertical columns termed as ‘ periods ’ example ; Co Ni. In spite of the periodic table depends upon its electronic configuration and properties Rb. 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