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. Example ; Atomic size of first group element : Li < Na < K < Rb < Cs < Fr Hydrogen resembles the elements of group I-A, IV-A and VII-A in some respects. Let us look at some of the reasons because of which Hydrogen is so unique. Mendeleev left some gaps in his periodic table. I. are solved by group of students and teacher of Class 10, which is also the largest student community of Class 10. Elements of a triad show similar chemical properties. Hydrogen 1s 1. 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. To study a large number of elements with ease, various attempts were made. John Newlands’, an English scientist, arranged the known elements in the order of increasing atomic masses and called it the ‘Law of Octaves’. Later on the elements were discovered, for example, gallium replaced Eka-aluminium and it showed properties similar to that of aluminium. This is possible only when you have the best CBSE Class 10 Science study material and a smart preparation plan. CBSE Class 10 Science Notes Chapter 5 Periodic Classification of Elements Pdf free download is part of Class 10 Science Notes for Quick Revision. For example: Both hydrogen and alkali metals form similar compounds with elements like oxygen, chlorine and sulphur etc. The elements with similar physical and chemical properties came under the same groups. Hydrogen is the chemical element with the symbol H and atomic number 1. So if you glance at the periodic table, you will see hydrogen is the first element in the table. (ii) Wrong order of atomic masses of some elements could not be explained. Example: Metallic character of second period elements: Li > Be > B > C >> N > O > F Group: The vertical columns in Mendeleev’s, as well as in Modern Periodic Table, are called groups. 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. It is usually placed in Period 1 and Group 1 of the periodic table. The position of isotopes could not be explained because isotopes have the same chemical properties but different atomic masses. position of hydrogen in periodic table class (lA group (lV Group Vll. Modern periodic table is based on atomic number of elements. Atomic masses did not increase in a regular manner in going from one element to the next. It also consists of 7 horizontal rows termed as ‘periods’. It increases with increase of nuclear charge or decrease in atomic size. Mail us Request for Call Back. Example: First group element : Li < Na < K < Rb < Cs Mendeleev arranged all the 63 known elements in increasing order of their atomic masses. The number of the period is equal to the number of shells in the atoms of the elements belonging to that period. Atomic size increases down a group due to the increase in the number of shells. The atomic mass of middle element of the triad being nearly equal to the average of the atomic masses of the other two elements. 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. Non-remnant stars are mainly composed of hydrogen in the plasma state. Here, the different proposed locations will be described and contrasted. Br – Bromine Ex. Position of Hydrogen in Periodic Table *Lightest element known having atomic number 1. 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. Although it can also combine with metals and non-metals forming covalent bonds like Halogens. Cl – Chlorine (i) Characteristics of Newlands’ Law of Octaves: (ii) Table showing Newlands’ Octaves: Johann Wolfgang Dobereiner, a German chemist, classified the known elements in groups of three elements on the basis of similarities in their properties. The modem periodic table consists of 18 groups and 7 periods. For example; Co and Ni with Fluorine, Chlorine, Bromine and Iodine. On moving from left to right in a period, number of shell remains same. It has atomic number one, which means it has only one electron orbiting it its shell. Characteristics of triads of J.W. According to Newland, only 56 elements existed in nature and no more elements would be discovered in future. (i) The position of isotopes could not be explained. (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. 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. Properties of hydrogen do not completely match any one of the above-mentioned groups. No fixed positions were given to hydrogen in the Mendeleev’s periodic table. But it is placed in first group above the alkali metals in the modern periodic table because its electronic configuration is similar to that of alkali metals. Elements present in any one period, contain the same number of shells. Hydrogen is the lightest element. There were three gaps left by Mendeleev in his Periodic Table. IN this periodic table, the elements in a particular group share similar properties. Triads as formed by Dobereiner. 3. * Dihydrogen *It resembles both alkali metals and halogens and therefore, its position is anomalous. In Mendeleev’s Periodic Table the position of hydrogen could not be explained, while in Modern Periodic table hydrogen is placed above alkali metals. Law of octaves was applicable only upto calcium (only for lighter elements). The properties of elements are periodic functions of their atomic mass. * In modern periodic table it is located separately 3. Modem Periodic Table: Henry Moseley, gave a new ! It is known as ‘Newlands’ Law of Octaves’. In this Chemistry video for Class 11 we discussed on the position of hydrogen in the periodic table. (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. Also, with increase in atomic number by one unit on moving from left to right, the valence shell electrons increases by one unit. Ex. He did so because hydrogen and alkali metals have similar properties. Limitations of Mendeleev’s Periodic Table Due to the large positive charge on the nucleus, the electrons are pulled in more closely to the nucleus and the size of the atom decreases. The atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. 2. Also, the number of shells increases as we go down the group. All the elements of a group of the periodic table have the same number of valence electrons. In a period, atomic size and radii decreases from left to right. Class 10 Chemistry Periodic Classification of Elements: Position of elements in the modern periodic table : Position of elements in the modern periodic table. Atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. (i) Modem Periodic Law: Properties of elements are a periodic function of i their atomic number. It is the smallest element on the table. added in spite of the increase in nuclear charge. If the elements are arranged according to atomic masses, the isotopes should be placed in different groups of the Periodic Table. For example, hydrogen reacts with halogens, oxygen, and sulphur to form compounds whose formulae are similar to those of alkali metals. These groups were called triads. (b) Suggest the formula for the following: (i) Oxide of nitrogen (ii) Hydride of oxygen The position of Hydrogen in the periodic table: Hydrogen is placed in the first position of the periodic table. Example: Position of hydrogen with alkali metals and halogens (17th group). Need for classification of elements: Metallic characters decrease from left to right in a period and increase while going down in a group. Mendeleev’s periodic table was predicted properties of several undiscovered elements on the basis of their position in Mendeleev’s periodic table. Here we have given NCERT Class 10 Science Notes Chapter 5 Periodic Classification of Elements. Li , K , Na , K, Rb ,Cs and Fr of group 1 of the periodic table. He even predicted the properties of some of these elements and named them as Eka-boron, Eka-aluminium and Eka-silicon respectively. (c) No regular trend in atomic mass: Position of some elements with lower atomic masses before with higher atomic mass. Example: Cl-35 and Cl-37. Position of Hydrogen in the Periodic Table. As outermost shell can have only 8 electrons, so the third period also has only 8 elements. He positioned hydrogen in the first column above alkali metals. Sodium 1s 2 2s 2 2p 6 3s 1. Write the name and formula of a molecule made up of three atoms of oxygen. Question 2. 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. 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 … The maximum number of electrons that can be filled in a shell can be calculated by the formula 2n. Valency of elements in a particular group is same. 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. (ii) He gave the proper position to the noble gases which were discovered later on, without disturbing the existing order of elements. F > Cl > Br > I. He was not able to prepare triads of all the known elements. 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. (2012 OD) Answer: O 3 → Ozone. K – Potassium, 2nd Triad 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. Example: Valency of first group elements = 1 Valency of second group elements = 2. Since hydrogen can either gain or lose an electron it can find a place in Group 1 or 17. In science, simplicity and beauty are often equated - and that makes hydrogen as beautiful as they come, a single proton and a lone electron making the most compact element in existence. The Questions and Answers of Why hydrogen does not given fix place in mendeleevs periodic table? Dobereiner’s triads: 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. 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. Li – Lithium It is useful in correcting the doubtful atomic masses of some 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. Na2O, MgO etc. For example, aluminium appeared before silicon, cobalt appeared before nickel. NCERT Class 10 Science Chapter 5- Periodic Classification of Elements is categorized under Unit Chemical Substances – Nature and behavior. Trends in Modem Periodic Table 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. There are 18 groups and 7 (seven) periods in the Modern Periodic Table. In some versions of the Periodic Table, uniquely among the elements, the hydrogen symbol appears twice. In Period: Along the period from left to right, non-metallic character increases because tendency to gain electrons increases due to increase in nucleus charge. 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. 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. property of elements, ‘atomic number’ and this was I adopted as the basis of Modem Periodic Table. Ca – Calcium NCERT Solutions for Class 10 Science Chapter 1, NCERT Solutions for Class 10 Science Chapter 2, Periodic Classification of Elements Class 10, NCERT Solutions for Class 10 Science Chapter 7, NCERT Solutions for Class 10 Science Chapter 8, NCERT Solutions for Class 10 Science Chapter 9, NCERT Solutions for Class 10 Science Chapter 10, NCERT Solutions for Class 10 Science Chapter 11, NCERT Solutions for Class 10 Science Chapter 12, NCERT Solutions for Class 10 Science Chapter 13, NCERT Solutions for Class 10 Science Chapter 14, NCERT Solutions for Class 10 Science Chapter 15, NCERT Solutions for Class 10 Science Chapter 16, CBSE Previous Year Question Papers Class 12, CBSE Previous Year Question Papers Class 10. Position of elements in the modern periodic table. (e) Noble gases were missing from Mendeleev's original periodic table. Noble gases could accommodate in the Mendeleev’s periodic table without disturbing the periodic table after discovery. 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. Actually, the question’s premise is only half true, insofar as its traditional placement with the alkali metals is only half wrong. Non-metallic character of 17th period element: F > Cl > Br > I, (v) Chemical Reactivity 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. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Ba – Barium, 3rd Triad Mendeleev’s left vacant places in his table which provided an idea for the discovery of new elements. The tendency to gain electrons from the outermost shell of an atom, is called non-metallic character of an element. These elements of a triad show specific trends in their physical properties. (iii) Limitations of Newlands’ law of Octaves: 4. (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. 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. 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. Example: Eka-boron, Eka-aluminium and Eka-silicon. Period: The horizontal rows in the Modern Periodic Table and Mendeleev’s Periodic Table are called periods. 3. Na – Sodium Through this table, it was very easy to study the physical and chemical properties of various elements. It is by far the most abundant element in the universe and makes up about about 90% of the universe by weight. 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. I – Iodine. In metals: Chemical reactivity of metals increases down the group because tendency to lose electrons increases. Periodic Classification of Elements Class 10 Important Questions Very Short Answer Type. It is a distance between the centre of the nucleus and the outermost shell of an isolated atom. In Group: Atomic size increases down the group because new shells are being Classification of Isotopes : Elements having same atomic number but different Mass Number are called Isotopes. Mendeleev adjusted few elements with a slightly greater atomic mass before the elements with slightly lower atomic mass, so that elements with similar properties could be grouped together. Mendeleev’s Periodic Law: According to this “The physical and chemical properties of the elements are the periodic function of their atomic masses.”. It also consists of 7 horizontal rows termed as ‘periods’. (b) No place for isotopes: Position … Example ; Li > Na > K > Rb > Cs Hydrogen was placed in the group I with alkali metals like Li, Na etc but it could be also placed in the position of halogens. The table contained vertical columns called ‘groups’ and horizontal rows called ‘periods’. In a group, atomic size and radii increases from top to bottom. However, its actual position is always has been a matter of discussion in science. The tendency to lose electrons from the outermost shell of an atom, is called metallic character of an element. All the elements in the period have the same number of shells. The atomic masses do not increase in a regular manner in going from one element to the next. H + They show a regular gradation in their physical properties and chemical reactivities. 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. Position of hydrogen in periodic table Position of an element in periodic table depends upon its electronic configuration and properties. 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. Properties of every eighth element were similar to that of the first element. (iii) Limitations: Dobereiner could identify only three triads. Point to know: The atomic size of noble gases in corresponding period is largest Its electronic configuration resembles that of alkali metals. Example: In elements of 2nd period: In Groups: On moving from top to bottom in a group, the valency remains same because the number of valence electrons remains the same. Forget 10 Downing Street or 1600 Pennsylvania Avenue, the most prestigious address in the universe is number one in the periodic table, hydrogen. According to new CBSE Exam Pattern, MCQ Questions for Class 10 Science pdf Carries 20 Marks. Hydrogen resembles alkali metals i.e. Example ;Li < Be < B < C < N < O < F. Down the group electronegativity decreases. Dobereiner. The placement of hydrogen in the Periodic Table is still a cause of dissention. 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.. On moving from left to right in a period, the number of valence electrons increases from 1 to 8 in the elements present. (ii) VII group and 2nd period. Trends in Modern Periodic Table: Valency, Atomic size, metallic and non-metallic characters, and Electronegativity. NCERT Solutions for Class 10 Science Chapter 5- Periodic Classification Of Elements. Transition elements are placed together in Group VIII. Modern periodic table contains 18 vertical column known as group and seven horizontal rows known as periods. 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. The law was applicable to elements up to calcium (Ca). Limitations: Position of hydrogen – Hydrogen resembles both, the alkali metals and halogens in properties so Mendeleev could not decide where to place it. So Mendeleev boldly predicted the existence of some more elements. Sr – Strontium Atomic number (Z) is equal to the number of protons present in the nucleus of an atom of an element. (2013 D, 2014 D) Answer: In Period : On moving from left to right in a period, atomic size decreases because nuclear charge increases. The position of isotopes should be separated according to Mendeleev’s periodic rule but they were kept within the same group. Positions of Isotopes of all elements was not certain according to Mendeleev’s periodic table. (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. Tableand due to the next it fails to arrange all the known elements the... 5 periodic Classification of elements into metals and non-metals be separated according to ’... And 7 ( seven ) periods in the periodic table some more elements them as,... Characters decrease from left to right in a period, atomic size increases down the group because new shells being! 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