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PERIODIC CLASSIFICATION OF ELEMENTS

• Elements are classified on the basis of similarities in their properties.

• Döbereiner grouped the elements into triads and Newlands gave the Law of Octaves.

• Mendeléev arranged the elements in increasing order of their atomic masses and according to their chemical properties.

• Mendeléev even predicted the existence of some yet to be discovered elements on the basis of gaps in his Periodic Table.

• Anomalies in arrangement of elements based on increasing atomic mass could be removed when the elements were arranged in order of increasing atomic number, a fundamental property of the element discovered by Moseley.

• Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and 7 horizontal rows called periods.

• Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character.

Periodic Law:‘Properties of elements are a periodic function of their atomic number.’

Atomic number gives us the number of protons in the nucleus of an atom and this number increases by one in going from one element to the next. Elements, when arranged in order of increasing atomic number Z, lead us to the classification known as the Modern Periodic Table. Prediction of properties of elements could be made with more precision when elements were arranged on the basis of increasing atomic number.

Position of Elements in the Modern Periodic Table :

The Modern Periodic Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’. Let us see what decides the placing of an element in a certain group and period. All elements of a group contain same number of valence electrons, which justifies similar chemical properties.

The atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.

periodic table

Atoms of different elements with the same number of occupied shells are placed in the same period. Na, Mg, Al, Si, P, S, Cl and Ar belong to the third period of the Modern Periodic Table, since the electrons in the atoms of these elements are filled in K, L and M shells.

Metallic & Non-metallic Properties:

Metals like Na and Mg are towards the left-hand side of the Periodic Table while the non-metals like sulphur and chlorine are found on the right-hand side. In the middle, we have silicon, which is classified as a semi-metal or metalloid because it exhibits some properties of both metals and non-metals.

In the Modern Periodic Table, a zig-zag line separates metals from non-metals. The borderline elements – boron, silicon, germanium, arsenic, antimony, tellurium and polonium – are intermediate in properties and are called metalloids or semi-metals. Metals tend to lose electrons while forming bonds, that is, they are electropositive in nature.

As the effective nuclear charge acting on the valence shell electrons increases across a period, the tendency to lose electrons will decrease. Down the group, the effective nuclear charge experienced by valence electrons is decreasing because the outermost electrons are farther away from the nucleus. Therefore, these can be lost easily. Hence metallic character decreases across a period and increases down a group.

As the trends in the electronegativity show, non-metals are found on the right-hand side of the Periodic Table towards the top. These trends also help us to predict the nature of oxides formed by the elements because it is know that the oxides of metals are basic and that of non-metals are acidic in general.

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  • APJSK - Biology 10 B
Weekly outline
  • Second Term

    Dear Students,

    Science refers to a system of acquiring knowledge. It augments the spirit of enquiry, creativity, objectivity and aesthetic sensibility in children. Biology is the branch of science dealing with the study of life. Biology as a discipline imply a significant responsibility for the protection and welfare of all living species.

    In this term we will be covering four chapters that are part of SA 2.

    CHAPTER 1: HOW DO ORGANISMS REPRODUCE?

    CHAPTER 2: HEREDITY AND EVOLUTION

    CHAPTER 3: OUR ENVIRONMENT

    CHAPTER 4: MANAGEMENT OF NATURAL RESOURCES

    • News forum
  • 1 January - 10 January

    WINTER BREAK WILL BE FROM 1 JANUARY - 10 JANUARY.

  • 12 January - 17 January

    Monday : 12 January

    Today we will start with the chapterOUR ENVIRONMENT.

    We will be able to

    • discuss what happens when humans add waste to environment.

    Tuesday : 13 January

    We will be able to

    • distinguish between biodegradable and non-biodegradable wastes.
    • list the affects of biodegradable and non-biodegradable wastes on the environment.

    Wednesday : 14 January

    We will have a double period, so we will be able to

    • describe the concept of ecosystem.
    • outline the various components of an ecosystem.
    • identify the producers and consumers of an ecosystem.
    • compare natural and artificial ecosystem and the factors that affect them.

    As an assignment do intext questions on page no. 257 of NCERT book and extra questions given in the class.

  • 19 January - 24 January

    Monday : 19 January

    We will have a double period, so we will be able to

    • explain the concept of food chain.
    • appraise the role of each organism in a food chain for sustaining the ecosystem.
    • compare the food chain prevalent inforest, in grassland and in a pond.
    • outline the flow of energy between various components of ecosystem.
    • establish relationship betweenvarious food chains prevalent infood web.
    • discuss the phenomenon of biological magnification.
    • explain human activities that affect the environment.

    As an assignment do intext questions on page no. 261 of NCERT book and extra questions given in the class.

    Wednesday : 21 January

    Since we have a practical class,we will observe analogous and homologous organs by using available specimens. We will be able to draw the diagram of specimens. Students from roll.no. 1- 15, will be coming to bio lab for the practical.

    Friday : 23 January

    We will be able to

    • define ozone layer.
    • explain the reason for the depletion of ozone layer.
    • suggest ways to reduce the problem ofwaste disposal and hence become better, more responsible, global citizens.

    Do questions at the end of the chapter.

  • 26 January - 31 January

    Tuesday : 27 January ; Wednesday : 28 January

    There will be no class as I am going for cbse science exhibition.

  • This week 2 February - 7 February

    Tuesday : 3 February

    Today we will start with the chapterMANAGEMENT OF NATURAL RESOURCES.

    We will be able to

    • reason out the need to manage our resources.
    • analyze the factors responsible for Ganga pollution.
    • discuss Ganga action plan.

    Wednesday : 4 February

    We will have a double period, so we will be able to

    • enlist 3 R's that help in saving environment.
    • reason out the importance of sustainable development.
    • compare advantages oflong term perspective with short-term aims in managing natural resources.
    • reason out the need for equitable distribution of resources.
    • evaluate the role of four types of stakeholders that are dependent on forest resources.

    As an assignment do intext questions on page no. 269 of NCERT book and extra questions given in the class.

  • 5 February - 11 February
  • 12 February - 18 February
  • 19 February - 25 February
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