10 th, Sci.I,Periodic classification of elements I.

 

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As we grown up, we forget the definition and some terms or do not fully/ totally understand the exact meaning of those words. Today’s main objective is to increase basic chemistry knowledge with gradual study . In science meaning of unchangeable terms are useful in day today life .

 🎻 Definition of element :- Element is a substance that cannot be broken down into simpler substances by chemical means.

Element is also defined as a pure substance made up of only one kind of atom which can’t be split up into two or more substance.

Ex. Silver Ag ,   Chlorine Cl

🪷 Atom :- An atom is the basic building block. Atom is the smallest unit of matter that has the characteristic properties of an element.

In the nucleus of atom positively charged protons p and neutral neutrons n are present.

Electrons e are revolve around the nucleus in specific orbit

🪼 What are the types of elements? 

On the basis of physical and chemical properties elements are of three types metals, nonmetals and metalloids.

🎷 Metals:- Those are lustrous , good conductor of heat and electricity and  gives electron in a chemical reaction are called metals. Ex copper Cu ,silver Ag , gold Au.

🌿 Nonmetals:- Those elements are poor conductor of heat and electricity, and accept electron in a chemical reaction are called non metals. Ex. Oxygen O , nitrogen N , sulphur S.

💐 The metalloids :- Those  elements shows properties of metals and nonmetals they are called as metalloids Ex. Boron B , silicon Si , germanium Ge , arsenic As

👉 * Isotopes : Those elements having same atomic number but different mass number they are called as isotopes of that element.

*🦢  Isobars are atoms of different chemical elements having equal values for atomic mass.

🦜* What are the types of matter ?

There are five types of matter but generally we know only 3 that are solid , liquid and gas but’ plasma ‘ and ‘Bose-Einstein condensate’ these are the next two states.

🐦* Atomic mass A :- the sum of protons and neutrons is called atomic mass of that element.

Ex. Na 

P = 11  n= 12    Atomic mass of sodium = p + n = 11 + 12 = 23

🐸* Atomic number Z :- The number of protons present in an atom or electrons which revolve around the nucleus is called its atomic number . Atomic number of sodium Na 11.

 * All the elements after Uranium ( atomic number 92 ) are man-made, these elements are radioactive.

For mor information you may refer following 🔗

https://iupac.org/what-we-do/periodic-table-of-elements/

☘️* Dobereiner’s triads :-

1. Dobereiner a German scientist made groups of three elements. He arranged these three elements in increasing order of their atomic mass.

2. He found that the atomic mass of the middle element was approximately mean of the other two elements.

📖 * Demerits of Dobereiner’s triads law :- Only few triads show approximately means but all the known elements could not be classified into the dobereiner’s triad.

⭐ * Newlands law of octaves :-1.  The English scientist Newlands arranges element in the increasing order of their atomic mass

2. he found the properties of the eighth element similar to the first one.

🎉 *  Limitations of Newlands’ octaves law 

1. This rule only applicable upto calcium Ca.

2. Metals Cobalt Co and Nickel Ni are placed under the note’ Do ‘ along with halogens

3. There was no provision to accommodate the newly discovered elements in newlands octave law.

🥳* Mendeleeve’s periodic law :- 1. Russian scientists mendeleeve arranged elements in the increasing order of their atomic mass.

2. Physical and chemical Properties of elements are periodic functions of their atomic masses.

( Periodic means – repetition of properties)

💥 * Merits of mendeleeve’s periodic table

1. On the basis of properties some elements atomic masses were revised.

Ex atomic mass of beryllium Be 14.09 was changed to correct value 9.4.

2. He had left three vacant places on his periodic table. Names were given as eka- boron , eka-aluminium, eka-silicon. He predicted their properties also. After discovery these elements are known as scandium Sc, gallium Ga and germanium Ge respectively. Predicted properties of these elements match with discovered elements.

3. When noble gases ( helium neon, argon ) were discovered mendeleeve created zero groups without disturbing the original periodic table.

🎊* Demerits of mendeleeve’s periodic table.

1. Place :-The elements Cobalt Co and Nickel Ni have the same whole number of atomic mass , so there was an ambiguity regarding their sequence in his table.

2. Isotopes :- There is no place for isotopes in Mendeleeves periodic tables though their atomic masses were different.

3. Atomic mass :- it was not possible to predict how many elements could be discovered between two heavy elements because the rise in atomic mass does not appear to be uniform.

4. Hydrogen :- hydrogen shows similarity in properties with halogens and alkali metals It is difficult to decide the correct position of hydrogen, whether the correct position of hydrogen is in the group of halogens or in a group of alkali metals.

🎇* Modern periodic law :- English scientist Henry Moseley arranges elements in the increasing order of their atomic number, the physical and chemical properties of elements are periodic function of their atomic number.

Group :- 18 vertical columns present in periodic table are called groups.

Periods :- 7 horizontal Rose present in periodic table are called periods.

*माणसाच्या वागण्यातून 

त्याची नीतिमत्ता कळत असते,*

              *आणि माणसाच्या कामातून, सकारात्मक* *विचारातून, 

सहकार्यातून त्याची गुणवत्ता कळत असते.* 

     *आपला दिवस आनंदी जावो.*🎷