Bridge
course 2021 -2022
Science and Technology Part 1
Unit No: Measurement of Matter
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Class: 10th Activity Set 3
Lets understand: Laws of chemical combination, Atom, Size ,Mass, Valency,Molecular mass
Reference: Std 9th chapter No,4 Measurement of Matter.
Expected Skills:
1> Chemical compounds, conservation of mass, Law of constant proportion,verify these principles and concluded .
2> Recongnise and write the molecular mass , concept of mole ,and molecular formulae of compound .And also explain them.
Let's keep in mind:
1)Laws of chemical combination :
The composition of a substance changes during a chemical change .compounds are formed by chemical combination of elements.On the basis of Dalton’s atomic theory and the laws of chemical combination different scientist write the molecular formulae of various compound. We canverify the laws of chemical combination by means of known molecular formulae.
2) Law of conservation of matter :
In 1785, the French Scientist Antoine Lavoisier inferred from his research that ‘there is no rise or drop in the weight of the matter during a chemical reaction.’ In a chemical reaction the total weight of the reactants is same as the total weight of the products formed due to the chemical reactions and this is called the law of conservation of matter.
3) Law of constant proportion:
“The proportion by weight of the constituent elements in the various samples of a compound is fixed,”
4) Atomic size:
>The size of an atom is determined by its radius.
>The atomic radius of an isolated atom is the distance between the nucleus of an atom and its outermost orbit.
>Atomic radius is expressed in nanometres..
>the size of atom depend on the number of orbit in them.
>The greater the number of orbits the larger the size.
5) Mass of atom :
>The mass of an atom is concentrated in its nucleus and it is due to the protons (p) and neutrons (n) in it.
>The number (p+n) in the atomic nucleus is called the atomic mass number .
> Protons and neutrons are together called nucleons.
>unit of atomic mass is dalton (u)/
6) Chemical Symbol of Elements:
>The current method of choosing chemical symbols is based on the method invented by Berzelius.
> The symbol of an element is either the first letter or the first and second/another specific letter in its name. Of the two letters, the first is a capital letter and the second is small.
7) Molecular mass:
>The molecular mass of a substance is the sum of the atomic masses of all the atoms in a single molecule of that subtance.
> molecular mass is also expressed in the unit Dalton (u).
8) Valency :
>The capacity of an element to combine is called its valency.
>The valency of an element is indicated by a specific number.
>It is the number of chemical bonds formed by one atom of that element with other atoms.
>“The number of electrons that an atom of an element gives away
or takes up while forming an ionic bond, is called the valency of
that element.”
Lets practice :
1) Complete the following table.
3) write down the cations and anions obtained from the compounds in
the following table.
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