class 9 atoms and molecules notes
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Answer:
Atoms and molecules are responsible for forming tiny sand particles, gargantuan black holes and everything in between. The atom is the most fundamental unit of matter, making up everything that we see around us. It is extremely small, measuring in at less than 0.1 to 0.5 nanometers.
Laws of Chemical Combination
Chemical Reactions
In a chemical reaction, two or more molecules interact to produce new compounds and are called reactants, whereas the newly formed compounds are called products.
In a chemical reaction, a chemical change must occur, which is generally observed with physical changes like precipitation, heat production, colour change, etc.
Law of conservation of mass
According to the law of conservation of mass, matter can neither be created nor destroyed in a chemical reaction. It remains conserved.
Mass of reactants will be equal to the mass of products.
Law of constant proportions
A pure chemical compound contains the same elements combined together in a fixed proportion by mass is given by the law of definite proportions.
For e.g., If we take water from a river or from an ocean, both have oxygen and hydrogen in the same proportion.
Atoms
An atom is the defining structure of an element, which cannot be broken by any chemical means.
The atomic symbol has three parts:-
The symbol X: the usual element symbol
The atomic number A: equal to the number of protons
The mass number Z: equal to the total number of protons and neutrons in an element.
Dalton’s Atomic Theory
The matter is made up of indivisible particles known as atoms.
The properties of all the atoms of a given element are the same, including mass. This can also be stated as all the atoms of an element have identical mass and chemical properties; atoms of different elements have different masses and chemical properties.
Atoms of different elements combine in fixed ratios to form compounds.
Atoms are neither created nor destroyed. The formation of new products (compounds) results from the rearrangement of existing atoms (reactants) in a chemical reaction.
The relative number and kinds of atoms are constant in a given compound.
Dalton’s Atomic Theory
To know more about Laws of Chemical Combination, visit here.
Atomic Mass
Atomic mass and atomic mass unit
Atomic mass is the total of the masses of the electrons, neutrons, and protons in an atom, or in a group of atoms, the average mass.
Mass of an atomic particle is called the atomic mass.
This is commonly expressed as per the international agreement in terms of a unified atomic mass unit (AMU).
It can be best defined as 1/12 of the mass of a carbon-12 atom in its ground state.