Atoms and molecules (science
short notes)
Topics to bi covered in this Notes
>law of chemical combination
>dalton's atomic theory
>modern day symbols of elements
>Atomic mass
>molecule
>chemical formulae
>molecules mass
>molar concept
The size of atom is 10^-9
●Law of conservation of mass
Definition: During a chamical reaction, the total mass reactants will be equal to the total
mass of the products
-> Mass Gon neither be created nor be destroyed in a Chemical reaction
Total mass of reactents = Total mass of product
●Law of contant proportions
Definition: Elements in a pure chemical compound are always present in the proportion by
mass regardless of how the compound is created
, ■DALTON'S ATOMIC THEORY (BY JOHN DALTON)
1.All matter is made up of tiny particles called atoms
2.Atoms are indivisilale particles, Atoms cannot be created nor be destroyed in a chemical
reaction
3.Atom of a given elements are identical in mass and chemical properties (Law of
conservation of mass)
4. Atom of different elements have different masess and chemical properties
5.Atoms combine in the ratio of small whole number to form compounds (Law of constant
proportions)
6.The relative number kinds of atoms are constant in a given compound
□Drawbacks of Dalton's atomic theory
●No Subatomic Particles: Atoms were indivisible, but we know about electons, protons,
neutrons
● Isotopes not Defined: atoms of an element have same mass, but isotopes of elements have
differend masses
●No isobars : Atoms of different elements have different masses, but isobars have some mass
number
■Atomic mass (AMU)
Mass of atoms of elements is called atomic mass
>Unit = U
Example
=1/12 of mass of a carbon - 12 atom
1 amu 1/12 of a carbon atom = 1/2 × 12/6.023 × 10²³ =1.66×10^-²³
■Atomic Existance
short notes)
Topics to bi covered in this Notes
>law of chemical combination
>dalton's atomic theory
>modern day symbols of elements
>Atomic mass
>molecule
>chemical formulae
>molecules mass
>molar concept
The size of atom is 10^-9
●Law of conservation of mass
Definition: During a chamical reaction, the total mass reactants will be equal to the total
mass of the products
-> Mass Gon neither be created nor be destroyed in a Chemical reaction
Total mass of reactents = Total mass of product
●Law of contant proportions
Definition: Elements in a pure chemical compound are always present in the proportion by
mass regardless of how the compound is created
, ■DALTON'S ATOMIC THEORY (BY JOHN DALTON)
1.All matter is made up of tiny particles called atoms
2.Atoms are indivisilale particles, Atoms cannot be created nor be destroyed in a chemical
reaction
3.Atom of a given elements are identical in mass and chemical properties (Law of
conservation of mass)
4. Atom of different elements have different masess and chemical properties
5.Atoms combine in the ratio of small whole number to form compounds (Law of constant
proportions)
6.The relative number kinds of atoms are constant in a given compound
□Drawbacks of Dalton's atomic theory
●No Subatomic Particles: Atoms were indivisible, but we know about electons, protons,
neutrons
● Isotopes not Defined: atoms of an element have same mass, but isotopes of elements have
differend masses
●No isobars : Atoms of different elements have different masses, but isobars have some mass
number
■Atomic mass (AMU)
Mass of atoms of elements is called atomic mass
>Unit = U
Example
=1/12 of mass of a carbon - 12 atom
1 amu 1/12 of a carbon atom = 1/2 × 12/6.023 × 10²³ =1.66×10^-²³
■Atomic Existance
