3. 1. Law of conservation of
mass
Law of conservation of mass
states that mass can neither be
created nor be destroyed.
4. 2. Law of constant proportions
A pure chemical compound
always contains same elements
combined together in the same
definite proportion by weight.
5. Postulates of Dalton’s atomic
theory
• All matter is composed of a very large number of very
small particles called atoms.
• Atoms are indivisible particles,which cannot be created
or destroyed in a chemical reaction.
• Atoms of a given element are identical in mass and
chemical properties.
• Atoms of different elements have different masses and
chemical properties.
• Atoms combine in the ratio of small whole numbers to
form compounds.
• The relative number and kinds of atoms are constant in a
given compound.
6. Atom
• An atom is the smallest
unit that maintains the
charateristics of an
element.
-Nucleus- The center of
the atom,contains protons
and neutrons
-Electron Cloud-Region
surroundings the nucleus
containing the electrons.
7.
8.
9. The Nucleus
• Proton – A positively charged sub-atomic
particle (+).The number of protons is the
same as the atomic number.
• Neutrons – A sub-atomic particle in the
nucleus.Neutron do not have a charge(0).
14. Molecules
• A molecule is defined as a stable neutral
group of at least two atoms in a definite
arrangement held together by very strong
chemical bonds.
• It can also be defined as a unit of two or
more atoms held together by covalent
bonds.
15. Chemical Bonds
Covalent bonds form when atoms share 2
or more valence electrons.
Covalent bond strength depends on the
number of electron pairs shared by the
atoms.
single double < triple
bond
< bond bond
