Download Basics of Atom

Basics of Atom
Lecture Note
Matter and an Atom
We can say that matter is anything that has both mass and volume or anything
that occupies space.
Matter is actually made up of building blocks called atoms. Atoms bonds to form
matter.
M ATTER
HAS
VOLUM E
M ASS
Atom is the smallest piece of matter that we can divide without losing the
chemical properties of the matter.
Elements and Compounds
When a material is formed from only one type of
atom then it is called an element. If a material is
made from a combination of more than one
type of atom then it is called a compound. For
example oxygen is an element and carbon
dioxide is a compound.
Structure of an Atom and the Subatomic Particles
But structurally, we can think of an atom like a tiny solar system. In the center of
the atom is the nucleus which is a cluster of protons and neutrons
Thus an atom consists of three main parts: protons, neutrons, and electrons.
These parts are known as subatomic particles or fundamental particles. An atom
has the same number of electrons (- ve charge) and protons (+ ve charge) to
make the atom electrically neutral. Let us here see proper definitions of these
subatomic particles one by one.
Proton - “A subatomic particle which has one unit
mass and one unit positive charge”.’
Electron - “A particle bearing one unit negative
charge and mass 1/1835th of a hydrogen atom”.
Neutron - “A subatomic particle which has a
mass almost equal to that of a proton and has no
charge”.
Atomic number, Mass number and Atomic mass
Atomic number of an element is equal to the
number of protons in the nucleus of the atom
of that element. It is represented by the
symbol Z.
The total number of protons and neutrons in
the nucleus of an atom is called the Mass
Number. It is represented by the symbol A.
The atomic mass may be considered to
be the total mass of protons, neutrons
and electrons in a single atom.
Molecule
Atoms bond together to form larger building blocks
of matter called molecules.
Two or more atoms share electrons to form a bond
and when atoms form bonds they form molecules
Water (H2O) is a molecule which is made up of two hydrogen atoms(H) and one
oxygen atom (O).
Nucleus and the Electromagnetic force between Nucleus and Electrons
Nucleus can be defined as the core of
the atom, which is made up of protons
and neutrons.
The mass of an atom is due primarily to
the mass of the nucleus but it occupies
only a tiny fraction of its volume
Since the nucleus is made of protons and neutrons it is positively charged while
the surrounding electrons are negatively charged
The electromagnetic force between these two opposite charges binds the atoms
together.