In Unit 2 (section 2.1)
we learned that matter refers to the substances that make up our universe. In
this unit, we will learn that all matter
on earth and in the universe is composed of atoms.
Atoms are the basic blocks of matter. If you are interested in knowing the early
chemical discoveries and the atomic theory, take a look at the suggested reading
on Dalton's Atomic Theory.
Let's look at what is inside an atom.
There are three subatomic particles that make up all atoms:
Protons and neutrons are found at the center of atom in the nucleus. Electrons
surround the nucleus of the atom.
Notice that the mass of the electron is much less, about 1/1835 that of
the proton. In other words, it takes about 1835 electrons to equal the mass
of one proton. So, most of the mass of the atom is concentrated at the center
of the atom in the nucleus.
Protons and electrons carry electric charges (positive and negative
species with like
species with unlike
Protons repel each other but electrons and
protons are attracted to each other.
Neutrons have no charge. There is no electrostatic force of attraction associated
with neutrons. The mass of the neutron is very close to that of the proton.
The diameter of the nuclei is of the order of 10-4 Å.
The atom is made up of mostly empty space in which electrons move.
Electrostatic attraction exists between the electrons and protons and keeps
the negatively electrons attracted to the positively charged nucleus.
An atom is electrically neutral. Since
the relative charge of the proton is +1 and the relative charge of the electron
is -1, there MUST BE equal number of electrons
and protons in an atom.