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Date:
ABC#
STRUCTURE OF THE ATOM
I
Atoms consist of a nucleus surrounded by
.
A. The NUCLEUS
1. The nucleus contains *
% of the mass of an atom.
2. The nucleus is made of *
3. PROTONS have a*
and*
.
charge.
(a) The mass of subatomic particles is measured with a unit called an*
(b) A proton has a mass of*
4.
which stands for
amu."
NEUTRONS have no charge, they are
.
(a) The mass of a neutron is slightly greater than the mass of a proton but it is still said to have a
mass of *
amu.
5. The ATOMIC NUMBER is the number of *
in the nucleus of an atom of.
(a) The ATOMIC NUMBER determines the identity of an element.
6. MASS NUMBER is the SUM of the *
of an atom.
and *
in the nucleus
(a) Atoms of the same element can have DIFFERENT NUMBERS OF NEUTRONS.
(b) Atoms of the same element with different numbers of neutrons are called *
(c) Example:
Oxygen: Atomic Number = *
(This means that all oxygen atoms have have *
protons)
99.8% of Oxygen atoms in nature have 8 protons and 8 neutrons for a mass number of *
0.04% of Oxygen atoms in nature have 8 protons and 9 neutrons for a mass number of *
0.02% of Oxygen atoms in nature have 8 protons and 10 neutrons for a mass number of *
7. Any sample of an element as it occurs in nature is a mixture of different ISOTOPES (atoms with the
same number of protons but different numbers of neutrons). More Information
(a) The number BELOW THE SYMBOL for each element on the periodic table is called the
*
*
.
(b) The average mass number of all the natural isotopes of an element is called
the *
*
B. ELECTRONS
1. Electrons have a *
neutron.
charge and have a mass of about 1/2000 of the mass of a proton or
2. The mass of an electron is so small, it is almost *
.
3. It is not possible to know exactly where the electrons are around the nucleus. We only know that
they exist somewhere within areas called*
4. The ORBITALS are arranged in*
(a) Electrons with the*
around the nucleus..
around the nucleus.
*
(b) Electrons with the *
are found near the nucleus.
*
are found farther from the nucleus.
5. Energy Levels with the atom
(a) The first energy level can hold *
electrons.
(b) The second energy level can hold *
electron.
(c) The third energy level can hold *
electrons.