After
reading this section you will be able to do
the following:
Explain
how electrons are arranged in an atom.
Describe
how elements maintain their electrical balance.
Maintaining
electrical balance
Each basic element has
a certain number of electrons and protons, which distinguishes
each element from all other basic elements. In most elements,
the number of electrons is equal to the number of protons. This
maintains an electrical balance in the structure of atoms since
protons and electrons have equal, but opposite electrostatic fields.
Pictured here is an atom
of copper, which is much more complex than either an atom of hydrogen
or helium.
The copper atom has 29
protons in its nucleus with 29 electrons orbiting the nucleus.
Notice that in the copper atom, the electrons are arranged in
several layers called shells. This is to graphically represent
that the electrons are at different energy levels within
the atom. The energy of an electron is restricted to a few particular
energy levels. The energy is said to be quantized, meaning
that it cannot vary continuously over a range, but instead is
limited to certain values. These energy levels or shells follow
a very predictable pattern. The closest shell to the nucleus can
have up to 2 electrons. The second shell from the nucleus can
have up to 8 electrons. The third shell can have up to 18 electrons.
The fourth shell can have up to 32 electrons, and so on. Atoms
can have this many electrons, but they do not have to have this
many electrons in each shell. The greater distance between the
electrons in the outer shells and the protons in the nucleus mean
the outer shell electrons experience less of a force of attraction
to the nucleus than do the electron in the inner shells.
In the next sub-unit
you will learn about the the outer shell of an atom called the
valence shell.
Review
Atoms
have their electrons arranged in layers called shells.
In order
to maintain electrical balance the number of electrons is equal
to the number of protons in most elements.
