When Mendeleev constructed his table based upon the properties
of the elements, he had no idea that the underlying atomic structure is what
gives each element its unique set of characteristics.
As we learned more about the subatomic world and discovered more elements
the periodic table was transformed into what we have today. Today's periodic
table is based upon the subatomic structure of the atoms, not the properties.
However, because the subatomic structure is what gives an element its properties,
the table very much resembles its early prototypes which were constructed
before we had any specific knowledge of atoms.
Recall from an earlier unit this year the dimensions of an atom. The nucleus
is 10,000 times smaller than the whole atom, yet this nucleus contains almost
all of the the mass. Most of the atom is empty space occupied by electrons
zipping around the nucleus.
So, an atom interacts with other atoms and the world around it via its outermost
electrons. The outermost electrons of an atom are its valence electrons.
To understand better how atoms can bond or why elements have the properties
that they do, we will need to understand the underlying electron configuration
(how the electrons exist around their nucleus).
Orbiitals
Electrons exist in orbitals, regions around the nucleus
where you are likely to find an electron. Imagine that the animation above
was accelerated to the point where you couldn't see the electrons, because
the are moving so fast they just form a blur. The blur described by the
pattern of electrons above would look like a sphere. This type of orbital
is known as an s orbital.
The pattern in which electrons move (or the region where you are likely
to find them) can take several forms, depending on the energy level of
the electrons. Some other common orbital shapes are the p orbital and
the d orbital.
