When elements combine to form new substances it's called chemical bonding. The force that holds
these atoms together is called a chemical bond. There are three different types of chemical bonds
that depend upon the number electrons in the outer shell of the atoms bonding. As you remember
from the last chapter, an atom has different levels that the electron can be in, as we add electrons to
the atom we fill up the inside level first then work your way out. All we will care about in this chapter is
the number of atoms in the outer layer.
Atoms from Groups I and II in the periodic table (alkali metals and alkaline earth metals) have one and
two extra electrons in their outer shell, if they could loose these electrons somehow they would then
have a full outer shell (the next shell down). Atoms from Groups 16 and 17 (Oxygen and the
Halogens) are missing one or two electrons in their outer shell, if they could gain one or two more
electrons, they would have a full outer shell. (Do you see where this is going yet?)
When an atom from Group 1(sodium) gets near an atom from Group 17 (chlorine) the chlorine atom
steals one electron from the sodium atom. This makes both atoms full on their outer shell but it makes
the chlorine atom a negative ion (it has an extra electron) and it makes the sodium atom a positive ion
(it has lost an electron). This opposite charge causes the two atoms to be attracted to each other.
(remember, opposites attract)
In a covalent bond the electrons 'share' the electrons in their outer shell with each other. Covalent bonding happens
between non-metals because all of the non-metals have mostly full electron rings, so loosing 4 to 7 electrons is not
possible. In a covalent bond the shared electrons orbit both nuclei which causes a strong bond between the atoms.
Atoms linked by covalent bonds are called molecules. A diatomic molecule is when two atoms of the same non-metal
bond. The simplest molecule is a diatomic hydrogen molecule (2 hydrogens)
|Metallic Bonds - Streaming
A metallic bond is a bond between two or more metals. The electrons in the outer level of metals in metallic bonds
flow freely between all of the nuclei. This creates a weak bond, but one that is flexible. Because of this bond metals
are malleable, ductile and can conduct heat and electric current.
We have now looked at the elements, what an atom of each one looks like and how they are
organized. You must be remember these things before you go on! For this chapter it may be best if
you remember the Bohr model of the atom with different levels for the electron.
Chapter 8 - Compounds and Molecules