Chemical Bonding

Chemical Families The Rutherford-Bohr models of the atom can be extended to develop a model of how chemical compounds form.

Steps for Drawing Atoms 1.Find the element on the periodic table. How many protons does it have? 2. Because atoms are neutral, the number of electrons will equal the number of protons 3. Draw a nucleus and write the number of protons in the center. 4. What row is the element in on the periodic table? This will be how many rings go around the nucleus.

Drawing Atoms The first ring around the nucleus can hold a maximum of 2 electrons. The second ring around the nucleus can hold a maximum of 8 electrons. The third ring can around the nucleus can hold a maximum of 8 electrons. The fourth ring around the nucleus can hold a maximum of 18 electrons.

Electron Shells for the First 20 Elements

You can see from the shell diagrams that the elements in each group show some differences. The atomic mass increases as you go down a group. The number of electrons increases as you go down a group. The radius of the atom increases as you go down a group to accommodate the extra electrons. In spite of these differences, all the atoms in a group have one thing in common – the number of electrons in the outer shell (outer shell electrons are used for bonding and are called valence electrons).

The Noble Gases Numerous laboratory experiments have confirmed that all noble gases are chemically stable. This means that they are highly unlikely to take part in a chemical change. In fact, only the very large noble gases can be made chemically reactive at all, but soon after a reaction occurs, the compound decomposes and allows the noble gas to return to its solitary self.

Noble gases have complete outer shells with eight electrons. Helium has 2 electrons in its outer shell and can take no more so it is said to have a full outer shell. Having a complete outer shell, with eight electrons, is often called a stable octet. The idea of a stable octet helps explain why other elements react.

The Halogens (one electron short of stability!)

Halogens have seven electrons in their outer shell. Halogens can lose those seven electrons to have a complete inner shell OR they could try and gain just one more electron. Halogens will react vigorously to try and gain one more electron to complete its outer shell.

The Alkali Metals (one electron beyond stability)

Alkali metals have one electron in their outer shell. Alkali metals can lose that one electron to have a complete inner shell OR they could try and gain seven more electrons. Alkali metals will react vigorously to try and lose the one outer shell electron to have a complete outer shell.

The Alkaline Earth Metals (two electrons beyond stability)

The alkaline earth metals have two electrons in their outer shell. Alkaline earth metals can gain six electrons to complete their out shells, or they could lose two electrons. Alkaline metals will react quite vigorously to lose two electrons, but not as vigorously as group 1.

Boron’s family have three electrons in their outer shell and will lose those three to have stable outer shells. Carbon’s family can gain or lose four electrons to have a stable octet. Nitrogen’s family have five outer shell electrons and will gain three to have a stable outer shell. Oxygen’s family have six electrons in their outer shell and will gain two electrons to have a stable octet.