Atoms, Bonding and the Periodic Table Understanding how “stuff” gets but together in nature.

The valence shell Valence electrons are electrons that are in the outer layer of orbit around the nucleus of an atom. These represent the electrons which are at the highest level of energy in the atom. The number of valence shell electrons determines many properties of the element including the ways it can bond to other atoms.

The Rule of octet The octet rule is a chemical rule of thumb that states how atoms of a low (<20) atomic number tend to combine so the total number of valence shell electrons is eight. When atoms have a total of eight electrons in the valence shell they have the same electron configuration as noble gases and are the most stable, and least likely to continue reacting.

Electron dot diagrams Each element has a specific number of valence shell electrons. The number of valence shell electrons range between one and eight. The electron dot diagram includes the chemical symbol for the atom and the valence shell electrons surrounding the chemical symbol. Each dot represents one valence shell electron.

Chemical bonds Atoms are more stable and less likely to react when they have eight electrons in their valence shell. Atoms become stable in one of two ways: First: The valence shell increases to eight electrons. (Electrons are gained) Second: An atom gives up the outer, loosely held electrons so that it establishes stability. (Electrons are lost). The chemical bond is the force of attraction that holds two atoms together as a result of the rearrangement of electrons between the atoms.

Relating periods and groups Chemical symbol Electrons in valence shell Li One Be Two B Three C Four N Five O Six F Seven Ne Eight The periodic table can tell us who many valence shells each atom contains. Each group (groups 1,2, 13-18) in the periodic table increases the number of valence shell electrons by one when moving across the table from left to right. Elements in groups 3-12 show a very different grouping regarding their valence shell electrons.

Electron valence shells

Inert Gases Inert gases are found in group 18. (Column at the far right of the periodic table). These atoms have eight electrons in the valence shell. These atoms are frequently not going to transfer their electrons to another atom. These atoms of the noble gases do form some compounds, but require several steps or an alteration of their environment in order to bond with other atoms.

Reactive metals and nonmetals Elements in the group to the left of the inert gases are the halogens, or group 17. This group contains elements which have seven valence shell electrons. These elements react very easily because they require only one electron to fill their valence shell. Alkali metals found in group 1 on the periodic table are also very reactive. The alkali metals react by losing one electron and establishing a stable valence shell. This is the reason why alkali metals are so reactive.

Other metals Metals found on the right and left sides of the periodic table react with other atoms in a general relationship to the number of electrons found in the valence shell. Elements found in groups 1, 2, and 13 will give or donate their electrons in order to establish a stable valence shell, especially in the presence of oxygen or members of the halogens (group 17). Metals react to the ease which they donate their electrons. Metals on the left of the periodic table will rapidly donate while elements on the right side of the periodic table will be much slower to react. (Example: gold (Au), group 10).

Other nonmetals Elements on the far right side of the periodic table are nonmetals (the exception are the noble gases). Five nonmetals are solids, four are gases, and one is a liquid. Nonmetals also lose or gain electron in order to establish a full and stable valence shell. Most nonmetals will gain electrons in order to form bonds, also nonmetals will form bonds by sharing electrons.