ATOMIC+BONDING

__WHAT IS CHEMICAL BONDING?__ A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is usually caused by the electromagnetic attraction between opposite charges. The atomic structure of any element is made up of a positively charged nucleus with a cloud of electrons revolving around it. An element’s atomic number indicates the number of positively charged protons in the nucleus. The atomic weight of an atom indicates how many protons and neutrons in the nucleus. To determine the number of neutrons, the atomic number is subtracted from the atomic weight. A stable atom will have equal numbers of negatively charged electrons and positively charged electrons. **__BEING STABLE - FILLING THAT SHELL__** Atoms like to have a balanced electrical charge. This makes them neutral, in charge, and stable. If stable they will not react with other atoms. The elements in Group 18, the Noble Gases, are like this. However, most atoms do not have a full outer, or Valence, electron shell. They have to exchange or share electrons to fill their Valence shell and become more stable. To do this they form compounds with other types of atoms. For example, magnesium, with an atomic number of 12, has two electrons in the inner shell, eight in the second shell and two in the outer shell. It is unstable and reacts readily with other atoms. BOHR DIAG Mg __NOTE:__ Shells are named using alphabetic characters. The first four shells are: K-L-M-N Each shell can hold a maximum number of electrons. This is, for each shell: <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11pt; text-align: center;">** 2 - 8 - 8 - 18 ** <span style="background-color: #ffffff; display: block; font-family: Calibri; font-size: 16pt; text-align: center;"> CLICK HERE FOR [|GREATER DETAIL OF ELECTRON SHELL CONFIGURATIONS] <span style="background-color: #ffffff; display: block; font-family: Calibri; font-size: 16pt; text-align: center;">__** FILLING THE OUTER ELECTRON SHELL **__ <span style="background-color: #ffffff; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;">__Completely full outer shell__ <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 16pt; text-align: center;">Atoms are at their most stable when they have no partially-filled electron shells. This is the case with the Noble, or inert, gases found on the extreme right of the periodic table. <span style="background-color: #ffffff; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;">__Mostly empty outer shell__ <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 16pt; text-align: center;">If an atom has only a few electrons in a shell, it will tend to __lose__ them to empty the shell. Elements that tend to do this are the metals, found on left of the periodic table. When metal atoms bond we call it a metallic bond. The fewer electrons in the outer shell, the more reactive the element. These are the Group 1 elements or Alkali metals. <span style="background-color: #ffffff; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;">__Nearly full outer shell__ <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 16pt; text-align: center;">When an atom has a nearly full electron shell, it will try to find electrons from another atom so that it can fill its outer shell. These elements are usually described as non-metals. The bond between two non-metal atoms is a covalent bond. Where metal and non-metal atom come together an ionic bond occurs. <span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;">__IDENTIFYING THE TYPE OF CHEMICAL BOND__ <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 14pt; text-align: center;">There are 2 types of bonds which we need to identify: IONIC and COVALENT. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;">** METAL + NON-METAL = IONIC NON-METAL + NON-METAL = COVALENT ** <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;">** __IONIC BONDING__ ** <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> Ionic bonding occurs when a metallic atom and a non-metallic exchange electrons. One atom will loose electron(s), dropping back to the lower full electron shell, and the other will gain electron(s) filling up to the next shell. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> The bond between Sodium (metal) and Chlorine (gas) is a good example of this bonding type. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> Sodium has one electron in its valence shell, to become stable it wants to give it away. Chlorine has seven electrons in its valence shell. It needs one more to fill it. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> To satisfy both atoms in filling their outer shells the Sodium atom gives away one electron to the chlorine atom which accepts it. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> In doing so the Sodium now has one more proton than electrons in its structure. It gets an electrical charge of +1 (Na+). Chlorine, gaining an electron now has one extra electron and gets an electrical charge of -1 (Cl-). <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> These charged atoms are called IONS. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> It is the attractive force between opposite electrostatic charges on the ions which holds the two atoms together as a stable. <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center;"> This is ionic bonding
 * <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center; text-align: left; vertical-align: middle;"> IONIC bonding occurs between metals and non-metals.
 * <span style="background-color: #ffffff; display: block; font-family: Verdana; font-size: 11px; text-align: center; text-align: left; vertical-align: middle;"> COVALENT bonding occurs between 2 non-metals.

<span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;">**__COVALENT BONDING__** <span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;"> Covalent bonding occurs between two non-metallic atoms. In this form of bonding electrons are shared between the atoms involved. <span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;"> In this molecule of Hydrogen Fluoride, for example, the electron from the hydrogen spends part of its time with the fluoride atom which lacks one electron in its valence shell.

<span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;"> Phosphorus Trichloride (PCl3) is another compound formed covalently by atoms sharing electrons.

<span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;"> The Phosphorus atom shares electron with 3 different chlorine atoms.

<span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;">__**LEWIS DIAGRAMS**__ <span style="background-color: #ffffff; color: red; display: block; font-family: Tahoma; font-size: 16pt; text-align: center;"> These diagrams show, as a series of dots, the valence electrons of atoms. That is only the outer shell electrons. However they only work for the first 18 elements in the periodic table.