Why does sodium become an ion

This is a good example of an atom that naturally has an unequal number of electron and protons. The net positive sodium ion is now attracted to the net negative chlorine ion and this attraction forms what we call an "ionic bond". But, in reality, we don't have just one sodium ion sticking to ion chlorine ion. Instead, a lattice of many sodium ions ionically bonds to a lattice of chlorine ions, and we end up with a crystalline solid.

Each sodium ion in the crystalline lattice of table salt is bound to the 6 nearest chlorine ions, and the same goes for each chlorine ion. The atoms in table salt are therefore already in the ionized state. Adding water does not ionize the atoms in salt, because they are already ionized.

Instead, the water molecules stick to the already formed ions in the salt. This type of attraction between fully charged components is called an ionic bond or a salt bridge.

Ionic bonds within a salt crystal may be quite strong. However, if a crystal of salt is dissolved in water, each of the individual ions becomes surrounded by water molecules, which inhibit oppositely charged ions from approaching one another closely enough to form ionic bonds.

The charged ends of the water molecules are so strongly attracted to the charged ions in the salt crystal that the water destroys the solid lattice structure of the salt and each sodium and chlorine ion becomes surrounded by a layer of sticky water molecules.

In chemistry, we say the salt has been dissolved by the water. It's like a rock band exiting the limousine into a crowd of fans and becoming separated as each band member gets surrounded by his own circle of fans. The second shell has six electrons 2 s 2 2 p 4 and needs two electrons to achieve octet. Oxygen will gain 2 electrons.

In many cases, elements that belong to the same group vertical column on the periodic table form ions with the same charge because they have the same number of valence electrons. Thus, the periodic table becomes a tool for remembering the charges on many ions. Note the convention of first writing the number and then the sign on a multiply charged ion. These diagrams have two advantages over the electron shell diagrams.

First, they show only valence electrons. Second, instead of having a circle around the chemical symbol to represent the electron shell, they have up to eight dots around the symbol; each dot represents a valence electron. These dots are arranged to the right and left and above and below the symbol, with no more than two dots on a side.

For example, the representation for sodium is as follows:. For the above diagrams, it does not matter what sides the dots are placed on in Lewis diagrams as long as each side has a maximum of two dots. These diagrams are called Lewis electron dot diagrams , or simply Lewis diagrams, after Gilbert N. Lewis, the American chemist who introduced them. Up to four dots are placed above, below, to the left, and to the right of the symbol in any order, as long as elements with four or fewer valence electrons have no more than one dot in each position.

The next dots, for elements with more than four valence electrons, are again distributed one at a time, each paired with one of the first four. In other words, place the dots singly on each side before pairing them. The Lewis electron dot diagram of fluorine, for example, with seven valence electrons, is constructed as follows:. For the main group elements, the number of valence electrons is the same as the group number listed at the top of the periodic table.

Starting with lithium and bromine atoms, use Lewis diagrams to show the formation of the ionic compound LiBr.

From the periodic table, we see that lithium is in the same column as sodium, so it will have the same valence shell electron configuration. That means that the neutral lithium atom will have the same Lewis diagram that the sodium atom has. Similarly, bromine is in the same column as chlorine, so it will have the same Lewis diagram that chlorine has.

Starting with magnesium and oxygen atoms, use Lewis diagrams to show the formation of the ionic compound MgO. Some ionic compounds have different numbers of cations and anions. In those cases, electron transfer occurs between more than one atom. For example, here is the formation of MgBr 2 :. This is called charge balance.

The number of each type of ion is indicated in the formula by the subscript. Most of the elements that make ionic compounds form an ion that has a characteristic charge.

Some elements, especially transition metals, can form ions of multiple charges. Chlorine Cl in its lowest energy state called the ground state has seven electrons in its outer shell. Again, it is more energy-efficient for chlorine to gain one electron than to lose seven. Therefore, it tends to gain an electron to create an ion with 17 protons, 17 neutrons, and 18 electrons, giving it a net negative —1 charge.

It is now referred to as a chloride ion. In this example, sodium will donate its one electron to empty its shell, and chlorine will accept that electron to fill its shell.

Both ions now satisfy the octet rule and have complete outermost shells. Note that these transactions can normally only take place simultaneously: in order for a sodium atom to lose an electron, it must be in the presence of a suitable recipient like a chlorine atom. Figure 1. In the formation of an ionic compound, metals lose electrons and nonmetals gain electrons to achieve an octet.