Ionic Bonding
Some atoms form Ionic Bonds with each other. These bonds usually form between atoms that have high differences in electronegativity, especially between metals and nonmetals.
In reality, all bonds are part ionic and part covalent. The percent of the bond that is ionic or covalent is determined in the difference in electronegativities. Any difference higher that 1.7 is considered ionic, as the bond type has greater than 50% ionic character.
Unlike covalent bonds, ionic bonds do not form molecules in the same way that covalent bonds do. There are formula units, which are the smallest ratios in whole numbers of the proportions of atoms in ionic compounds. For example, table salt (NaCl) has only one of each sodium and chlorine in a formula unit. However, each NaCl is not separate from the others. They form 3D crystals that contain uncountable numbers of formula units of the ionic compound all bound to eachother in ways that their charges are as neutralized as possible.
In reality, all bonds are part ionic and part covalent. The percent of the bond that is ionic or covalent is determined in the difference in electronegativities. Any difference higher that 1.7 is considered ionic, as the bond type has greater than 50% ionic character.
Unlike covalent bonds, ionic bonds do not form molecules in the same way that covalent bonds do. There are formula units, which are the smallest ratios in whole numbers of the proportions of atoms in ionic compounds. For example, table salt (NaCl) has only one of each sodium and chlorine in a formula unit. However, each NaCl is not separate from the others. They form 3D crystals that contain uncountable numbers of formula units of the ionic compound all bound to eachother in ways that their charges are as neutralized as possible.
In the image at right, the 3D structure of table salt is shown. The black dots represent chlorine (Cl) atoms and the white dots represent sodium (Na). As you can see, the sodium bind to the chlorine, which binds to another sodium and so on. The ratio of sodium to chlorine in the crystal is 1 to 1, leaving the formula NaCl, or technically Na1Cl1. When the bonds are formed and the atoms take their places in the crystal, they take places where they are as far as possible away from atoms of the same charge. Since sodium has a charge of +1 and chlorine of -1, they are attracted to each other. So the sodium atoms take places directly across form each other around the chlorine atom, at all six available sides. The same goes for chlorine around every available side of the sodium atoms. The image at the bottom right demonstrates the TRUE structure of a salt crystal, with every atom taking place around atoms of opposite charge.
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In addition, if the formula unit was MgI2, for Magnesium Iodide crystals, then there are two Iodine atoms for every one Magnesium atom in the crystal. This is because Magnesium has a +2 charge and sodium only +1, meaning that there have to be twice as many sodium atoms as magnesium atoms in a crystal. This forms the structure you can see below. As all crystals have more locations for more atoms to fit in, they can be grown and grown indefinitely. More and more formula units can be added to a crystal in spaces of attraction to atoms of the opposite charge.
Dissociation of Ions in Liquids + Ionic Equations
Certain ionic compounds, including substances such as Sodium Chloride, Copper Sulfate, and all the nitrates are soluble in water. When ionic compounds dissolve, they dissociate into their component ions that are then dispersed throughout the liquid. For example, NaCl becomes one Na+ ion and one Cl- ion. In this state, they are able to react with other ions that may be in the solution. For example, each mole of Potassium Ferricyanide (K3[Fe(CN)6]) and Copper Sulfate (CuSO4) added to water will form 3 moles of K+ ions, 1 mole of Fe(CN)6 ions, one mole of Copper ions, and one mole of Sulfate ions. So, one mole of both the Potassium Ferricyanide and Copper Sulfate produces 6 moles of ions in solution. This can be represented by the following Ionic Equation:
As you can see, in an ionic equation all of the ions are treated as individual reactants and products. So the Potassium ions (K+) and the Ferricyanide ions (Fe(CN)6) both are treated as individual reactants as they are both present in dissociated form in the solution. After balancing, the correct ionic equation is shown below:
Which has the final regular form of:
Sometimes, however, ions of dissolved compounds do not react while the other ions do. These non-reacting ions are referred to as spectator ions. They remain in the solution after the other compounds have finished reacting. So, for the above equation, Potassium and Sulfate are both considered to be spectator ions because they remain dissolved in the solution after the copper and ferricyanide have finished reacting. The ionic equation that remains after the spectator ions have been removed is referred to as the net ionic equation, demonstrated below:
As you can see, only the ions that actually participate in the reaction are represented. They form the precipitate Copper Ferricyanide and so are removed from the solution.