The blue dots are the sodium atoms; the pale green dots are the larger chlorine atoms. Ionic bonds between each atom forms a relatively strong bond and a three-dimensional, cubic structure. Below is a look at just a single layer:. Note that each positive sodium ion is next to a negative chlorine ion. Now imagine this arrangement continuing outward in all directions with thousands of billions of atoms. Sometimes atoms will share electrons instead of transferring them between the two atoms.
This sharing allows both atoms to fill their outermost shell while forming a very strong bond between the atoms. Elements such as carbon C and Silicon Si form strong covalent bonds. Below is a picture showing the electron sharing that occurs in the mineral diamond. Diamonds are made of pure carbon and its the way that the carbon atoms are bonded that makes diamond the hardest substance.
Each carbon atom has 4 electrons blue dots in its outer shell. This allows the atom to share electrons with 4 other carbon atoms surrounding it as the middle carbon atom is doing. Each of these in turn will share the remaining 3 electrons with adjacent carbon atoms beside, above and below it, and those with other carbon atoms, etc. Similarly, covalent bonding between silicon and oxygen atoms makes strong bonds that form a large group of minerals called silicates more on those later. Metallic bonds form when the outer shell electrons are shared between neighboring atoms.
For example, in Fig. In Figure 2. P olyatomic ions can bond with monatomic ions or with other polyatomic ions to form compounds. In order to form neutral compounds, the total charges must be balanced. A molecule or compound is made when two or more atoms form a chemical bond that links them together. As we have seen, there are two types of bonds: ionic bonds and covalent bonds. In an ionic bond, the atoms are bound together by the electrostatic forces in the attraction between ions of opposite charge.
Ionic bonds usually occur between metal and nonmetal ions. For example, sodium Na , a metal, and chloride Cl , a nonmetal, form an ionic bond to make NaCl. In a covalent bond, the atoms bond by sharing electrons.
Covalent bonds usually occur between nonmetals. For example, in water H 2 O each hydrogen H and oxygen O share a pair of electrons to make a molecule of two hydrogen atoms single bonded to a single oxygen atom.
In general, ionic bonds occur between elements that are far apart on the periodic table. Covalent bonds occur between elements that are close together on the periodic table. Ionic compounds tend to be brittle in their solid form and have very high melting temperatures. Covalent compounds tend to be soft, and have relatively low melting and boiling points. Water, a liquid composed of covalently bonded molecules, can also be used as a test substance for other ionic and covalently compounds.
Ionic compounds tend to dissolve in water e. Properties of ionic and covalent compounds are listed in Table 2. The properties listed in Table 2. Like other ionic compounds, sodium chloride Fig.
Chlorine gas Fig. Ionic and covalent compounds also differ in what happens when they are placed in water, a common solvent. For example, when a crystal of sodium chloride is put into water, it may seem as though the crystal simply disappears.
Three things are actually happening. Ionic compounds like sodium chloride dissolve, dissociate, and diffuse. Covalent compounds, like sugar and food coloring, can dissolve and diffuse, but they do not dissociate.
Without stirring, the food coloring will mix into the water through only the movement of the water and food coloring molecules. As water evaporates, the salt solution becomes more and more concentrated. Eventually, there is not enough water left to keep the sodium and chloride ions from interacting and joining together, so salt crystals form. This occurs naturally in places like salt evaporation ponds Fig.
Salt crystals can also be formed by evaporating seawater in a shallow dish, as in the Recovering Salts from Seawater Activity. This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. So the transfer of the electron to chlorine in NaCl produces ions, each of which can exist independently of any one partner.
As they are oppositely charged there will be an attraction between them — this attraction is the ionic bond. In sodium chloride, each ion is surrounded by as many ions of opposite charge as space allows. In this case the number is six Figure 1. Yes — you can pass chlorine gas over sodium and a reaction will take place to form sodium chloride.
A much more likely process is for ionic compounds form from solutions in water in which the ions are already present and crystallise out of solution when water is evaporated. However — this apart — the basic definition of the ionic bond still stands — that is the electrostatic attraction between cations and anions. Making the decision to study can be a big step, which is why you'll want a trusted University.
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