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This article discusses the bonding in ionic, covalent, and metallic compounds, including their structures, functions, melting points, electrical conductivity, and solubility. It also explores the differences between polar and nonpolar covalent bonds and the properties of polar molecules.
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BondingIonicCovalentMetallicDetermined by difference in Electronegativity between atoms.
Ionic Compounds • Crystalline solids (made of ions) • High melting and boiling points • Conduct electricity when melted or dissolved. • Many soluble in water but not in nonpolar liquid • Covalent Compounds • Gases, liquids, or solids (made of molecules) • Low melting and boiling points • Poor electrical conductors in all phases • Many soluble in nonpolar liquids but not in water
Ionic Compounds • Structure and Function • Covalent Compounds • Structure and Function
Most covalent compounds have relatively low melting points and boiling points.While the ions in an ionic compound are strongly attracted to each other, covalent bonds create molecules that can separate from each other when a lower amount of energy is added to them. Therefore, molecular compounds usually have low melting and boiling points. Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds.The enthalpy of fusion is the amount of energy needed, at constant pressure, to melt one mole of a solid substance. The enthalpy of vaporization is the amount of energy, at constant pressure, required to vaporize one mole of a liquid. On average, it takes only 1% to 10% as much heat to change the phase of a molecular compound as it does for an ionic compound. Covalent compounds tend to be soft and relatively flexible.This is largely because covalent bonds are relatively flexible and easy to break. The covalent bonds in molecular compounds cause these compounds to take form as gases, liquids and soft solids. As with many properties, there are exceptions, primarily when molecular compounds assume crystalline forms.Covalent compounds tend to be more flammable than ionic compounds.Many flammable substances contain hydrogen and carbon atoms which can undergo combustion, a reaction that releases energy when the compound reacts with oxygen to produce carbon dioxide and water. Carbon and hydrogen have comparable electronegativies so they are found together in many molecular compounds. When dissolved in water, covalent compounds don't conduct electricity.Ions are needed to conduct electricity in an aqueous solution. Molecular compounds dissolve into molecules rather than dissociate into ions, so they typically do not conduct electricity very well when dissolved in water. Many covalent compounds don't dissolve well in water.There are many exceptions to this rule, just as there are many salts (ionic compounds) that don't dissolve well in water. However, many covalent compounds are polar molecules that do dissolve well in a polar solvent, such as water. Examples of molecular compounds that dissolve well in water are sugar and ethanol. Examples of molecular compounds that don't dissolve well in water are oil and polymerized plastic. Note that network solids are compounds containing covalent bonds that violate some of these "rules". Diamond, for example, consists of carbon atoms held together by covalent bonds in a crystalline structure.
Ionic vs. Covalent • Ionic – Chlorine takes the electron from sodium. • Covalent – Two oxygen atoms share the electrons equally.
Positive and negative IONSAttraction between positive and negative.
Positive and negative IONSBecomes brittle when the like charges line up and repel.
Video • Video – Metallic bonding and metallic properties
Polaritystrength of 2 students tugging on a rope. Tug of war with equal (covalent) strength, with offset (weak and strong polar) strength and if one completely takes the rope (ionic).
Polar Covalent • Oxygen has higher electronegativity than Hydrogen. • The electrons spend more time closer to the Oxygen atom.
Ionic - TransferCovalent -Equal sharingPolar Covalent - Unequal sharing
