A compound is a substance that is created when two or more elements are bonded by a chemical reaction. It is difficult to split a compound back into its original elements. Compounds do not necessarily take on the characteristics of the elements that form them. For example, sodium is a metal and chlorine is a gas. Together they form a compound called sodium chloride, which is not like either of them. In fact, sodium chloride is the chemical name for the salt that we put on our food.
In chemistry, a compound is a substance that results from a combination of two or more different chemical elements, in such a way that the atom s of the different elements is held together by chemical bonds that are difficult to break. These bonds form as a result of the sharing or exchange of electron s among the atoms. The smallest unbreakable unit of a compound is called a molecule.
A compound differs from a mixture, in which bonding among the atoms of the constituent substances does not occur. In some situations, different elements react with each other when they are mixed, forming bonds among the atoms and thereby producing molecules of a compound. In other scenarios, different elements can be mixed and no reaction occurs, so the elements retain their individual identities. Sometimes, when elements are mixed, the reaction occurs slowly (as when iron is exposed to oxygen); in other cases it takes place rapidly (as when lithium is exposed to oxygen). Sometimes, when an element is exposed to a compound, a reaction occurs in which new compounds are formed (as when pure elemental sodium is immersed in liquid water).
Often, a compound looks and behaves nothing like any of the elements that comprise it. Consider, for example, hydrogen (H) and oxygen (O). Both of these elements are gases at room temperature and normal atmospheric pressure. But when they combine into the familiar compound known as water, each molecule of which contains two hydrogen atoms and one oxygen atom (H 2 O), the resulting substance is a liquid at room temperature and normal atmospheric pressure.
The atoms of a few elements do not readily bond with other elements to form compounds. These are called noble or inert gases: helium, neon, argon, krypton, xenon, and radon. Certain elements readily combine with other elements to form compounds. Examples are oxygen, chlorine, and fluorine.
1: Pure water is a compound made from two elements – hydrogen and oxygen. The ratio of hydrogen to oxygen in water is always. Each molecule of water contains two hydrogen atoms bonded to a single oxygen atom.
2: Pure table salt is a compound made from two elements – sodium and chlorine. The ratio of sodium ions to chloride ions in sodium chloride is always.
3: Pure methane is a compound made from two elements – carbon and hydrogen. The ratio of hydrogen to carbon in methane is always.
4: Pure glucose is a compound made from three elements – carbon, hydrogen, and oxygen. The ratio of hydrogen to carbon and oxygen in glucose is always.
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