Mixture and compound Essay Example | Topics and Well Written Essays - 750 words

Mixture and compound - Essay Example A compound comprises of a fixed ratio, for example, in water, there are two hydrogen molecules for every oxygen molecule. In mixtures, the ratios of the individual elements vary, depending on the use of the mixture. A mixture is also only composed of the constituent element, and the properties of the mixture are those of the individual elements (Phillips, 1998). A compound on the other hand, is a new substance with new chemical properties, e.g. common salt, a white compound, does not bear any resemblance to sodium, a grey metal, or chlorine, a greenish-yellow gas (Phillips, 1998). To distinguish a mixture from a compound, use their chemical properties (Patten, 1995). A mixture retains the properties of the individual substance that are part of its composition. For example, air is a mixture of gasses and is has properties of all the gasses, e.g. it supports burning, a chemical property of oxygen gas as other elements in the air do not support burning (Patten, 1995). Compounds have an all together different set of chemical properties from those of the constituent elements (Phillips, 1998). It is not possible to tell the chemical composition of a compound without a chemical test, unlike a mixture. Therefore, changes in color, chemical properties and physical properties are the distinguishing factors between compounds and mixtures (Phillips, 1998). When elements combine to form compounds, different types of bonds hold their atoms together (a bond is the energy that hold the atoms in a compound together), covalent, ionic, dative and metallic bonds (Pettifor, 1995). Covalent bonds exist between two non-metallic elements such as oxygen and carbon. When carbon burns in the air, a chemical reaction occurs, leading to the formation of carbon dioxide. Due the bond between these two elements is a dative bond (a special form of the covalent bond). A chemical reaction between two non-metals leads to the formation of a covalent bond (Pettifor, 1995). Due to an almost full out er energy level, non-metals do not lose electrons in a reaction; instead, they share the electrons in the outermost rings to form octets in the case of oxygen and carbon (Sebera, 1964). When a metal reacts with a non-metal, the metal donates the electrons in its outermost shell to the non-metal. That way, both atoms have complete shells in their outermost energy levels. In ionic bonding, the metal acquires a positive charge due to more protons than electrons in an atom while the non-metallic atom acquires a negative charge. These two opposite charges attract, holding the compound strongly together. While the covalent bond is strong between the atoms involved, the resultant structure I held by weak Van der Waals forces of attraction, which explains why ionic compounds lean to have a higher melting point than covalent compounds (Sebera, 1964). To achieve stability, elements need their outermost energy levels filled with electrons (Pettifor, 1995). For metals, their outermost energy le vels are comprised of a maximum of three electrons e.g. in aluminum. Elements with four electrons are non-metals , but some of them such as silicon and carbon have metallic properties, e.g. graphite, an allotrope of carbon conducts electricity, a property of metals (Sebera, 1964). In chemical reactions, it is easier to dislodge the few electrons in the outer shell than to gain electrons needed to fill the outermost