Description the Difference between a Mixture and a Compound - Essay Example

Description the Difference between a Mixture and a Compound A compound is a substance made up of two or more elements combined in a constant ratio (Campbell and Reece, 2004). By virtue of the law of constant composition, the proportion of the mass of elements forming a chemical compound is always fixed no matter the source of the compound. For instance, the combination of the elements sodium (Na) and chloride (Cl) in a 1:1 ratio always forms table salt or sodium chloride (NaCl) (Campbell and Reece, 2004). Regardless of where it comes from, water (H2O) is a chemical compound always composed of 11.2% hydrogen and 88.8% oxygen. In addition, a compound has properties beyond those of its constituent elements (Carey, 2000). Sodium for instance, exists as a metal in pure form while pure chlorine exists in a gaseous state. But when combined, the resulting compound (NaCl) exhibits a new set of characteristics different from that of the component elements. And since the chemical properties of its constituents are not retained once they are combined, the components of a compound cannot be separated from each other by simple mechanical means (Carey, 2000). Separation requires chemical or energy input (Kimball, 2011). On the other hand, a mixture is a combination of two or more substances in varying proportions (Senese, 2005). For instance, bronze is a metal mixture of copper and tin, which may contain as little as 4%, or as much as 12% of tin. The constituents of a mixture do not come together to form new molecules; the components simply mix while preserving its chemical characteristics (Kimball, 2011). When salt is dissolved in water to form saltwater, the chemical identities of each substance remains unaltered. In addition, no new compound is created from the mixture of H2O and NaCl. Because each component retains its chemical integrity, mixtures can be easily be separated into its components by physical means (Kimball, 2011). 2. Suppose that you have a pure substance. How can you tell whether it is a compound or an element? An element is the simplest pure substance. It is composed only of a single type of atom and therefore could no longer be broken down by chemical techniques (McMurry and Fay, 2003). Oxygen for instance, is an element composed of oxygen atoms only. The element copper is composed solely of copper atoms. Meanwhile, a compound is a pure substance composed of two or more kinds of atoms chemically combined together (McMrray and Fay, 2003). Methane (CH4) for instance, is a compound consisting of a single carbon atom chemically bonded to four hydrogen atoms. Water (H20) is also a compound consisting of two atoms of hydrogen and a single oxygen atom. Following this line of thinking, the distinction between a compound and an element lies on its capability to be broken down into simpler substances. For example, water, when subjected to hydrolysis will separate into hydrogen and oxygen atoms. When a pure substance could no longer be decomposed into simpler substances, it is an element. 3. What is the difference between ionic and covalent compounds? Substances held together by ionic bonds are called ionic compounds (Campbell and Reece, 2004). An ionic bond is formed when ions of opposite charges (positive and negative charges) attract, such as when an atom of sodium encounters an atom of chlorine (Campbell and Reece, 2004). When these two atoms meet, one electron of sodium is transferred to chlorine, creating charged species in the process (Campbell and Reece, 2004). Sodium, which lost one electron, gains a positive charge while chlorine, which received one electron, gains a negative charge. Because of the opposite charges exhibited by these atoms, they attract each other to form NaCl. On the other hand, covalent bonds are formed by sharing of valence electrons by two atoms (Nave, 2010). Valence electrons are those electrons found in the outermost orbital shell of an electron (Campbell and Reece, 2004). When two hydrogen atoms, each with a single valence electron meet, the outermost orbitals overlap to allow sharing of electrons (Campbell and Reece, 2004). As a result, each hydrogen atom now shares two electrons, holding the two atoms together in a covalent bond to form H2 molecule. 4. Explain why ionic compounds are formed when a metal from the left side of the periodic table reacts with a nonmetal from the right side. Give two examples of such compounds. The nonmetals on the right side of the periodic table exhibit greater electronegativity compared to the elements on the right side (Nave, 2010). Electronegativity is the tendency to attract electrons (Campbell and Reece, 2004). Hence, the more electronegative an atom is, the stronger its capability to pull electrons to itself and gain a negative charge (Campbell and Reece, 2004). Meanwhile, the metals on the left side of the periodic table are less electronegative. This means that they have a higher tendency to loss their electrons and gain a positive charge. Hence, when a metal and nonmetal reacts, by virtue of the difference in their electronegativity, an ionic bond is created, forming an ionic compound (Nave, 2010). Examples of which are calcium oxide (CaO) and magnesium chloride (MgCl2). 5. Explain why covalent bonds are formed when nonmetals from the right side of the periodic table bond with each other. Give two examples of such compounds. In the event when two reacting atoms demonstrate an equal electronegativity- such as that exhibited by two atoms of the same element- or almost the same electronegativity, the tendency is to share rather than transfer electrons (Nave, 2010). This sharing of electrons between atoms forms covalent bonds. The propensity to share electrons is driven by the need to reach an octet (8 valence electrons) in order to stabilize the outermost shell of an atom (Campbell and Reece, 2004). Examples of covalent compounds are sulfur dioxide (SO2) and nitrogen dioxide (NO2). References: Senese,F. 2005. Matter. Accessed at:http://antoine.frostburg.edu/chem/senese/101/matter/index.shtml. Date Accessed: May 14, 2012 Campbell, N., and Reece, Jane. 2004. Biology. 6th ed. Peason Education South Asia PTE LTD. Jurong, Singapore. Pp. 28-36 Carey, F. 2000. Organic Chemistry. The McGraw-Hill Companies, Inc. New York. Ch1 Kimball, J. 2011. Mixtures and Compounds- Kimball’s Biology Pages. Accessed at: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Mixtures.html. Date Accessed: May 14, 2012 McMurry, J., and Fay, R. 2003. Chemistry. 4th edition. Prentice Hall. San Diego, USA. Ch. 1-2 Nave, R. 2010. Chemical Bonding. Accessed at: http://hyperphysics.phy- astr.gsu.edu/hbase/chemical/bond.html. 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