Elements, Compounds and Mixtures - Research Paper Example

Elements, Compounds and Mixtures A mixture is physical combination of two or more pure substances. A compound consists of two or more elements, which are chemically combined together. Mixtures have variable combinations, but in compounds, the respective elements combine in specific ratios (Steven and Susan, 2008). Example of a mixture is a salt solution consisting of water (H2O) and sodium chloride (NaCl). The two substances, water and sodium chloride are pure substances, and in a mixture, they are not chemically combined and hence can be isolated using physical processes, such as evaporation. However, water (H2O) is a compound consisting of a chemical combination of two elements, namely hydrogen and oxygen. Similarly, pure sodium chloride is a compound consisting of sodium and chlorine. Compounds are formed through a chemical reaction involving two or more elements resulting into a new substance. In the chemical reaction, heat energy is either generated or used, leading to drastic change in mass of the product from the initial constituents. The new substance formed in the chemical reaction has different physical and chemical properties from the substituent elements (Oxlade, 2007). However during formation of mixtures, no new substance is formed because it is a physical process. The resulting mixture could exist in different physical state but it still retains the physical and chemical properties of individual pure substances that formed it. In addition, formation of mixtures is not accompanied with changes in mass. Therefore, the weight of the mixture is the cumulative weights of individual pure substances in it. A pure substance could be a compound or an element. An element consists of the same type of atoms, which are shown using the same symbol. For example metals such sodium (Na), iron (Fe), copper (Cu), Magnesium (Mg) are elements. Non-metals such Sulphur(S), Phosphorous (P), Carbon(C) and hydrogen( H2), chlorine,(Cl2) among others are also elements. However, a compound consist of two or more different atoms, indicated using different symbols. For example sodium chloride (NaCl), carbon monoxide (CO), and sodium carbonate (Na2CO3 ) among others. An element cannot be split into simpler components, but compound can be split into the substituent elements or atoms (Patten, 1995). For instance, you cannot split hydrogen element into other different atoms because it consists of the same type of atoms. However, water, which is a compound, can be split into hydrogen and oxygen atoms. Similarly, sodium carbonate can be split into sodium, carbon and oxygen atoms). Ionic bond is formed through a complete transfer of electrons, from the outermost energy level of one atom to another in order for the individual atoms to become stable. The atom that loses electron(s) becomes positively charged while the recipient atom becomes negatively charged. The electrostatic attraction between the two opposite charges creates the ionic bond (Steven and Susan, 2008). For example when sodium element reacts with chlorine, one electron is completely transferred from sodium atom and is attracted to the chlorine atom. Consequently, the sodium atom, from which an electron is removed, becomes positively charged because protons in the nucleus exceed electrons by one and hence it becomes sodium ion Na+. The chlorine atom becomes negatively charged after receiving the electron from sodium, forming chloride ion (Cl-). Both sodium (Na+) and chloride (Cl-) ions form ionic bond, because of mutual attraction between opposite charges. Covalent bond is formed when two atoms share pair(s) of electrons in their outermost energy levels (Steven and Susan, 2008). This bond occurs mainly in gaseous and non-metallic elements and compounds. Since there is no transfer of electrons from the atoms involved, covalent substances are not charged and hence they are neutral. The atoms involved in covalent bonding become stable through shared pair(s) of electrons. For example chlorine atom consists of seven electrons in its outer energy levels. In its molecular form, chlorine gas (Cl2) consists of two chlorine atoms, linked by strong covalent bond. The covalent bond in chlorine molecule forms when both atoms share a pair of electrons (each electron from individual atom) in their outer energy levels. Hence, ionic bond forms from attraction of oppositely charged ions, while covalent bonds arise from sharing of electron pairs(s) in the outermost energy levels of atoms. Ionic bonds forms mainly in reactions involving metals and non metals. Reaction of halogens with group 1, 2 and 3 metals form ionic compounds. Covalent bonds occur mostly in non-metallic elements and compounds. For example, sulphur dioxide molecule is composed of covalent bonds between oxygen atoms and sulphur. Ionic compounds are formed when metals from the left side of the periodic table react with non-metals from the right side of the table. Metals from the left side include group one, two and three elements. Group one metals include lithium, sodium, potassium, while group 2 has magnesium and calcium. Aluminium is a group three metal. Non-metals on the right side of periodic table include elements such fluorine, chlorine and bromine (Steven and Susan, 2008). Oxygen and sulphur are also non-metals. In order to acquire chemical stability, metals in group one, two and three react by loss of respective electrons in their outermost energy levels (Oxlade, 2007). Hence, group one metals lose one electron, and group two and three lose two and three electrons respectively in order to acquire stability. Similarly, non metals become stable by gaining electrons in their outermost energy levels. Group sixteen elements gain two electrons while halogens gain a single electron in order to acquire stability. Therefore, when non metals and metals react, ionic bond is formed because complete transfer of electrons takes place, where metals donate their outermost electrons to the non metals. These forms cations and anions, which are positively and negatively, charged ions respectively. Non metals on the right side of the periodic table are highly electronegative than metals on the left side (Patten, 1995). Hence, it is easier for metals to lose electrons than to gain. Examples of ionic compound are sodium fluoride (NaF) and calcium chloride (CaCl2). Sodium fluoride is formed when sodium metal reacts with fluorine as shown 2Na + F2 2NaF Similarly, calcium chloride forms when calcium metal reacts with chlorine as shown below Ca+ Cl2 CaCl2 Covalent bonds forms when non-metals from the right side of periodic table bond with each other. These elements are highly electronegative, which implies that they attract electrons towards their nucleus with great force (Oxlade, 2007). Due to high electronegativity, they cannot lose or gain electrons to or from another, and instead share the required number of electrons in order to acquire stability. Hence these elements exist as molecules when they bond with each other or other non-metals. Examples include nitrogen (N2), oxygen (O2), fluorine, (F2), and chlorine (Cl2). Others include Nitrogen dioxide (NO2). Oxygen molecule has two strong covalent bonds formed when the two oxygen atoms share two pairs of electrons in their outermost energy levels. Nitrogen dioxide (NO2) has strong covalent bonds between nitrogen and oxygen atoms formed by sharing of pairs of electrons between the two different elements. References Oxlade, C. (2007). Elements and compounds: Elements in action. 2nd ed. London: Heinemann Patten, J.M. (1995). Elements, compounds and mixtures. New York: Rourke Book Company. . Steven, Z., and Susan, Z.(2008). Chemistry. Chicago: Cengage Learning. Read More