Physical Properties of Materials - Research Paper Example

Chemistry Research Paper 07 March Physical Properties of Materials Introduction Matter is made up of particles that are thought to be in constant random motion. The materials that we encounter on a day-to-day basis are no exception. Physical properties may be described as the attributes that can be examined or quantified without interfering with the chemical constituents of a particular material. Factors such as temperature and pressure cause materials to go through certain modifications. However, these alterations are physical because the molecules that constitute the materials remain unaltered. This paper looks at the physical properties of materials in a bid to understand the interactions between matter and energy. It also pays particular attention to metals such as gold and silver. Physical Appearance The appearance of a substance is the first aspect that is observed before embarking on the details of other physical properties. Various substances have their characteristic appearances that set them apart from other materials. Water, for example, is usually described as a clear colorless liquid. Though many other substances have this appearance, a careful scrutiny of other physical properties helps to ascertain that indeed the liquid is water. Gold has a bright yellow shiny appearance especially when it is a large mass. Silver, on the other hand, has a bright, white metallic appearance. The appealing appearances of gold and silver make them the most popular metals in the manufacture of jewelry. Ductility and Malleability Ductility is the capacity of a substance to distort under the effect of tensile force. This property enables metals to be stretched and shaped into wires. Malleability, conversely, is the ability of a substance to distort under the influence of compressive forces. This property makes it possible for metals to be molded and hammered to form sheets. Gold is one of the most malleable and ductile metals ever known. Silver is ductile and malleable as well though not as malleable and as ductile as gold. Effect of Temperature on Materials An increase in temperature often causes changes in the physical states of materials. For example, solids often change to liquids and liquids change to vapor. Conversely, a decrease in temperature causes materials to revert to their original states. The instants at which these modifications occur are referred to as phase transitions (“Physical Properties of Material”). The change of a solid to a liquid is known as melting. The temperature at which this process happens is the melting point. The conversion of a liquid to vapor usually occurs at a transition temperature referred to as boiling point. At this temperature, the pressure of the liquid is equivalent to the atmospheric pressure of 1 atmosphere (approximately 760 mmHg). Therefore, changes in pressure influence the boiling points of substances. Pure substances are known to have sharp melting and boiling points. It is, therefore, possible to assess the purity of a substance by evaluating its boiling point. The melting point and boiling point of gold are 1062 oC (Belval 24) and 2000 oC respectively. For silver, the melting point is 962oC while the boiling point is 2212oC. In industrial applications, the boiling and melting points of materials are used to determine the functions of those materials in industrial processes. In situations where the boiling point or melting point is the only hindrance to using a given material in a certain process, the addition of another material may help improve the melting temperature. One such use is in the preparation of antifreeze used in automobile radiators. Heat and Electrical Conductivity The presence of valence electrons in the outermost energy levels in the atoms of substances gives rise to electrical and heat conductivity as these valence electrons are responsible for conducting. The extent of conduction is proportional to the number of free electrons and ions. Materials that have valence electrons and free ions are, therefore, known as conductors and can conduct electricity (Fahlman 239). They include metals such as copper, silver, and aluminium and ionic compounds. Insulators, in contrast, are materials that lack free electrons and are incapable of electrical and heat conductivity. They include substances like plastic, paper, rubber, and wood. Other substances such as silicon and germanium can only conduct under certain conditions of temperature. These substances are known as semiconductors and are used in the development of electrical circuits in electronics. When temperature or an electric potential difference is applied to the end of a material, the extent of flow of current or heat across a unit-area section is known as the thermal or electric conductance coefficient. The opposition to the flow of current is referred to as resistance. Therefore, good conductors have low resistance, whereas poor conductors have high resistance. Gold and silver are known to be excellent conductors of heat and electricity with electrical conductivities of 4.1×107 and 6.30×107s/m respectively. The thermal conductivities of gold and silver are 318 and 429 W.m-1.K-1. Thermal Expansion Coefficient Heating of materials causes the molecules in the material to vibrate and move about within the structure of the material. As a result, the material may expand. The rate of expansion of a material is measured as the thermal expansion coefficient, which is the extent of expansion (length) per unit of temperature (degree Kelvin). Conversely, cooling the material causes it to reduce in size. This facet influences the functioning materials especially in structural assemblies. Thermal expansion causes deformation and breakage of moving parts. Therefore, constructions such as railways and bridges in areas that experience temperature extremes need to factor the thermal expansion of materials used in the construction of such structures. Magnetic Properties The earth behaves like a big magnet. In substances, the atoms are usually arranged in certain orientations known as dipoles. When the dipoles in a substance have a north-south orientation, the substance is said to be magnetic because putting the object in the magnetic field of the earth (B) induces a field intensity of (B) in the substance. The proportion of B to H is referred to as magnetic susceptibility. Paramagnetism occurs when materials are attracted to a magnetic field, whereas diamagnetism happens when there is repulsion. Non-magnetic substances are those that do not exhibit a response in a magnetic field while magnetic substances are those that are affected by magnetic fields. The term ferromagnetic denotes strongly magnetic substances such as nickel, iron and cobalt. Gold and silver are diamagnetic as all the electrons are paired in such a manner that there is no stable net magnetic moment for each atom. Density Density is the mass of a substance for each unit of volume (Belval 25). The density of a substance is usually unique for each substance and can be used to identify it. The density of gold is just about 19.3 g/cm3 while silver has a density of 10.49 g/cm3 (“A Comparison of the Physical Properties of Gold, Silver, Platinum and Copper”). Solubility The solubility of a substance denotes the quantity of substance that dissolves in 100 milliliters of solvent (“Physical Properties of Material”). Temperature and type of solvent significantly influence the solubility of materials. Polar solvents such as ethanol and water dissolve polar substances, whereas nonpolar solvents such as benzene and methane dissolve nonpolar substances. The development of cleaning agents takes into account the solubility of dirt in the cleaning agent. The conventional gold does not dissolve in water, and neither does silver. However, a mixture of concentrated nitric acid and hydrochloric acid blended in the ratio of three to one can dissolve gold. This mixture of acids is referred to as aqua regia. Recent research has seen attempts to prepare synthetic gold that dissolves in water (Oh et al. 7604). This gold is made in the form of gold nanoparticles in the aqueous phase. Conclusion The physical properties of a particular material determine how it is used. Therefore, it is necessary that the physical properties of materials are examined in detail before deciding to put them to use in various applications. Works Cited A Comparison of the Physical Properties of Gold, Silver, Platinum and Copper n.d. Web. 08 March 2014. . Belval, Brian. Gold. New York, NY: The Rosen Publishing Group, 2007. Print. Fahlman, Bradley D. Materials Chemistry. 2nd ed. 2011. New York: Springer. Print. Oh, Eunkeu, Kimihiro Susumu, Ramasis Goswami and Hedi Mattoussi. “One-Phase Synthesis of Water-Soluble Gold Nanoparticles with Control over Size and Surface Functionalities.” Langmuir, 26.10 (2010): 7604–7613. Print. Physical Properties of Material n.d. Web. 08 March 2014. . Read More