Silicon is a metalloid situated in the third period and in the group 14 of the periodic table. Its atomic number is 14 and its atomic weight is 28. In this essay the basic periodic trends will be discussed and it will be determined whether silicon follows them. This essay will also discuss how the position of this element on the periodic table explains its chemical and physical properties and how these properties reflect the practical application of the element and its compounds.
Silicon is the eighth most abundant element by mass 1, however, it is mostly present as compounds. Over 90% of the Earth’s crust is made of silicate minerals and the most common compound of silicon, SiO2, is the most abundant chemical compound in the Earth’s crust, which is known better as beach sand 2. However, silicon was not discovered until late 1700s. In 1787 Antoine Lavoisier proposed that silica, silicon dioxide, was an element. Sir Humphry Davy proclaimed in the early 1800s that silica was in fact made up of more than one element. In 1824, Jöns Jacob Berzelius finally isolated silicon 3.
Silicon’s atomic number places this element in the metalloid part of the periodic table, giving it both metal and non-metal properties. The number 14 indicates that silicon has 14 protons and 14 electrons in the neutral state. The number of neutrons in its most common isotope is 14. Being in the group IV silicon has four valence electrons. Silicon is situated in the third period of the periodic table, which means that it has three orbitals. Moreover, this element is situated in the p-block, meaning that its characteristic orbital is 3p. The electronic configuration for silicon in the ground state is Ne3s23p2.
A few specific patterns in certain aspects of the element can be found in the periodic table of elements. Atomic radii decrease when moving across the period due to the increasing attraction forces and increase when going down the group due to the increasing number of orbitals. When comparing to silicon’s neighbors in the periodic table, this element has an atomic radius (118 pm) intermediate of those of phosphorus (110 pm) and aluminium (143 pm). Its radius is bigger than that of carbon (77 pm) and smaller than that of germanium (102 pm). Electronegativity increases when moving towards the top right corner of the periodic table, where fluorine, the most electronegative element, is situated. Silicon has an electronegativity (1.9) higher than that of aluminium (1.6) and lower than that of carbon (2.5). First ionization energy, the energy required to remove one mole of electrons from one mole of gaseous atom, increases when moving across the period due to the increasing nuclear charge and also increases when moving down the group due to the shielding effect. Silicon has a higher first ionization energy (787 kJ mol?1) than aluminium (578 kJ mol?1) and germanium (762 kJ mol?1) and a lower first ionization energy than carbon (1086 kJ mol?1) and phosphorous (1012 kJ mol?1). Electron affinity, the ability of an atom to accept an electron, decreases down a group of elements due to the increasing atomic radii and increases across the period due to the decreasing atomic radii. Electron affinity is higher for silicon (134 kJ mol?1) than for aluminium (42 kJ mol?1) and germanium (119 kJ mol?1). If following the trend, the electron affinity of silicon should be lower than that of phosphorus (72 kJ mol?1), however, it is not, as phosphorus has a half-filled orbital and is less likely to accept electrons. It is expected that the electron affinity of carbon (122 kJ mol?1) would be higher than that of silicon, however, it is lower, due to the small size of carbon and strong electronic repulsion. Silicon also has a vacant d-orbital which attract electrons more. Metallic character decreases when moving across the period due to the decreasing radii and increases when going down the group due to the increasing radii. Silicon has less metallic character than aluminium and germanium but more than carbon and phosphorus.
Silicon does not exist in nature in its pure form, however, under normal conditions it is a rather inert dark grey solid 4. Silicon forms a giant covalent crystal lattice in a cubical diamond shape, similar to that of germanium and carbon 5. This structure is very hard and resistant to breaking or damaging. This is why silicon has such a high melting point (1687 K) and boiling point (3538 K) 4. Silicon is a semiconductor as there are no obviously free electrons in the structure, and although it conducts electricity, it doesn’t do so in the same way as metals 6. Similarly to its neighbor, aluminium, silicon forms a surface layer of its dioxide to protect itself from oxidation 7. Due to this, silicon does not react with the air in normal conditions. Water vapor reacts with silicon to form silicon dioxide and hydrogen 8. Silicon reacts with gaseous sulfur at 600 °C and gaseous phosphorus at 1000 °C 8. Halogens react with silicon readily despite the dioxide layer; fluorine at room temperature (SiF4 is formed), chlorine at about 300 °C (SiCl4), and bromine and iodine at about 500 °C (SiBr4 and SiI4) 8. Silicon does not react with most aqueous acids apart from a mixture of concentrated nitric acid and hydrofluoric acid. It dissolves in hot aqueous alkali to form silicates 8.
Silicon dioxide (SiO2), also known as silica, is one of the best-studied compounds. It has twelve crystal modifications 9. The most abundant of them is ?-quartz, in its pure form occurring as rock crystal; impure forms include rose quartz, amethyst, and many others. It is also an important component of many rocks such as granite 9. Many other minerals found on Earth are composed of other modifications of silica. Silicon dioxide is rather inert chemically. It can react with fluorine at room temperature to form silicon tetrafluoride, carbon and hydrogen can also react with ot at high temperatures 7. It does not react with any acids other than hydrofluoric acid. It slowly dissolves in hot concentrated alkalis 7.
Industrial production of silicon includes converting silica to pure silicon by heating it with petroleum coke in in three submerged electric arc furnaces 10. Silicon and its compounds due to their hard structure is used widely in manufacturing structural components, such as cement, concrete, bricks, glass and many others. It is also used in electronics, machinery, as a waterproofing component and in explosives 4.