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Answers
Answer:
Iron
Explanation:
Iron is a chemical element with symbol Fe (from Latin word Ferrum). Its atomic number is 26 and atomic mass is 55.85. It has a melting point of 1538 deg C and boiling point of 2862 deg C. The density of iron is 7.87 grams/cu cm. It is a metal in the first transition series. Like the elements of other group 8 elements (ruthenium and osmium), iron exists in a wide range of oxidation states, ?2 to +6, although +2 and +3 are the most common. Iron as a common metal is mostly confused with other metals such as different types of steels.
Iron is by mass the most common element on the earth, forming much of earth’s outer and inner core. It is the fourth most common element and the second most common metal in the earth crust. Steels contain over 95 % Fe. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water.
Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals which form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, exposing fresh surfaces for corrosion.
Iron objects have been found in Egypt dating from around 3500 BCE (Before Common Era). They contain around 7.5 % nickel, which indicates that they were of meteoric origin. The ancient Hittites of Asia Minor (today’s Turkey) were the first to smelt iron from its ores around 1500 BCE. The ‘Iron Age’ had begun at that time. The first person to explain the various types of iron was René Antoine Ferchault de Réaumur who wrote a book on the subject in 1722. This explained how steel, wrought iron, and cast iron, were to be distinguished by the amount of charcoal (carbon) they contained. The industrial revolution which began during that century relied extensively on this metal.
In iron, the basic building blocks are the individual atoms of Fe. The grains are called crystals and they are made up of atoms. All of the atoms are uniformly arranged in layers. If lines are drawn connecting the centres of the atoms, a three-dimensional array of little cubes stacked together to fill space is generated. At room temperature, the cubes have an atom at each of the eight corners and one atom right in the middle of the cube. This crystal structure is called a body-centered cubic (bcc) structure, and the geometric arrangement of atoms is often called a bcc lattice. The crystal lattice can be envisioned as three sets of intersecting planes of atoms, with each plane set parallel to one face of the cube. Iron with a bcc structure is called ferrite. Another name for ferrite is ‘alpha’ iron.
Upon heating, iron experiences two changes in crystal structure. The first change occurs when the iron is heated to 912 deg C. At this temperature the crystal structure changes spontaneously from bcc to a new structure called face-centered cubic (fcc). In fcc structure, atoms lie on the corners of a cube as well as one atom at each of the six faces of the cube. Like the low temperature bcc structure, this structure is called either austenite or ‘gamma’ iron.