The Fundamentals of Chemistry
Chemistry is a fascinating and complicated science. In chemistry classes, students learn about the fundamentals of this science and its many applications in our daily lives.
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The molecular weight (MW) of a compound is the total mass of all the atoms in that compound. This is calculated by identifying the compound, finding its chemical formula (for example, water has a chemical formula of H2O), and then finding the atomic weights of each element in the compound. Each atomic weight is then multiplied by the number of atoms of that element in the compound (i.e., the number of hydrogen atoms in water is 6 and the number of carbon atoms in hexane is 14).
The molecular weight is then added together to get the compound’s molar mass. The molecular weight is usually expressed in unified atomic mass units (u) and can be converted to grams per mole using the molecular weight conversion factor or molar mass calculator. It can also be used to convert from molar mass to kilograms and back again. The molecular weight is also sometimes called the “formula weight,” which is the equivalent of the molar mass.
Atoms are so small that their weight cannot be measured directly. However, their mass can be measured relative to that of an atom of hydrogen. Dalton used experimental results to prepare the first Table of Atomic Weights. Early atomic weights were compared to the mass of oxygen-16, but after three isotopes of oxygen were discovered, it was decided in 1961 that carbon-12 would be the standard atom. An atom’s weight is now given in unified atomic masses, which are equal to one-twelfth the mass of an atom of carbon-12.
A “standard atomic weight” is the expected value that a chemist might expect to find in most naturally occurring samples of an element. Because the isotopic composition of natural terrestrial material varies, tabulated values are sometimes indicated with an interval. For example, Xe (xenon) has a characteristic terrestrial isotopic composition that prevents it from being a true single-atomic-weight element. Instead, its atomic weight is quoted as a range of two numbers, Xe(a), and Xe(b). The last significant figure in these tabulated values is only accurate to +-2 for all but twelve of the elements.
The atomic number of an element is the number of protons in its nucleus. An equal number of protons and electrons gives an atom a neutral charge. These electrons occupy orbits around the nucleus. The outermost orbits are available to form chemical bonds with other atoms.
In the periodic table, each element has an atomic number that is unique. This number is indicated by a symbol above the element’s name. The symbol is often shortened to an abbreviation of the element’s name, such as H for hydrogen or Cl for chlorine. A number may also be added to the symbol, which indicates a specific isotope.
For example, tungsten (W) is a steel-gray colored metal with the atomic number of 74 in the periodic table. It is a transition metal and can be found in many compounds including tungsten carbide, tungsten oxide, and tungsten filaments used in lamps. The name tungsten is derived from the Swedish word for “heavy stone.” The mineral scheelite, which is the source of the chemical, was found to interfere with the smelting of tin.
‘Reactivity’ is a term used to describe the tendency of chemical substances to undergo chemical reactions. The reactivity of an element can be predicted by its position on the periodic table and in groups or families of elements. The metals in the lower left corner of the periodic table react rapidly with water and other substances.
Reactivities are based on the propensity of electrons in an atom to interact with orbitals of other atoms to form chemical bonds. This is rationalised at the atomic level using older valence bond theory and atomic orbital theories, but also more accurately at the quantum level by the Schrodinger equation and molecular orbital theory.
In addition to its use in washing soda and water, the compound molybdenum is a valuable industrial ingredient in high-temperature furnaces and for arc welding electrodes. Chronic exposure to molybdenum compounds may cause pulmonary fibrosis.