• 1.) Ionic compounds form crystal lattices rather than amorphous solids. Although molecular compounds form crystals, they frequently take other forms plus molecular crystals typically are softer than ionic crystals. At an atomic level, an ionic crystal is a regular structure, with the cation and anion alternating with each other and forming a three-dimensional structure based largely on the smaller ion evenly filling in the gaps between the larger ion.
  • 2.) Just as ionic compounds have high melting and boiling points, they usually have enthalpies of fusion and vaporization that can be 10 to 100 times higher than those of most molecular compounds. The enthalpy of fusion is the heat required melt a single mole of a solid under constant pressure. The enthalpy of vaporization is the heat required for vaporize one mole of a liquid compound under constant pressure.
  • 3.) Ionic crystals are hard because the positive and negative ions are strongly attracted to each other and difficult to separate, however, when pressure is applied to an ionic crystal then ions of like charge may be forced closer to each other. The electrostatic repulsion can be enough to split the crystal, which is why ionic solids also are brittle.
  • 4.) A familiar example of an ionic compound is table salt or sodium chloride. Salt has a high melting point of 800ºC. While a salt crystal is an electric insulator, saline solutions (salt dissolved in water) readily conduct electricity. Molten salt is also a conductor. If you examine salt crystals with a magnifying glass, you can observe the regular cubic structure resulting from the crystal lattice. Salt crystals are hard, yet brittle — it’s easy to crush a crystal. Although dissolved salt has a recognizable flavor, you don’t smell solid salt because it has a low vapor pressure.
  • 5.)An example of a Chemical Formula is H2O.  In case you didn’t know, this is the chemical formula or water.  It means that there are two atoms of hydrogen and one atom of oxygen for every molecule of water.  The subscript (lower and smaller) two after the H indicates that there are two hydrogen molecules, as hydrogen is abbreviated H.  Also, since there is no subscript after the O, this indicates that there is only one oxygen atom in one molecule.  
  • 6.) The molecular formula, sometimes known as the true formula, tells us the actual number of the different elements in one molecule of a compound. In a molecular formula, each element is written as their symbols in the periodic table, and the number of atoms for each element is shown by the subscript (the small number to the lower right of the element.
    7.) The word empirical is defined as something that is verified by observation. In chemistry, we verify facts by performing experiments. So, the empirical formula is defined as the simplest ratio of whole numbers of elements that make up a compound, and this type of formula is derived from experimental data.
  • 8.) Chemical reactions are an integral part of technology, of culture, and indeed of life itself. Burning fuels, smelting iron, making glass and pottery, brewing beer, and making wine and cheese are among many examples of activities incorporating chemical reactions that have been known and used for thousands of years. Chemical reactions abound in the geology of Earth, in the atmosphere and oceans, and in a vast array of complicated processes that occur in all living systems.
  • 9.) Chemical reactions must be distinguished from physical changes. Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same. No matter what its physical state, water (H2O) is the same compound, with each molecule composed of two atoms of hydrogen and one atom of oxygen. However, if water, as ice, liquid, or vapour, encounters sodium metal (Na), the atoms will be redistributed to give the new substances molecular hydrogen (H2) and sodium hydroxide (NaOH). By this, we know that a chemical change or reaction has occurred.
  • 10.) The first substantive studies in this area were on gases. The identification of oxygen in the 18th century by Swedish chemist Carl Wilhelm Scheele and English clergyman Joseph Priestley had particular significance. The influence of French chemist Antoine-Laurent Lavoisier was especially notable, in that his insights confirmed the importance of quantitative measurements of chemical processes. In his book Traité élémentaire de chimie (1789; Elementary Treatise on Chemistry), Lavoisier identified 33 “elements”—substances not broken down into simpler entities. Among his many discoveries, Lavoisier accurately measured the weight gained when elements were oxidized, and he ascribed the result to the combining of the element with oxygen. The concept of chemical reactions involving the combination of elements clearly emerged from his writing, and his approach led others to pursue experimental chemistry as a quantitative science.

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