Thermodynamics: Molecules

Everything is made of atoms, which are the smallest representative parts of each of the ninety-two elements that occur in nature. Elements are either metals, such as iron, copper or calcium or non-metals such as carbon, oxygen or nitrogen. Chemistry is concerned with the way atoms link together to form molecules, which are the natural chemical units of matter. Molecules represent the smallest particle of a chemical compound which retains the characteristics and chemical properties of the compound. With the rare exception of certain single atom molecules, almost all molecules consist of two or more atoms linked together. An atom of the violently active metal sodium (Na) linked to an atom of the poisonous gas chlorine (Cl), for instance, gives one molecule of common salt (NaCl) — an important body ingredient. Structure of the atom: There are two distinct regions to an atom. The first is a dense closely packed nucleus made up of protons and neutrons. Protons are positively charged and neutrons are neutral in charge. Together they make up much of the mass of the atom. They both have similar masses. Surrounding the nucleus are electrons. These are arranged in shells, or …show more content…
The third shell usually holds eight electrons as well, but can hold up to eighteen in specific circumstances. The number of electrons in the outermost shell of an atom is the same as its group number. In other words, hydrogen has one electron in its outer shell and is in Group I, carbon has four electrons in its outer shell and is in Group IV, and so on. Elements with the same number of electrons in their outer shell have similar chemical properties. Isotopes Neutral elements always have the same number of protons and electrons. However, they can have differing numbers of neutrons, so some atoms of a particular element may be heavier than other atoms of the same