One of the major themes of general chemistry - which also illustrates how chemistry relates to everyday life - is the correlation of the properties of substances that we observe - often with our unaided senses - on a macroscopic scale with processes that occur on the ultra-microscopic scale of atoms and molecules. In fact, the events occurring at the atomic and molecular level are fundamental in explaining the observations of chemistry in the macroscopic realm. This is what a good scientific theory does of course: it serves as a powerful explanatory principle. We need to start our study of chemistry with a basic understanding of the major features of atomic theory, one of the greatest achievements of 20th-century science.
Most of us have been exposed to enough science to know that atoms - as shown in the illustration - are composed of a nucleus, which contains protons and neutrons, while the bulk of the actual "volume" of an atom is somehow occupied by a "cloud" of electrons surrounding the nucleus. The simplest atom is the hydrogen atom, which consists of a single proton as its nucleus, and a single electron.
We likely have a sense that there are many different types of atoms, and that these typically combine in various ways to form stable arrangements of atoms called molecules. Indeed this is - as suggested above - what chemistry is fundamentally all about. We want to learn the answers to questions such as: Why do atoms combine to form molecules, how are the atoms in a molecule arranged in space, and how do these arrangements determine the properties of substances that we observe in the macroscopic realm? In other words, we want to know the how and why of chemical bonds, what the molecular structures (or strictly speaking, models of molecular structure) look like, and how molecular structure influences the bulk properties of matter. As a preview of what form the answers we seek will take in terms of atomic theory, it can be said that it is the electrons of atoms that play the predominant role in chemical bonding and molecular structure, with the properties of nuclei influencing the numbers of electrons atoms have, as well as the patterns of their distribution about the nucleus. We will learn much more about atomic theory and electron configurations later in the course. We will also investigate the nature of chemical bonds and examine molecular structure. Subsequently, we will relate our understanding of molecular structure to the macroscopic properties of substances.
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CHEM 101 - Atoms: An introduction. (2018). Guweb2.gonzaga.edu. Retrieved 11 October 2018, from http://guweb2.gonzaga.edu/faculty/cronk/CHEM101pub/atoms01.html