An Introduction to Chemistry

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Matter is anything that takes up space and has mass. Chemistry is the study of matter, its properties, and properties of the substances that matter creates. At this point, we understand that cells are the basic subunits of all living things. But instead of analyzing cells on a grander scheme as in anatomy and physiology, we can study cells on a smaller, molecular level. This section will provide further information on atoms and their binding properties, which create the molecules and compounds that further comprise the cell and thus the organism.

An Overview of Matter


  • Matter is anything that takes up space and has mass.
  • An atom is the basic unit of matter. Atoms are also known as elements.
  • An atom is composed of protonsneutrons, and electrons. Protons and neutrons are found in the nucleus, and electrons are found in the electron cloud that surrounds the nucleus.
  • The number of protons in an atom determines its identity (which element it is).
  • The mass number of an atom is determined by adding the number of protons and the number of neutrons.
  • The charge of an atom is determined by the numbers of protons and electrons.
  • Isotopes are atoms of the same element that have different numbers of neutrons and, therefore, different masses.

The Periodic Table of Elements


All known atoms/elements are organized into the Periodic Table of Elements. Specific trends exist within the Periodic Table.

  • Each element has a name and chemical symbol, usually a letter abbreviation, unique to the atom.
  • The periodic table provides an atom’s atomic number and atomic mass. Elements in the table are listed in order of increasing atomic mass.
  • Periodic tables differ in the information they provide, and an example of a block is shown. This block shows the name of the element and its chemical symbol, which is an abbreviation for the name. The chemical symbol is one, two, or three letters with the first letter capitalized and all subsequent letters letter lowercase. The symbol for the element argon is Ar.
  • Each element is assigned an atomic number. The atomic number is equal to the number of protons in a single atom of that element and is how an element is identified. Argon, for example, has an atomic number of 18. Therefore, every atom of argon has 18 protons, regardless of how many neutrons or electrons it has.
  • Electrons are located in an atom’s electron cloud, divided into shells. Atoms are constantly seeking to gain, share, or give up electron in order to have a full shell.
  • Valence electrons are the unpaired electrons in the outermost shell.
  • Atoms in the same column, or group, have the same number of valence electrons in their outermost shell. An atom’s outermost shell is equal to the row that the element is located in.
  • Exceptions to the trends exist. Transition metals (atoms in columns 3-12) have 2 valence electrons.
  • Atoms in columns 13-18 have the number of valence electrons equal to the column number minus 10. Noble gasses have 8 valence electrons and a full outermost shell.
  • Helium is considered a noble gas because it has a full outermost shell. However, it only has 2 valence electrons in the first electron shell level.

Did You Know?


While many elements have chemical symbols that resemble their names, like argon (Ar), some elements have chemical symbols that are different from their names. This is because the symbols are derived from either the Latin or the Greek names for the elements rather than the English names. The symbol for sodium is Na because the Latin name for the element is natrium.

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