High School Biology/Matter

An atom is a positively charged nucleus of protons and neutrons, surrounded by shells of negatively charged electrons. Elements differ from each other in the amount of protons in their atoms, likewise atoms from the same element can have different numbers of neutrons or electrons. Isotopes are atoms of an element which have different amounts of neutrons in their nucleus.

The atoms of some elements prefer to gain a more stable state through the gain or loss of electrons. These atoms are capable of receiving, losing, or sharing electrons with other atoms. Atoms are capable of doing so through the use of atomic bonds. There are three common types of bonds: Covalent, Hydrogen, and Ionic bonds. Ionic bonds occur when one atom is willing to release an electron, while another atom is seeking an extra electron. Through loosing an electron, an atom becomes positively charged (a cation), while gaining an electron causes the atom to gain a negative charge (an anion). Because opposite charges attract, these two atoms will join together to form an ionic bond. Covalent bonds occur when two or more atoms share electrons. Covalent bonds form with pairs of atoms being shared, with atoms being able to form multiple covalent bonds. Covalent bonds themselves are separated into two distinct groups, polar bonds and non-polar bonds. If the involved atoms are sharing their electrons equally, then the charges cancel each other out. However should the sharing be unequal, then the atomic bond gains a charge and becomes polarized. The majority of the bonds discussed within the text book will be composed of weak bonds, mainly for the reason that weak bonds can easily be broken when the atoms are needed for other purposes. Hydrogen bonds are a common weak bond. A hydrogen bond occurs when a hydrogen atom forms a polar covalent bond with another atom. Since hydrogen requires another electron to achieve stability, it will forcibly bond with other atoms to form a polar hydrogen bond. Water is a prime example of hydrogen bonding. Due to two electrons being required to form a hydrogen bond, a single hydrogen atom will attract two oxygen atoms and form the most recognized of molecules, H2O.