History and Methods of science Essay

Isotope, one or two or more species of atom having the same atomic number, hence constituting the same element, but differing on mass number. As atomic number is equivalent to the number of protons in the nucleus, and mass number is the sum total of the protons plus the neutrons in the nucleus, isotopes of the same element differ from one another only in the number of neutrons in their nuclei. Source: â€Å"Isotope,† Microsoft Encarta 2006 (DVD), Redmond, WA: Microsoft Corporation 2005. Atom, tiny basic building block of matter. All the material on earth is composed of various combinations of atoms. Atoms are the smallest particles of a chemical element that still exhibit all the chemical properties unique to that element. A row of 100 million atoms would be only about a centimeter long. Understanding atoms is key to understanding the physical world. More than 100 different elements exist in nature. Each with its own unique atomic makeup. The atoms of these elements react with one another and combine in different ways to form a virtually unlimited number of chemical compounds. When two or more atoms combine, they form a molecule. For example, two atoms of the element hydrogen (H) combine with one atom of the element oxygen (O) to form a molecule of water. Source: â€Å"Atom,† Microsoft Encarta 2006 (DVD), Redmond, WA: Microsoft Corporation 2005.