9781422279472

Hydrogen H 1

ment. These elements are arranged into rows and columns by increas- ing atomic number. The atomic number equals the number of protons in the nucleus of the atom. Each element has a unique atomic number. Oxygen has an atomic number of 8 because it has eight protons in its nucleus. The nucleus of an atom may also contain neutrons. When an atom has the same number of protons as an element on the chart, but a different number of neutrons, it is called an isotope . Each element on the periodic table has its own unique chemical and physical properties. The chart helps keep track of elements with certain properties by arranging them into columns, groups, or rows. In addition to the atomic number, each square in the periodic table also lists the name of the element and its abbreviation (H for hydrogen), along with other important information such as the number of neutrons in the nucleus of one atom of an element, the number of electrons that surround the nucleus, the atomic mass, and the general size of the atom. The periodic table is a very useful tool as one begins to investi- gate chemistry and science in general. (For lots more on the periodic table, read Understanding the Periodic Table , another book in this series.) This book is about the element hydrogen. Hydrogen is element number 1 on the periodic table, and is the most abundant element in

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