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How are elements arranged on the Periodic Table?
A table in which the chemical elements are arranged in order of increasing atomic number. Elements with similar properties are arranged in the same column (called a group), and elements with the same number of electron shells are arranged in the same row (called a period).
The periodic table contains an enormous amount of important information:
Atomic number: The number of protons in an atom is referred to as the atomic number of that element. The number of protons defines what element it is and also determines the chemical behavior of the element. For example, carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight.
Atomic symbol: The atomic symbol (or element symbol) is an abbreviation chosen to represent an element ("C" for carbon, "H" for hydrogen and "O" for oxygen, etc.). The atomic symbol for gold is "Au".
Atomic weight: The standard atomic weight of an element is the average mass of the element in atomic mass units (amu). Individual atoms always have an integer number of atomic mass units; however, the atomic mass on the periodic table is stated as a decimal number because it is an average of the various isotopes of an element. The average number of neutrons for an element can be found by subtracting the number of protons (atomic number) from the atomic mass.
Atomic weight for elements 93-118: For naturally occurring elements, the atomic weight is calculated from averaging the weights of the natural abundances of the isotopes of that element. However, for lab-created trans-uranium elements — elements with atomic numbers higher than 92 — there is no "natural" abundance. The convention is to list the atomic weight of the longest-lived isotope in the periodic table. These atomic weights should be considered provisional since a new isotope with a longer half-life could be produced in the future.
What information does the Periodic Table provide for scientists?
The periodic table of the elements is a table in which elements are arranged according to their atomic numbers, electronic configurations and properties. The position of an element in the periodic table gives us an idea about the element's properties. We can also get an idea about the types of reactions the element will be involved in and the expected products. This helps in designing experiments and processes. The properties of known as well as 'yet to be discovered' elements can be deduced from the periodic table. This not only helps in the study of the elements, but also in their applications in various scientific and engineering purposes. The table also helps us classify elements (including the ones that are yet to be discovered).
Thus, a scientist can derive a significant amount of information about the elements from the periodic table.
What do families/groups have in common?
Families of the Periodic Table
Remember that Mendeleev arranged the periodic table so that elements with the most similar properties were placed in the same group. A group is a vertical column of the periodic table. All of the 1A elements have one valence electron. This is what causes these elements to react in the same ways as the other members of the family. The elements in 1A are all very reactive and form compounds in the same ratios with similar properties with other elements. Because of their similarities in their chemical properties, Mendeleev put these elements into the same group. Group 1A is also known as the alkali metals. Although most metals tend to be very hard, these metals are actually soft and can be easily cut.
Group 2A is also called the alkaline earth metals. Once again, because of their similarities in electron configurations, these elements have similar properties to each other. The same pattern is true of other groups on the periodic table. Remember, Mendeleev arranged the table so that elements with the most similar properties were in the same group on the periodic table.
It is important to recognize a couple of other important groups on the periodic table by their group name. Group 7A (or 17) elements are also called halogens. This group contains very reactive nonmetal elements.
The noble gases are in group 8A. These elements also have similar properties to each other, the most significant property being that they are extremely unreactive, rarely forming compounds. We will learn the reason for this later, when we discuss how compounds form. The elements in this group are also gases at room temperature.
Vocabulary
• Group (family): A vertical column in the periodic table.
• Alkali metals: Group 1A of the periodic table.
• Alkaline earth metals: Group 2A of the periodic table.
• Halogens: Group 7A of the periodic table.
• Noble gases: Group 8A of the periodic table.
• Transition elements: Groups 3 to 12 of the periodic table.
