Reading_ The Modern Periodic Table (2023)

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IS3T1 Modern Periodic Table Reading [Figure1] Look at substances A–C in the photos in Figure 1. They look very different from one another, but they have something important in common. All three are elements, or pure substances. Can you identify which elements they are? The First Periodic Table In the 1860s, a scientist named Dmitri Mendeleev also saw the need to organize the elements. He created a table in which he arranged all of the elements by increasing atomic mass from left to right across each row. When he placed eight elements in each row and then started again in the next row, each column of the table contained elements with similar properties. He called the columns of elements groups. Mendeleev’s table is called a periodic table and the rows are called periods. That’s because the table keeps repeating from row to row, and periodic means “repeating.” The Modern Periodic Table A periodic table is still used today to organize the elements. You can see a simple version of the modern periodic table in the periodic table below. The modern table is based on Mendeleev’s table, except the modern table arranges the elements by increasing atomic number instead of atomic mass. Atomic number is the number of protons in an atom, and this number is unique for each element. The modern table has more elements than Mendeleev’s table because many elements have been discovered since Mendeleev’s time. Reading the Table In the periodic table below, each element is represented by its chemical symbol, which consists of one or two letters. The first letter of the symbol is always written in uppercase, and the second letter—if there is one—is always written in lowercase. For example, the symbol for copper is Cu. It stands for cuprum , which is the Latin word for copper. The number above each symbol in the table is its unique atomic number. Notice how the atomic numbers increase from left to right and from top to bottom in the table.
Periods of the Modern Periodic Table Rows of the modern periodic table are called periods , as they are in Mendeleev’s table. From left to right across a period , each element has one more proton than the element before it. Some periods in the modern periodic table are longer than others. For example, period 1 contains only two elements: hydrogen (H) and helium (He). In contrast, periods 6 and 7 are so long that many of their elements are placed below the main part of the table. They are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some of the elements in period 7 have recently been discovered and named. In December 2015, the International Union of Pure and Applied Chemistry (IUPAC) verified the existence of four new elements 113, 115, 117, and 118 and approved their addition to the periodic table. These elements complete period 7 of the periodic table. Groups of the Modern Periodic Table Columns of the modern table are called groups , as they are in Mendeleev’s table. However, the modern table has many more groups—18 compared with just 8 in Mendeleev’s table. Elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gasses, such as neon (Ne). (Neon is the element inside the light in opening photo C.) In contrast, all elements in group 1 are very reactive solids. They react explosively with water, as you can see in Figure 3 . [Figure3] The alkali metal sodium (Na) reacting with water. Classes of Elements All elements can be classified in one of three classes: metals, metalloids, or nonmetals. Elements in each class share certain basic properties. For example, elements in the metals class can conduct electricity, whereas elements in the nonmetals class generally cannot. Elements in the metalloids class fall in between the metals and nonmetals in their properties. An example of a metalloid is arsenic (As). (Arsenic is the element in opening photo B.) In the periodic table above, elements are color coded to show their class. As you move from left to right across each period of the table, the elements change from metals to metalloids to nonmetals. Summary ● The modern periodic table is used to organize all the known elements. Elements are arranged in the table by increasing atomic number. ● In the modern periodic table, each element is represented by its chemical symbol. The number above each symbol is its atomic number. Atomic numbers increase from left to right and from top to bottom in the table. ● Rows of the periodic table are called periods. From left to right across a period, each element has one more proton than the element before it. ● Columns of the periodic table are called groups. Elements in the same group have similar properties. ● All elements can be classified in one of three classes: metals, metalloids, or nonmetals. Elements in each class share certain basic properties. From left to right across each period of the periodic table, elements change from metals to metalloids to nonmetals.
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