![]() This electron takes up residence in yet another orbit, a third electron shell in sodium. Sodium's eleventh electron cannot fit into either its first or its second shell. Remember that the second shell can only carry eight electrons. Because the number of electrons in the second shell increases, we can begin to imagine why the chemical properties gradually change as we move from oxygen to fluorine to neon. Neon, with ten electrons, carries two in the first and eight in the second. Fluorine, with nine electrons, carries two in its first shell and seven in the second. Thus, in our example discussed above, oxygen, with eight protons and eight electrons, carries two electrons in its first shell and six in its second shell. The capacity of the first electron shell is two electrons and for the second shell the capacity is eight. As lower shells are filled, additional electrons reside in more-distant shells. Each shell has a limited capacity for electrons. Located randomly around an atom's nucleus, but they occur in specific electron shells (see our Atomic Theory II module for more information). Niels Bohr's theory of the atom tells us that electrons are not In other words, the way in which an atom's electrons are arranged around its nucleus affects the properties of the atom. The "periodic" nature of chemical properties that Mendeleev had discovered is related to the electron configuration of the atoms of the elements. Correct! Electron configuration and the table ![]() Sodium is similar to lithium in terms of chemical properties. Elements in a given group in the periodic table share many similar chemical and physical properties.ī. Columns in the periodic table are called groups. Moves from left to right in a given period, the chemical properties of the elements slowly change. Rows in the periodic table are called periods. Thus sodium begins a new row in the periodic table and is placed directly beneath lithium, highlighting their chemical Sodium (Na, z = 11), however, is a silver metal that is solid at room temperature, much like the element lithium (z = 3). The next element in order of atomic number is more similar (chemically speaking) to the first element in the row above it thus a new rowįor example, oxygen (O), fluorine (F), and neon (Ne) (z = 8, 9 and 10,respectively) all are stable nonmetals that are gases at room temperature. At the end of each row, a drastic shift occurs in chemical properties. As one moves from left to right in a row of the periodic table, the properties of the elements gradually change. Unfortunately, there was a slightly different system in place in Europe.The modern periodic table of elements is based on Mendeleev's observations however, instead of being organized by atomic weight, the modern table is arranged by atomic number (z). The first two groups are 1A and 2A, while the last six groups are 3A through 8A. The traditional system used in the United States involves the use of the letters A and B. There are two different numbering systems that are commonly used to designate groups, and you should be familiar with both. These two rows are pulled out in order to make the table itself fit more easily onto a single page.Ī group is a vertical column of the periodic table, based on the organization of the outer shell electrons. Periods 6 and 7 have 32 elements, because the two bottom rows that are separate from the rest of the table belong to those periods. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements. A new period begins when a new principal energy level begins filling with electrons. There are seven periods in the periodic table, with each one beginning at the far left. \) (Credit: User:Cepheus/Wikimedia Commons Source: (opens in new window) License: Public Domain)Ī period is a horizontal row of the periodic table.
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