The next subshell to be filled is the 3 s subshell. Figure 8.15 “The 2 p Subshell.” For B through Ne, the 2 p subshell is being occupied. On the right side of the periodic table, these six elements (B through Ne) are grouped together (Figure 8.15 “The 2 p Subshell”). Figure 8.14 “The 2 s Subshell.” In Li and Be, the 2 s subshell is being filled.įor the next six elements, the 2 p subshell is being occupied with electrons. Figure 8.14 “The 2 s Subshell” shows that these two elements are adjacent on the periodic table. The next two electrons, for Li and Be, would go into the 2 s subshell. Figure 8.13 “The 1 s Subshell.” H and He represent the filling of the 1 s subshell. These two elements make up the first row of the periodic table (see Figure 8.13 “The 1 s Subshell”). Their electron configurations are 1 s 1 and 1 s 2, respectively with He, the n = 1 shell is filled. Why does the periodic table have the structure it does? The answer is rather simple, if you understand electron configurations: the shape of the periodic table mimics the filling of the subshells with electrons. Figure 8.12 “The Periodic Table.” View an accessible periodic table online. A periodic table is shown in Figure 8.12 “The Periodic Table.” The elements are listed by atomic number (the number of protons in the nucleus), and elements with similar chemical properties are grouped together in columns. In Chapter 3 “Atoms, Molecules, and Ions”, we introduced the periodic table as a tool for organizing the known chemical elements. Determine the expected electron configuration of an element by its place on the periodic table.Relate the electron configurations of the elements to the shape of the periodic table.Valence electrons: The electrons in the highest occupied principal energy level of an atom. Inner-shell electrons: Those electrons that are not in the outer shell and are not involved in the reactivity of the element. The periods (rows) of the periodic table indicate the number of shells that surround a nucleus.The group numbers (columns) of the periodic table indicate the total number of outer electrons in the valence shell.Valence electrons govern many chemical properties, reactivity, and bonding.Valence electrons are the outermost electron in an electron configuration.These are named after the orbitals, so there is an s-block, p-block, d-block and f-block.Ĭhemistry Question Pack Passage 19 Question 106 The periodic table can be broken up into different blocks based on which orbitals their valence electrons occupy. Thus, group number is a good predictor of how reactive each element will be. Group 1 elements have just one valence electron while group 18 elements have eight (except for helium which has only two electrons total). In general, the number of valence electrons is the same within a column and increases from left to right within a row. Similarly, an element’s column number gives information about its number of valence electrons and reactivity. In addition, the position of an element in the periodic table-its column, or group, and row, or period-provides useful information about how those electrons are arranged.Ĭonsidering the first three rows of the table, each row corresponds to the filling of a different electron shell: helium and hydrogen place their electrons in the 1n shell, while second-row elements like Li start filling the 2n shell, and third-row elements like Na continue with the 3n shell. In a neutral atom, the number of electrons will equal the number of protons. Remember, elements are placed in order on the periodic table based on their atomic number. Inner-shell electrons are not involved directly in the element’s reactivity or in the formation of compounds. In general, atoms are most stable and least reactive when their outermost electron shell is full. Valence electrons, the electrons in the outermost or valence shell, are important as they provide insight into an element’s chemical properties and are the ones gained, lost, or shared during a chemical reaction. The properties of an atom relate directly to the number of electrons in various orbitals. Valence electrons are the electrons in the highest occupied principal energy level of an atom.Įlements are organized by period and group, with the period corresponding to the principal energy level and the group relating to the extent the subshells are filled.
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