TAILIEUCHUNG - Ebook Essential chemistry atoms, molecules, and compounds: Part 2

(BQ) Part 2 book "Essential chemistry atoms, molecules, and compounds" has contents: The elements, chemical reactions - making molecules, chemical bonds; common compounds, uncommon results. | 5 The Elements T he periodic table orders the elements in a way that helps chemists understand why atoms behave as they do. What makes fluorine react violently with cesium while its nearest neighbor neon is reluctant to react with anything? In other words, what gives the elements their properties and what order lies below the surface of their seemingly random nature? Scientists know now that the periodicity of the elements is due largely to recurring patterns in their electron configurations. The periodic table orders the elements in columns, rows, and blocks. The elements in a column are called a group. Group 1 elements are in the column on the far left of the periodic table. Group 2 elements are in the next column. The progression continues to Group 18 on the far right. The elements in a column have very similar properties. The elements in blocks or rows 58 The Elements  59 have a few similar characteristics, but they are not as closely related as the elements in a column. Periodic tables can be constructed that contain many different kinds of data. The table on page 110 includes the symbol, atomic number, and atomic mass of each element. The table on page 112 includes the electron configurations. Let’s begin with the electron configurations. The system of notation used in this periodic table to spell out electron configurations is based on the noble gases—unreactive elements with filled electron shells. The first noble gas is helium. Thus, the electron configuration of lithium, the next heaviest element, is shown as [He]2s1. This means that lithium has the electron configuration of helium plus one additional electron in the 2s orbital. Molybdenum (Z = 42) has an electron configuration [Kr]5s14d3. Thus, molybdenum has the electron configuration of krypton plus one electron in the 5s orbital and three in 4d orbitals. The electron configurations of all the elements are depicted this way. Looking closely, some interesting similarities between the elements become

• Hoá học
• Essential chemistry atoms
• Essential chemistry
• The elements
• Chemical reactions
• Making molecules
• Chemical bonds
• Common compounds
• Meet the atom
• The quantum model
• The electrons
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