To obtain an octet, these atoms form three covalent bonds, as in NH 3 (ammonia). Group 15 elements such as nitrogen have five valence electrons in the atomic Lewis symbol: one lone pair and three unpaired electrons. The transition elements and inner transition elements also do not follow the octet rule: Because hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule. These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon in CCl 4 (carbon tetrachloride) and silicon in SiH 4 (silane). For example, each atom of a group 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach an octet. The number of bonds that an atom can form can often be predicted from the number of electrons needed to reach an octet (eight valence electrons) this is especially true of the nonmetals of the second period of the periodic table (C, N, O, and F). The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the octet rule. This allows each halogen atom to have a noble gas electron configuration. The other halogen molecules (F 2, Br 2, I 2, and At 2) form bonds like those in the chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom. Each Cl atom interacts with eight valence electrons: the six in the lone pairs and the two in the single bond. A dash (or line) is sometimes used to indicate a shared pair of electrons:Ī single shared pair of electrons is called a single bond. The Lewis structure indicates that each Cl atom has three pairs of electrons that are not used in bonding (called lone pairs) and one shared pair of electrons (written between the atoms). For example, when two chlorine atoms form a chlorine molecule, they share one pair of electrons: We also use Lewis symbols to indicate the formation of covalent bonds, which are shown in Lewis structures, drawings that describe the bonding in molecules and polyatomic ions. Appendix L: Standard Electrode (Half-Cell) Potentials.Appendix K: Formation Constants for Complex Ions.Appendix I: Ionization Constants of Weak Bases.Appendix H: Ionization Constants of Weak Acids.Appendix G: Standard Thermodynamic Properties for Selected Substances.Appendix F: Composition of Commercial Acids and Bases.Appendix D: Fundamental Physical Constants.Appendix C: Units and Conversion Factors.Second Law of Thermodynamics and Gibbs Free Energy.Application: Precipitation and Dissolution.Shifting Equilibria: LeChatelier’s Principle.Chemical Equilibria and Applications Toggle Dropdown Collision Theory and Factors Affecting Reaction Rates.Solutions and Colligative Properties Toggle Dropdown Liquids, Solids, and Modern Materials Toggle Dropdown Thermochemical Guidelines, Enthalpy of Formation and Hess's Law.Solution Stoichiometry and Combustion Analysis.Writing and Balancing Chemical Equations.Stoichiometry of Chemical Reactions Toggle Dropdown Determining Empirical and Molecular Formulas.Composition of Substances and Solutions Toggle Dropdown Molecular and Ionic Compounds and Their Nomenclature.Early Ideas and Evolution of Atomic Theory.Atoms, Molecules and Ions Toggle Dropdown Measurements and Uncertainty in Measurement.Classification, Physical and Chemical Properties.
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