![]() Note the usefulness of the periodic table in predicting likely ion formation and charge ( Figure 13.2). (A discussion of the theory supporting the favored status of noble gas electron numbers reflected in these predictive rules for ion formation is provided in a later chapter of this text.) It has the same number of electrons as atoms of the next noble gas, krypton, and is symbolized Brâ. This results in an anion with 35 protons, 36 electrons, and a 1â charge. For example, the neutral bromine atom, with 35 protons and 35 electrons, can gain one electron to provide it with 36 electrons. Atoms of group 17 gain one electron and form anions with a 1â charge atoms of group 16 gain two electrons and form ions with a 2â charge, and so on. When atoms of nonmetal elements form ions, they generally gain enough electrons to give them the same number of electrons as an atom of the next noble gas in the periodic table. The name of a metal ion is the same as the name of the metal atom from which it forms, so Ca2+ is called a calcium ion. It has the same number of electrons as atoms of the preceding noble gas, argon, and is symbolized Ca2+. This results in a cation with 20 protons, 18 electrons, and a 2+ charge. For example, a neutral calcium atom, with 20 protons and 20 electrons, readily loses two electrons. To illustrate, an atom of an alkali metal (group 1) loses one electron and forms a cation with a 1+ charge an alkaline earth metal (group 2) loses two electrons and forms a cation with a 2+ charge, and so on. Atoms of many main-group metals lose enough electrons to leave them with the same number of electrons as an atom of the preceding noble gas. You can use the periodic table to predict whether an atom will form an anion or a cation, and you can often predict the charge of the resulting ion. (b) A sodium cation (Na+) has lost an electron, so it has one more proton (11) than electrons (10), giving it an overall positive charge, signified by a superscripted plus sign. (a) A sodium atom (Na) has equal numbers of protons and electrons (11) and is uncharged. When the electronegativity difference is very large, as is the case between metals and nonmetals, the bonding is characterized as ionic. In a diatomic molecule with two identical atoms, there is no difference in electronegativity, so the bond is nonpolar or pure covalent. The difference in electronegativity between two atoms determines how polar a bond will be. The ability of an atom to attract a pair of electrons in a chemical bond is called its electronegativity. In polar covalent bonds, the electrons are shared unequally, as one atom exerts a stronger force of attraction on the electrons than the other. In pure covalent bonds, the electrons are shared equally. The charges of anions formed by the nonmetals may also be readily determined because these ions form when nonmetal atoms gain enough electrons to fill their valence shells.Ĭovalent bonds form when electrons are shared between atoms and are attracted by the nuclei of both atoms. The charges of cations formed by the representative metals may be determined readily because, with few exceptions, the electronic structures of these ions have either a noble gas configuration or a completely filled electron shell. Covalent compounds usually form from two nonmetals.Ītoms gain or lose electrons to form ions with particularly stable electron configurations. Compounds that do not contain ions, but instead consist of atoms bonded tightly together in molecules (uncharged groups of atoms that behave as a single unit), are called covalent compounds. ![]() Ionic compounds generally form from metals and nonmetals. Ions can be either monatomic (containing only one atom) or polyatomic (containing more than one atom).Ĭompounds that contain ions are called ionic compounds. Positively charged ions are called cations, and negatively charged ions are called anions. Thus, nonmetals tend to form negative ions. Similarly, nonmetals (especially those in groups 16 and 17, and, to a lesser extent, those in Group 15) can gain the number of electrons needed to provide atoms with the same number of electrons as in the next noble gas in the periodic table. By this means, a positively charged ion is formed. ![]() Metals (particularly those in groups 1 and 2) tend to lose the number of electrons that would leave them with the same number of electrons as in the preceding noble gas in the periodic table. ![]()
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