Figure: The Effect of Charge and Distance on the Strength of Electrostatic Interactions: As the charge on ions increases or the distance between ions decreases, so does the strength of the attractive (−…+) or repulsive (−…− or +…+) interactions. The strength of these interactions is represented by the thickness of the arrows. One example of an ionic compound is sodium chloride (NaCl; Figure below), formed from sodium and chlorine. In forming chemical compounds, many elements have a tendency to gain or lose enough electrons to attain the same number of electrons as the noble gas closest to them in the periodic table. When sodium and chlorine come into contact, each sodium atom gives up an electron to become a Na+ ion, with 11 protons in its nucleus but only 10 electrons (like neon), and each chlorine atom gains an electron to become a Cl− ion, with 17 protons in its nucleus and 18 electrons (like argon), as shown in part (b) in Figure: Covalent and Ionic Bonding. Solid sodium chloride contains equal numbers of cations (Na+) and anions (Cl−), thus maintaining electrical neutrality. Each Na+ ion is surrounded by 6 Cl− ions, and each Cl− ion is surrounded by 6 Na+ ions. Because of the large number of attractive Na+Cl− interactions, the total attractive electrostatic energy in NaCl is great. Figure: Sodium Chloride: an Ionic Solid: The planes of an NaCl crystal reflect the regular arrangement of its Na+ (purple) and Cl− (green) ions. Consistent with a tendency to have the same number of electrons as the nearest noble gas, when forming ions, elements in groups 1, 2, and 3 tend to lose one, two, and three electrons, respectively, to form cations, such as Na+ and Mg2+. They then have the same number of electrons as the nearest noble gas: neon. Similarly, K+, Ca2+, and Sc3+ have 18 electrons each, like the nearest noble gas: argon. In addition, the elements in group 13 lose three electrons to form cations, such as Al3+, again attaining the same number of electrons as the noble gas closest to them in the periodic table. Because
Figure: Metals That Form More Than One Cation and Their Locations in the Periodic Table: With only a few exceptions, these metals are usually transition metals or actinides. Figure: The Relationship between the Names of Oxoanions and the Number of Oxygen Atoms Present Note the Pattern Cations are always named before anions. Most transition metals, many actinides, and the heaviest elements of groups 13–15 can form more than one cation. Summary Ionic compounds are named according to systematic procedures, although common names are widely used. Systematic nomenclature enables us to write the structure of any compound from its name and vice versa. Ionic compounds are named by writing the cation first, followed by the anion. If a metal can form cations with more than one charge, the charge is indicated by roman numerals in parentheses following the name of the metal. Oxoanions are polyatomic anions that contain a single metal or nonmetal atom and one or more oxygen atoms. Key Takeaway There is a systematic method used to name ionic compounds. 2.4 Naming Covalent Compounds Learning Objective To name covalent compounds that contain up to three elements.
The simplest alkane is methane (CH4), a colorless, odorless gas that is the component of natural gas. In larger alkanes whose carbon atoms are joined in an unbranched chain (straight-chain alkanes), each carbon atom is bonded to at most two other carbon atoms. The structures of two simple alkanes are shown in the Figure below, and the names and condensed structural formulas for the first 10 straight-chain alkanes are in the Table below. The names of all alkanes end in -ane, and their boiling points increase as the number of carbon atoms increases. Figure: Straight-Chain Alkanes with Two and Three Carbon Atoms Name Number of Carbon Atoms Molecular Formula Condensed Structural Formula Boiling Point (°C) Uses methane 1 CH4 CH4 −162 natural gas constituent ethane 2 C2H6 CH3CH3 −89 natural gas constituent propane 3 C3H8 CH3CH2CH3 −42 bottled gas butane 4 C4H10 CH3CH2CH2CH3 or CH3(CH2)2CH3 0 lighters, bottled gas pentane 5 CH3(CH2)3CH3 36 solvent, gasoline hexane 6 C6H14 CH3(CH2)4CH3 69 solvent, gasoline heptane 7 C7H16 CH3(CH2)5CH3 98 solvent, gasoline