nic Bonds PROBLEM 1.2 Referring to the periodic table as needed, write electron config urations for all the elements in the third period SAMPLE SoLUTION The third period begins with sodium and ends with argon ompanied by a sample so The atomic number z of sodium is 11. and so a sodium atom has 11 electro the other parts of the prob. The maximum number of electrons in the 1s, 25, and 2p orbitals is ten, and so the und in Appendix 2, eleventh electron of sodium occupies a 3s orbital. The electron configuration of and detailed solutions are sodium is 15252px 22py 22p 23s ed in the Study Neon, in the second period, and argon, in the third, possess eight electrons in their valence shell; they are said to have a complete octet of electrons. Helium, neon, and argon belong to the class of elements known as noble gases or rare gases. The noble gases are characterized by an extremely stable"closed-shell"electron configuration and are very unreactive. 1.2 IONIC BONDS Atoms combine with one another to give compounds having properties different from the atoms they contain. The attractive force between atoms in a compound is a chemi cal bond. One type of chemical bond, called an ionic bond, is the force of attraction between oppositely charged species (ions)(Figure 1.5). lons that are positively charged are referred to as cations; those that are negatively charged are anions. FIGURE 1.5 An Whether an element is the source of the cation or anion in an ionic bond depends is the force of el on several factors, for which the periodic table can serve as a guide. In forming ionic attraction between compounds, elements at the left of the periodic table typically lose electrons, forming a sitely, charged ions, illus- cation that has the same electron configuration as the nearest noble gas. Loss of an elec tron from sodium, for example, gives the species Na, which has the same electron con- solid sodium chloride, each sodium ion is surrounded by six chloride ions and vice Sodium atom Electron A large amount of energy, called the ionization energy, must be added to any atom The sI (Systeme Int ternational in order to dislodge one of its electrons. The ionization energy of sodium, for example, d'" Unites) unit of energy is is 496 kJ/mol (119 kcal/mol). Processes that absorb energy are said to be endothermic. the joule o). An older unit is Compared with other elements, sodium and its relatives in group IA have relatively low ganic chemists still express ionization energies. In general, ionization energy increases across a row in the periodic ergy changes in units of table Elements at the right of the periodic table tend to gain electrons to reach the elec kcalmol =4.184 kJ/mol) tron configuration of the next higher noble gas. Adding an electron to chlorine, for exam- ple, gives the anion CI, which has the same closed-shell electron configuration as the noble gas argon ci(g) Chlorine atom Electron Chloride ion Energy is released when a chlorine atom captures an electron Energy-releasing reactions are described as exothermic, and the energy change for an exothermic process has a negative sign. The energy change for addition of an electron to an atom is referred to as its electron affinity and is -349 kJmol (-83 4 kcal/mol) for chlorine Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsitePROBLEM 1.2 Referring to the periodic table as needed, write electron config￾urations for all the elements in the third period. SAMPLE SOLUTION The third period begins with sodium and ends with argon. The atomic number Z of sodium is 11, and so a sodium atom has 11 electrons. The maximum number of electrons in the 1s, 2s, and 2p orbitals is ten, and so the eleventh electron of sodium occupies a 3s orbital. The electron configuration of sodium is 1s 2 2s 2 2px 2 2py 2 2pz 2 3s 1 . Neon, in the second period, and argon, in the third, possess eight electrons in their valence shell; they are said to have a complete octet of electrons. Helium, neon, and argon belong to the class of elements known as noble gases or rare gases. The noble gases are characterized by an extremely stable “closed-shell” electron configuration and are very unreactive. 1.2 IONIC BONDS Atoms combine with one another to give compounds having properties different from the atoms they contain. The attractive force between atoms in a compound is a chemi￾cal bond. One type of chemical bond, called an ionic bond, is the force of attraction between oppositely charged species (ions) (Figure 1.5). Ions that are positively charged are referred to as cations; those that are negatively charged are anions. Whether an element is the source of the cation or anion in an ionic bond depends on several factors, for which the periodic table can serve as a guide. In forming ionic compounds, elements at the left of the periodic table typically lose electrons, forming a cation that has the same electron configuration as the nearest noble gas. Loss of an elec￾tron from sodium, for example, gives the species Na, which has the same electron con- figuration as neon. A large amount of energy, called the ionization energy, must be added to any atom in order to dislodge one of its electrons. The ionization energy of sodium, for example, is 496 kJ/mol (119 kcal/mol). Processes that absorb energy are said to be endothermic. Compared with other elements, sodium and its relatives in group IA have relatively low ionization energies. In general, ionization energy increases across a row in the periodic table. Elements at the right of the periodic table tend to gain electrons to reach the elec￾tron configuration of the next higher noble gas. Adding an electron to chlorine, for exam￾ple, gives the anion Cl, which has the same closed-shell electron configuration as the noble gas argon. Energy is released when a chlorine atom captures an electron. Energy-releasing reactions are described as exothermic, and the energy change for an exothermic process has a negative sign. The energy change for addition of an electron to an atom is referred to as its electron affinity and is 349 kJ/mol (83.4 kcal/mol) for chlorine. Cl(g) ±£ Chlorine atom 1s 2 2s 2 2p6 3s 2 3p5 Cl(g) Chloride ion 1s 2 2s 2 2p6 3s 2 3p6 e Electron  Na(g) ±£ Sodium atom 1s 2 2s 2 2p6 3s 1 [The (g) indicates that the species is present in the gas phase.] Na(g) Sodium ion 1s 2 2s 2 2p6 e Electron  1.2 Ionic Bonds 11
FIGURE 1.5 An ionic bond is the force of electrostatic attraction between oppo￾sitely charged ions, illus￾trated in this case by Na (red) and Cl (green). In solid sodium chloride, each sodium ion is surrounded by six chloride ions and vice versa in a crystal lattice. In-chapter problems that contain multiple parts are ac￾companied by a sample solu￾tion to part (a). Answers to the other parts of the prob￾lem are found in Appendix 2, and detailed solutions are presented in the Study Guide. The SI (Système International d’Unites) unit of energy is the joule (J). An older unit is the calorie (cal). Most or￾ganic chemists still express energy changes in units of kilocalories per mole (1 kcal/mol 4.184 kJ/mol). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website