TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy. What is ionization energy? The energy required to remove an electron from an atom is called ionization energy. • This energy is measured when an element is in its gaseous state. • The energy required to remove the first electron from an atom is called the first ionization energy. • The energy required to remove the second electron from an atom is called the second ionization energy and so on and so forth. ☺ TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and Trendsionic radii, electronegativity, in andionization ionization energy. energy Looking at the data for alkali metals and noble gases, first ionization energy generally decreases from top to bottom within a group. Looking at the data from sodium to argon, first ionization energy generally increases across a period. TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and Explanationionic radii, electronegativity, for trendsand ionization energ iny. ionization energy Down a Group As the distance from nucleus to electrons increases within a group: • Nuclear charge has a smaller effect on the electrons in the highest occupied energy level due to shielding effects (Zeff is constant) and this means less energy is required to remove an electron from this energy level—first ionization energy is lower Across a Period In general, the first ionization energy of representative elements tends to increase from left to right across a period. This trend can be explained by the nuclear charge and the shielding effect. • The nuclear charge increases across the period, but the shielding effect remains constant (Zeff increases across a group.) • As a result, there is an increase in the attraction of the nucleus for an electron. Thus, it takes more energy to remove an electron from an atom. TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy. What is electronegativity? Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound. • Scientists use factors such as ionization energy to calculate values for electronegativity. • In your own words, describe the difference between ionization energy and electronegativity? TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy. Electronegativity Values for Selected Elements (Pauling Units) H 2.1 Li Be B C N O F 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Na Mg Al Si P S Cl 0.9 1.2 1.5 1.8 2.1 2.5 3.0 K Ca Ga Ge As Se Br 0.8 1.0 1.6 1.8 2.0 2.4 2.8 Rb Sr In Sn Sb Te I 0.8 1.0 1.7 1.8 1.9 2.1 2.5 Cs Ba Tl Pb Bi 0.7 0.9 1.8 1.9 1.9 TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and ionicTrends radii, electronegativity, in and electronegativity ionization energy. In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period. • Metals at the far left of the periodic table have low values. • Nonmetals at the far right (excluding noble gases) have high values. • The values among the transition metals are not as regular. In your own words, explain these trends in electronegativity TEKS 5C: Use the Periodic Table to identify and explain periodic trends, including atomic and ionicSummary: radii, electronegativity, and ionization periodic energy. trends.