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6.3 Periodic Trends > Chapter 6 The Periodic Table 6.1 Organizing the Elements 6.2 Classifying the Elements 6.3 Periodic Trends 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > CHEMISTRY & YOU How are trends in the weather similar to trends in the properties of elements? Although the weather changes from day to day, the weather you experience is related to your location on the globe. 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size Trends in Atomic Size What are the trends among the elements for atomic size? 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size In general, atomic size increases from top to bottom within a group, and decreases from left to right across a period. 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size One way to think about atomic size is to look at molecules, the units that form when atoms of the same element are joined together. • Because the atoms are identical, the distance between the nuclei (centers) of these atoms can be used to estimate the size of the atoms. 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size • The atomic radius is one-half of the distance between the nuclei of two atoms of the same element when they are joined. 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size The distances between atoms in a molecule are extremely small so the atomic radius is measured in picometers (pm). – There are one trillion, or 1012, picometers in a meter. 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Trends in Atomic Size The distance between the nuclei in an iodine molecule is 280 pm. Distance between the nuclei 280 pm • Atomic radius is onehalf the distance between the nuclei, a value of 140 pm (280/2) is assigned to the radius of the iodine atom. 140 pm Atomic radius Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size Group Trends in Atomic Size As the atomic number increases within a group 2 things occur. 1.) the charge on the nucleus increases 2.) number of occupied energy levels increases. • These variables affect atomic size in opposite ways. 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size Group Trends in Atomic Size 1.) The increase in positive charge draws electrons closer to the nucleus. (smaller) 2.) The increase in the number of occupied orbitals shields electrons in the valence level from the attraction of protons in the nucleus. (larger) • The shielding effect is greater than the effect of the increase in nuclear charge. 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Interpret Graphs Group Trends in Atomic Size Atomic radius (pm) The atomic radius within a group increases as the atomic number increases. • This increase is an example of a trend. Atomic number Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Trends in Atomic Size Periodic Trends in Atomic Size Across a period, the electrons are added to the same principal energy level. Atomic radius (pm) • The shielding effect is constant for all elements in a period. Atomic number • The increasing nuclear charge pulls the electrons in the highest occupied energy level closer to the nucleus, and the atomic size decreases. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Atomic Size The figure below summarizes the group and period trends in atomic size. Atomic Atomic 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What are the trends for atomic size? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What are the trends for atomic size? In general, atomic size increases from top to bottom within a group and decreases from left to right across a period. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Ions An atom is electronically neutral because it has equal numbers of protons and electrons. • An atom of barium (Ba) has 56 positively charged protons and 56 negatively charged electrons. • The net charge on a barium atom is zero. (+56) + (-56) = 0 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Ions Ions How do ions form? 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Ions Positive and negative ions form when electrons are transferred between atoms. • Metals tend to form ions by losing one or more electrons from their highest occupied energy levels. • Non-metals tend to form ions by gaining one or more electrons in their highest occupied energy levels. 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Ions • An ion is an atom or group of atoms that has a positive or negative charge. An ion with a positive charge is called a cation. • The charge for a cation is written as a superscript with a number followed by a plus sign. • If the charge is 1+, the number 1 is usually omitted from the symbol for the ion. – For example, Na1+ is written as Na+. 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Ions • An ion is an atom or group of atoms that has a positive or negative charge. An ion with a negative charge is called an anion. • The charge for an anion is written as a superscript with a number followed by a minus sign. • If the charge is 1-, the number 1 is usually omitted from the symbol for the ion. – For example, Br1- is written as Br -. 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What type of element tends to form anions? What type tends to form cations? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What type of element tends to form anions? What type tends to form cations? Nonmetals tend to form anions. Metals tend to form cations. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionic Size Trends in Ionic Size What are the trends among the elements for ionic size? 23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionic Size Ionic size tends to increase from top to bottom within a group. Generally, the size of cations and anions decreases from left to right across a period. 24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionic Size During reactions, metal atoms tend to lose electrons and nonmetal atoms tend to gain electrons. • This transfer of electrons has a predictable effect on the size of the ions that form. • Cations are always smaller than the atoms from which they form. • Anions are always larger than the atoms from which they form. 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionic Size Group Trends in Ionic Size Metals tend to lose all their outermost electrons when forming ions. • The ion loses one occupied energy level. Non-Metals tend to attract electrons when forming ions. • The ion fills its valence energy level. 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Trends in Ionic Size Group Trends in Ionic Size For each of these elements, the ion is much smaller than the atom. • The radius of a sodium ion (95 pm) is about half the radius of a sodium atom (191 pm). • When a sodium atom loses an electron, the attraction between the remaining electrons and the nucleus is increased. As a result, the electrons are drawn closer to the nucleus. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Trends in Ionic Size Group Trends in Ionic Size The trend is the opposite for nonmetals, like the halogens in Group 17. • For each of these elements, the ion is much larger than the atom. – For example, the radius of a fluoride ion (133 pm) is more than twice the radius of a fluorine atom (62 pm). – As the number of electrons increases, the attraction of the nucleus for any one electron decreases. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Trends in Ionic Size Period Trends in Ionic Size From left to right across a period, two trends are visible—a gradual decrease in the size of the positive ions (cations), followed by a gradual decrease in the size of the negative ions (anions). Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionic Size The figure below summarizes the group and period trends in ionic size. Size of anions decreases Ion size generally increases Size of cations decreases 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What are the trends for ionic size? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What are the trends for ionic size? Ionic size tends to increase from top to bottom within a group. Generally, the size of cations and anions decreases from left to right across a period. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionization Energy Sometimes an electron overcomes the attraction of the protons in the nucleus and escape the atom. • 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. 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionization Energy Trends in Ionization Energy What are the trends among the elements for first ionization energy? 34 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionization Energy First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period. 35 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Interpret Data Ionization Energies of Some Common Elements Symbol First Second Third H 1312 He (noble gas) 2372 5247 Li 520 7297 11,810 Be 899 1757 14,840 C 1086 2352 4619 O 1314 3391 5301 F 1681 3375 6045 Ne (noble gas) 2080 3963 6276 Na 496 4565 6912 Mg 738 1450 7732 S 999 2260 3380 1520 2665 3947 K 419 3096 4600 Ca 590 1146 4941 Ar (noble gas Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionization Energy Ionization energies can help you predict what charge will be on an ion when it forms. • It is easy to remove one electron from Group 1 atoms, but difficult to remove a second electron. (1+ charge) • It is easy to remove two electrons from a Group 2 atoms, but difficult to remove a third electron. (2+ charge) 37 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Interpret Graphs Group Trends in Ionization Energy First ionization energy (kJ/mol) Look at the data for noble gases and alkali metals. Atomic number 38 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Ionization Energy Group Trends in Ionization Energy • Due to the shielding effect, less energy is required to remove an electron so the first ionization energy is lower. • Due to the effect of nuclear charge increase, more energy is required to remove an electron so the first ionization energy is higher. 39 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . Ionization Energy generally decreases (shielding, electrons are farther away) 6.3 Periodic Trends > Trends in Ionization Energy 40 The figure below summarizes the group and period trends for the first ionization energy. Ionization Energy generally increases (nucleus is stronger) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity A property called electronegativity is used to predict the type of bond that will form during a reaction. 41 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity A property called electronegativity is used to predict the type of bond that will form during a reaction. • Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound. 42 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity Trends in Electronegativity What are the trends among the elements for electronegativity? 43 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity 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. • By contrast, nonmetals at the far right (excluding noble gases) have high values. • Values among transition metals are not as regular. 44 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Interpret Data This table lists electronegativity values for representative elements in Groups 1 through 17. Electronegativity Values for Selected Elements H 2.1 45 Li 1.0 Be 1.5 B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Na 0.9 Mg 1.2 Al 1.5 Si 1.8 P 2.1 S 2.5 Cl 3.0 K 0.8 Ca 1.0 Ga 1.6 Ge 1.8 As 2.0 Se 2.4 Br 2.8 Rb 0.8 Sr 1.0 In 1.7 Sn 1.8 Sb 1.9 Te 2.1 I 2.5 Cs 0.7 Ba 0.9 Tl 1.8 Pb 1.9 Bi 1.9 • The data in this table is expressed in Pauling units. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity The least electronegative elements are cesium and francium, with an electronegativity of 0.7. • They have the least tendency to attract electrons. • When they reacts, they tends to lose electrons and form cations. 46 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity The most electronegative element is fluorine, with a value of 4.0. • Because fluorine has such a strong tendency to attract electrons, when it is bonded to any other element it either attracts the shared electrons or forms an anion. 47 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Trends in Electronegativity This figure summarizes several trends that exist among the elements. 48 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What are the trends for electronegativity values? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . What are the trends for electronegativity values? 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Key Concepts In general, atomic size increases from top to bottom within a group and decreases from left to right across a period. Positive and negative ions form when electrons are transferred between atoms. First ionization energy tends to decrease from top to bottom within a group and decrease from left to right across a period. 51 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > Key Concepts Ionic size tends to increase from top to bottom within a group. Generally, the size of cations and anions decreases from left to right across a period. 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. 52 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. . 6.3 Periodic Trends > END OF 6.3 53 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .