Chapter 7 Periodic Properties of the Elements

Transcription

1 Sec$on 7.12 Periodic Trends in Atomic Proper0es Chapter 7 Periodic Properties of the Elements

2 Sec$on 7.12 Periodic Development Trends of in the Atomic Periodic Proper0es Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.

3 Sec$on 7.12 Periodic Mendeleev Trends and in the Atomic Periodic Proper0es Table Chemists mostly credit Mendeleev because he also used chemical proper$es to organize the table and predicted some missing elements and their expected proper$es, including germanium.

4 Sec$on 7.12 Periodic Atomic Number Trends in Atomic Proper0es Mendeleev s table was based on atomic masses. It was the most fundamental property of elements known at the $me. About 35 years later, the nuclear atom was discovered by Ernest Rutherford. Henry Moseley developed the concept of atomic number experimentally. The number of protons was considered the basis for the periodic property of elements.

5 Sec$on 7.12 Periodic Trends in Atomic Proper0es Periodic Trends Ioniza$on Energy Electron Affinity Atomic Radius

6 Sec$on 7.12 Periodic Trends in Atomic Proper0es Ioniza$on Energy Energy required to remove an electron from a gaseous atom or ion. X(g) X + (g) + e Mg Mg + + e I 1 = 735 kj/mol (1 st IE) Mg + Mg 2+ + e I 2 = 1445 kj/mol (2 nd IE) Mg 2+ Mg 3+ + e I 3 = 7730 kj/mol *(3 rd IE) *Core electrons are bound much more $ghtly than valence electrons.

7 Sec$on 7.12 Periodic Trends in Atomic Proper0es Ioniza$on Energy In general, as we go across a period from le^ to right, the first ioniza$on energy increases. Why? Electrons added in the same principal quantum level do not completely shield the increasing nuclear charge caused by the added protons. Electrons in the same principal quantum level are generally more strongly bound from le^ to right on the periodic table.

8 Sec$on 7.12 Periodic Trends in Atomic Proper0es Ioniza$on Energy In general, as we go down a group from top to bobom, the first ioniza$on energy decreases. Why? The electrons being removed are, on average, farther from the nucleus.

9 Sec$on 7.12 Periodic Trends in Atomic Proper0es The Values of First Ioniza$on Energy for the Elements in the First Six Periods

10 Sec$on 7.12 Periodic Trends in Atomic Proper0es Successive Ioniza$on Energies (KJ per Mole) for the Elements in Period 3

11 Sec$on Electron 7.12 Affinity Periodic Trends in Atomic Proper0es Energy change associated with the addi$on of an electron to a gaseous atom (typically exothermic) X(g) + e X (g) In general as we go across a period from le^ to right, the electron affini$es become more nega$ve. Not much difference in a group.

12 Sec$on 7.12 Periodic Trends in Atomic Proper0es Atomic Radius In general as we go across a period from le^ to right, the atomic radius decreases. Effec$ve nuclear charge increases, therefore the valence electrons are drawn closer to the nucleus, decreasing the size of the atom. In general atomic radius increases in going down a group. Orbital sizes increase in successive principal quantum levels.

13 Sec$on 7.12 Periodic Trends in Atomic Proper0es Atomic Radii for Selected Atoms

14 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals The Periodic Table Final Thoughts 1. It is the number and type of valence electrons that primarily determine an atom s chemistry. 2. Electron configura$ons can be determined from the organiza$on of the periodic table. 3. Certain groups in the periodic table have special names. Copyright Cengage Learning. All rights reserved 14

15 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals Special Names for Groups in the Periodic Table Copyright Cengage Learning. All rights reserved 15

16 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals The Periodic Table Final Thoughts 4. Basic division of the elements in the periodic table is into metals and nonmetals. Copyright Cengage Learning. All rights reserved 16

17 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals Metals Versus Nonmetals Copyright Cengage Learning. All rights reserved 17

18 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals Metals Versus Nonmetals Metals tend to form ca$ons. Nonmetals tend to form anions. Copyright Cengage Learning. All rights reserved 18

19 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals The Alkali Metals Li, Na, K, Rb, Cs, and Fr Most chemically reac$ve of the metals Ø React with nonmetals to form ionic solids Going down group: Ø Ioniza$on energy decreases Ø Atomic radius increases Ø Density increases Ø Mel$ng and boiling points smoothly decrease Copyright Cengage Learning. All rights reserved 19

20 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals The Alkali Metals Their reac$ons with water are famously exothermic.

21 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals Alkaline Earth Metals Compare to Alkali Metals Alkaline earth metals have higher densi$es and mel$ng points than alkali metals. Their ioniza$on energies are low, but not as low as those of alkali metals.

22 Sec$on 7.13 Group The Proper0es 6A Increasing of a Group: in Metallic The Alkali Character Metals down the Group Oxygen, sulfur, and selenium are nonmetals. Tellurium is a metalloid. The radioac$ve polonium is a metal.

23 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals Group 7A Halogens The halogens are typical nonmetals. They have highly nega$ve electron affini$es, so they exist as anions in nature. They react directly with metals to form metal halides.

24 Sec$on 7.13 The Proper0es of a Group: The Alkali Metals Group 8A Noble Gases The noble gases have very large ioniza$on energies. Their electron affini$es are posi$ve (can t form stable anions). Therefore, they are rela$vely unreac$ve. They are found as monatomic gases.