Chapter 5 Periodic Table Dmitri Mendeleev: Russian Chemist credited with the discovery of the periodic table. How did he organize the elements? According to similarities in their chemical and physical properties. Arranged elements in order of increasing atomic weight. What did he notice? When elements are arranged in order of increasing atomic weight, their chemical and physical properties repeated at regular intervals. What did he predict? The existence of elements that had specific properties. See Figure 2 on page 134. Compare to Modern Periodic Table. 1
How did Henry Moseley change the periodic table? He discovered atomic number, and found that when elements are arranged in the periodic table, their atomic number increases by 1. He then arranged the elements in order of increasing atomic number, rather than atomic mass. What is the periodic law? When elements are arranged in order of increasing atomic number, their chemical and physical properties show a repeating pattern. Describe the modern periodic table: Elements with similar properties are arranged in groups or families. (Columns) Elements within a group have several things in common: 1. They have similar electron configurations. 2. They have the same number of valence electrons. 3. They form ions with the same charge. 4. They exhibit the same type of chemical behavior. Valence Electrons: Electrons that are able to be gained, lost, or shared in the formation of chemical compounds. The s and p electrons in the outermost energy level. Core Electrons: All of the other electrons. Properties of the Representative Elements S block Group IA Family Name Alkali metals 1. [ ] ns 1 2. 1 valence e- 2
3. +1 (losing 1 electron) Na+, K+, Li+ etc. 4. Most Highly reactive metals on the periodic table. So reactive they are never found in pure form. Group II A Family Name Alkaline Earth Metals 1. [ ] ns 2 2. 2 valence e- 3. lose 2 e- to form 2+ ions. Ca 2+, Mg 2+, Ba 2+ 4. Also very reactive, but not as much as group IA. Not found in nature in pure form. P block Group IIIA Family Name Aluminum Family 1. [ ] ns 2 np 1 2. 3 valence e- 3. lose 3 e- to form 3+ ions. Al 3+ 4. Not as highly metallic as group IA and IIA. This group also has a metalloid (B) in it. Group IVA Family Name Carbon Family 1. [ ] ns 2 np 2 2. 4 valence e- 3. lose or gain 4 e- to form 4+ or 4- ions. (Tends to share e- instead) 4. Lots of variety in this family nonmetal (C) metalloids (Si, Ge) metals Pb, Sn. Group VA Family Name Nitrogen Family 1. [ ] ns 2 np 3 2. 5 valence e- 3
3. gains 3 e- to form 3- ions. N 3-4. Nitrogen is most common element in atmosphere air is 78% Nitrogen. Group VIA Family Name Chalkogens (Chalk-formers) 1. [ ] ns 2 np 4 2. 6 valence e- 3. gains 2 e- to form 2- ions. S 2-, O 2-4. Form chalk like compounds (oxides) ex Calcium and magnesium oxides. Group VIIA Family Name Halogens _ (salt-formers) 1. [ ] ns 2 np 5 2. 7 valence e- 3. gain 1 e- to form 1- ions. F-, Cl-, Br- 4. Most active nonmetals. (They really want to GAIN electrons.) Form salt compounds with active metals. NaCl. MgCl 2 KCl CaCl 2 Group VIIIA Family Name Noble Gases 1. [ ] ns 2 np 6 2. 8 valence e- 3. No ions formed since configuration is stable as is. 4. Inert or nonreactive Rule of Octet: Atoms tend to gain, lose, or share electrons in order to acquire a complete set of valence electrons. (s 2 p 6 =8) or just s 2 if the atom is in period 1 or 2. 4
Periodic Trends Periodic Trends are: Periodic Trends we will study: 1. Atomic Radius 2. Ionic Radius: 3. Ionization Energy: 4. Electron Affinity: 5. Electronegativity: 1. Atomic Radius a. What is the trend as you move from left to right across a period? b. Explain a: c. What is the trend as you move from top to bottom down a family? d. Explain c: 2. Ionic Radius a. What is the trend as you move from left to right across a period? b. Explain a: c. What is the trend as you move from top to bottom down a family? d. Explain c: e. What does isoelectronic mean? 5
f. Suppose an anion and a cation are isoelectronic; which has a larger radius? g. Explain f: h. Copper forms two different cations; Cu 2+, and Cu +. Which has a larger radius? i. Explain h: 3. Ionization Energy A. ionization energy can be thought of as a reflection of the attraction of the nucleus for the. B. Atoms with High Ionization Energy hold on to their valence electrons. C. Examples of groups/ families with high ionization energies: D. Atoms with low ionization energies are likely to : E. Examples of groups/ families with low ionization energy? F. What is the trend in ionization energy as you move from left to right across the periodic table? G. Successive Ionizations 1. First Ionization Energy: 2. Second ionization Energy: 3. Third Ionization Energy: H. See table 3 on page 155. 1. Where is the largest jump in successive ionization energies of Aluminum? 2. Which electron is being removed in the first, ionization of Al? 6
3. Write the reaction for 2: 4. Which electron is being removed in the 2 nd ionization of Al? The 3 rd? The fourth? 5. Write the reactions for the 2 nd, 3 rd, and 4 th ionizations: 6. Summary In successive ionizations of an element, the largest jump in energy occurs after: The large energy jump indicates: 7. Write the reactions for the successive ionizations of Magnesium. See table 3 on page 155 for Ionization energies. 4. Electron Affinity (EA) A. EA values can be positive or negative. 1. If EA is positive: 2. What type of element has a positive EA? 3. If EA is negative: 4. What kind of element has a negative EA? 7
B. In general, what is the trend in EA as you move down a group? 6. In general, what is the trend in EA as you move from left to right across a period? 7. What group/ family has the most highly negative EA? Why? 5. Electronegativity A. This property is different from the other periodic trends since it focuses on the elements behavior in a chemical bond. B. Scale of Electronegativity: 1. High electronegativity: 2. Low electronegativity: c. What happens to electronegativity as you go from left to right across the periodic table? D. What happens to electronegativity as you go down a group/ family? E. Which element is the most electronegative element? F. Which element is the least electronegative? G. Memorize the electronegativity of second period of elements, plus H, Cs, and Cl. You will need to know these for chemical bonding. 8