Electronegativity and Bonding How does electronegativity predict the type of bonds atoms form? Why? By this point in your academic career, you have probably learned the two most common types of chemical bonds: ionic bonds and covalent bonds. Ionic bonds transfer electrons and covalent bonds share them. But what does that really mean? And how can an atoms electronegativity unit help you understand and predict the types of chemical bonds that form between atoms. Model 1-Electronegativity Values on the Periodic Table 1. What does electronegativity tell you about an element? Measure of an atom’s ability to take electrons FROM ANOTHER ATOM a. If an element has a high electronegativity, the element is good at… Gaining electrons b. If an element has a low electronegativity, the element… Loses electrons easily 2. Do you notice a pattern between metals and non-metals in Model 1? Electronegativity of metals is lower than those of non-metals 1 3. As you move down a group on the periodic table what typically happens to electronegativity? It decreases 4. As you move from left to right across a period what typically happens to electronegativity? It increases 5. Which corner of the periodic table are the elements that are the best at attracting electrons? Top right 6. Which corner of the periodic table are the elements that have difficulty holding onto to their electrons? Bottom left 7. Make a prediction: if two atoms with very different electronegativities get close together, the atoms are likely to (share electrons / transfer electrons / bounce off without reacting). Explain your reasoning below. 8. Make a prediction: if two atoms with similar electronegativities get close together, the atoms are likely to (share electrons / transfer electrons / bounce off without reacting). Explain your reasoning below. 2 Model 2 – Using Electronegativity Difference to Determine Bond Type Bond What’s Holding the Electronegativity Example Type Bonds Together? Difference NaCl Ionic Transfer of electrons 3.16 (chlorine) ~1.7 or greater - 0.93 (sodium) 2.23 ~ 1.7 of less CO2 Covalent Sharing of electrons 3.44 (oxygen) - 2.55 (carbon) 0.89 Element Electronegativity Good at attracting F 3.98 e- in a bond O 3.44 Cl 3.16 N 3.04 Br 2.96 I 2.66 S 2.58 C 2.55 H 2.20 P 2.19 Si 1.90 Cu 1.90 Fe 1.83 Al 1.61 Mg 1.31 Ca 1.00 Li 0.98 Na 0.93 Has difficulty K 0.82 attracting e- in a bond Fr 0.7 3 Use Model 2 to determine the types of bonds formed between the following elements: 9. Fluorine and Potassium a. Difference in Electronegativity: 3.98 – 0.82 = 3.16 b. Type of Bond formed: ionic or covalent 10. Silicon and Oxygen a. Difference in Electronegativity: 3.44 – 1.90 = 1.54 b. Type of Bond formed: ionic or covalent 11. Calcium and Chlorine 3.16 – 1.00 = 2.16 a. Difference in Electronegativity: b. Type of Bond formed: ionic or covalent 12. Aluminum and Chlorine 3.16 – 1.61 = 1.55 a. Difference in Electronegativity: b. Type of Bond formed: ionic or covalent 13. Sodium & Oxygen 3.44 – 0.93 = 2.51 a. Difference in Electronegativity: b. Type of Bond formed: ionic or covalent 14. Look back at your answers to questions 7 & 8. Were your predictions correct? If not, revise your answers. Answers will vary 15. Use your answers from questions 9-13 to complete the following statements: a. Ionic bonds most often form between (metals and non-metals/ non-metals and non-metals/metals and metals) b. Covalent bonds most often form between (metals and non-metals/ non-metals and non-metals/metals and metals) 4 .