Unit 5: Bonding. Place a checkmark next to each item that you can do. If a sample problem is given, complete it as evidence.

Transcription

1 Unit 5: Bonding Place a checkmark next to each item that you can do. If a sample problem is given, complete it as evidence. Intramolecular Forces: forces of attraction within the same molecule. Examples: ionic bonds, covalent bonds, metallic bonds 1. I can define intramolecular forces and intermolecular forces and give examples of each. Intermolecular Forces: forces of attraction between different molecules. Examples: Van der Waals (dipole-dipole forces, dispersion forces), hydrogen bonding, molecule-ion attraction. BARF stands for Break Absorb Release Form This means that when a bond is FORMED, energy is released and when a bond is BROKEN, energy is absorbed. 2. I can explain and apply the meaning of BARF as it applies to chemical bonding. 3. I can state the number of valence electrons that an atom attains to be most stable. 4. I can state the three types of chemical bonds. 5. I can define ionic bond, covalent bond, and metallic bond in terms of the types of elements (metals, nonmetals) from which they are formed. Given the balanced equation: N + N N 2 Which statement describes the process represented by this equation? A) A bond is formed as energy is absorbed. B) A bond is formed as energy is released. C) A bond is broken as energy is absorbed. D) A bond is broken as energy is released. Atoms are most stable when they have 8 valence electrons. The three types of chemical bonds are ionic, covalent, and metallic. Ionic Bond: form between a metal and a nonmetal. Electrons are transferred from the metal to the nonmetal. The metal becomes a positive ion and the nonmetal becomes a negative ion and the two oppositely charged ions attract. Covalent Bond: form between two or more nonmetals. Electrons are shared between the atoms. Metallic Bond: form between the same metal. The metals lose their electrons and the positive ions that form are attracted to the sea of mobile electrons.

2 In an ionic bond, the valence electrons of the metals are transferred to the nonmetal so that each atom attains a stable octet (like noble gases). In these 6. I can define ionic, covalent, and metallic bonds based on what happens to the valence electrons. compounds, the electronegativity difference is large (usually greater than 1.7). In a covalent bond, the valence electrons of the two nonmetals are shared so that each atom attains a stable octet. In these compounds, the electronegativity difference is small (usually less than 1.7). In a metallic bond, positive ions are immersed in a sea of mobile electrons. 7. I can determine the compound that has the greatest ionic character. Which of the following compounds has the greatest ionic character? A) LiCl B) CaCl 2 C) BCl 3 D) RbCl Draw Lewis dot diagrams for the following ionic compounds: 8. I can draw a Lewis dot diagram to represent an ionic compound. NaCl CaCl 2 Physical properties of ionic substances are: they have hard, crystalline 9. I can state the properties of ionic substances. structures as a solid (crystal lattice geometric pattern), they have high melting and boiling points, they conduct electricity as a liquid and in solution (aq) (mobile charges), they are soluble (dissolve in water). A solid substance was tested in the lab. The results are shown below. *dissolves in water *is an electrolyte * has a high melting point 10. I can identify a substance as ionic based on its properties. Based on these results, the solid substance could be A) Hg B) AuCl C) CH 4 D) C 12 H 22 O 11 Based on bond type, which compound has the highest melting point? A) CH 4 B) C 12 H 22 O 11 C) NaCl D) C 5 H I can state the number of electrons that are shared in single and multiple covalent bonds. In a single covalent bond, 2 electrons or 1 pair is shared. In a double covalent bond, 4 electrons or 2 pairs are shared. In a triple covalent bond, 6 electrons or 3 pairs are shared.

3 Draw Lewis dot diagrams for the following molecular substances and identify their shapes. (Use the CNOF table) H 2 O - bent CO 2 - linear 12. I can draw a Lewis dot diagram to represent a molecular (covalently bonded) substance and identify its shape as linear, bent, trigonal pyramidal, or tetrahedral. I 2 - linear NH 3 trigonal pyramidal CH 4 - tetrahedral CHCl 3 tetrahedral Physical properties of molecular substances are: they can exist in all I can state the properties of molecular substances. phases, they are usually not soluble in water, solids are soft, they are poor conductors in any phase (no mobile charges), they have low melting and boiling points. 14. I can identify a substance as molecular based on its properties.

4 15. I can state the type of bonding that occurs in compounds containing polyatomic ions. 16. Given the chemical formula for a compound, I can determine the type(s) of bonding in the compound. Compounds containing polyatomic ions have both ionic and covalent bonding. State the type(s) of bonding in the following compounds: NaCl - ionic CO - covalent Hg - metallic Na 3 PO 4 - ionic and covalent Explain, in terms of valence electrons, why the bonding in methane (CH 4 ) is similar to the bonding in water (H 2 O). 17. In terms of valence electrons, I can find similarities and differences between the bonding in several substances. In both molecules, the valence electrons are shared between the two atoms to form a covalent bond. Explain, in terms of valence electrons, why the bonding in HCl is different than the bonding in NaCl. In HCl the valence electrons are shared to form a covalent bond, while in NaCl the valence electrons are transferred to form an ionic bond. Polar covalent bonds are formed when different nonmetals share electrons 18. I can explain the difference between a polar covalent bond and a nonpolar covalent bond. unequally. The electronegativity difference is between 0 and 1.7. Nonpolar covalent bonds are formed when the same nonmetals share electrons equally. The electronegativity difference is zero. 19. I can explain how to determine the degree of polarity of a covalent bond. 20. I can explain why one covalent bond is more or less polar than another covalent bond. The degree of polarity of a covalent bond is determined by the electronegativity difference between the elements. Explain, in terms of electronegativity difference, why the bond between carbon and oxygen in a carbon dioxide molecule is less polar than the bond between hydrogen and oxygen in a water molecule. The difference in electronegativity between carbon and oxygen is less than the difference in electronegativity between hydrogen and oxygen. 21. I can determine which end of a polar covalent bond is slightly negative and which end is slightly positive and explain why. Draw a water molecule and include slight charges. Explain why you assigned each atom its charge. Oxygen is slightly negative because it has a higher electronegativity and hydrogen is slightly positive because it has a lower electronegativity.

5 22. I can define symmetrical and asymmetrical. Symmetrical: a molecule in which all slight charges cancel (looks the same when the molecule is turned upside down). There is an equal distribution of charge in a symmetrical molecule. Asymmetrical: a molecule in which all slight charges do not cancel (looks different when the molecule is turned upside down). There is an unequal distribution of charge in an asymmetrical molecule. SNAP means symmetrical nonpolar asymmetrical polar. Why is a molecule of CH 4 nonpolar even though the bonds between the carbon and hydrogen are polar? 23. I can explain and apply the meaning of SNAP as it relates to determining molecule polarity. A) The shape of the CH 4 molecule is symmetrical. B) The shape of the CH 4 molecule is asymmetrical. C) The CH 4 molecule has an excess of electrons. D) The CH 4 molecule has a deficiency of electrons. Explain, in terms of charge distribution, why a molecule of water is polar. Water is asymmetrical so the slight charges that exist do not cancel out (the molecule has asymmetrical distribution of charge). Determine which molecules are polar and which are nonpolar. Justify your answer. 24. I can determine if a molecular is polar or nonpolar. H 2 O polar, asymmetrical I 2 nonpolar, symmetrical (nonpolar bonds) NH 3 polar, asymmetrical CO 2 nonpolar, symmetrical CH 4 nonpolar, symmetrical CHCl 3 polar, asymmetrical Dipole-Dipole: a type of van der Waal s force that exists between polar molecules. The slight negative end of one polar molecule is attracted to the slight positive end of another polar molecule. 25. I can define the different types of intermolecular forces. Dispersion: a type of van der Waal s force that exists between nonpolar molecules. The attraction comes from the temporary slight charges that exist when the electrons move around the nucleus. Wherever the electron is, it brings a slight negative charge with it. Hydrogen Bonding: occurs between the hydrogen atom in one molecule and a nitrogen, oxygen, or fluorine atom in another molecule (H-NOF). Hydrogen bonds are very strong and explain the unusually high boiling point of water. Molecule-Ion Attraction: exists between ions of an ionic compound and the molecules of a polar liquid. This attraction is present in all solutions (aq) and explains how a substance dissolves.

6 26. I can state the relationship between polarity and intermolecular force strength. 27. I can state the relationship between size of the molecule and intermolecular force strength. 28. I can state the relationship between the strength of the intermolecular forces and vapor pressure. 29. Given the physical state of some substances, I can compare the relative strength of the intermolecular forces. As the polarity of the molecule increases, the strength of the forces increases. As the size of the molecule increases, the strength of the forces increases. As the strength of the forces increases, vapor pressure decreases. At STP, iodine (I 2 ) is a crystal and fluorine (F 2 ) is a gas. Compare the strength of the intermolecular forces in a sample of I 2 at STP to the strength of the intermolecular forces in a sample of F 2 at STP. Since I 2 is a solid, it must have stronger intermolecular forces of attraction compared to fluorine, which is a gas. The stronger the forces of attraction, the closer the particles are arranged. 30. Given the boiling points (or freezing points) of some substances, I can compare the relative strength of the intermolecular forces. At STP, CF 4 boils at C and NH 3 boils at C. Which substance has stronger intermolecular forces? Justify your answer. NH 3 has stronger intermolecular forces of attraction because it has a higher boiling point. The stronger the forces of attraction, the higher the boiling point is. Which compound has hydrogen bonding between its molecules? 31. I can answer questions about hydrogen bonding. A) CH 4 B) CaH 2 C) KNO 3 D) H 2 O The relatively high boiling point of water is due to water having A) hydrogen bonding B) metallic bonding C) nonpolar covalent bonding D) strong ionic bonding In which system do molecule-ion attractions exist? A) NaCl (aq) B) NaCl (s) C) C 6 H 12 O 6 (aq) D) C 6 H 12 O 6 (s) Which diagram best illustrates the ion-molecule attractions that occur when the ions of NaCl (s) are added to water? 32. I can answer questions about molecule-ion attraction.