6 Chemical Formulas Chemical Bonding Stoichiometry Chapter 6 Chemical Bonding Stoichiometry COURSE NAME: CHEMISTRY 101 COURSE CODE: 402101-4

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Chemical Formulas 4

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7 Chemical Bonding Ionic bond Na + Cl → Na+ Cl- Ionic bond is formed when metal (electropositive element) lose electrons forming positive ion and nonmetal (electronegative element) gain these electrons forming negative ion.The ionic bond results from the electrostatic attraction between the positive (cation) and negative ion (anion). An example of an ionic compound is NaCl where Na is of low ionization potential and Cl is of high electron affinity. Thus, an electron is taken up by Cl from Na to become Cl- and Na then becomes Na+. Electrostatic attraction then occurs between the two ions to form ionic bond. Na + Cl → Na+ Cl- 7

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Covalent Bond (electron –pair bond) The bond formed when two atoms mutually share their electrons. In the other words, it is the bond formed by sharing a pair of electrons by two atoms e.g. H· + H· → H··H or (H-H) 9

Thus, the structure is written as Hδ+ ─ Clδ- When the two atoms are of similar electronegativity the covalent bond is nonpolar. On the other hand, when the two atoms are of different electronegativity, the bond is polar covalent bond e.g. H-Cl ; chlorine atom is more electronegativily and attracts the bond electrons more strongly than hydrogen. Thus, the structure is written as Hδ+ ─ Clδ- Chlorine carries partial negative charge but the hydrogen carries partial positive charge. 10

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Coordination bond This bond formed when a pair of electrons from one atom is shared between two atoms. Also it can be defined as the bond formed by the interaction of two atomic orbitals one is doubly occupied and the other is empty; the first is called donor and the second is called acceptor. Donor Acceptor Compound We write simply the product as H3N+BF3- 12 13

Where A and B are strongly electronegative atoms Hydrogen bond The attractive force that binds a hydrogen atom which is covalently attached with a strongly electronegative atom of a molecule with another electronegative atom of some other molecule. Thus the existence of hydrogen bond between A-H and B-H molecules can be shown as: Aδ-Hδ+ ….. Bδ-Hδ+ Where A and B are strongly electronegative atoms 13 14

Stoichiometry Definition: predicting the amounts of reactants and/or products that will be involved in a reaction Must use a balanced reaction Why? Because matter can neither be created nor destroyed. If you try to use a reaction like: H2 + O2H2O 14

You will have one oxygen atom that does not get used You will have one oxygen atom that does not get used. You have to take that into consideration otherwise the reaction is not an accurate description of what is happening Since you are only using ½ of the O2 molecule: H2 + ½ O2H2O This is the same as: 2 H2 + O2 2 H2O Coefficients tell you the relative amounts of products and reactants Coefficients are in units of moles 15

Using the coefficients we can write mole ratios Example: N2 + 3 H2 2 NH3 Recall that the coefficient on N2 is 1 but is not explicitly written in the reaction Coefficients: N2 = 1 H2 = 3 NH3 = 2 Using the coefficients we can write mole ratios 16

Definition: mole ratio gives the relative amounts of reactants and products 17

MOLE to MOLE Stoichiometry 18

MASS to MASS Stoichiometry 19

You can use this version of the mole map to solve stoichiometry problems. 20

21 1. Determine the number of moles of aluminum in 0.2154 kg of Al. A) 1.297 x 1023 mol B) 5.811 x 103 mol C) 7.984 mol D) 0.1253 mol E) 7.984 x 10-3 mol 2. How many phosphorus atoms are there in 2.57 g of P? A) 4.79 x 1025 B) 1.55 x 1024 C) 5.00 x 1022 D) 8.30 x 10-2 E) 2.57 3. What is the coefficient for CO2 when the following chemical equation is properly balanced using the smallest set of whole numbers? C4H10 + O2 ----> CO2 + H2O A) 1 B) 4 C) 6 D) 8 E) 12 21

5. Calculate the number of moles of H2O formed when 0 5. Calculate the number of moles of H2O formed when 0.200 mole of Ba(OH)2 is treated with 0.500 mol of HClO3 according to the chemical reaction shown below. Ba(OH)2 + 2 HClO3 ----> Ba(ClO3)2 + 2 H2O A) 1.00 mol B) 0.600 mol C) 0.500 mol D) 0.400 mol E) 0.200 mol 4. What mass of copper(II) nitrate would be produced from the complete reaction of 45.6 g of copper, according to the chemical reaction shown below? Cu + 2 AgNO3 ----> Cu(NO3)2 + 2 Ag A) 0.72 g B) 21.1 g C) 98.7 g D) 135 g E) 187 g 22

6. The limiting reagent is the substance: A) present in greatest quantity B) limits the number of reagents present C) determined by the amount of reactants present D) that determines the maximum amount of possible product 7. One mole of H2 A) contains 6.0 x 1023 H atoms. B) contains 6.0 x 1023 H2 molecules. C) contains 1 g of H2. D) is equivalent to 6.02 x 1023 g of H2. E) None of the above. 23

24 8. How many oxygen atoms are present in 5.2 g of O2? A) 5.4 x 10-25 atoms B) 9.8 x 1022 atoms C) 2.0 x 1023 atoms D) 3.1 x 1024 atoms E) 6.3 x 1024 atoms 9. What is the mass of 5.45 x 10-3 mol of glucose, C6 H12O6? A) 0.158 g B) 982 g C) 3.31 x 104 g D) 0.982 g E) None of the above. 10. Determine the mass percent of iron in Fe4[Fe(CN)6] 3. A) 45% Fe B) 26% Fe C) 33% Fe D) 58% Fe E) None of the above. 11. When it is correctly balanced, the correct coefficients for the equation below are PCl3 + H2O ----> H3PO3 + HCl A) 1, 3, 1, 1 B) 1, 3, 1, 3 C) 1, 1, 1, 3 D) 2, 3, 2, 3 24