1. Chemical Bonding

2. Objectives  Define the key terms  Distinguish between ionic and molecular compounds  Define cation and anion and relate them to metal and nonmetal  Distinguish among chemical formulas, molecular formulas, and formula units  Use experimental data to show that a compound obeys the law of definite proportions

3. Key Terms  Monatomic – consist of a single atom In nature, only the noble gases tend to exist as isolated atoms. In nature, only the noble gases tend to exist as isolated atoms.  Molecule – two or more atoms; smallest electrically neutral unit of a substance that still has the properties of that substance  Molecular compound – compounds composed of molecular units

4. The Noble Gases  Helium – less dense than air; often used to inflate balloons  Passing an electric current through a noble gas produces neon lights: Neon (orange-red) Neon (orange-red) Helium (yellowish) Helium (yellowish) Argon (lavender) Argon (lavender) Krypton (whitish) Krypton (whitish) Xenon (blue) Xenon (blue)

5. Molecules  Diatomic – consist of two atoms O 2 (oxygen) and carbon monoxide (CO) O 2 (oxygen) and carbon monoxide (CO)  Triatomic – consist of three atoms O 3 (ozone) and water (H 2 O) O 3 (ozone) and water (H 2 O)

6. Properties of Molecular Compounds  Low melting and boiling points  Exist as gases or liquids at room temperature  Composed of atoms of two or more nonmetals  Proteins and hormones in the body

7. Ions  Ion – an atom or group of atoms that has a positive or negative charge Formed when an atom or group of atoms loses or gains electrons Formed when an atom or group of atoms loses or gains electrons Two Types: Two Types: 1. Anion – negative charge 1. Anion – negative charge 2. Cation – positive charge (Circle the top 2. Cation – positive charge (Circle the top of the t in the word cation and it looks of the t in the word cation and it looks like a positive sign.) like a positive sign.)

8. CationAnion ChargePositive (Circle the top of the “t” - it’s a +) Negative Metal/Nonmetal Metal (Cation and Metal both have a “t” as the 3 rd letter of the word) Nonmetal Name Same as element Ends in “ide”

9. Ionic Compounds  Contain both cations and anions  Electrically neutral because the total positive charge of the cations is equal to the total negative charge of the anions  Properties: 1. Exist as solid crystals at room 1. Exist as solid crystals at room temperature temperature 2. Have relatively high melting points 2. Have relatively high melting points 3. Composed of a metallic element 3. Composed of a metallic element combined with a nonmetallic element combined with a nonmetallic element  Salts in body fluids

10. Examples  Atoms Ne He C  Molecules CH 4 O 2 H 2 O  Cations Ca 2+ Na + Fe 3+  Anions F - O 2- Cl -  Cations lose electrons and thus gain a positive charge  Anions gain electrons and thus gain a negative charge

11. Key Terms  Chemical formula – shows kinds and numbers of atoms in the smallest representative unit of the substance Two Types: Two Types: 1. Molecular formula – shows kinds and numbers of atoms present in a molecule of a compound 1. Molecular formula – shows kinds and numbers of atoms present in a molecule of a compound 2. Formula unit – smallest whole number ratio of ions in the compound 2. Formula unit – smallest whole number ratio of ions in the compound

12. Examples of Formula Units  NaCl (one Na + to one Cl -)  MgCl 2 (one Mg 2+ to two Cl - )  What is the ratio of AlCl 3 ?  1:3

13. Law of Definite Proportions  In samples of any chemical compound, the masses of the elements are always in the same proportions  Describes the composition of one compound  Consistent with Dalton’s atomic theory: If atoms combine in simple whole-number ratios, their proportions by mass must always be the same

14. Law of Multiple Proportions  Whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.  Compares the compositions of two different compounds containing the same elements

15. Objectives  Know key terms  Use the periodic table to determine the charge on an ion  Determine the names and formulas of the most common polyatomic ions

16. Key Terms  Monatomic ion – ions consisting of only one atom  Polyatomic ions – tightly bound groups of atoms that behave as a unit and carry a charge

17. Ionic Charges of Monatomic Ions  Metallic elements tend to lose electrons to form cations  Group 1A: 1+ Charge  Group 2A: 2+ Charge  Group 3A: 3+ Charge Note: Aluminum is the only common Group 3A metal. Note: Aluminum is the only common Group 3A metal.

18. Charges of Group A Nonmetals  Subtract the group number from 8  Nonmetals tend to gain electrons and form anions  Group 5A: 3- Charge Note: The three nonmetals are N, P, and Bi. Note: The three nonmetals are N, P, and Bi.  Group 6A: 2- Charge  Group 7A: 1- Charge

19.  The majority of elements in groups 14 (4A) and 18 (0) usually do not form ions.  The elements in Group 18 rarely form compounds  Ordinarily, the two nonmetals in Group 14, carbon and silicon, are found in molecular compounds.

20. Summary of Ionic Charges  Group 1A: 1+ Charge  Group 2A: 2+ Charge  Group 3A: 3+ Charge  Group 4A: none (generally) Note: Cations of tin and lead have more than one ionic charge. Note: Cations of tin and lead have more than one ionic charge.  Group 5A: 3-  Group 6A: 2-  Group 7A: 1-  Group 0 : none

21. Cations of Transition Metals  Many have more than one common ionic charge  Example: Fe 2+ and Fe 3+  Two methods of naming such cations: 1. Stock system: A Roman numeral in parenthesis indicates the numerical value of the charge; there is no space between the element name and the first parenthesis 1. Stock system: A Roman numeral in parenthesis indicates the numerical value of the charge; there is no space between the element name and the first parenthesis Examples: iron(II) ion and iron(III) ion Examples: iron(II) ion and iron(III) ion

22.  2. Root word with different suffixes (Older method and less preferred (Older method and less preferred because it does not give the charge) because it does not give the charge) Example: Ferrum is Latin for iron. Use ferr as root word and ous (smaller) or ic (larger) Example: Ferrum is Latin for iron. Use ferr as root word and ous (smaller) or ic (larger) Fe 2+ ferrous ion Fe 2+ ferrous ion Fe 3+ ferric ion Fe 3+ ferric ion

23.  A few transition metals have only one ionic charge:  Silver: Ag+  Cadmium and Zinc: Cd 2+ and Zn 2+  Note: Many transition metal compounds are used as pigments.

24. Polyatomic Ions  Grouped by charge  Most names end in ite or ate Exceptions: Exceptions: 1. Ammonium cation (NH 4 + ) 1. Ammonium cation (NH 4 + ) 2. Cyanide anion (CN - ) 2. Cyanide anion (CN - ) 3. Hydroxide anion (OH - ) 3. Hydroxide anion (OH - )  ite ending indicates one less oxygen atom than the ate ending

25. Examples iteate SO 3 2- sulfite SO 4 2- sulfate NO 2 - nitrite NO 3 - nitrate ClO 2 - chlorite ClO 3 - chlorate

26. Formulas beginning with Hydrogen  Imagine the H to represent a hydrogen ion (H + ) combined with another polyatomic ion  Example: HCO 3 - A combination of H + and CO 3 2- A combination of H + and CO 3 2- Hydrogen carbonate Hydrogen carbonate Note that the charge on the ion (HCO 3 - ) is the algebraic sum of the ionic charges. Note that the charge on the ion (HCO 3 - ) is the algebraic sum of the ionic charges.

27. Facts to Know  The hydrogen carbonate anion, hydrogen phosphate anion and the dihydrogen phosphate anion are all essential components of living systems  The cyanide ion is extremely poisonous to living systems because it blocks a cell’s means of producing energy.  Most laundry and household bleaches contain the hypochlorite anion.