1. Chemical Bonding Chapter 7

2. Chemical Bonds Chemical Bond – a link between atoms resulting from the neutral attraction of their nuclei for electrons Chemical Bond – a link between atoms resulting from the neutral attraction of their nuclei for electrons force of attraction between atoms force of attraction between atoms

3. Ionic bond Ionic Bond – chemical bond resulting from the transfer of electrons from one bonding atom to another Ionic Bond – chemical bond resulting from the transfer of electrons from one bonding atom to another Ex. NaCl Ex. NaCl Ionic Bonds form ionic compounds which are composed of ions. Ionic Bonds form ionic compounds which are composed of ions.

4. Characteristics of an ionic bond -high melting points (shows a strong bond) -high melting points (shows a strong bond) -brittle -brittle -dissolve in water -dissolve in water -good conductors of electricity in solution -good conductors of electricity in solution

5. Octet Rule Octet Rule – atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. Octet Rule – atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. Example of an ionic bond: Example of an ionic bond: Consider NaCl – (table salt) Consider NaCl – (table salt) Na – 1s 2 2s 2 2p 6 3s 1 Na – 1s 2 2s 2 2p 6 3s 1 Cl – 1s 2 2s 2 2p 6 3s 2 3p 5 Cl – 1s 2 2s 2 2p 6 3s 2 3p 5

6. What happens? What happens? Na loses 1e- to form an octet Na loses 1e- to form an octet becomes Na + ion becomes Na + ion called CATION called CATION Cl gains 1e- to form an octet Cl gains 1e- to form an octet becomes Cl - ion becomes Cl - ion called ANION called ANION

7. Using Lewis Dot diagrams Using Lewis Dot diagrams used to show valence electrons used to show valence electrons dot represents valence electrons (or x’s and o’s) dot represents valence electrons (or x’s and o’s) random order random order Na Cl -> Na+ + Cl - Na Cl -> Na+ + Cl -

8. Formulas Empirical Formula – chemical formulas which gives the simplest whole number ratio of atoms of elements in a compound. Empirical Formula – chemical formulas which gives the simplest whole number ratio of atoms of elements in a compound. -cation ALWAYS written first -cation ALWAYS written first -total “+” must equal total “-“ -total “+” must equal total “-“

9. Monoatomic ions – made of ONLY 1 element Monoatomic ions – made of ONLY 1 element Must remember the charge of the ion Must remember the charge of the ion Cations:Anions: Cations:Anions: Group 1: +1Group 17: -1 Group 1: +1Group 17: -1 Group 2: +2Oxide: -2 Group 2: +2Oxide: -2 Silver: +1Sulfide: -2 Silver: +1Sulfide: -2 Zinc: +2Nitride: -3 Zinc: +2Nitride: -3 Aluminum: +3Phosphide:-3 Aluminum: +3Phosphide:-3

10. Polyatomic ions ions which consist of more than one atom ions which consist of more than one atom they act as a whole and carry a net charge they act as a whole and carry a net charge Examples of Polyatomic Ions Examples of Polyatomic Ions Hydroxide - OH -,Acetate – C 2 H 3 O 2 - Hydroxide - OH -,Acetate – C 2 H 3 O 2 - Hypochlorite – ClO -,Sulfate – SO 4 -2 Hypochlorite – ClO -,Sulfate – SO 4 -2 Nitrate – NO 3 -,Carbonate – CO 3 -2 Nitrate – NO 3 -,Carbonate – CO 3 -2 Bicarbonate – HCO 3 -,Phosphate – PO 4 -3 Bicarbonate – HCO 3 -,Phosphate – PO 4 -3

11. Binary Compounds Binary Ionic Compounds Binary Ionic Compounds - contain ions of only 2 elements. - contain ions of only 2 elements. - Need to know the ratio of elements in the compound - Need to know the ratio of elements in the compound

12. Writing formulas: Criss-Cross method write symbols of the elements or polyatomic ions putting the charge as a superscript write symbols of the elements or polyatomic ions putting the charge as a superscript put parenthesis around only the polyatomic ion put parenthesis around only the polyatomic ion crisscross the numbers not the charges and represent as subscripts crisscross the numbers not the charges and represent as subscripts

13. Writing formulas…. reduce if possible reduce if possible eliminate and rewrite any subscript of 1 and any parenthesis whose subscript is 1. eliminate and rewrite any subscript of 1 and any parenthesis whose subscript is 1. Example: Na and O form Example: Na and O form Na 2 O Na 2 O

14. Covalent Bonds Covalent Bond – chemical bond resulting from the sharing of electrons between bonding atoms Covalent Bond – chemical bond resulting from the sharing of electrons between bonding atoms Ex. CO 2 Ex. CO 2

15. 7.2 Covalent Bonds Molecule- a group of atoms grouped together by covalent bonds. Molecule- a group of atoms grouped together by covalent bonds. Molecular substance – a substance made up of molecules. Molecular substance – a substance made up of molecules.

16. Molecular vs. Empirical Molecular formula – tells you how many atoms are in a single molecule of the compound. Molecular formula – tells you how many atoms are in a single molecule of the compound. Ex. C 6 H 12 O 6 glucose Ex. C 6 H 12 O 6 glucose The empirical formula can be written for molecular formulas. The empirical formula can be written for molecular formulas. Ex. CH 2 O glucose Ex. CH 2 O glucose

17. Properties of covalent bonds Properties of Covalent Bonds Properties of Covalent Bonds Bonds can be polar depending on the Electronegativity of the atoms. Bonds can be polar depending on the Electronegativity of the atoms. If one atom is significantly more electronegative than the other, the electron density will change. If one atom is significantly more electronegative than the other, the electron density will change.

18. The atom that is more electronegative will pull the electrons closer to it and cause a partial negative on that atom. The atom that is more electronegative will pull the electrons closer to it and cause a partial negative on that atom. **Electronegative difference must be between 0.5 and 1.9 **Electronegative difference must be between 0.5 and 1.9 If the electronegatives are similar, the bond will be nonpolar (electronegative difference less than 0.4) If the electronegatives are similar, the bond will be nonpolar (electronegative difference less than 0.4)

19. Ionic bonds Involves transfer of electrons Forms ions Forms ions Usually forms between metal and nonmetal and/or polyatomic atom Usually forms between metal and nonmetal and/or polyatomic atom substances usually soluble in water substances usually soluble in water high melting point high melting point

20. solutions are usually good conductors of electricity solutions are usually good conductors of electricity compounds are brittle compounds are brittle formulas are expressed as empirical formulas formulas are expressed as empirical formulas 9.Electronegativity difference greater than 1.9 9.Electronegativity difference greater than 1.9 10.strong bond 10.strong bond 11. criss cross 11. criss cross