Bonding

1. Bonding Chapter 5

2. Bonding • When atoms combine they form a chemical bond • The force of attraction between two or more atoms.

3. Valence Electrons • Are the outer most electrons of an atom. • They play a huge role in how an atom bonds.

4. Lewis Structure • Is a diagram of atoms that only shows the valance electrons • Ex: Cl Na H Ar

5. The Octet Rule • The octet rule says that atoms tend to gain, lose or share electrons so they can have eight electrons in their outer shell. • They do this because they are more stable with a complete outer shell. • There are some situations where it does not apply. For example, hydrogen wants to take one on to complete its outer shell with 2 electrons.

6. Oxidation Numbers • Oxidation numbers represent the charges that an ion has when it gains or loses its valence electrons. • They are listed as a + or –above each column on the periodic table.

7. Ion • An ion is an atom which has lost or gained one or more electrons, making it positively or negatively charged. • A negatively-charged ion, gains an electrons so it has more electrons then it has protons. It is called an anion. • A positively-charged ion, looses electrons so it has more protons then electrons. It is called a cation. • A polyatomic ion is an ion that is made up of more than one atom. • Poly= Many Atomic= Atoms • Ex: NH4+ is the chemical formula for an ammonium ion. It contains two elements nitrogen and hydrogen and has a positive charge.

8. Ionic Bonds • Bonds that form as a result of the attraction between positive and negative ions. The atoms are attracted to each other because of their opposite charges • We call the compound that results from the bond an Ionic Compound. • Usually form between a metal and a nonmetal

9. K F In an IONIC bond, electrons are lost or gained, resulting in the formation of IONS in ionic compounds.

10. K F

11. K F

12. K F

13. K F

14. K F

15. _ + K F The compound potassium fluoride consists of potassium (K+) ions and fluoride (F-) ions

16. _ + K F The ionic bond is the attraction between the positive K+ ion and the negative F- ion

18. Formulas • Reminder: A chemical formula is the combination of symbols that show the elements in the compound. i.e. MgCl2 • If a molecule contains more than one atom of a particular element, you indicate it by using a subscript after the chemical symbol (ex: the 2 in MgCl2). • It tells you the ratio of atoms in the compound (MgCl2 has a 1:2 ratio). • If no subscript is written the number 1 is understood( NaCl there is a 1:1ratio). • A coefficientacts as a multiplier for all of the atoms in the entire compound, it is found in front of the chemical formula • Ex: the 5 in 5 MgCl2

19. Example MgCl2 Here we have one molecule of magnesium chloride.  The subscript 2 in the formula above only pertains to the chlorine in the compound.   The total number of atoms in the compound is 3. Now let us put a coefficient in front of the molecule and see how that changes things. 5 MgCl2 The coefficient 5 refers to the entire molecule.   It shows that there are 5 compounds of magnesium chloride. Since each molecule is made up of 3 atoms, the total number of atoms is now 15.  There are 5 magnesium atoms and 10 chlorine atoms. How many atoms are in the following bond 3Na2S Sodium(Na)____ Sulfur(S)____ Sodium Sulfide(3Na2S) ____ = total atoms 6 3 9

21. Naming Ionic Compounds • The name of the positive ion comes first, followed by the name of the negative ion. • The metal will be the positive because it gives away electrons and the nonmetal will be the negative because it gains electrons. • If the negative ion is a single element the end of its name changes to–ide. • Ex: NaCl- Sodium ChlorideMgO- Magnesium Oxide • If the negative ion is polyatomic, its name usually ends in –ate or –ite. • Ex: NH4NO3- Ammonium nitrate • What is the name of the ionic compound with the formula K2S? ______________ Potassium Sulfide

22. Properties of Ionic Compounds • Hard • Brittle • Crystals • High melting points- NaCl melts at 801˚C= 1473.8 ˚F • When dissolved in water they are electrolytes. • An electrolyte solution is one that can conduct electricity. • Ionic bonds in solid from are poor conductors.

23. Covalent Bonds • The chemical bond formed when two atoms share electrons. • Usually form between nonmetals. • We call the neutral group of atoms joined by a covalent bond a molecule.

24. In covalent bonding, atoms still want to follow the octet rule and have a complete valance shell

25. In covalent bonding, atoms still want to follow the octet rule and have a complete valance shell But rather than losing or gaining electrons, atoms now share an electron pair.

26. In covalent bonding, atoms still want to follow the octet rule and have a complete valance shell But rather than losing or gaining electrons, atoms now share an electron pair. The shared electron pair is called a bonding pair

27. Chlorine forms a covalent bond with itself Cl2

28. How will two chlorine atoms react? Cl Cl

29. Cl Cl Each chlorine atom wants to gain one electron to achieve a full outer shell.

30. Cl Cl Neither atom will give up an electron. What’s the solution –what can they do to achieve an octet?

31. Cl Cl

32. Cl Cl Cl Cl

33. Cl Cl

34. Cl Cl

35. Cl Cl complete

36. Cl Cl complete

37. Cl Cl The complete outer shell is achieved by each atom sharing the electron pair in the middle

38. Cl Cl The complete outer shell is achieved by each atom sharing the electron pair in the middle

39. Cl Cl This is the bonding pair

40. Cl Cl It is called aSINGLE BOND

41. Cl Cl Single bonds are abbreviated with a dash

42. Cl Cl This is the chlorine molecule, Cl2

43. O2 Oxygen is also one of the diatomic molecules

44. O O How will two oxygen atoms bond?

45. O O Each atom has two unpaired electrons

46. O O Oxygen atoms want to gain two electrons.

47. O O Both electron pairs are shared.

48. O O 6 valence electrons plus 2 shared electrons = full valance shell

49. O O 6 valence electrons plus 2 shared electrons = full valance shell

50. O O two bonding pairs, making a doublebond