1. Chapter 22
Chemical Bonds

2. Section 1
Stability in Bonding

3. Compounds Compounds are elements that are combined
Compounds usually have new or different properties than the elements that make up the compound

4. Formulas
A chemical formula tells what elements are in a compound, and how many atoms of each element in a unit of that compound
H2O
In each unit, there are 2 hydrogen atoms and 1 oxygen atom

5. Chemical Bonds
The force that holds two atoms together is called a chemical bond.
They may form by the attraction of a positive nucleus and a negative electron
They can also form between a positive an negative ion
Remember, opposites attract!

6. Electron Dot Structure
It is a diagram showing valence electrons.
It is useful when showing chemical bonds.

7. Valance Electrons All atoms have valence electrons.
Atoms want to be stable.
To be stable, the valence shell needs to be full.
Most elements need 8 electrons in their outer shell to be full. This is called the Octet Rule.
Exceptions: hydrogen & helium which need 2
This is why elements bond.

8. Formation of a positive ion
A positive ion forms when an atom loses one or more electrons.
When the atom loses an electron, it does not become a different element because it still has the same number of protons.
A positively charged ion is called a cation.
Elements on the left side of the periodic table tend to lose some of their electrons.

9. Groups 1, 2, 3
When an element from group 1 loses all its valence electrons, it picks up a +1 charge.
When an element from group 2 loses all its valence electrons, it picks up a +2 charge.
When an element from group 3 loses all its valence electrons, it picks up a +3 charge.

10. Formation of a negative ion
Elements on right side of the periodic table have great attraction for electrons so they gain electrons to fill their valence shell.
Elements become anions when they gain an electron, and then become negatively charged.

11. Anion Rule of Thumb
Group 5, 6, and 7 elements could lose all their valence electrons, but as a rule of thumb they usually gain them. Remember each element wants 8 valence electrons.
So, 8 – Group # = electrons needed
Group 5 gains 3 and has a 3- charge
Group 6 gains 2 and has a 2- charge
Group 7 gains 1 and has a 1- charge

12. 22.1 Bond Analysis: paragraphs
Compare / contrast Na and Cl with NaCl.
What does the formula tell about BaF2?
Explain why some elements are stable but others are more stable as compounds
In CH3COOH, list the elements and how many there are of each.

13. Formation and Nature of Ionic Bonding
Chapter 22 Section 2
Formation and Nature of Ionic Bonding

14. Electrostatic Force
NaCl forms from attraction between oppositely charged ions.
They are held together by an electrostatic force.
This force is called an ionic bond

15. Ionic Bonds
In ionic bonds, electrons are transferred from one atom to another
Ionic bonds form between metals and nonmetals
This is to fulfill the octet rule
Atoms want to have a full outer shell of electrons

16. Ionic Bond Electron Exchange

17. Formation of an ionic bond
Ionic bonds form between metals and nonmetals
Na atom transfers valence electron to Cl
Na becomes a positive ion, Na +
Cl becomes a negative ion, Cl -

18. Different Ionic Bonds
Ionic bonds between metals and the non-metal oxygen are called oxides.
Most other ionic bonds are salts.

19. Ionic Compounds Many ionic compounds are binary
Ionic compounds contain only 2 elements
Ionic compounds contain a metallic cation and a nonmetallic anion

20. Why do atoms bond? Atoms want to have a full outer shell
Noble gas configuration
With ionic bonding , electrons are transferred
Electrons can also be shared

21. What is a Covalent Bond?
The chemical bond that results from the sharing of valence electrons
Shared electrons are part of outer energy levels of both atoms involved
Generally occurs when elements are relatively close on the periodic table

22. What is a Molecule?
Formed when two or more atoms bond covalently

23. Covalent Bond Electron Sharing

24. Formation of a Covalent Bond
H, N, O, F, Cl, Br and I occur in nature as diatomic molecules
The molecules formed are more stable this way
Hydrogen is H2
Oxygen is O2
Etc.

25. Sigma Bonds Sigma bonds are single covalent bonds.
They occur when an electron pair is shared in the center between 2 atoms.
The valence atomic orbital of one atom overlaps or merges with another.

26. Multiple Covalent Bonds
In many molecules, atoms attain a noble-gas configuration by sharing more then one pair of electrons between 2 atoms.
C, N, O and S most often form multiple bonds.

27. Double or Triple Bonds Bonds can be double or triple
Double bonds occur when 2 pairs of electrons are shared
Triple bonds occur when 3 pairs of electrons are shared

28. Bond Length
This is the distance from the center of one nucleus to the center of the other nucleus of 2 bonded atoms.
Single bonds are the longest.
Multiple bonds are shorter.
Double bonds are longer then triple bonds
The more bonds there are means there is more attraction, so the distance is shorter.

29. Covalent Bond Strength
Covalent bonds are not as strong as ionic bonds.
Melting temperature of salt is 801 degrees C, sugar is 185 degrees C.
Covalent bonds can be broken.
The strength depends on how much distance separates the nuclei.
The shorter the bond length means the bond is stronger due to higher attraction forces.

30. 22.2 Bond Analysis: paragraphs
Explain why at atom may make an ionic bond with only certain other atoms.
Compare/contrast the possession of electrons in ionic and covalent bonds.
Name the types of particles formed by covalent bonds.

31. Formulas for Ionic Compounds
Section 3
Formulas for Ionic Compounds

32. How do we determine charge?
Binary ionic compounds are composed of positively charged monatomic ions of a metal and negatively charged monatomic ions of a nonmetal.
A monatomic ion is a one-atom ion.
Charge depends on its place on the periodic table.
Look at periodic table for Oxidation Numbers or for Group Numbers.

33. What are the charges on the following monatomic ions?

34. Beryllium

35. Be2+

36. Iodine

37. I-

38. Nitride

39. N3-

40. Oxidation Number
The charge of a monatomic ion can also be known as the oxidation state.
Transition metals have more then 1 oxidation number

41. Oxidation State
Oxidation state equals the number of electrons transferred from an atom to form an ion.
When sodium and chlorine react, sodium atom transfers 1 electron to chlorine atom.
Oxidation state of sodium is 1+
Oxidation state of chlorine is 1-
Negative sign shows the electron was transferred to chlorine.

42. Writing Chemical Formulas
In chemical formulas, the symbol of the cation is always written first.
The anion symbol follows the cation.
Subscripts are used to represent the number of ions of each element in the ionic compound.
If there are no subscripts, the number is one.

43. What is going on with this chemical reaction?
Na Cl-

44. Answer
Ratio is 1:1
Sum of the oxidation numbers if they react is zero.
One sodium ion transfers 1 electron to one chloride ion.
The compound formula is NaCl.

45. Naming ions and ionic compounds
8-3 Part 2
Naming ions and ionic compounds

46. Naming Ionic Compounds
Name cation first and the anion second.
Monatomic cations use the element name.
Cs+ is cesium
Monatomic anions take their name from the root of the element name plus the suffix –ide.
CsBr is cesium bromide
Examples: oxide, phosphide, nitride, sulfide

47. Naming Ionic Compounds cont.
Group 1A and 2A metals have only 1 oxidation number. Transition metals and metals on the right side of the periodic table have more then 1 oxidation number
Fe2+ and O2- is FeO, named iron (II) oxide
Fe3+ and O2- is Fe2O3, named iron (III) oxide

48. Special Ions Name Cu(I) Cu(II) Fe(II) Fe(III) Cr(II) Cr(III) Pb(II)
Pb(IV)
Ox # 1+ 2+ 3+ 4+

49. Polyatomic Ions Some ionic compounds are not binary
Compounds may have more than 2 elements
These are called polyatomic ions
Poly means many
NaHCO3

50. Polyatomic Ion Examples
Charge
Name
Formula 1+
Ammonium
NH4+ 1-
Acetate
Chlorate
Hydroxide
Nitrate
C2H3O2-
ClO3-
OH-
NO3- 2-
Carbonate
Sulfate
CO32-
SO42- 3-
Phosphate
PO43-

51. Naming Ionic Compounds cont.
If a compound contains a polyatomic ion, simply name the ion.
Polyatomic ion OH- is called hydroxide, so
NaOH is sodium hydroxide

52. 22.3 Bond Analysis: paragraphs
Write formulas for potassium iodide, magnesium hydroxide, aluminum sulfate, and chlorine heptoxide.
Write the names for KCl, Cr2O3, NH4Cl, Ba(ClO3)2, and PCl3.
Explain why sodium and potassium will or will not react to bond with each other.