1. Bonding

2. Unit Overview Types of bonds Why/how bonds form
Lewis structures (again)
Writing chemical formulas
Naming compounds

3. Chemical Bonds
link between atoms due to mutual attraction of nuclei for e-

4. Chemical Bonds Why bond???
Bonding can result in lower potential energy (this is usually associated with a release of energy)
Lower energy = greater stability (greatest stability = completed energy level/octet)

5. Chemical Bonds
Octet rule – in forming compounds, each atom, by gaining/losing/sharing e- achieves an octet of e- in its highest occupied energy level

6. Chemical Bonds
Bonds are classified by how the valence e- are distributed around nuclei of combined atoms

7. Types of Chemical Bonds
Ionic bond – results from electrostatic attraction between positive and negative ions (usually done when metal bonds w/ nonmetal)

8. Types of Chemical Bonds
Ionic bond
Created by transfer of e-
Active metals readily give up their e-, usually to a nonmetal atom
Oppositely charged ions are formed by this process of transferring e-
Cation: + charge
Anion: - charged ion

9. Types of Chemical Bonds
Ionic bond
Forming ionic bonds: e- are transferred from atom with lower EN value to one with higher value
How can you determine if bond is ionic? See if atoms are active metal & non-metal or look up EN values to get difference. (if EN difference is 1.7  4.0, ionic bond)

10. Types of Chemical Bonds
Ionic bond
Types of ions
Monoatomic – single element with charge
Polyatomic – 2 or more elements with charge

11. Types of Chemical Bonds
Ionic bond
Ionic compound – composed of positive & negative ions combined so that the positive & negative charges are equal in number (Ex. NaCl instead of Na2Cl or NaCl2)

12. Properties… Ionic Compounds
Held together tightly (attraction of charges)
High MP
High BP
Hard & brittle crystalline solids
Dissolve in water (generally)
Carry a current (very well) in water

13. Representing Ionic Compounds
Empirical formula or Formula unit – indicates lowest whole number ratio of cations to anions in any sample of an ionic compound
(ex. NaF = 1 Na+ ion + 1 F- ion)
This “unit” doesn’t represent something that can be isolated, it is only the smallest possible ratio to make a neutral electrical charge
# of ions in one formula unit depends on the charges of the ions to be combined (ex. B + F, Na + Cl, K + O, etc)

14. Representing Ionic Compounds
Just a thought…
Can you use the periodic table to determine the charge of an ion?
Yes, how many e- are in the outer shell (valence e-).

15. Representing Ionic Compounds
Determining formula units by the crisscross & “accounting” methods
Ca + Br
K + P
Al + O
Ca + O
Al3+ + CN1-
Mg2+ + PO43-

16. Representing Ionic Compounds
Lewis structures
Diagrams that show valence e- as dots, the inner e- and nucleus are included in the letter symbol for the element being represented

17. Representing Ionic Compounds
Lewis Structures
Group 1
Group 2
Group 13
Group 14
Group 15
Group 16
Group 17
Group 18

18. Representing Ionic Compounds
Lewis Structures
Structures of individual elements may be joined to form compounds
pairs of dots (or a dash) between symbols represent bonds (or electron pairs), dots adjacent only to one symbol are unshared e-

19. Representing Ionic Compounds
Lewis Structures
Structures of individual elements may be joined to form compounds
Lone (unshared) pair of e- – pair of e- that is not involved in bonding, but instead belongs exclusively to one atom

20. Representing Ionic Compounds
How to represent ionic bonds with Lewis diagrams KI
BaCl2
LiBr
Rb2O
CaO
Na3P
MgH2

21. Types of Chemical Bonds
Metallic bond – force of attraction that holds metals together; consists of the attraction of free-floating valence e- for positively charged metal ions

22. Types of Chemical Bonds
Covalent (molecular) bond – results from the sharing of e- between two atoms (usually done w/ nonmetal atoms)

23. Covalent Bonds The e- are not always equally shared (like tug of war)
Bonds between 2 unlike atoms are never completely covalent - can represent these bonds by showing partial charges on respective atoms
Non-polar covalent – e- are shared equally ( which only happens between two identical atoms)
Polar covalent – e- are not equally shared (due to differences in EN)

24. Covalent Bonds
Atoms that are bonded covalently form stable particles called molecules
Ex. CO2, H2O2, SO2, O2
7 diatomic molecules to know - H2, N2, O2, F2, Cl2, I2, Br2
first 5 are room temp, I2 is a solid, & Br2 is a liquid

25. Covalent Bonds
Molecular compound – chemical compound whose simplest formulas are molecules

26. Properties… Molecular Compounds Most are not tightly held
Most have low MP (due to weak attractions)
Most have low BP
Usually soft, amorphous solids
Some dissolve in water
Do not carry current well in water

27. Representing Molecular Compounds
Molecular formula – shows the types and numbers of atoms combined in a single molecule of a compound
Ex. CO2, H2O2, SO3, O2
Chemical formula – shorthand representation of the composition of a substance using atomic symbols and numerical subscripts

28. Representing Molecular Compounds
Structural formula – indicates kind, number, arrangement, and bonds of the atoms in a molecule (or polyatomic ion)
Single bond – one pair of shared e- between two atoms
Double bond – two pairs of shared e- between two atoms
Triple bond – three pairs of shared e- between two atoms

29. Representing Molecular Compounds
Structural formula – indicates kind, number, arrangement, and bonds of the atoms in a molecule
Ex.

30. Representing Molecular Compounds
Lewis Structures
Ex. F2, NH3, H2O, CH4, O2, CO2, N2, CH2O, C2H2, PI3
(must draw structures)

31. Representing Molecular Compounds
Lewis structures
Octet exceptions:
Less than full octet
Ex: Boron compounds such as BF3

32. Representing Molecular Compounds
Lewis structures
Octet exceptions:
More than full octet – atoms beyond 2nd period, most often S & P (extra e- go to 3d level)
Ex: SF4

33. Representing Molecular Compounds
Lewis Structures
Octet exceptions:
Molecules w/odd # of e- - not full octet, short-lived & unstable
Ex: NO, SO32-, NH41+