1. Chapter 18 Chemical Bonds

2. 18-1 – Electrons and Bonding
Combined Elements
Atoms bond with other atoms to become stable
Elements combine to form compounds and molecules

3. 18-1 – Electrons and Bonding
Remember Periodic Trends
Number of valence electrons increases as you move left to right
All elements in the same column have the same number of valence electrons
Number of valence electrons determines how atom will react with other atoms

4. 18-1 – Electrons and Bonding
Remember Lewis Structures to represent valence electrons

5. 18-1 – Electrons and Bonding
Stability of an Atom
Depends on how full the outer energy level is
Filled energy levels = stable
Unfilled energy levels = unstable
Octet Rule
8 is the number toward stability
Exceptions to the octet rule is hydrogen and helium

6. 18-2 – Ionic and Covalent Bonds
Atoms are electrically neutral
Why?
Ions are not electrically neutral
Can be negative or positive
Atoms tend to lose or gain electrons so they end up with an outermost occupied shell that is filled to capacity
The Periodic table can be used to determine the type of ion that an atom tends to form

7. 18-2 – Ionic and Covalent Bonds
Positive Ion (cation)
Negative Ion (anion)

8. Ionic Bonds Result from an Transfer of Valence Electrons
18-2 – Ionic and Covalent Bonds
Ionic Bonds Result from an Transfer of Valence Electrons
Result of transfer of electrons forms a positive ion and a negative ion
Ionic Bond –
Ionic Compounds –
Characteristics of Ionic Bonds –

9. 18-2 – Ionic and Covalent Bonds

10. 18-2 – Ionic and Covalent Bonds
Ionic Bonds: One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone.  If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged.  The two ions (that's where the name ionic comes from) are attracted very strongly to each other as a result of the opposite charges.

11. 18-2 – Ionic and Covalent Bonds
Properties of Ionic Compounds
Solids at room temperature
High melting and boiling points
Dissolve in water and separates into ions
Conducts electricity

12. Covalent Bonds Result from a Sharing of Valence Electrons
18-2 – Ionic and Covalent Bonds
Covalent Bonds Result from a Sharing of Valence Electrons
Covalent bond –
Covalent Compound –
Molecule –
Characteristics of Covalent Bonds –
Can be single, double, or triple

13. 18-2 – Ionic and Covalent Bonds

14. 18-2 – Ionic and Covalent Bonds

15. 18-2 – Ionic and Covalent Bonds
Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly.  Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs.  The molecule is not "polar" meaning one side does not have more charge than the other.

16. 18-2 – Ionic and Covalent Bonds
Properties of Covalent Compounds
Exist as solids, liquids, or gases
Molecules in covalent compounds easy to separate
Lower melting and boiling points
Generally, do not dissolve in water
Do not conduct electricity

17. H2O C6H12O6 NaCl O2 CO2 18-3 – Chemical Formulas Chemical Formulas
The symbols of each element in a molecule of the substance
A number indicating how many atoms of each element are in each molecule of the substance
H2O
C6H12O6
NaCl O2
CO2

18. 18-3 – Chemical Formulas Subscripts
Small numbers to the right of the symbol
Subscripts of 1 are not written

19. 18-3 – Chemical Formulas Prefixes
Indicate the number of atoms in a molecule of the compound (covalently bonded compounds)
Prefix
Meaning
Example
di–
two
sulfur dioxide (SO2)
tri–
three
nitrogen trifluoride (NF3)
tetra–
four
carbon tetrachloride (CCl4)
penta–
five
phosphorus pentachloride (PCl5)
hexa–
six
sulfur hexafluoride (SF6)

20. 18-3 – Chemical Formulas
Names of some of the elements in these compounds are slightly different from their regular element names.
For example, the symbol O by itself represents the element oxygen, but when oxygen combines with carbon to form CO2, its name changes to oxide.
In a compound made up of two elements, the name of the first element stays the same. The ending of the second element changes to –ide.

21. (NH4)3PO4 Fe(OH)2 18-3 – Chemical Formulas
Some of the compounds above contain parentheses in their chemical formulas.
Parentheses are used for grouping.
(NH4)3PO4
Fe(OH)2

22. 18-3 – Chemical Formulas Writing formulas for Ionic Compounds
Use oxidation numbers from the periodic table
Use oxidation numbers to write formulas

23. 18-3 – Chemical Formulas

24. 18-3 – Chemical Formulas Naming Ionic Compounds
Write name of positive ion
Check oxidation number of positive ion
Write root name of negative ion
Add ending “-ide”

25. 18-3 – Chemical Formulas

26. 18-3 – Chemical Formulas Naming Covalent Compounds Use element name
Add prefixes to designate number of atoms

27. 18-3 – Chemical Formulas

28. 18-3 – Chemical Formulas Writing formulas for Covalent Compounds
Think about valence electrons and how atoms will share electrons
Use element name
Add prefixes to designate number of atoms

29. 18-3 – Chemical Formulas