1. Chemistry
Writing Formulas

2. CHEMICAL FORMULAS AND CHEMICAL COMPOUNDS

3. Types of Bonds IONIC COVALENT
Bond Formation
e- are transferred from metal to nonmetal
e- are shared between two nonmetals
Type of Structure
crystal lattice
true molecules
Physical
State
solid
liquid or gas
Melting
Point
high
low
Solubility in
Water
yes
usually not
Electrical Conductivity
yes (solution or liquid) no
Other
Properties

4. Ionic Bonding - Crystal Lattice
Types of Bonds
Ionic Bonding - Crystal Lattice
The crystals are made up of alternating positive and negative ions.

5. Covalent Bonding - True Molecules
Types of Bonds
Covalent Bonding - True Molecules
Diatomic Molecule

6. Types of Bonds METALLIC e- are delocalized among metal atoms
Bond Formation
e- are delocalized among metal atoms
Type of Structure
“electron sea”
Physical
State
solid
Melting
Point
very high
Solubility in
Water no
yes (any form)
Electrical Conductivity
Other
Properties
malleable, ductile, lustrous

7. Metallic Bonding - “Electron Sea”
Types of Bonds
Metallic Bonding - “Electron Sea”
The valence electrons move freely around the atoms

8. Predicting Ionic Charges
Group 1:
Lose 1 electron to form 1+ ions H+
Li+
Na+ K+

9. Predicting Ionic Charges
Group 2:
Loses 2 electrons to form 2+ ions
Be2+
Mg2+
Ca2+
Sr2+
Ba2+

10. Predicting Ionic Charges
Loses 3
electrons to form
3+ ions
Group 13:
B3+
Al3+
Ga3+

11. Predicting Ionic Charges
Lose 4
electrons or gain
4 electrons
Group 14:
C, Si and Ge, +4 and -4; Sn and Pb +4

12. Predicting Ionic Charges
Nitride
Gains 3
electrons to form
3- ions
Group 15:
P3-
Phosphide
As3-
Arsenide

13. Predicting Ionic Charges
Oxide
Gains 2
electrons to form
2- ions
Group 16:
S2-
Sulfide
Se2-
Selenide

14. Predicting Ionic Charges
F1-
Fluoride
Br1-
Bromide
Group 17:
Gains 1
electron to form
1- ions
Cl1-
Chloride
I1-
Iodide

15. Predicting Ionic Charges
Stable Noble gases do not form ions!
Group 18:

16. Vocabulary Chemical Bond
electrical attraction between nuclei and valence e- of neighboring atoms that binds the atoms together
bonds form in order to…
decrease energy
increase stability

17. BINARY IONIC COMPOUNDS
BINARY - TWO ELEMENTS: A METAL AND A NONMETAL
MOST ARE SALTS
OTHER COMPOUNDS ARE OXIDES

18. Writing Chemical Formulas
We use the “criss cross” method
Translate the names of the elements to symbols.
Use the periodic table to find the charges.
Find the charge on the positive ion, and write it above the symbol. Write the charges small!
Find the charge on the negative ion, and write it above the symbol. Write the charges small!!

19. The numbers, not the charges, determine the subscripts.
If the charges do not have the same number, then you need subscripts.

20. Writing Chemical Formulas
Example: potassium bromide
Potassium is K, bromine is Br
K+1 Br KBr
Since -1 and +1 = 0, the charges cancel each other out, and subscripts are not needed.

21. Writing Chemical Formulas
Example: magnesium chloride
Mg+2 Cl-1
MgCl2
The 2 from magnesium’s charge will become a subscript. We do not use a 1 for a subscript.
We need 2 chlorines for every one magnesium

22. Writing Chemical Formulas
Example: lithium sulfide
Li+1 S-2
Li2S
The 2 from sulfur’s charge will become a subscript. We do not use a 1 for a subscript.
We need two lithium atoms for every one sulfur atom

23. Writing Chemical Formulas
Example: aluminum oxide
Al+3 O-2
Al2O3
This time, the numbers are “criss crossed” in both directions. Each element will get a subscript.

24. Check your subscripts!
Compounds do not have a charge. They are zero. So, the charges on the ions must equal zero. Check to be sure!
Al2O3
(2 Al ions) (+3) = +6
(3 O ions) (-2) = -6
+6 and -6 = 0

25. Writing Formulas You try these: magnesium bromide strontium oxide
aluminum sulfide
zinc iodide
Answers
MgBr2
SrO
Al2S3
ZnI2

26. POLYATOMIC COMPOUNDS Contain three or more atoms
Use the list on your blue sheet.

27. Writing Formulas Calcium carbonate Ca+2CO3-2 CaCO3 Sodium sulfate
Na+1SO4-2
The 1 from Na is not used as a subscript.
Na2SO4

28. Always check the charges and write them above the symbols
Always check the charges and write them above the symbols! After you are comfortable with the charges, you may leave them off.
If you have more than one polyatomic ion in a compound, you must enclose the ion in parenthesis, then use a subscript. No parenthesis if there is not a subscript!!!

29. MORE FORMULAS Magnesium nitrate Mg+2 NO3-1 Mg(NO3)2
You must put parenthesis around the NO3 ion because you have two of them.
Do not use parenthesis around single atoms

30. More polyatomic compounds
Barium phosphate
Ba+2 PO4-3
Ba3(PO4)2
Ammonium carbonate
(NH4)+1 CO3-2 +1 -2
(NH4)2 CO3

31. Writing formulas
Calcium carbonate
Sodium sulfate

32. MORE FORMULAS Sr+2OH-1 Sr(OH)2 Strontium hydroxide
This compound is tricky because you may forget to add parenthesis around the hydroxide ion.
Sr+2OH-1
Sr(OH)2

33. REMEMBER TO: WRITE THE CORRECT SYMBOL
WRITE THE CORRECT CHARGE ABOVE THE ION
BRING DOWN THE NUMBER FOR THE SUBSCRIPT IF NEEDED.
REWRITE THE FORMULA WITHOUT THE CHARGES.