1. Putting Atoms Together

2. Learning Goal for Today
Understand how chemical formulas are used to represent compounds
Learn characteristics of ionic and molecular compounds.

3. Elements and Compounds
Terminology… Recall:
Atoms and Molecules
Elements and Compounds
Atoms
2 or more
chemically joined
Molecules
Elements
2 or more
chemically joined
Compounds

4. A molecule consists of two or more atoms that are chemically joined together.

5. A chemical formula indicates the type and number of atoms in a molecule.
Note: the coefficient in front of the formula multiplies the number of atoms of each element in the formula.
Example:
2CO2  means 2 carbon and 4 oxygen atoms

6. Types of Molecules (Overview)
Molecular Element:
Two non-metal atoms of the same element
A.k.a. “diatomic molecules”
H2 , N2 , O2 , F2 , Cl2 , Br2 , I2

7. Types of Molecules 2. Molecular Compounds: 3. Ionic Compounds:
Formed with ≥2 different non-metals
Held with covalent bonds
Examples:
CO2  carbon dioxide
H2O  water
3. Ionic Compounds:
positively and negatively charged ions
Commonly formed from metals and non-metals
Held with ionic bonds
Examples:
NaCl  sodium chloride
MgCl2  magnesium chloride

8. Try This
Handout: “Chemical Formula”

9. Ionic Bonding
Ion:
a particle that has either a positive or negative charge
“forms when an atom loses or gains one or more electrons without changing its number of protons”
Examples:
Mg  loses two electrons  Mg2+
Br  gains one electron  Br-

10. Ionic Bonding Cation: a positively charged ion
forms when an atom loses one or more electrons, leaving more protons (+) than electrons (-) and resulting in a net positive charge
Example:
Na+ Na
11 p+
12n0

11. Ionic Bonding Cation: a positively charged ion
forms when an atom loses one or more electrons, leaving more protons (+) than electrons (-) and resulting in a net positive charge
Example:
Na  loses one e- Na
11 p+
12n0

12. Ionic Bonding Cation: a positively charged ion
forms when an atom loses one or more electrons, leaving more protons (+) than electrons (-) and resulting in a net positive charge
Example:
Na  loses one e-  Na+
Na+
11 p+
12n0

13. Ionic Bonding Anion: a negatively charged ion
forms when an atom gains one or more electrons, leaving more electrons (-) than protons (+) and resulting in a net negative charge
Example: Cl Cl
17 p+
18 n0

14. Ionic Bonding Anion: a negatively charged ion
forms when an atom gains one or more electrons, leaving more electrons (-) than protons (+) and resulting in a net negative charge
Example:
Cl  gains one e- Cl
17 p+
18 n0

15. Ionic Bonding Anion: a negatively charged ion
forms when an atom gains one or more electrons, leaving more electrons (-) than protons (+) and resulting in a net negative charge
Example:
Cl  gains one e-  Cl-
Cl-
17 p+
18 n0

16. Ionic Bonding Ionic Bond:
a bond formed when a metal and a non-metal transfer electrons
held together by the attraction between the positively charged metal (cation) and the negatively charged non-metal (anion)
Example:
NaCl  [Na]+[Cl]-

17. Ionic Bonding Na
11 p+
12 n0 Cl
17p+
18n0

18. Ionic Bonding Na
11 p+
12 n0 Cl
17p+
18n0

19. Ionic Bonding
Na+
11 p+
12 n0
Cl-
17p+
18n0

20. Naming Ionic Compounds
Name the metal
Name the non-metal
Add “ide” to the non-metal
Name of Metal Name of non-metal + ide
Sodium chloride

21. How do we find the formula?
Li1+ and O2-
What do you notice?

22. 2 Lithium atoms
1 Oxygen atom
Li2O

23. Here’s the trick Li 1+ O 2- Li 1+ O 2- Li2O1 Li2O
Write the symbols and charges
2. Crisscross
3. Write symbols with subscripts
Li 1+ O 2-
Li O 2-
Li2O1
Li2O

24. Try This!
“Ions and Ionic Bonding” worksheet

25. Molecular (Covalent) Bonding
formed when two non-metal atoms share electrons

26. Covalent Bonding
Very strong bond; requires a lot of energy to form/break
Example:
H2  H—H

27. Covalent Bonding
1 p+ H
1 p+ H

28. Covalent Bonding
1 p+ H
1 p+ H

29. Covalent Bonding
1 p p+
H—H

30. Prefixes for Naming Molecular Compounds
# atoms
Prefix 1
Mono 2 Di 3
Tri 4
Tetra 5
Penta 6
Hexa

31. Never use “Mono” for the first element!
Ex. CO2
x Monocarbon dioxide
 Carbon dioxide

32. Formula  Name Ex. H2O1 Write the name of each element
Write the subscripts as prefixes
Change ending of last element to “ide”
Ex. H2O1
Hydrogen oxygen
2. Dihydrogen monoxygen
3. Dihydrogen monoxide

33. Now you try
CCl4

34. How did you do? CCl4 1. Carbon chlorine 2. Carbon tetrachlorine
3. Carbon tetrachloride

35. Name  Formula Write the names as symbols
Write the prefixes as subscripts
Dihydrogen Dioxide
1. H O
2. H2O2

36. Now you try
Dinitrogen Tetroxide

37. How did you do?
Dinitrogen Tetroxide
N O
2. N2O4