1. Chemical Symbols and Formulas

2. Chemical Symbols
Each element is assigned a unique one, or two letter symbol.
Some of the more common elements have a single symbol, such as O for oxygen and H for hydrogen.
The elements are given systematic names that represent their atomic number.

3. Chemical Symbols
Sometimes the letters of the symbol do not correspond to the English element but relate to the Latin or Greek name:
For example: Some periodic tables have K (postassium) labeled as (Latin – Kalium), and Na (sodium) labeled as (Latin – Natrium)

4. Diatomic Molecules
When writing the symbols of uncombined elements, always written as monatomic, that is without a script.
A subscript is a number to the right and slightly below a symbol that tells the number of atoms present
A subscript is not written if only one atom is present.

5. Diatomic Molecules

6. Chemical Formulas
Compounds are composed of combinations of elements chemically combined in definite proportions by weight (mass).
Formulas use chemical symbols and numbers to show both qualitative and quantitative information about the substance.

7. Chemical Formulas
Qualitative information relates to things that cannot be counted or measured; such as what elements are in the compound.
Quantitative information deals with things that can either be counted or measured; such as the number of atoms of each is present in a unit of a compound.

8. Chemical Formulas
In the formula of a compound, the symbols for the elements supply the qualitative information.
The formula CO tells the reader that the compound consist of carbon and oxygen.

9. Chemical Formulas Notice the difference between CO and Co.
The first combination of two elements in a compound, carbon dioxide, while the second is the symbol for cobalt.

10. Chemical Formulas

11. Types of Formulas
Two basic types of formulas provide different types of information about a compound.
Empirical formulas include all types of compounds.
Molecular formulas are important when considering compounds formed atoms sharing electrons.

12. Empirical Formulas
Empirical formulas represents the simplest integer ratio in which atoms combine to form a compound.
Ionic substances do not form discrete of molecules, but rather an array of ions (charged particles).

13. Empirical Formulas
Ionic formulas indicate the ration of ions in a compound in the simplest ratio.
The formula MgCl tells us that for every magnesium ion in the compound there are two chloride ions.
Formulas for ionic substances are empirical formulas. 2

14. Molecular Formulas
Covalent Bonds: chemical bonds that involve the sharing of a electron pair.
Covalently bonded substances form discrete units called molecules.

15. Molecular Formulas
In some cases, such as H O, the empirical formula not only represents the simplest ratio, but it also represents that actual ratio of the atoms in a molecule of water.
In other cases, the molecular formula may be a multiple of the empirical formula. 2

16. Molecular Formulas For example:
The molecular formula of glucose is C H O
which is six times the empirical formula CH O 6 12 6 6

17. Molecular vs. Empirical

18. Atoms, Compounds, and Ions
How do you know what elements form a compound and in what proportion?
To understand how elements form compounds, an understanding of atoms and ions is essential.

19. Atoms, Compounds, and Ions
Atoms and compounds are electrically neutral; that is, they do not have a net charge.
Both atoms and compounds contain positively charged protons and negatively charged electrons, but there are equal numbers of positive and negative charges, producing a neutral atom or compound.

20. Atoms, Compounds, and Ions
Ions, however, are not neutral and may be either positively or negatively charged.
An ion that contain more protons than electrons will be positively charged, while and ion with more electrons will have a negative charge.