1. Elements and Compounds
Section 3.4
Elements and Compounds

2. Composition of Matter

3. Pure Substances

4. Elements Building blocks of matter
A pure substance that cannot be separated into simpler substances
91 elements occur naturally on Earth
116 total known elements

5. The Periodic Table
The periodic table is the most useful tool to a chemist.
You get to use it on every test.
It organizes lots of information about all the known elements.

6. Pre-Periodic Table Chemistry
was a mess!!!
No organization of elements.
Imagine going to a grocery store with no organization!!
Difficult to find information.
Chemistry didn’t make sense.

7. Dmitri Mendeleev HOW HIS WORKED…
Put elements in rows by increasing atomic weight.
Put elements in columns by the way they reacted.
SOME PROBLEMS…
He left blank spaces for what he said were undiscovered elements. (Turned out he was right!)
He broke the pattern of increasing atomic weight to keep similar reacting elements together.

8. Rows or Periods
Now the elements are put in rows by increasing ATOMIC NUMBER!!
The horizontal rows are called periods and are labeled from 1 to 7.

9. Columns/Groups/Families
The vertical columns are called groups are labeled from 1 to 18.
Elements in the same group have similar chemical and physical properties!!
(Mendeleev did that on purpose.)
Because they share common traits, they are also referred to by family names

10. More on the Periodic Table in Chapter 6!!

11. Compounds Two or more elements chemically combined
10 million known compounds
Table salt, aspirin, water

13. Law of Definite Proportions
Characteristic of compounds
A compound is always composed of the same elements in the same proportion by mass

14. Percent by Mass Percent by mass (%) = mass of element x 100
mass of compound

16. Law of Multiple Proportions
Characteristic of compounds
When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers