1. 4.1 Organizing the Elements People often organize things to make them more useful. –Cupboards –Closets –Study notes for tests Up to the mid-1800s, scientists were busy discovering new elements. Then they tried to organize the elements alphabetically. But every time a new element was discovered, the whole list had to be changed.

2. Organizing the Elements Other methods of organization were considered but later discarded. –State (gas, solid, liquid) –Color –Taste John Dalton then found a quantity that could be measured for an element - its atomic mass. Several scientists then tried to arrange the known elements by their atomic masses. The best arrangement was produced by a Russian scientist, Dmitri Mendeleev.

3. Organizing the Elements Mendeleev began arranging the elements in order of increasing atomic mass and noticed that many elements shared common properties. These elements typically belonged to the same vertical column of his table. Mendeleev’s arrangement showed a regular pattern. Mendeleev’s periodic law states: If the elements are arranged according to their atomic mass, a pattern can be seen in which similar properties occur regularly.

4. Organizing the Elements Mendeleev’s periodic table was a major breakthrough in the understanding of the elements. However, it was discovered later on that using the atomic mass was not the proper way to organize the elements. The key was to use the atomic number or the number of protons. Therefore, a new law was born. The modern periodic law states : If the elements are arranged according to their atomic number, a pattern can be seen in which similar properties occur regularly.