Jo ann Payton, age 17, of Hayneville, Ala., for her question:
How did they figure the atomic numbers?
The atomic age is a gift from the science of physics. It grew gradually through centuries as men probed into the nature of matter. In the past 100 years, many scientists from different nations added scraps of knowledge about the atoms from which all substances are made. We now have an orderly picture of these atomic elements.
The periodic table of elcments gives the basic data on more than 100 different atoms. In the 1800s, scientists knew of only 50 of these elements. They sorted them into classes, such as metals and non metals, and compared their weights. In 1869, dimitri mendcleey arranged the known elements in a chart of rows and columns which made him known as the great grandfather of our periodic table.
Mendeleev placed elements that were similar in chemical nature in the same column. The hard, glossy elements, copper, silver and gold, were listed one below the other, each heavier than the one above it. An orderly picture emerged with each element having its own atomic weight.
More elements were discovered and placed in their slots in the periodic table. In the 20th century, the atom probers used x rays and saw that the wave length of each element is one degree less than the next. Then the electrical nature of the atom was discovered. Between 1911 and 1913, it was found that each atom is made mostly from electrical particles.
Rutherford of England found that the bulk of the atom is in the central nucleus. Bohr of Denmark suggested that the massive nucleus is in the center, amid one or more outer electrons. Moseley of England found that the proton particles of the nucleus carry a charge of positive electricity, and each electron carries an equal charge of negative electricity.
This information soon revealed another orderly atomic pattern. Each element on the periodic table progresses by one proton. The number of protons in the nucleus of an atom is, of course, the atomic number of an element. Hydrogen is with one proton is atomic number one; helium., with two protons, is atomic number two.
In a neutral atom, the number of swarming electrons equals and balances the number of protons in its nucleus. The atomic number then reveals the number of electrons in an element. This information is vital to the chemist, because the number of electrons tends to determine the formation of chemical, compounds, such as salt and sugar.