The Modern Periodic Table

Dimitri Mendeleev was a Russian chemist who organized the elements on the periodic table according to atomic mass. When he arranged the elements in order of increasing mass he found that the properties of the elements repeated in periodic (hence the name of the table) intervals.

For example, the eighth element in an arrangement (sodium) had properties similar to the first element in the arrangement (lithium) and the fifteenth element (potassium). Based on these similar properties, Mendeleev called the arrangement a “chemical family”. Mendeleev, in his prediction wisdom, left spaces on his table for elements that had not yet been discovered.

The periodic table is organized into groups (the numbers from 1-18 across the top of the table) and periods (the numbers 1-7 down the left side of the table). Groups are vertical and periods are horizontal. The elements in each group increase atomic mass as you move down the group. The elements in each period increase atomic mass as you move from left to right across the period.

Although groups can be referred to by their number some groups have special names based on their unique or interesting properties.

Some Interesting Groups on the Periodic Table Alkali metals (Group 1) react rapidly when exposed to air and water. Some of these reactions are so intense that they can cause explosions. For example, sodium (Na) and water react violently and cause explosions. These are the most reactive metals. Hydrogen (a gas) is found in Group 1 with the metals because it is also extremely reactive.

Alkali earth metals (Group 2) are reactive soft, low-density metals. Halogens (Group 17) are the most reactive non-metals on the periodic table. Chlorine (Cl) can cause serious respiratory problems if inhaled and Bromine (Br) can cause serious skin burns.

Ironically, sodium (Na) a very reactive alkali metal combines with chlorine (Cl) a very reactive non-metal to produce NaCl (table salt) which we consume daily.

The noble gases (Group 18) are called “noble” because they are chemically calm. These elements can be excited by electricity to produce colors but are unchanged in the process.