Series: Science Key Concepts Series
Episode: Periodic Table: Element Groups
Element groups in the periodic table have common properties. Chapter 1. Mendeleev's Periodic Table: In 1869, Dmitri Mendeleev, a brilliant Russian chemist, was searching for a possible relationship between an element’s atomic mass and its chemical properties. With the symbol for each then known element (60) and its mass represented on a card, he arranged the cards in order of increasing atomic mass in a series of vertical columns. He then adjusted elements within the vertical columns so that those with similar chemical properties were next to each other in the same horizontal rows. His genius was that where ever an empty space appeared, he predicted an element would be discovered with a given atomic mass and its expected chemical properties. And so they were with approximately the same atomic mass. Since Mendeleev, new discoveries of an atom’s nucleus, which contains protons and neutrons, while electrons orbit the nucleus, has led to a different arrangement of elements in the modern periodic table. Now each element, reading from left to right along a row, called a period, and from top row to bottom, has exactly one more proton in its nucleus. An element’s atomic number equals the number of protons in its nucleus. One proton more or less creates a different element. An element’s atomic mass equals the number of protons plus neutrons it its nucleus. For every positively charged proton in the nucleus of an atom, there is one negatively charged electron circling that nucleus. In the modern periodic table, it is now elements in the same column, called a group, which share the same chemical properties Chapter 2. Noble Gases: Properties and Uses. The six elements, all gases, in the far right column (or group) of the periodic table, group 18, like all groups, share a common structure in their outermost electron shell. That outermost shell, whatever its electron capacity, is always full. That makes these elements extremely non-reactive, and that’s why they are called the Noble Gases. Being non-reactive chemically is a very useful property. Luminescent lights, known as neon lights, are a familiar use of the noble gases neon, helium, or argon or a mixture of them within a clear glass tube. Pass an electric current through the gas, and the color we see is electrical energy absorbed by the gas, then emitted as light energy in a visible color – different gases, different colors. Because there is no chemical reaction, their chemical properties remain unchanged, and these lights can last for up to 30 years. Fluorescent lights have a fluorescent coating on the inside of a glass tube, and are filled with a noble gas. Electrical energy passed through the gas is absorbed and emitted as light energy, which in turn can be absorbed by a variety of fluorescent coatings and then radiated as visible light energy in any one of a spectrum of colors. A welding torch releases a flow of the noble gas argon, so unreactive, it shields the hot metal from oxygen in the air to prevent oxidation or an explosion. Deep divers replace a nitrogen-oxygen mixture with a helium-oxygen mixture because helium being a smaller, lighter molecule than nitrogen, allows for faster passage through body cell membranes during a rapid ascent. The physical property of density in which helium is lighter than air, makes it both useful and safe in airships. An experiment shows that as one goes down the group of noble gases, each is more dense than the preceding one. Chapter 3. Transitional Metals: Properties and Uses. A large block of elements in the middle of the periodic table, are the transitional metals with common properties that are very useful. They are not as reactive as elements in groups 1 & 2 on the far left of the periodic table. All have the following common, useful properties with examples given for each. They are hard for tools; shiny for decorative purposes, malleable, ductile, good tensile strength for construction, conduct heat and electricity well, sonorous for musical instruments, high melting points for safe use as a tungsten light filament, combine in alloys which are stronger & harder than pure metal, as catalysts in automobile catalytic converters to change noxious gases into safe ones. Solutions of transitional metal compounds are colorful, and how they are used artistically as glazes for kiln fired pottery is illustrated.