Families or Groups

When Mendeleev created his periodic table, he did not know why certain elements had similar chemistry. He placed the elements in their positions because they exhibited similar chemical behaviors. Thus, the vertical columns in Mendeleev's table were composed of elements with similar chemistry. These vertical columns are called groups, or families. In this section, you are going to see that the elements in the same groups are related to each other by their electron configurations. Since the families of elements were organized by their chemical behavior, it is predictable that the individual members of each chemical family will have similar electron configurations. Because of the similar electron configuration, elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gases, such as neon (Ne). In contrast, all elements in group 1 are very reactive solids. The names of the groups are summarized in the picture below.

Groups. See description

Groups description

To get interested in looking at the various families (groups) on the periodic table, watch the video clip below from NOVA: "Hunting the Elements." This New York Times technology columnist David Pogue examines how atomic structure determines reactivity. Also meet Theo Gray, chemist and author, who helps David explore how the electron configuration of an atom affects its ability to combine with other atoms.

Alkali Metals (Group 1)

All the elements located in Group 1 have just one valence electron. This makes them very reactive. There are 6 metals in the Alkali Metals Family as seen in the picture below. Notice from the drawing of the atoms that although the size of the atom changes as you go down the Periodic Table, all of the atoms have 1 valence electron (outermost electron).

image of the period table elements in group 1: alkali metals

The metals in the Alkali Metal Family are the most reactive metals. The reactivity of alkali metals actually increases as you go down the group (from the top to the bottom), so lithium (Li) is the least reactive alkali metal and francium (Fr) is the most reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with group 17 elements, which are very "eager" to gain an electron. We will look at forming compounds more in the next module. In the video below, you can see just how reactive the alkali metals are through a demonstration of adding the metals to water.

Besides being very reactive, alkali metals share a number of other properties.

Alkali metals are all solids at room temperature.
Alkali metals are low in density, and some of them float on water.
Alkali metals are relatively soft. Some are even soft enough to cut with a knife, like the sodium pictured below.

image of sodium getting cut with knife

Alkaline Earth Metals (Group 2)

All the elements located in Group 2 have just two valence electrons. There are 6 metals in the Alkaline Earth Family as seen in the picture below. Notice from the drawing of the atoms that although the size of the atom changes as you go down the periodic table, all of the atoms have 2 valence electrons (outermost electrons). Because of having only two valence electrons, they readily give up their two valence electrons to achieve a full outer energy level which is the most stable arrangement of electrons. As a result, they are very reactive, although not quite as reactive as the alkali metals in Group 1. For example, alkaline Earth metals will react with cold water, but not explosively as alkali metals do. Because of their reactivity, alkaline Earth metals never exist as pure substances in nature. Instead, they are always found combined with other elements.

image of the period table elements in group 2: alkaline earth metals

The reactivity of alkaline Earth metals increases from the top to the bottom of the group. That's because the atoms get bigger from the top to the bottom, so the valence electrons are farther from the nucleus. When valence electrons are farther from the nucleus, they are attracted less strongly by the nucleus and more easily removed from the atom. This makes the atom more reactive.

For a demonstration on how an Alkaline Earth Metal reacts with oxygen and in water, watch the video below.

As you have seen in the video demonstration above, magnesium burns very brightly. Because of this, it is used in flares and fireworks. Magnesium alloys with aluminum provide lightweight and sturdy materials for airplanes, missiles, and rockets. Several antacids use magnesium hydroxide to neutralize excess stomach acid.

Calcium compounds are widely found in limestone, marble, and chalk. Calcium is an important constituent of cement. Other uses include calcium chloride as a deicer and limestone as a white pigment in paints and toothpaste. Calcium is also the most abundant metal in the human body, occurring as calcium compounds such as calcium phosphate and calcium carbonate. These calcium compounds are found in bones and make them hard and strong. The skeleton of the average adult contains about a kilogram of calcium. Because calcium—like barium—absorbs x-rays, bones show up white in x-ray images. Calcium is an important component of a healthy human diet. Children who don't get enough calcium while their bones are forming may develop a deficiency disease called rickets, in which their bones are softer than normal and become bent and stunted. Adults who don't get enough calcium may develop a condition called osteoporosis, in which the bones lose calcium and become weak and brittle. People with osteoporosis are at high risk of bone fractures.

Strontium is widely used in fireworks and magnets. Barium compounds can be used in paints, filler for rubber, plastic, and resins, and as a contrast medium for X-rays. Many beryllium compounds are toxic, but these materials have been employed in metal alloys.

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