The Most Reactive Family on the Periodic Table

6.nine: Hydrogen and Alkali Metals

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You probably think of water as a substance that can put out fires. But some elements are and so reactive that they burn down in h2o. In fact, they virtually explode in water. An instance is shown in the photo below. About iii pounds of sodium were added to water, and the outcome was an explosive reaction. Why is sodium such a reactive element? In this section, yous volition observe out.

Figure \(\PageIndex{1}\): Sodium reacting with water.

The First Group

Sodium \(\left( \ce{Na} \correct)\) is an chemical element in group 1 of the periodic table of the elements. This grouping (cavalcade) of the tabular array is shown beneath. Information technology includes the nonmetal hydrogen \(\left( \ce{H} \right)\) and six metals called brine metals. Elements in the same grouping of the periodic table have the same number of valence electrons. These are the electrons in the outer free energy level of the atoms that can be involved in chemical reactions. Valence electrons determine many of the properties of an element, then elements in the same group take similar properties. All the elements in group ane have just one valence electron. This makes them very reactive.

Figure \(\PageIndex{2}\): Group 1 of the periodic tabular array.

Reactivity of Group 1 Elements

Hydrogen is a very reactive gas, and the alkali metals are even more reactive. In fact, they are the most reactive metals and, along with the elements in group 17, are the virtually reactive of all elements. The reactivity of alkali metals increases from the superlative to the lesser of the grouping, and so lithium \(\left( \ce{Li} \right)\) is the least reactive alkaline metal and francium \(\left( \ce{Fr} \right)\) is the nigh reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with grouping 17 elements, which are very "eager" to gain an electron.

Other Properties of Alkali Metals

As well beingness very reactive, alkali metals share a number of other properties:

• Brine metals are all solids at room temperature.
• Alkali metals are low in density, and some of them float on h2o.
• Alkali metals are relatively soft. Some are even soft enough to cut with a knife, like the sodium pictured in the figure below.

Figure \(\PageIndex{3}\): Elemental sodium is soft enough to cutting with a knife.

A Closer Look

Although all grouping 1 elements share certain backdrop, such every bit being very reactive, they are not alike in every style. Three different group 1 elements are described in more item below. Detect the ways in which they differ from one another.

Figure \(\PageIndex{4}\): Hydrogen has the smallest, lightest atoms of all elements. Pure hydrogen is a colorless, odorless, tasteless gas that is nontoxic merely highly flammable. Hydrogen gas exists mainly as diatomic ("two-cantlet") molecules \(\left( \ce{H_2} \right)\), as shown above. Hydrogen is the almost abundant element in the universe and the third most abundant element on Earth, and occurs mainly in compounds such every bit water.

Effigy \(\PageIndex{5}\): Potassium is a soft, silverish metallic that ignites explosively in water. Information technology hands loses its one valence electron to form positive potassium ions \(\left( \ce{K^+} \right)\), which are needed past all living cells. Potassium is so important for plants that it is establish in nearly all fertilizers, like the one shown here. Potassium is abundant in Earth's crust in minerals such as feldspar.

Figure \(\PageIndex{vi}\): Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, equally y'all can see in the atomic model above, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements, such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time.

Summary

• Group i of the periodic table includes hydrogen and the brine metals.
• Because they have just one valence electron, grouping one elements are very reactive. As a issue, they are found in nature only in combination with other elements.
• Alkali metals are all solids at room temperature. They are relatively soft and low in density.
• From the superlative to the bottom of grouping 1, the elements take heavier, more reactive atoms.

Explore More

At the following URL, click on "Group 1 data and graphs". Use the information in the group one tabular array to fill in the blanks beneath with either increases or decreases.

From the pinnacle to the bottom of group 1, backdrop of the alkali metals change as follows:

ane. Melting signal _________.

2. Boiling point _________.

three. Density _________.

4. Atomic radius _________.

5. Number of electrons _________.

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Source: https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/06%3A_The_Periodic_Table/6.09%3A_Hydrogen_and_Alkali_Metals

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