What are silvery metals ,soft highly reactive metals too reactive to be found free in nature, low melting and boiling temperatures, low densities called

You might be referring to alkali metals.

Alkali metals are in group 1 of the periodic table.

Alkali metals have a silvery color. Like nearly all main group metals, they reflect light from the entire visible spectrum.

Each of the group 1 atom have one single valence electron. Removing that electron is easy. They are one electron away from the nearest noble gas element. Removing that extra electron will give the atom an empty valence shell. The atom gains stability through that process.

Alkali metals will readily lose its electrons to non-metals such as oxygen, chlorine, and fluorine. They react with water to form a base and hydrogen gas- hence the name alkali. They are too reactive to exist in nature as metals. That's one of the reasons why power packs containing lithium (an alkali metal) should not be cut open at home. They might catch fire when exposed to the air and have a good chance of creating an explosion.

Alkali metals have low m.p. and b.p. among all the metals. They are easy to cut under room temperature. The softness (a.k.a. malleability), melting point, and boiling point of a metal depends on the strength of the bond between its atoms. Each of the group 1 alkali metal atom has one single electron, whereas metals like aluminum have three. Metallic bonds between alkali metal atoms are much weaker than those between aluminum atoms. As a result, it takes less energy to pull alkali metal atoms apart. They are easier to melt, boil, or cut than metals from other groups. For example, it is possible to tear a chunk of sodium but not iron apart by hand.

Alkali metals are likely to be less dense than any other metals on the periodic table. Elements from the same period have an equal number of electron shells. Alkali metals have less protons per atom than elements from the rest of the period. They weakly attract their electron shells and have a large atomic and ionic radius. An alkali metal will have a lofty structure, while metals to the right of the period are more tightly packed.  Alkali metals will have less mass per unit space and have a lower density. For example, typical power banks contain lithium ions rather than nickel. Lithium is lighter than nickel; it allows the battery pack to store more energy per unit mass.

increased stability in the completion of fluorine's outer shell.

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