What are alkali metals on the periodic table?

• Alkali metals are all the elements present in the first group of the periodic table.
• Alkali metals in order from top to bottom are Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr).

Chemical properties of alkali metals:

• Alkali metals are electropositive in nature. This means that the atoms of these elements tend to lose their valence electrons and form positively charged ions.
• Alkali metals donate one electron to form positive ions during chemical reactions or in their solutions

• Alkali metals form ionic compounds with non metals
• Alkali metals combine with halogens or group 7 non metals to form strong ionic salts. For example Lithium Fluoride (LiF), Sodium Chlordine (NaCl), Potassium Chloride(KCl), potassium iodide (KI), etc.
• Alkali metals when dissolved in water react to form their respective metal alkalis and liberate hydrogen. For example when sodium metal is dissolved in water it forms sodium hydroxide, a powerful alkali: 2Na + 2H2O -> 2NaOH + H2

Physical properties of alkali metals:

• Alkali metals have low melting and boiling points
• Alkali metals are malleable, ductile and can be cut with the help of a knife
• Alkali metals are lustrous, but their lustrous surface gets oxidized quickly on exposure to the atmosphere and so they appear as dull, white colored metals after a few seconds of cutting them.

Why do alkali metals include hydrogen, even though hydrogen is a nonmetal?

The elements are arranged in the periodic table in increasing order of their atomic numbers, and so atomic number forms the basis of arrangement of elements in the periodic table. Since atomic number of an element relates closely to its valency, electronegativity and chemical properties, the arrangement of elements in the periodic table is affected by their valency, elect negativity and chemical properties as well, although not based on it. Hydrogen although being a non metallic gas by physical nature, has a valency of +1, that is, it’s atoms have only one electron in their outermost shells, which it loses during chemical reactions to form positively charged ions. This is the case with all the alkali metals in the periodic table and no other element except the alkali metals including hydrogen show this characteristic in the periodic table. Due to this property hydrogen atoms behave like metal atoms in chemical reactions with other non metals, similar to the nature of alkali metals. Thus it is appropriate to place hydrogen in the alkali metals of the periodic table.

Placing hydrogen with helium would break the rule of having elements of similar chemical properties and valencies in one group of the periodic table.

Which similar properties do alkali metals exhibit?

Alkali metals exhibit a number of similar physical and chemical properties:

Electronic configuration

Each alkali metal has a single valence electron. The inner shells of their atoms are filled with electrons to their capacity (octet/duplet). Thus during chemical reactions the alkali metals tend to lose their outermost electron to get a balanced electronic configuration. In doing so, they form positively charged ions.

The general electronic configuration of alkali metals can be written as [Noble gas] ns¹, since the outermost electron in each alkali metal atom goes to the ns-orbital.

Atomic properties

Atomic properties of alkali metals exhibit a gradual gradation from top to bottom. The atomic radius increases gradually from 152 pm for Lithium to 265 pm for Cesium. Similarly the ionic radius also increases from top to bottom, starting from 76 pm for Lithium to 167 pm for Cesium.

Alkali metals have the greatest atomic as well as ionic radii in their respective rows because the nuclear charge (pull) on the valence shell increases on moving from left to right in a row due to increase in the atomic number, whereas the number of shells in each atom remains the same throughout the row. Thus, on moving from left to right, the increasing nuclear charge in each element's atoms pulls the electron shells closer to itself, thereby decreasing the atomic/ionic radii.

Alkali metals have atomic radius greater than ionic radius for each atom, because they form ions by loosing their single valence electron, which reduces the number of electron shells and increases the amount of positive charge in the nucleus attracting the electron shells closer to it.

Physical properties

Alkali metals have low melting and boiling points and densities. This is due to the fact that inter-atomic forces between atoms are weak owing to the presence of a single valence electron in all atoms, which weakens the formation of metallic bonds (same atom bonds) within the same atoms.

With respect to variation, melting and boiling points decrease down the group and density increases down the group.

All alkali metals are lustrous: they are silvery white metals which when freshly cut show a lustrous surface, as on exposure to air they get oxidized quickly and thus loose their luster. They are malleable and ductile and can be cut with a knife.

Electronegativity

Alkali metals have low electronegativities because their atomic sizes are large and they have only one valence electron, so the nuclear pull on the valence electron is less and it tends to get donated to other electronegative atoms during chemical reactions.

What are alkali metals?

All the elements present in the first group of the periodic table are called alkali metals.

The alkali metals from top to bottom are:

• Hydrogen (H)
• Lithium (Li)
• Sodium (Na)
• Potassium (K)
• Rubidium (Rb)
• Cesium (Cs)
• Francium (Fr)

Since alkali metals are present in the first group, they have the same number of valence electrons in their atoms. For the same reason alkali metals show similarity in physical and chemical properties. For example, alkali metals all have a valency of +1, alkali metals are all transparent white lustrous metals, alkali metals are highly chemically reactive; They react with oxygen as soon as they are exposed to air, react with water to form their respective hydroxides; Their hydroxides are all strong alkali's.