The Full Wiki

Alkali metal: Wikis

Advertisements
  
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Encyclopedia

From Wikipedia, the free encyclopedia

Group → 1
↓ Period 1 1
H
2 3
Li
3 11
Na
4 19
K
5 37
Rb
6 55
Cs
7 87
Fr

The alkali metals are a series of chemical elements forming Group 1 (IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). (Hydrogen, although nominally also a member of Group 1, very rarely exhibits behavior comparable to the alkali metals). The alkali metals provide one of the best examples of group trends in properties in the periodic table, with well characterized homologous behavior down the group.

Contents

Properties

The alkali metals are all highly reactive and are never found in elemental form in nature. As a result, in the laboratory they are stored under mineral oil or paraffin oil. They also tarnish easily and have low melting points and densities. Potassium and rubidium possess a weak radioactive characteristic due to the presence of long duration radioactive isotopes.

The alkali metals are silver-colored (caesium has a golden tinge), soft, low-density metals, which react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to form a singly charged positive ion, i.e. cation.

Hydrogen, with a solitary electron, is usually placed at the top of Group 1 of the periodic table, but it is not considered an alkali metal; rather it exists naturally as a diatomic gas. Removal of its single electron requires considerably more energy than removal of the outer electron for the alkali metals. As in the halogens, only one additional electron is required to fill in the outermost shell of the hydrogen atom, so hydrogen can in some circumstances behave like a halogen, forming the negative hydride ion. Binary compounds of hydride with the alkali metals and some transition metals have been prepared. Under extremely high pressure, such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal; see metallic hydrogen.

Alkali metals have the lowest ionization potentials in their respective periods, as removing the single electron from the outermost shell gives them the stable inert gas configuration. Their second ionization potentials are very high, as removing an electron from a species having a noble gas configuration is very difficult.

Series of alkali metals, stored in mineral oil ("natrium" is sodium.)

Alkali metals are famous for their vigorous reactions with water, and these reactions become increasingly violent as one moves down the group. The reaction with water is as follows:

Alkali metal + water → Alkali metal hydroxide + hydrogen gas

With potassium as an example:

2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

Trends

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:

Z Element No. of electrons/shell
1 Hydrogen 1
3 Lithium 2, 1
11 Sodium 2, 8, 1
19 Potassium 2, 8, 8, 1
37 Rubidium 2, 8, 18, 8, 1
55 Caesium 2, 8, 18, 18, 8, 1
87 Francium 2, 8, 18, 32, 18, 8, 1

The alkali metals show a number of trends when moving down the group - for instance: decreasing electronegativity, increasing reactivity, and decreasing melting and boiling point. Density generally increases, with the notable exception of potassium being less dense than sodium, and the possible exception of francium being less dense than caesium.

Alkali metal Standard Atomic Weight (u) Melting Point (K) Boiling Point (K) Density (g·cm−3) Electronegativity (Pauling)
Lithium 6.941 453 1615 0.534 0.98
Sodium 22.990 370 1156 0.968 0.93
Potassium 39.098 336 1032 0.89 0.82
Rubidium 85.468 312 961 1.532 0.82
Caesium 132.905 301 944 1.93 0.79
Francium (223) 295 950 1.87 0.70

Compounds

Alkali metals form a very wide range of amalgams.[1]

References

See also

External links

Explanation of above periodic table slice:
Alkali metals Atomic numbers in black are solids Solid borders indicate primordial elements (older than the Earth) Dashed borders indicate natural radioactive elements with no isotopes older than the Earth
Advertisements

Simple English

Alkali metals are the chemical elements in group one of the periodic system. They are silver-coloured when pure, soft and have only one electron in the outermost shell. They like to make reactions in which they give up this single electron and then have a charge of +1. They react strongly with water and because of this, they have to be stored in petrol. Alkali metals are the first group in the periodic table. They are never found in nature uncombined because they are unstable and they react fast to other elements. They bond well with all elements except the noble gases. When they are in air, they turn black. They have a one valence electron.

The alkali metals are: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr). Lithium is the least reactive, and francium is the most reactive, although it is very rare.

Sodium is the most important alkali metal. One of the most important salts of sodium is sodium chloride (NaCl) (common 'table salt'). It also forms a hydroxide, sodium hydroxide (NaOH), which is commonly called 'caustic soda'. It is a very strong base.

[[File:|thumb|The alkali metals]]


Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message