(alkali metals with definition, importance, and reductive nature.)
The term alkali refers to any substance with a pH greater than 7, which forms a chemical salt when combined with an acid, which produces hydroxide ions when dissolved in water.
Alkali metals are known as elements of the first group in the periodic table except for hydrogen, which includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr). Characteristics of alkali metals include:
- Since these metals are alkali metals when they interact with water, the hydrogen atom separates into the water molecule to form hydrogen, while the other hydrogen atom binds with oxygen to form hydroxide.
- All elements of the first group in the periodic table have one valence electron, and the electronic distribution has s1, which means that it participates in chemical reactions.
- Alkali metals are shiny, soft enough to cut into the knife, and usually have a white color, but the cesium is a yellowish-white color, and when placed in the flame, most of them give distinctive colors, for example, lithium glows in light red, and sodium appears yellow The potassium heated gives violet, dark red rubidium and light blue cesium, so it is possible to differentiate these metals according to the colors they produce when heated.
- Sodium is the sixth most abundant element on Earth (2.6%), potassium is the seventh (2.4%), lithium and rubidium are considerably less abundant, and cesium is a very rare element. With very small amounts of uranium ores.
- Alkaline metals are highly reactive elements, so they are found in nature with other elements, and some simple minerals containing them such as halite (sodium chloride), sulfite (potassium chloride), and carnalite (potassium chloride, magnesium chloride) are dissolved in water, making Metals are easy to extract and purify, yet complex, insoluble minerals in water are more abundant in the earth’s crust.
- Alkali metals easily react with oxygen and water vapor in the atmosphere (lithium also reacts with atmospheric nitrogen), react strongly, often violently with water to produce hydrogen, form strong caustic solutions, and react with most common non-metallic materials such as halogens and sulfur. , Halogens, and phosphorus, also interact with many organic compounds, especially those containing halogen, or a hydrogen atom that is easy to replace.
- Alkali metals tend to form positively charged ions (cations) when they interact with nonmetals, resulting in the production of highly melting compounds, which are solid crystals that are interconnected by ionic bonds that result from the mutual attraction forces between positive and negative electric charges.
The importance of alkali metals
The importance of alkali metals, like other elements found in nature or that can be obtained from the laboratory by extracting them from their compounds, are of great importance:
- Potassium and sodium are essential elements in the formation of animal and plant tissues.
- Sodium-ion is the primary ion in the surrounding cell fluid in order to control the amount of water inside the cell and to control the diastole and contractility of the muscles, while the potassium ion is the primary ion inside the cell especially the plant cells.
- Give food a good taste by adding table salt, sodium chloride.
- Plant fertilizers to increase agricultural production such as the use of potassium nitrate and sodium nitrate for this purpose.
Alkaline earth metals
Alkaline earth metals are defined as elements of the second group in the periodic table, which include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Comes:
- All earth alkali metals except beryllium from corrosive alkaline hydroxides.
- All alkali earth metals and their compounds except radium are found in fairly commercial applications, especially magnesium alloys, and a variety of calcium compounds.
- Alkaline earth metals are highly reactive, although less reactive than alkali metals.
- Due to the intensity of the reaction of alkali earth metals, they can not be found freely in nature, but they occur naturally and are common in a wide range of compounds and minerals.
- Biological and geological processes. Radium is an exception, a rare element, and all its isotopes are radioactive and have no commercial uses, although its compounds were used frequently to treat cancer in the first half of the 20th century, which were replaced by considerably less expensive alternatives.
- Alkaline earth metals have an electron equivalent in the outer shell, and the outer’s orbit is complete.
- Alkali earth metals are characterized by low electron affinities and electronegativities.
- Alkali earth metals have a relatively low density.
- Alkali earth metals have melting points and relatively low boiling points compared to metals.
- Elements of this group easily form divalent cations such as Ca + 2, Mg + 2.
- Alkaline earth metals are usually elastomeric, malleable, soft, and relatively strong.
- All earth-core metals react with halogens to form halides, which are ionic crystals, except for beryllium chloride, which is a covalent compound.
- Alkaline earth metals are good conductors of electricity. Pure alkaline earth metals are characterized by their luster and their white silver color, but they react quickly with air to form external oxide layers.
- Testing alkali earth metals with a flame can be useful in identifying the compounds they contain. For example, calcium is burned to produce an orange-red color, strontium burns to produce a scarlet color, and barium produces a green color. These metals are used in fireworks.
- Barium is commonly used by patients with digestive problems. They are given a chalky solution made of barium to drink, which appears when taking dental rays.
The reductive nature of alkali metals
All alkali metals are strong reducing agents. Of all alkali metals, lithium is the most reductive, while sodium is the weakest. Although lithium has the highest ionization energy, it is a powerful reducing agent.
Oxygen acid salts
Carbonates and bicarbonates
In this group, the thermal stability of carbonates and bicarbonates increases as we move from top to bottom. Lithium carbonate is unstable when exposed to heat as it breaks down and results in CO2. Lithium bicarbonate (HCO 3) is never solid.
Li 2 CO 3 → Li 2 O + CO 2
We also note in this group that the solubility of carbonates and bicarbonates in water increases as we move in the group from top to bottom, as follows:
Li 2 CO 3 <Na 2 CO 3 <K 2 CO 3 <Rb 2 CO 3 <Cs 2 CO 3
Bicarbonate is as follows:
NaHCO 3 <KHCO 3 <RbHCO 3 <CsHCO 3
When LiNO 3 is heated, it disintegrates NO 2 and O 2.
4LiNO 3 → 2LiO + 4NO 2 + O 2
The nitrate of other elements in the same group disintegrates when exposed to heat to give oxygen only.
2NaNO 3 → 2NaNO 2 + O 2
Lithium sulfate Li 2 SO 4 is insoluble in water, while other sulfates such as Na 2 SO 4 and K 2 SO 4 are soluble in water.
The hydrogen atom in organic compounds is replaced by an alkali metal, forming salts such as sodium acetate, sodium benzoate, etc.
CH 3 COOH + NaHCO 3 → CH 3 COONa + H 2 O + CO 2
You may also like: