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Main Group Elements​

Remember your last visit of a book store to purchase a book. You asked for a book and shopkeeper gave you within a minute. The shop was full of different books. Then how come he brought a desired book this much quickly. In book stores all books are arranged into various categories and sub-categories. They are arranged on shelves accordingly. Therefore you can easily check the location of the books. Has there been something like a bookstore in chemistry? Have you known that there are total 114 elements discovered till today. 

You have learnt about atom, molecule ad compound. Terms like atomic number are mass number play an important role for collecting information about the elements. There should be some way to arrange these elements. So when you want to know about any element, you can collect all information by seeing that arrangement. Now we have a long form of the periodic table which is a tabular arrangement of element on the basis of atomic number.

Now we know about long form of the periodic table of elements but long back there was no information about all elements. Alexandre Beguyer de Chancourtois was first recognized periodicity in the physical properties of the elements in 1862. Later William Odling intrigued by atomic weights and the periodicity of the elements. Let's discuss one of the parts of the long form of the periodic table that is known as main group elements.

Main Group Elements Chemistry

S- block elements

S - block elements consists of 1 and 2 group of the periodic table. They are metals, except for Hydrogen, the first member of the group. Hydrogen is a gas and has just one electron in it. It usually forms a covalent bond, unlike other metals in the s- block.

The first group elements, from Lithium(Li), Sodium(Na), Potassium(K), Rubidium(Rb), cesium(Cs) and Francium(Fr) are all soft metals. They are called as alkali metals since they form strongly alkaline oxides and hydroxides. Francium is a radioactive element.

Alkali metals or the first A group have just one electron in their valence shell. (ns¹). They are highly malleable and ductile. They are bright and give distinctive luster, when freshly cut. They are electropositive in nature and have very less first ionization constant. They produce coloration during the flame test.

Important

Lithium - Crimson red
Na - Golden yellow
K, Rb and Cs -Violet

This helps in detecting the presence of these elements in their salts.

Alkaline earth metals are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium(Sr), Barium (Ba) and Radium(Ra). The oxides of the three metals, Ca, Sr and Ba were known much earlier than the metals themselves and were called alkaline earths, since they were alkaline in character and occurred in nature as earths- Lime(CaO), Strontia (SrO) and Baryta (Bao). 

This made the elements as alkaline earth metals. They have two electrons in their valence shell and have a configuration of ns². Radium is the radioactive member, though it possess similar properties like its group members. They are also electropositve in nature and have low first and second ionization energies. These elements are metals with distinctive luster when freshly cut.

In the flame tests, they give the following colors

Important

Ca- Brick red
Sr- Crimson
Ba- Apple green
Sr- Crimson
Be and Mg - No color

P - block Element

P- block elements form the other end of the periodic table separated from the 's' block by the transition elements. There are six groups in the p- block elements, the main group elements. They are

Boron Group 

1. General configuration: ns², np¹
2. The elements that form this group are: Boron (B), Aluminium (Al), Gallium (Ga), Indium (In) and Thallium (Tl)
3. Boron is a semi metal, resembling mostly the non metals, while the other members are metals

Carbon Group 

1. General configuration: ns², np².
2. Carbon(C), Silicon(Si), Germanium(Ge), Tin(Sn and Lead(Pb).
3. This group is a perfect example for a group containing all types of elements.
4. C and Si are non metals,
5. Ge is a metalloid while Sn and Pb are metals.

Nitrogen Group 

1. General configuration: ns², np³.
2. This group accommodates Nitrogen (N, phosphorus(P), Arsenic(As), antimony (Sb) and and Bismuth(Bi).
3. Bismuth is a metal, While N and P are non metals.
4. As and Sb are metalloids.

Oxygen group

1. General configuration: ns², np⁴.
2. This group contains: Oxygen(O). Sulfur(S), Selenium(Se), Tellurium(Te) and Polonium(Po). They are all non metals.
3. Polonium is radioactive metal.

Halogens

1. General configuration: ns², np⁵.

2. Just one electron less than the noble gases, these elements are highly non metallic and electronegative in nature. And they are also very very reactive.

Noble gases - Elements of 18^th group

1. These consist of gaseous elements of group 18, the last group in 'p' block.
2. All noble gases have a general outermost electronic configuration of ns² and np⁶. Helium has an electronic configuration of 1s² and is an exception to the general electronic configurations of noble gases.
3. Noble gases are very less reactive due to their completely filled shells.
4. They have also been called as aerogens or rare gases because except Radon, all of them are present in the atmosphere in very small amount and were obtained in small amount in the beginning.

Main Group Elements and Their Compounds​

S- block elements are metals. So, they form a lot of compounds with non metals. These compounds are ionic in nature. They possess one or two extra electrons in their incompletely filled valence shell. So, these elements tend to give away the electrons, to form compounds.

Example:

Mg + Cl₂ → MgCl₂ 

Na + O₂ → Na₂O₂

Except for the first elements of both group and hydrogen. the compounds formed by the elements of the first two groups of main group elements are ionic in characteristics.

P- block elements, as we know, contain all the three varieties of elements- metals, metalloids and non metals. So, their compounds have different characteristics. Even in the same group, for example, the carbon group. Carbon only forms covalent bond while Tin and lead forms ionic bonds. 

C + H₂ → CH₄ (Covalent)
Pb + 2Cl₂ → PbCl₄ (Ionic)

Halogens, the last but one group, are highly reactive elements. They form both covalent and ionic bonds. With metals, they extract the one extra electron, forming ionic bond. With carbon, sulfur, etc, the non metals, they form covalently bonded compounds.

C +2 F₂ → CF₄ (Covalent)
Na + F → NaF (Ionic)

Oxygen is also very reactive and most abundant gas in nature. It is present as Ozone. Due to their reactivity, elements like oxygen, all halogens, Sulfur, etc. do not exist as simple mono atomic elements. They exist as diatomic elements. Sulfur can occur as hexa atomic and octa atomic element too. Also, we know that carbon is so reactive that a whole subdivision of chemistry is devoted to its compounds- the Organic chemistry.
Very few compounds of Xenon are known. Xenon forms xenon di, tetra, and hexa fluorides, with a formula of XeF₂, XeF₄, XeF₆.
Xenon trioxide is also known and is prepared mostly from its fluorides or from its oxy fluoride.

XeOF₄ + 2H₂O → 4HF + XeO₂

Only one fluoride, krypton tetra fluoride is known. They are less stable than the Xenon fluorides.

This excessive reactivity of both s and p block is due to their quest to achieve the noble gas or the completely filled configuration. In the process, these main group elements react among themselves and with other elements of different groups to achieve their configuration.