Inorganic Chemistry: Main Group Elements

• Inorganic chemistry focuses on the synthesis, structure, properties, and uses of compounds that do not contain carbon-hydrogen bonds.
• Some organometallic compounds are included in inorganic chemistry.
• Main group elements are those occupying the s and p blocks of the periodic table.
• These include groups 1 and 2 (alkali and alkaline earth metals) and groups 13 to 18. Hydrogen and helium are generally excluded.

General Properties

• Main group elements exhibit a wide range of properties.
• These range from highly reactive metals (e.g., sodium) to inert gases (e.g., neon).
• Their valence electron configurations determine their chemical behavior.
• They generally follow the octet rule (or duet rule for hydrogen and lithium).
• This describes their tendency to achieve a stable electron configuration with eight valence electrons.

Group 1: Alkali Metals

• Alkali metals (Li, Na, K, Rb, Cs, Fr) are highly reactive.
• They have a single valence electron (ns¹).
• They readily lose this electron to form univalent cations (M⁺).
• They react vigorously with water, oxygen, and halogens.
• Reactivity increases down the group due to decreasing ionization energy.
• They form ionic compounds with nonmetals.
• They have low ionization energies, low electronegativities, and small atomic radii.

Group 2: Alkaline Earth Metals

• Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra) are reactive, but less so than alkali metals.
• They have two valence electrons (ns²).
• They tend to form divalent cations (M²⁺).
• They react with water and oxygen, but generally require heating.
• They form ionic compounds, but with some covalent character, especially with Be and Mg.
• They have higher ionization energies and electronegativities compared to the alkali metals.

Group 13: Boron Group

• The boron group (B, Al, Ga, In, Tl) exhibits a transition from nonmetallic to metallic character.
• Boron is a metalloid.
• Aluminum, gallium, indium, and thallium are metals.
• They have three valence electrons (ns²np¹).
• Boron tends to form covalent compounds due to its high ionization energy and small size.
• Aluminum is amphoteric, reacting with both acids and bases.
• Heavier elements exhibit the inert pair effect i.e. the increasing stability of the ns2 electron pair, leading to the formation of stable univalent compounds In⁺, Tl⁺.

Group 14: Carbon Group

• The carbon group (C, Si, Ge, Sn, Pb) also shows a transition from nonmetallic to metallic character.
• Carbon is a nonmetal, silicon and germanium are metalloids, and tin and lead are metals.
• They have four valence electrons (ns²np²).
• Carbon can form four covalent bonds, leading to a vast array of organic and inorganic compounds.
• Silicon forms polymeric structures similar to carbon, but with different properties.
• Heavier elements can exhibit +2 oxidation states due to the inert pair effect.

Group 15: Nitrogen Group

• The nitrogen group (N, P, As, Sb, Bi) includes nonmetals, metalloids, and metals.
• Nitrogen and phosphorus are nonmetals, arsenic and antimony are metalloids, and bismuth is a metal.
• They have five valence electrons (ns²np³).
• Nitrogen forms strong multiple bonds, leading to the existence of diatomic N₂.
• Phosphorus exists as allotropes such as white phosphorus which is highly reactive, and red phosphorus which is more stable.
• They can form compounds in +3 and +5 oxidation states.

Group 16: Oxygen Group (Chalcogens)

• The oxygen group (O, S, Se, Te, Po) are called chalcogens.
• They include nonmetals, metalloids, and metals.
• Oxygen and sulfur are nonmetals, selenium and tellurium are metalloids, and polonium is a metal.
• They have six valence electrons (ns²np⁴).
• Oxygen is a strong oxidizing agent.
• Sulfur forms various allotropes and a wide range of compounds.
• They commonly exhibit -2, +4, and +6 oxidation states.

Group 17: Halogens

• Halogens (F, Cl, Br, I, At) are highly reactive nonmetals.
• They have seven valence electrons (ns²np⁵).
• They readily gain one electron to form univalent anions (X⁻).
• They exist as diatomic molecules (X₂).
• Reactivity decreases down the group due to decreasing electronegativity.
• They form acids with hydrogen (HX).
• They are strong oxidizing agents.

Group 18: Noble Gases

• Noble gases (He, Ne, Ar, Kr, Xe, Rn) are generally inert.
• They have a full valence shell (ns²np⁶, except He which has 1s²).
• They have high ionization energies and low electron affinities.
• Krypton, xenon, and radon can form compounds with highly electronegative elements such as fluorine and oxygen.
• They are used in lighting, insulation, and other specialized applications.

Key Concepts in Main Group Chemistry

• Electronegativity: The ability of an atom to attract electrons in a chemical bond.
• Ionization Energy: The energy required to remove an electron from an atom.
• Electron Affinity: The change in energy when an electron is added to an atom.
• Atomic and Ionic Radii: The size of atoms and ions, which influences their properties.
• Oxidation State: The charge an atom would have if all bonds were ionic.
• Inert Pair Effect: The tendency of heavier elements in groups 13-16 to form stable compounds with oxidation states two less than the group valency.
• Allotropes: Different structural forms of the same element (e.g., diamond and graphite for carbon).
• Catenation: The ability of an element to form chains or rings with itself (e.g., carbon).
• Lewis Acids and Bases: Main group compounds often act as Lewis acids (electron acceptors) or Lewis bases (electron donors).
• Acid-Base Chemistry: Reactions involving proton transfer or electron pair donation/acceptance.
• Redox Chemistry: Reactions involving electron transfer (oxidation and reduction).
• Structure and Bonding: Understanding the shapes and bonding in main group compounds using VSEPR theory and molecular orbital theory.