Main Group Elements: Properties and Reactivity

• Main group elements reside in the s and p blocks of the periodic table
• Hydrogen and helium are excluded
• Groups 1, 2, and 13-18 are included

General Properties

• Main group elements demonstrate diverse physical and chemical properties
• Properties change predictably down groups and across periods
• Valence electron configuration and electronegativity dictate reactivity

Group 1: Alkali Metals

• Alkali metals consist of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr)
• They are soft, silvery metals
• They have low densities
• They have low melting and boiling points
• They are very reactive
• Single valence electron is readily lost, forming +1 cations
• React intensely with water, producing hydrogen gas and metal hydroxides
• Ionic compounds are formed with nonmetals
• Depending on the metal, reaction with oxygen yields oxides, peroxides, or superoxides
• Ionization energy decreases down the group, increasing reactivity

Group 2: Alkaline Earth Metals

• Alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra)
• Compared to alkali metals, they are harder and denser
• Their melting and boiling points are higher
• They are reactive, though less so than alkali metals
• Two valence electrons are lost to form +2 cations
• Reactivity with water is less vigorous than alkali metals
• Ionic compounds are formed with nonmetals
• Beryllium is amphoteric, reacting with both acids and bases
• Magnesium reacts slowly with cold water, but more rapidly with steam

Group 13: Boron Group

• The boron group consists of boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl)
• Boron is a metalloid with unique properties
• Aluminum is a metal, the most abundant in Earth's crust
• Other members are also metals
• Boron forms covalent compounds
• Aluminum can form both covalent and ionic compounds
• Boron is electron-deficient, often forming polymeric structures or Lewis acid-base adducts
• Aluminum reacts with both acids and bases
• Aluminum forms a protective oxide layer in air
• Stability of the +3 oxidation state decreases down the group
• Thallium exhibits a stable +1 oxidation state

Group 14: Carbon Group

• Carbon group includes carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb)
• Carbon is a nonmetal capable of extensive catenation
• Silicon and germanium are metalloids
• Tin and lead are metals
• Carbon exists in allotropic forms like diamond and graphite
• Silicon is a semiconductor
• It forms the basis of many minerals
• Carbon forms strong covalent bonds
• It forms a variety of organic compounds
• Silicon forms polymeric structures with oxygen
• It forms silicates
• The stability of the +2 oxidation state increases down the group
• Lead(II) compounds are more stable than lead(IV) compounds

Group 15: Nitrogen Group

• Nitrogen group includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi)
• Nitrogen and phosphorus are nonmetals
• Arsenic and antimony are metalloids
• Bismuth is a metal
• Nitrogen exists as a diatomic gas (N2)
• It forms a variety of oxides and nitrogen-containing compounds
• Phosphorus exists in several allotropic forms including white, red, and black phosphorus
• It forms oxides and phosphates
• Nitrogen can form multiple oxidation states ranging from -3 to +5
• Bismuth exhibits a stable +3 oxidation state
• It forms bismuth(III) compounds

Group 16: Oxygen Group (Chalcogens)

• Oxygen group includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po)
• Oxygen and sulfur are nonmetals
• Selenium and tellurium are metalloids
• Polonium is a metal
• Oxygen exists as a diatomic gas (O2) and ozone (O3)
• It forms oxides with most elements
• Sulfur exists in various allotropic forms
• It forms sulfides and sulfates
• Oxygen is highly electronegative
• It forms hydrogen bonds
• Sulfur is less electronegative than oxygen

Group 17: Halogens

• Halogens include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At)
• They are nonmetals
• They exist as diatomic molecules
• They are highly electronegative
• They readily gain one electron to form -1 anions
• They form acids when reacted with hydrogen
• They react with metals to form salts
• Reactivity decreases down the group
• Fluorine is the most reactive halogen
• Astatine is radioactive

Group 18: Noble Gases

• Noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn)
• They are monatomic gases
• They are generally unreactive due to their full valence shells
• They are also known as inert gases
• They have high ionization energies
• They have positive electron affinities
• Xenon and krypton are known to form some compounds, particularly with fluorine and oxygen
• Radon is radioactive

Periodic Trends

• Atomic Size: Increases down a group due to the addition of electron shells
• Atomic Size: Decreases across a period due to increasing nuclear charge
• Ionization Energy: Decreases down a group due to increasing atomic size
• Ionization Energy: Increases across a period due to increasing nuclear charge
• Electronegativity: Decreases down a group due to increasing atomic size
• Electronegativity: Increases across a period due to increasing nuclear charge
• Metallic Character: Increases down a group due to decreasing ionization energy
• Metallic Character: Decreases across a period due to increasing ionization energy