💏Intro to Chemistry Unit 18 – Representative Elements: Metals to Nonmetals

Key Concepts and Definitions

• Representative elements include elements in groups 1, 2, and 13-18 on the periodic table
• Metals are elements that are typically shiny, malleable, ductile, and good conductors of heat and electricity
  • Examples of metals include sodium (Na), magnesium (Mg), and aluminum (Al)
• Nonmetals are elements that are typically dull, brittle, and poor conductors of heat and electricity
  • Examples of nonmetals include carbon (C), nitrogen (N), and oxygen (O)
• Metalloids are elements that have properties intermediate between metals and nonmetals
  • Examples of metalloids include silicon (Si), germanium (Ge), and arsenic (As)
• Valence electrons are the electrons in the outermost shell of an atom and determine an element's chemical properties
• Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond
  • Increases from left to right across a period and decreases from top to bottom within a group

Periodic Table Organization

• Representative elements are organized into groups (vertical columns) and periods (horizontal rows) on the periodic table
• Groups are numbered 1-18 and contain elements with similar chemical properties due to their electron configurations
  • Group 1 elements (alkali metals) have 1 valence electron and are highly reactive
  • Group 2 elements (alkaline earth metals) have 2 valence electrons and are less reactive than alkali metals
  • Groups 13-18 (p-block elements) have varying numbers of valence electrons and exhibit diverse properties
• Periods are numbered 1-7 and represent the number of electron shells in an atom
  • Elements in the same period have the same number of electron shells but different numbers of valence electrons
• The periodic table is divided into four blocks based on the subshell in which the valence electrons reside: s-block, p-block, d-block, and f-block

Properties of Representative Elements

• Physical properties of representative elements vary depending on their group and period
  • Metallic character decreases from left to right across a period and increases from top to bottom within a group
  • Atomic radius decreases from left to right across a period due to increasing effective nuclear charge and increases from top to bottom within a group due to the addition of electron shells
• Chemical properties of representative elements are determined by their valence electron configurations
  • Reactivity of metals increases from top to bottom within a group due to the ease of losing valence electrons
  • Reactivity of nonmetals increases from left to right across a period due to the increasing tendency to gain electrons
• Electrical conductivity is higher in metals compared to nonmetals due to the presence of delocalized electrons
• Thermal conductivity is higher in metals compared to nonmetals due to the efficient transfer of kinetic energy through delocalized electrons

Trends Across Groups and Periods

• Ionization energy is the energy required to remove an electron from an atom and increases from left to right across a period and decreases from top to bottom within a group
  • Alkali metals have the lowest ionization energies, while noble gases have the highest
• Electron affinity is the energy released when an atom gains an electron and increases from left to right across a period and decreases from top to bottom within a group
  • Halogens have the highest electron affinities, while noble gases have the lowest
• Electronegativity increases from left to right across a period and decreases from top to bottom within a group
  • Fluorine (F) has the highest electronegativity, while francium (Fr) has the lowest
• Metallic character decreases from left to right across a period and increases from top to bottom within a group
  • Cesium (Cs) is the most metallic element, while fluorine (F) is the least metallic

Reactivity Patterns

• Alkali metals (group 1) are highly reactive and readily lose their valence electron to form ionic compounds with nonmetals
  • React vigorously with water to produce hydrogen gas and metal hydroxides (e.g., 2Na + 2H2O → 2NaOH + H2)
• Alkaline earth metals (group 2) are less reactive than alkali metals but still form ionic compounds with nonmetals
  • React with water to produce hydrogen gas and metal hydroxides, but less vigorously than alkali metals
• Halogens (group 17) are highly reactive nonmetals that readily gain an electron to form ionic compounds with metals
  • React with metals to form metal halides (e.g., 2Na + Cl2 → 2NaCl)
• Noble gases (group 18) are generally unreactive due to their complete valence electron shells
  • Can form compounds under extreme conditions, such as xenon tetrafluoride (XeF4)
• Metals tend to lose electrons and form cations, while nonmetals tend to gain electrons and form anions in chemical reactions

Common Compounds and Applications

• Sodium chloride (NaCl) is a common ionic compound formed between sodium (group 1) and chlorine (group 17) and is used as table salt
• Potassium nitrate (KNO3) is an ionic compound formed between potassium (group 1) and nitrate (NO3-) and is used in fertilizers and pyrotechnics
• Calcium carbonate (CaCO3) is an ionic compound formed between calcium (group 2) and carbonate (CO3^2-) and is the main component of limestone and marble
  • Used in the production of cement, as a dietary supplement, and as an antacid
• Aluminum oxide (Al2O3) is an ionic compound formed between aluminum (group 13) and oxygen (group 16) and is used as an abrasive and refractory material
• Sulfuric acid (H2SO4) is a common acid formed from hydrogen (group 1) and sulfate (SO4^2-) and is used in the production of fertilizers, detergents, and batteries

Lab Experiments and Demonstrations

• Flame tests can be used to identify the presence of certain metal ions based on the characteristic colors they produce when heated in a flame
  • Sodium produces a bright yellow flame, potassium produces a violet flame, and copper produces a blue-green flame
• Reactivity series experiments demonstrate the relative reactivities of metals by observing their ability to displace other metals from their compounds
  • For example, zinc can displace copper from copper sulfate solution (Zn + CuSO4 → ZnSO4 + Cu)
• Electrolysis of molten salts can be used to isolate highly reactive metals, such as sodium and potassium, from their compounds
  • An electric current is passed through the molten salt, causing the metal ions to be reduced at the cathode and the nonmetal ions to be oxidized at the anode
• Precipitation reactions can be used to demonstrate the formation of insoluble ionic compounds when solutions containing their constituent ions are mixed
  • For example, mixing solutions of lead(II) nitrate and potassium iodide produces a yellow precipitate of lead(II) iodide (Pb(NO3)2 + 2KI → PbI2 + 2KNO3)

Real-World Connections

• Sodium and potassium are essential elements in biological systems, playing crucial roles in nerve impulse transmission, muscle contraction, and fluid balance
• Calcium is a key component of bones and teeth and is also involved in blood clotting and muscle function
• Nitrogen and phosphorus are essential nutrients for plant growth and are commonly added to soils as fertilizers
  • Overuse of these fertilizers can lead to environmental problems, such as eutrophication of water bodies
• Halogens are used in a variety of applications, including water treatment (chlorine), antiseptics (iodine), and fire extinguishers (bromine)
• Semiconductors, such as silicon and germanium, are crucial materials in the electronics industry, used in the production of computer chips, solar cells, and other devices
• Transition metals, such as iron, copper, and gold, have been used by humans for thousands of years in tools, weapons, and jewelry due to their unique properties and relative abundance