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Chemical Bonding

This text provides an overview of metallic, ionic, and covalent bonding, including the characteristics of compounds formed through these bonds. It also discusses the empirical and molecular formulas, and the importance of the octet rule in chemical bonding.

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Chemical Bonding

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  1. Chemical Bonding

  2. Metallic Bonding and Compounds Metallic Bonds Characteristics of Compounds Metal + metal Conduct electricity and heat Usually solid at room temp (range of m.p./b.p.) Not soluble in water Luster is shiny Malleable and ductile • Electrons are shared loosely • Electrostatic (positive-negative) attraction between kernels (nuclei and non-valence electrons) and a “sea” of free floating valence electrons

  3. Metallic Bonding and Compounds • Alloy: a mixture (usually a solid) that contains two or more elements and has the characteristics of a metal • Compositions of Selected Alloys • stainless steel 74% Fe, 18% Cr, 8% Ni, .18% C • coinage silver 90% Ag, 10% Cu • plumber’s solder 67% Pb, 33% Sn • brass 67% Cu, 33% Zn • 18 carat gold 75% Au, 10-20% Ag, 5-15% Cu • nichrome 60% Ni, 40% Cr *note that the elements in an alloy are not present in specific ratios (the percentages may be adjusted)

  4. Ionic Bonding and Compounds Ionic Bonding Characteristics of Compounds metal + nonmetal called “salts” solids at room temperatures (high m.p. and b.p.) may dissolve in water to form electrolytes (can conduct electricity) conduct electricity when molten (liquid at high temperature) brittle crystalline, NOT molecules they form 3D crystal arrays of alternating anions and cations • electrons are transferred • Bond is an electrostatic attraction between a cation and an anion (ions) • atoms are often less stable than ions • metals lose electrons to form positive ions to achieve stability cations • example: sodium • non-metals gain electrons to form negative ions to achieve stability anions • example: chlorine

  5. Covalent Bonding and Compounds Covalent Bonds Characteristics of Compounds nonmetal + nonmetal solids/liquid/gas at room temperatures (variable m.p. and b.p.) may dissolve in water but doesn’t form an electrolyte doesn’t conduct electricity when solid or molten (liquid at high temperature) forms molecules • electrons are shared • electrostatic attraction between electrons and nuclei

  6. Covalent Bonding and Compounds • unshared pair - valence electrons that are not shared in bonds • single bond - only a single pair of electrons are shared between two atoms (see examples above) • double bond - two pairs of electrons are shared between two atoms • examples: formaldehyde- H2CO oxygen- O2 • triple bond - three pairs of electrons are shared between two atoms • examples: nitrogen N2 ethyne, or acetylene, C2H2

  7. Compounds • Compounds are substances made up of two or more elements in fixed proportions. • Electrically neutral (equal numbers of positive and negative charges) • Atoms combine by gaining, losing, or sharing electrons to form chemical bonds • Atoms achieve greater stability in bonding with other atoms

  8. 3 Types of bonding • Metallic • (metal + metal) • Ionic • (metal + nonmetal) • Covalent/molecular • (nonmetal + nonmetal)

  9. Classify each compound as: M- MetallicI- IonicC- Covalent • KCl • Brass (Cu + Zn + Sn) • CO2 • NO2 • Sterling silver (Ag + Cu) • SnF2 • CH4 • MgCl2 • NH3 • LiF

  10. Chemical Formulas • Chemical formula- what elements it contains and the ratio of the atoms of those elements • Example: NaCl (sodium chloride) Contains 1 sodium atom and 1 chlorine atom • Example: H2O (water) The formula is a combination of the symbols H and O and the subscript number 2 Contains 2 Hydrogen atoms and 1 Oxygen atom

  11. Chemical Formulas • Subscript means “written below” and is written after the symbol. • It tells how many atoms of that element are in one unit of the compound. • If the symbol has no subscript, the unit contains only one atom of that element.

  12. Octet Rule • Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons • Think of ionic bond formation as a process: • electrons are lost/gained to achieve a stable octet of electrons • ions form • ions brought together by electrostatic attractions. • Lewis Dot Diagrams: • Recall that a way to show and emphasize an atom’s valence electrons is to draw the element’s dot diagram • Li Be N O Cl Si Ar

  13. Empirical vs. Molecular Formulas • empirical formula • shows the lowest whole number ratio of atoms in a compound • always used for ionic compounds • can be useful for partially describing covalent compounds • example: Ca2+ and F- combine to form CaF2 • molecular formula • shows the actual number of atoms in a single molecule • cannot be used for ionic compounds • examples: sucrose- C12H22O11 and glucose- C6H12O6 • Questions: • What is the empirical formula for sucrose? • What is the empirical formula for glucose? ________

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