Chemical Bonding Metallic Bonding and Compounds Metallic Bonds

Chemical Bonding

Metallic Bonding and Compounds Metallic Bonds Characteristics of Compounds • Electrons are shared loosely • Electrostatic (positivenegative) attraction between kernels (nuclei and non-valence electrons) and a “sea” of free floating valence electrons • 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

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)

Ionic Bonding and Compounds Ionic Bonding Characteristics of Compounds • 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 • 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 – example: sodium • non-metals gain electrons to form negative ions to achieve stability anions – example: chlorine – they form 3 D crystal arrays of alternating anions and cations

Covalent Bonding and Compounds Covalent Bonds • electrons are shared • electrostatic attraction between electrons and nuclei 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

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- H 2 CO oxygen- O 2 • triple bond - three pairs of electrons are shared between two atoms – examples: nitrogen N 2 ethyne, or acetylene, C 2 H 2

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

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

Classify each compound as: M- Metallic I- Ionic C- Covalent • • • KCl Brass (Cu + Zn + Sn) CO 2 NO 2 Sterling silver (Ag + Cu) Sn. F 2 CH 4 Mg. Cl 2 NH 3 Li. F

Chemical Formulas • Chemical formula- what elements it contains and the ratio of the atoms of those elements – Example: Na. Cl (sodium chloride) Contains 1 sodium atom and 1 chlorine atom – Example: H 2 O (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

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. Familiar Name Chemical Name Formula Lye Sodium Hydroxide Na. OH Ammonia NH 3 Sand Silicon Dioxide Si. O 2 Battery Acid Sulfuric Acid H 2 SO 4

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

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: Ca 2+ and F- combine to form Ca. F 2 • molecular formula – shows the actual number of atoms in a single molecule – cannot be used for ionic compounds • examples: sucrose- C 12 H 22 O 11 and glucose- C 6 H 12 O 6 • Questions: – What is the empirical formula for sucrose? – What is the empirical formula for glucose? ____