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Chemical Bonds

Physical Science 11/27/12. Chemical Bonds. Bonding Atoms. A compound is made of two or more elements that are chemically combined. Held together by chemical bonds Why do atoms bond? each atom wants a full outermost energy level

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Chemical Bonds

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  1. Physical Science 11/27/12 Chemical Bonds

  2. Bonding Atoms • A compound is made of two or more elements that are chemically combined. • Held together by chemical bonds • Why do atoms bond? • each atom wants a full outermostenergy level • gain, lose, and share valence electrons to achieve the duetor octet rule aka: “being happy” • gives each atom an electron configuration similar to that of a noblegas ex. Group 18: He, Ne, Ar

  3. Chemical Bonds • 3 types • ionic, covalent, metallic • determines the structure of the compound • structure affects propertiesof the compound • melting/boiling pts, conductivity etc.

  4. Chemical Structure • The arrangement of atoms in a substance • Molecular Models • Models used to show different aspects of chemical structures • Some models represent bond length and angles. bond length: the averagedistance between the nuclei of two bonded atoms bond angles: the angle formed by two bonds to the sameatom

  5. Molecular Models of Compounds • Ball and stick • atoms are represented by balls • bonds are represented by sticks • good for “seeing” angles • Structural formula • chemical symbols represents atoms • lines are used to represent bonds • good for “seeing” angles O H H

  6. Space filling • colored circles represent atoms, and the space they take up • no bonds, no bond angles • Electron Dot/Lewis Dot Structure • chemicalsymbol represent atom • dots represent valenceelectrons • 2 center dots represent a bond • no bond angles, no bond length

  7. Ionic bondsare formed by the attraction between oppositely charged ions (a metal and a nonmetal) • cation: positive ion:lost electrons • Formed by metals • anion: negative ion: gainedelectrons • Formed by nonmetals

  8. ex. Na+ + Cl- = NaCl • Each positive sodium ion attracts many negative chloride ions. These negative chloride ions attract many more positive sodium ions, and so on.

  9. Ionic bonds form networks instead of molecules • repeating pattern of multiple ions • Chemists refer to the smallest ratio of ions in ionic compounds. The ratio of sodium to chloride ions in sodium chloride is 1:1. There is one sodium ion for every one chloride ion. • One Na+ and one Cl- form what is known as a formula unit.

  10. Properties of Ionic Compounds • Structure affects properties • strong attraction between ions creates a rigid framework, or lattice structure: aka: crystals ex, cubes, hexagons, tetragons • high melting/boiling pt • shatter when struck (think of it as one unit) • Solids at room temperature • conductivity • solid: ions are close together and in fixed positions (can’t move) - NO conductivity • Dissolved in liquid: ions are freely moving due to a broken lattice structure - Good conductivity

  11. Covalent bonds • chemical bond in which two atoms share a pair of valenceelectrons • Occurs between two atoms with similar electronegativities (neither atom is “strong” enough to take the electron away from the other) • Electronegativity = the power of an atom in a molecule to attract electrons to itself • can be a single, double, or triple bond single: share 2 e-’s double: share 4 e-’s triple: share 6 e-’s • usually formed between nonmetals • mostly low melting/boiling points • most do not conduct electricity because they are not charged • Liquid or gas at room temperature

  12. Covalent Bonds • Non Polar - bonded atoms that share e-’s equally - sameatoms bonded ex. Cl – Cl: Cl2 • Polar - bonded atoms that do not share e-’s equally - different atoms bonded H ex. H – N – H: NH3 IONIC AND COVALENT BONDS ANIMATION

  13. Example: H2O Example: H2

  14. Metallic Bonds • a bond formed by the attraction between a positively charged metalion (cation) and the sharedelectrons that surround it (sea of electrons) • Properties - Good conductivity: electrons can move freely - Malleable: lattice structure is flexible

  15. Polyatomic Ions • An ion made of two or more atoms • Charged molecules (have an overall negative or positive charge as a group) • Act as a single unit in a compound • Basic building blocks of many ionic compounds

  16. Polyatomic ion examples CO32- carbonate HCO3- hydrogen carbonate (bicarbonate) NO3- nitrateitrate NO2- nitrite SO42- sulfate SO32- sulfite PO43- phosphate HPO42- hydrogen phosphate OH- hydroxide O22- peroxide

  17. Parenthesis are used to group atoms of a polyatomic ion. Copper (II) chlorate: Cu(ClO3)2 Iron (II) nitrate: Fe(NO3)2 No parenthesis are needed if there is not more than one of the polyatomic ion present, such as in NaOH.

  18. Objectives • Recognize monoatomic ions, metals with multiple ions and polyatomic ions • Name and determine chemical formulas for monoatomic ions, metals with multiple ion and polyatomic ions

  19. Naming Ions • Monoatomic Ions - cation -name of element with ion ex. (Na) Sodium (Na+) Sodium ion - anion - name of element with the suffix –ide ex. (Br) Bromine (Br-) Bromide • Ions with multiple cations - transition metals - most form 2+, 3+ and 4+ ex. Cu+, Cu2+

  20. Naming Metals with Multiple Ions • Transition Metals - form multiple ions - in order to name the ion use a romannumeral to indicate the charge ex. Cu2+: Copper (II), Titanium (III): Ti3+ Practice Problems: Fe3+: Iron (III) Mercury (III): Hg3+ Pb4+: Lead (IV) Chromium (II): Cr2+

  21. Polyatomic Ions • Definition - an ion made of one or more atoms that are covalently bonded and that act as a unit (atoms that have lost or gained electrons) ex. CO3 2- , NH4+ - behave the same as other ions - polyatomic ions can combined like any other ion (as a unit) ex. NH4NO3 1:1 ratio (NH4)2SO4 2:1 ratio

  22. Polyatomic Ions • Naming polyatomic ions - not logical - rules for some compounds • -ite & -ate endings - indicates the presence of oxygen - called oxyanions - if (-) does not specify how many oxygen atoms are present ex. Sulfate:4, Nitrate:3, Acetate:2

  23. Polyatomic Ions Cont. - often several oxyanions differ only in the number of oxygen atoms present ex. Sulfur - ion with more oxygen takes the –ate ending ex. SO4 - ion with less takes the –ite ending ex. SO3 • Common Oxyanions * Make sure you know these: memorize

  24. Polyatomic Ions Cont. • Common Polyatomic Ions

  25. Objectives • Name ionic compounds from formulas • Determine the chemical formulas for ionic compounds from compound name

  26. Naming Ionic Compounds • Naming ionic compounds (binary) Formula to Name - name of cation followed by the name of the anion ex. NaCl: Sodium Chloride ZnO: Zinc (II) Oxide CuCl2: Copper (II) Chloride - formulas must indicate the relative number of cations and ions if transitional

  27. Naming Ionic Compounds • Practice Problems MgBr2 Magnesium Bromide KI Potassium Iodide CuCl2 Copper (II) Chloride Fe2S3 Iron (III) Sulfide

  28. Formulas of Ionic Compounds • Writing formulas for ionic compounds Name to Formula - balance the cation charge and anion charge, leaving NO netcharge - use subscripts to denote the number of atoms in the formula ex. NaCl: Na+ Cl- : NaCl CaCl: Ca2+ Cl- : CaCl2 **1 to 1 ratios do not designate charge** **Criss-Cross charges into subscripts**

  29. Practice Problems • Write the formula for the following atoms a. lithium oxide Li2O b. beryllium chloride BeCl2 c. titanium (III) nitride TiN d. cobalt (III) hydroxide Co(OH)3

  30. Naming Covalent Compounds • Prefix System # of atoms prefix 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca

  31. Naming Covalent Compounds Cont. • Rules for the prefix system 1. less electronegative element is given first. It is given a prefix only if it contributes more than one atom to a molecule of the compound 2. The second element is named by combining (a) a prefix indicating the number of atoms contributed by the atom (b) the root of the name of the second element, and (c) the ending –ide 3. The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel ex. Monoxide or pentoxide

  32. Naming Covalent Compounds Cont. Naming covalent compounds from formula 1. SiO2 Silicon dioxide 2. PBr3 Phosphorus tribromide 3. CI4 Carbon tetraiodide 4. N2O3 Dinitrogen trioxide

  33. Writing Formulas for Covalent Compunds • Writing formulas from names • Carbon Dioxide CO2 • Dinitrogen Pentoxide N2O5 3. Triphosphorus monosulfide P3S 4. Sulfur Monobromide SBr

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