Chemical Bonds Bonding Atoms Why do atoms bond
Chemical Bonds
Bonding Atoms • Why do atoms bond? - each atom wants a full outermost energy level - gain, lose, and share valence electrons to achieve the duet or octet rule aka: “being happy” - gives each atom an electron configuration similar to that of a noble gas ex. Group 18: He, Ne, Ar
Chemical Bonds • Chemical Bonds - attractive force that holds atoms or ions together - 3 types ionic, covalent, metallic - determines the structure of compound - structure affects properties - melting/boiling pts, conductivity etc.
Chemical Structure/Models • Chemical Structure/Molecular Models - arrangement of bonded atoms or ions - bond length: the average distance between the nuclei of two bonded atoms - bond angles: the angle formed by two bonds to the same atom
Molecular Models of Compounds • Ball and stick - atoms are represented by balls - bonds are represented by sticks * good for “seeing” angles • Structural - chemical symbols represents atoms - lines are used to represent bonds * good for “seeing” angles H H O
Molecular Models Cont. • Space filling - colored circles represent atoms, and the space they take up - no bonds, no bond angles • Electron Dot/Lewis Structure - chemical symbol represent atom - dots represent valence electrons - 2 center dots represent a bond - no bond angles, no bond length
Ionic Bonds / Ionic Compounds • Definition - bond formed by the attraction between oppositely charged ions cation: positive: lost e-’s anion: negative: gained e-’s - oppositely charged ions attract each other and form an ionic bond ex. Na+ + Cl- = Na. Cl - electrons are transferred from one atom to another - negative ions attract more positive ions, and soon a
Networks / Crystal Lattices • Networks - repeating pattern of multiple ions ex. Na. Cl - every Na ion is next to 6 Cl ions - strong attraction between ions creates a rigid framework, or lattice structure: aka: crystals ex, cubes, hexagons, tetragons
Properties of Ionic Compounds • Structure affects properties - strong attractions between ions: strong bonds - high melting/boiling pt - shatter when struck (think of it as one unit) - conductivity solid: ions are so close together, fixed positions, (can’t move) NO conductivity liquid: ions are freely moving due to a broken lattice structure Good conductivity
Covalent Bonds • Definition - chemical bond in which two atoms share a pair of valence electrons - can be a single, double, or triple bond single, 2 e-’s (-); double, 4 e-’s (=); triple, 6 e-’s( ) - always formed between nonmetals - mostly low melting/boiling points • 2 types of bonds - polar - non polar
Covalent Bond Cont. • Non Polar - bonded atoms that share e-’s equally - same atoms bonded ex. Cl – Cl: Cl 2 • Polar - bonded atoms that do not share e-’s equally - different atoms bonded H ex. H – N – H: NH 3
Metallic Bonds • Definition - a bond formed by the attraction between positively charged metal ion (cation) and the shared electrons that surround it (sea of electrons) ex. Cu • Properties - Conductivity: Good: electrons can move freely - Malleable: lattice structure is flexible
Predicting Bond Type
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+, Cu 2+
Naming Ionic Compounds • Naming ionic compounds (binary) Formula to Name - name of cation followed by the name of the anion ex. Na. Cl: Sodium Chloride Zn. O: Zinc (II) Oxide Cu. Cl 2: Copper (II) Chloride - formulas must indicate the relative number of cations and ions if transitional
Naming Ionic Compounds • Practice Problems Mg. Br 2 Magnesium Bromide KI Potassium Iodide Cu. Cl 2 Copper (II) Chloride Fe 2 S 3 Iron (III) Sulfide
Formulas of Ionic Compounds • Writing formulas for ionic compounds Name to Formula - balance the cation charge and anion charge, leaving NO net charge - use subscripts to denote the number of atoms in the formula ex. Na. Cl: Na+ Cl- : Na. Cl Ca. Cl: Ca 2+ Cl- : Ca. Cl 2 **1 to 1 ratios do not designate charge** **Criss-Cross charges into subscripts**
Practice Problems • Write the formula for the following atoms a. lithium oxide Li 2 O b. beryllium chloride Be. Cl 2 c. titanium (III) nitride Ti. N d. cobalt (III) hydroxide Co(OH)3
Naming Covalent Compounds • Prefix System # of atoms 1 2 3 4 5 6 7 8 9 10 prefix mono di tri tetra penta hexa hepta octa nona deca
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
Naming Covalent Compounds Cont. Naming covalent compounds from formula 1. Si. O 2 Silicon dioxide 2. PBr 3 Phosphorus tribromide 3. CI 4 Carbon tetraiodide 4. N 2 O 3
Writing Formulas for Covalent Compunds • Writing formulas from names 1. Carbon Dioxide CO 2 2. Dinitrogen Pentoxide N 2 O 5 3. Triphosphorus monosulfide P 3 S 4. Sulfur Monobromide SBr
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