Untitled Flashcards Set

Unit 5: Covalent Compounds



8.1: Covalent Bonds

  • Bond formed from atoms sharing electrons

  • Covalent compounds are called molecules

  • Ionic compounds are called formula units

  • Covalent bonds form so that atoms become stable (octet in their valence shell because of the shared electrons)

  • Covalent compounds form between nonmetals

  • Diatomic elements are elements in nature that are bonded to themselves

    • H2  N2   O2   F2   Cl2   Br2   I2

  • A single covalent bond is when one pair of electrons is shared

  • A double covalent bond is when two pairs of electrons are being shared

  • A triple covalent bond is when three pairs of electrons are being shared

  • The strength of covalent bonds depends on the length of a bond, the shorter the stronger

  • Atomic radius makes the bond length increase

  • Bond length decreases as the number of bonds increases

  • Strength increases as the number of bonds between the carbon atoms increase

  • Bond Dissociation Energy is the amount of energy required to break a specific covalent bond

  • Bond dissociation energy is always a positive value

  • Breaking bonds is endothermic

  • The shorter the bond length the greater the bond dissociation energy






















8.2: Naming Molecules

  • Covalent Compound naming

    • First element: write the name with the correct prefix based on subscript (never use mono)

    • Second element: write the name with the correct prefix based on subscript, change the ending to -ide (all prefixes are usable)

    • When there is o-o or a-o, first value is left out

  • Covalent Compound formulas

    • First element: write the symbol and add the subscript based on prefix (no prefix  = no subscript)

    • Second element: write the symbol of the second element and add the subscript based on prefix

    • DO NOT REDUCE THE SUBSCRIPTS

  • Binary acids do not contain oxygen (HX)

    • Starts with the prefix hydro

    • Hydro_ic acid = -ide

  • Oxyacids contain oxygen (HXO)

    • Starts with the root of the anion

    • Never starts with hydro

    • _ous acid = -ite (sprite is delicious)

    • _ic acid = -ate (I ate something icky)

  • Hydrogen ions are added to the anion in order to make a neutral compound


























Chapter 21: Hydrocarbons

  • Hydrocarbons contain only 2 elements (hydrogen and carbon)

  • Simplest hydrocarbons are called alkanes

  • Mnemonic for the first four prefixes

    • Monkeys - Meth (1)

    • Eat - Eth (2)

    • Peeled - Prop (3)

    • Bananas - But (4)

  • Alkanes formula: CnH2n+2

  • Alkenes formula: CnH2n

  • Alkynes formula: CnH2n-2

  • Alcohol formula: CnH2n+1OH

  • Unsaturated: if bond contains double/triple bonds

  • Saturated: if bond contains only single bonds

  • Straight-chain Hydrocarbons: contains any number of carbon atoms, one after the other, in a chain pattern

  • Cyclic Hydrocarbons: form a ring (draw a polygon with n sides), add prefix cyclo, do not follow alkane formula

  • Cyclic Alkanes

    • Cyclopropane

    • Cyclobutane

    • Cyclopentane

    • Cyclohexane

    • Cycloheptane

  • Aromatic Compounds: contain the benzene ring

    • Typically used to make dyes/moth repellent

  • Alcohol covalent bonding occurs with carbon, not ionic bonding with a metal therefore not basic

  • To name alcohols, drop the -ane, add -anol

  • ACIDS - If the compound starts with H; Use the naming acids rules. 

  • ORGANIC - If the compound starts with C and contains quite a few H’s and perhaps some O’s;  Use the naming organic compounds rules. 

  • IONIC - if the compound starts with a metal or ammonium ion, it is most likely ionic;  Use the naming  ionic compounds rules. 

  • COVALENT - If the compound starts with a nonmetal other than H or C; use the naming binary molecular compounds rules.










8.3: Molecular Structures

  • How to draw Lewis Structures

    • Sum the valence electrons from all the atoms.

      • If it is an ion  - add an electron for each negative charge and subtract an electron for each positive charge. 

    • Divide your sum by 2 to figure out the number of pairs 

    • Determine your central atom - it is the least electronegative element (Usually occurs first and least in the formula)

    • Write the symbol for the central atom and connect the terminal ends (bonded atoms) with single bonds.

      • NOTE: Hydrogen can NEVER be the central atom

    • Complete the octets of atoms bonded to the central atom

      • NOTE: Hydrogen can only have a duet.  It’s special like that. 

    • If there are leftover pairs of electrons  - place them on the central atom 

      • NOTE: Central atom can hold more than an octet ONLY if the element is from periods 3-7

    • If you don’t have enough electrons to give the central atom an octet - try using multiple bonds

  • Resonance: a condition that occurs when 2 or more valid structures can be written




























8.4: Molecular Geometry

  • VSEPR Theory: Valence Shell Electron Pair Repulsion

    • After pairing electrons repel each other in molecules

    • Unshared pairs (lone pairs) exert a greater repulsion force, they take up more space

  • How do you determine the geometry of a molecule?

    • Draw the Lewis structure

    • Add up bonding pairs & lone pairs on the central atom

    • Count double/triple bonds as ONE BOND 

  • Molecular geometry is determined by the ratio of bonding pairs to lone pairs

  • Electron geometry is determined by the amount of bonds or lone pairs coming off the central atom

  • Linear

    • 2 bonding pairs, 0 lone pairs

    • 180 degrees

    • Molecular geometry: linear

    • Electron geometry: linear

  • Trigonal Planar

    • 3 bonding pairs, 0 lone pairs

    • 120 degrees

    • Molecular geometry: trigonal planar

    • Electron geometry: trigonal planar

  • Tetrahedral

    • 4 bonding pairs, 0 lone pairs

    • 109.5 degrees

    • Molecular geometry: Tetrahedral

    • Electron geometry: Tetrahedral

  • Trigonal Pyramidal

    • 3 bonding pairs, 1 lone pair

    • 106.7 degrees

    • Molecular geometry: Trigonal pyramidal

    • Electron geometry: Tetrahedral

  • Bent

    • 2 bonding pairs, 2 lone pairs

    • 104.5 degrees

    • Molecular geometry: Bent

    • Electron geometry: Tetrahedral

  • Trigonal Bi-Pyramidal

    • 5 bonding pairs, 0 lone pairs

    • 120 degrees equatorial, 90 degrees axial

    • Molecular geometry: Trigonal bi pyramidal

    • Electron geometry: Trigonal bi pyramidal

  • Octahedral

    • 6 bonding pairs, 0 lone pairs

    • 90 degrees

    • Molecular geometry: octahedral

    • Electron geometry: octahedral

  • Seesaw

    • 4 bonding groups, 1 lone pair

    • 90 and 120 degrees, 173 degrees axial

    • Molecular geometry: seesaw

    • Electron geometry: trigonal bipyramidal

  • T-shaped

    • 3 bonding groups, 2 lone pairs

    • 90 degrees, 175 degrees axial

    • Molecular geometry: t shaped

    • Electron geometry: trigonal bipyramidal

  • Square Pyramidal

    • 5 bonding groups, 1 lone pair

    • 90 degrees

    • Molecular geometry: square pyramidal

    • Electron geometry: octahedral

  • Square Planar

    • 4 bonding groups, 2 lone pairs

    • 90 degrees

    • Molecular geometry: square planar

    • Electron geometry: octahedral
























8.5: Bond Character & Molecular Polarity


  • What determines molecular polarity?

    • Bond Character (evaluated using electronegativity)

    • Shape/symmetry of the molecule

  • Nonpolar Covalent: equal sharing (Zero)

  • Polar Covalent: unequal sharing because of electronegativity differences(Greater than zero, less than 1.7)

  • Ionic: complete transfer of electrons (Greater than 1.7)

  • Electronegativity: measure of the ability of an atom to attract electrons to form chemical bonds

    • More electronegative atoms have a greater pull on the electrons in their shared bond

  • Ionic Bond - the electrons completely taken by the nonmetal from the metal therefore there is a large difference in electronegativity

  • Covalent Bond - electrons are shared between two nonmetals, there is a smaller difference in electronegativity

  • Bond character is determined by calculating the electronegativity difference between both bonded atoms

  • All of the terminal atoms must be identical, if it is linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral, then its nonpolar

  • Square planar is the only structure that is symmetrical and has lone pairs

  • Shapes are not symmetrical when the central atoms have lone pairs or different terminal ends

  • Bent, trigonal pyramidal, seesaw, t shaped, and square pyramidal will be polar

  • Covalent bonds are strong but intermolecular forces are weak, therefore..

    • They have lower melting/boiling points

    • Many exist as gases or they vaporize easily

    • Relatively soft in solid state

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