Unit 6: Molecular Compounds

Atoms Monatomic = 1 atom

Molecules Molecule = 2 or more nonmetal atoms acting as a unit

Diatomic = molecules of 2 of the same atoms

Low melting and boiling points Do not conduct electricity in H2O Molecular Compounds Composed of molecules Low melting and boiling points Do not conduct electricity in H2O Gases or liquids at room temp 2 or more different nonmetals

Molecular Compounds Prefix system used

Molecular Compounds Prefix system used

Molecular Compounds Prefix1element1 prefix2element2 + -ide Except mono is never used on element1

Acids – 6 common Acids?

Common Acids Formula Name HCl hydrochloric acid HNO3 nitric acid H2SO4 sulfuric acid H2CO3 carbonic acid H3PO4 phosphoric acid HC2H3O2 acetic acid

electrons are shared between nonmetals in groups 4A,5A,6A,7A Covalent Bonding electrons are shared between nonmetals in groups 4A,5A,6A,7A

Rules for drawing Lewis structures Covalent Bonding Rules for drawing Lewis structures 1. Add valence electrons for all atoms

2. Write symbols for atoms to show arrangement of atoms Covalent Bonding 2. Write symbols for atoms to show arrangement of atoms C is always in the middle H is always outside Least electronegative atom is in the middle

3. Complete the octets of atoms bonded to central atom, except H Covalent Bonding 3. Complete the octets of atoms bonded to central atom, except H 4. Place leftover electrons on central atom 5. If central atom is incomplete try a multiple bond

Single Covalent Bonding bond in which two atoms share a pair of electrons Ex] H2

Single Covalent Bonding Structural Formulas - a shared pair of electrons are represented by a dash

Single Covalent Bonding Examples: Fluorine Dihydrogen monoxide Ammonia Carbon tetrachloride Phosphorous tribromide

Double and Triple Covalent Bonding Double bonds: share 2 pairs of electrons, (=) Triple bonds: share 3 pairs of electrons Examples: Nitrogen Carbon dioxide

Practice – Draw Lewis Structures Br2 SiCl4 HCl O2 HCN CO

Resonance Structures structures that occur when it is possible to write 2 or more valid lewis structures that have the same number of electron pairs for a molecule or ion Example - O3

Polyatomic Ions covalently bonded Examples: NH4+ SO32- ClO3-

Exceptions to the Octet Rule Some substances do not obey the octet rule and can have an incomplete or expanded octet Examples: BF3, PCl5, SF6, XeF4

Practice – Draw Lewis Structures SO2 SO42- H3O+ OH- BH3 XeF2 H2O2 NCl3 NO3-

Molecular Geometry Shape of a molecule is determined by the bond angle which is based on the number of electron domains in the molecule

Molecular Geometry A pair of electrons, single, double, and triple bonds each consist of 1 electron domain

1. Draw Lewis structure and count e-d’s Molecular Geometry To Predict Shapes: 1. Draw Lewis structure and count e-d’s 2. Predict bond angles and molecular geometry using table

Molecular Geometry

Molecular Geometry Examples: CO2 BF3 CBr4 PCl5 SF6

Molecular Geometry Practice: Predict Shape and Angle BeF2 BCl3 SiH4 AsF5 NO3- ClO4-

Intramolecular vs. Intermolecular Intramolecular Forces – forces within molecules – chemical bonds (ionic and covalent bonds) Intermolecular Forces (IMF’s) – forces between molecules – dispersion, dipole-dipole, hydrogen bonding

Intermolecular Forces Broken during phase change The stronger the IMF, the higher the mp/bp

Types of Intermolecular forces London Dispersion forces: All molecules can experience an instantaneous dipole moment based on polarizability Strength depends on MM

Types of Intermolecular forces dipole-dipole forces: polar molecules attract to each other when the positive end of one molecule is near the negative end of another Depends on polarity

Types of Intermolecular forces hydrogen bonding: attraction between the H atom in a molecule with H-F, H-O, or H-N and an unshared electron pair on N,F, or O

Types of Intermolecular forces hydrogen bonding:

Types of Intermolecular forces Strength of IMF’s: Dispersion < dipole-dipole < hydrogen bonding

Types of Intermolecular forces Identify the IMF in each: Ar H2O HCl CH3OH H2 HF H2S

Properties of Water

Unique Properties of Water 1. Hydrogen bonds cause density of solid H2O to be less than liquid H2O, so ice floats. 2. Hydrogen bonds cause high surface tension in water.

https://www.youtube.com/watch? v=Hm52rkh68JA Properties of Water https://www.youtube.com/watch? v=Hm52rkh68JA