science 4

how do 3D molecular structures and electronegativity help predict intermolecular forces

they reeal molecular polarity, which helps identify the types and strengths of intermolecular forces

what are four ways to represent molecular structures

space filling models

ball and stick models

perspective formulars

lewis structures

why can single signma bonds rotate easily

sigma bonds have cylindrical electron density, allowing rotation without breaking the bond

why is rotation around pi bond difficult

rotation disrupts sideways orbital overlap, effectively breaking the pi bond

what happens to potential energy during C-C bond rotation

staggered conformations have lower energy

eclispsed conformations have higher energy

what do lewis structures and VSEPR

electron group geometry and molecular shape

what is electron group geometry

the arrangement of all electron groups around a central atom

what deterimes molecular shape

the arrangements of bonded atoms around the central atom

lone pairs affect the shape

how to determine hybridization from a lewis structure

count electron groups

2 = sp

3= sp2

4= sp3

what determines bond angles in a molecule

electron group geometry, molecular shape, and lone-pair repulsion

how to count sigma and pi bonds

single bond = 1 sigma

double bond = 1 sigma + 1 pi

triple bond = 1 sigma + 2pi

what is forma sharge used for

selecting the best lewis structure by favoring minimal formal charges and appropriate charge placement

what is the formal chrage equation

formal charge = valence electrons - nonbonding electron = ½ (bonding electrons)

what are hydrocarbon isomers

compounds with the same molecular formula but different structural arrangements

how do you determine bond polarity

compare electronegativies

electrons are pulled toward the more electronegative atom

how do you determine molecular polarity

consider bond dipoles and molecular geometry. if dipoles dont cancel, the molecule is polar

how do you identify electron density in a molecule

electron density shift toward more electronegative atoms, creating partial negative regions

what are london dispersion forces

attractions caused by temporary and induced dipoles

present in all molecules

what are dipole dipole interactions

attractions between the permanent partial positive and negative ends of polar molecules

what is hydrogen bonding

a strong dipole attraction when H bonded to N, O, or F interacts with N, O, or F

how do intermolecular forces affect boiling and melting points

stronger intermolecular forces generally produce higher melting and boiling points

what is the order of common intermolecular force strengths

LDF < dipole dipole < HD

how to identigy intermolecular forces between molecules of the same substances

all molecules: London dispersion

polar molecules: dipole-dipole

molecules with H bonded to N, O, or F: hydrogen bonding

How to predict differences in physical properties between substances

compare molecular structure, polarity, and intermolecular forces. stronger attractions generally mean higher boiling and melting points

what is the difference between covalent and ionic bonding

covalent bonds share electrons

ionic bonding involves electrostatic attraction between ions

what is the continuum of bonding

bonding ranges from pure covalent to increasingly ionic(unequal sharing)

why do metals form positive ions

metals tend to lose electrons, forming positively charged cations

why do nonmetals form negative ions

nonmetals tend to gain electrons, forming negatively charged anions

what is the structure of ionic compounds

repeating three dimensional crystal lattice of positively and negatively charged ions

why do ionic compounds have high melting and boiling points

strong electrostatic attractions between oppositely charged ion require substantial energy to overcome

why are ionic compounds hard and brittle

they resist deformation, but shifting layers brings like charged together, causing repulsion and cracking

how do coulombic interactions explain ionic versus molecular properties

ionic compounds have strong ion-ion attractions

molecular compounds have weaker intermolecular attractions