Chapter 3 - Kaplan MCAT Gen Chem Review

2025-2026

elements come together to form

molecules

molecules are held together by

chemical bonds

chemical bonds are formed via

valence electrons

atoms usually bond to ___ rule

octet

incomplete octet

elements stable with fewer than 8 in valence

expanded octet

-can hold more than 8 in valence

-any element in period 3 or greater

molecule with an odd number of electrons cannot

distribute to give 8 to each

ionic bond

electrons from an atom with low ionization energy are transferred to an atom with high ionization energy

the ions in an ionic bond are held together by

electrostatic attraction between the opposite charges

__ bonds create a lattice of rows of cations and anions (in solid state)

ionic

in the lattice structure of ionic bonds, the attractive forces between + and - ions are ______

maximized

ionic bonds are usually formed between ___ and ___

metals and nonmetals

EN

electronegativity

covalent bond

electron pair is shared between 2 atoms with similar electronegativities

bond order

number of shared electron pairs between 2 atoms

bond length

avg distance between the 2 nuclei of atoms in a bond

more shared electrons =

-smaller bond length

-more energy needed to break

bond energy

energy required to break a bond by separating its components into their isolated, gaseous, atomic states

greater bond energy =

stronger bond

nonpolar

electron pair shared equally

types of covalent bonds

-nonpolar

-polar

-coordinate covalent

nonpolar bonds occur when the atoms have

nearly identical electronegativities

diatomic molecules

only 2 atoms bonded (H_2, CL_2, N_2)

polar

electron pair shared equally

polar bonds occur when atoms have

-moderately different electronegativities

-one atom partially neg, one partially pos

in a digram for a polar bond, arrow points toward

negative end

dipole moment of polar bond formula

p=qd

p=qd meaning

p=dipole moment

q=magnitude of charge

d=displacement vector separating 2 partial charges (in debye units, coulomb-meters)

coordinate covalent

if both electrons are contributed by 1 atom

coordinate covalent bonds are indistinguishable from

other covalent bonds

coordinate covalent bonds are typically found in

lewis acid-base reactions

lewis dot diagram rules

-H always in terminal position

-halogens usually in terminal position

-least electronegative atom central

formal charge

difference between ‘the number of electrons assigned to an atom in a lewis structure’ and ‘the number of electrons normally found in that atoms valence shell’

formal charge formula

V-(N_nonbonding)-(1/2)(N_bonding)

V-(N_nonbonding)-(1/2)(N_bonding) meaning

V = normal # of electrons in atoms valence shell

N_nonbonding = # of nonbonding electrons

N_bonding = # of bonding electrons (double the # of bonds)

charge of an ion/compound

the sum of the formal charges of the atoms comprising it

resonance structures

same arrangement of atoms but different placement of electrons

valence shell electron pair repulsion (VSEPR)

-uses lewis dot structures to predict the molecular geometry of covalently bonded molecules

-arranges electron pairs around central atom

electric geometry

spatial arrangement of all pairs of electrons around the central atom, including the bonding and lone pairs

molecular geometry

the spatial arrangement of only the bonding pairs of electrons

coordination number

the number of atoms that surround and are bonded to a central atom

no net dipole moment=

bond dipoles cancel each other out, nonpolar

net dipole moment=

bond dipoles do not cancel each other out, polar

bonding orbital

forms when the signs of the 2 atomic orbitals are the same

antibonding orbital

forms when the signs of the 2 atomic orbitals are different

sigma bond

when orbitals overlap head-tohead

sigma bonds (do / do not) allow for free rotation

do

pi bond

when orbitals overlap so that there are 2 parallel electrons around cloud densities

π bonds (do / do not) allow for free rotation

do not

london dispersion forces

the attraction or repulsive interactions of the short-lived and rapidly shifting dipoles

if electron density is unequally distributed it causes

formation of short-lived dipoles

london dispersion forces are a type of

van der waals force

weakest intermolecular attraction

london dispersion forces

london dispersion forces are only significant when molecules are ____

in close proximity

if molecule is more easily polarizable, it posesses (larger/smaller) dispersion forces

larger

dipole-dipole interactions

in polar molecules, pos region of one molecule is close to neg region of another

dipole-dipole interaction vs london dispersion forces

duration

dipole-dipole interactions are denoted by

dashed lines, indicating temporary

hydrogen bonds

pos charged hydrogen atom interacts with the partial neg charge of Fluorine, Oxygen, or Nitrogen on nearby molecules

hydrogen bonds are an unusually strong form of

dipole-dipole interaction

hydrogen bonds may be ____ or ____

intra- or intermolecular

strongest intermolecular attraction

hydrogen bond