Unit 2: Molecular and Ionic Compound Structure and Properties

2 main types of bonding

INTRA and INTER

INTRA meaning

within (inside) compounds,

Ionic bonding

metal plus nonmetal, giant lattice of ions

Covalent bonding

nonmetal plus nonmetal, discrete molecules

Dative or Coordinate bonding

(e- deficient species)

Discrete molecules

INTER meaning

(interactions between covalent molecules)

ALL WEAK, but HB is strongest

interbonding strongest to weakest

HB, dipole dipole, LDF

Hydrogen Bonding

(attached directly to N O F)

permanent dipole

Dipole- Dipole

(polar molecules)

permanent dipoles

London Dispersion Forces

(non-polar molecules)

induced dipoles

Inter bonding is based on…

… the Coulombic attractions between opoosite charges

atoms in a cov bond:

: pair of e- shared by atoms, each atom in the bond as electronegativity

electronegativity

ability of an atom w/in a cov bond to attract e- to itself

most electroneg element

flourine

if pair of atoms that are cov bonded hv same electroneg…

…e- in bonds equally shared, is NONPOLAR

if one atom has much higher electroneg than other…

…e- are more attracted towards the MORE ELECTRONEG atom

e- cloud is distorted, e- charge density is redistributed

Dipole

Creation of opposite charges at either end of the molecule, bond is POLAR COVALENT

presence/lack of dipoles and intermolecular coulombic attraction between atoms…

…determines type of IMF present in cov bonded compounds

IMF type can influence properties

Discrete molecules

cov bonding, when Ve- are shared

one shared pair of e-

single bond

two shared pairs of e-

double bond

When are atoms attracted to each other?

When outer e- of 1 atom are electrostatically attracted to nuclei of another atom

When attraction between two atoms is stable…

…gives lower potential energies

When is PE raised and atoms become less stable in a bond?

When atoms get too close to each other

nucleis start to repel each other

So when is a bond ofmred?

when the distance between the atoms hv the forces of attraction and repulsion resulting in the lowest most stable potential energy

bond length

a distance where forces of attraction and repulsion= most stable PE

Bond strength

potential energy when bond length distance

the greater the # of e- invlved…

the strongewr the attraction

shorter the bond length=

= stronger bond strength

Bond dissociation energy (BDE)

strength of the bond in a diatomic covalent molecule

“ X kJ of energy put in OR released to break/make the bond”

pos sign in bond energy

addition of energy, endothermic= energy needed to break a bond

neg sign in bond energy

release of energy, exothermic= bond is being made

Ionic bonding involved…

transfer of e- between atoms to form ions

where to find metals on pt?

on the left

where to find nonmetals on pt?

on the right

ionic bond usually formed between…

…. a metal and nonmetal

ionic bonds

strong electrostatic forces between charged particles

ionic bond is strong because…

… electrostatic forces are large

CONCEPT: Coulombs law and ionic bonds

CONCEPT:

C’s law predicts that force INC w/ INC charge and DEC distance between charges, so strongest ionic bonds are formed between ions that are small and highly charged

ions that are highly charged aka…

aka high charge densities

how are ions held in an ionic solid?

rigidly, in fixed position, 3D lattice

ionic solid compound properties

not malleable, ductile, tends to be brittle

cleaves when ordered structure is disrpted

high melting and boiling points, low volatility, low vapor pressures

When are ionic substances able to conduct electricity?

when liquid or in solution (aq)

idea of “like dissolves like”

ionic solid dissolves, polar water molecules attracted to opp charged ions and get into the lattice

forces of attractions formed when ionic solid dissolves

ion to dipole

name when ion to dipole

hydration

ions are HYDRATED, becoming free to move= can conduct electricity

if cation is small and highly charged…

…has ability to distrot charge cloud around anion

Fajans rule

A principle used to predict whether a bond will be covalent or ionic based on the charges and sizes of ions. It states that if a cation is small and highly charged, and the anion is large and polarizable, the bond is more likely to have covalent character. This occurs due to the cation's ability to distort the electron cloud of the anion, leading to shared electron characteristics.

what does fajans rule help with?

assess degree of distortion

degree of distortion

polarization

distortion at a max when:

1. cation is small and highly charged (high charge density)

2. anion is large and highlyu charged (e- more loosely held)

less electroneg symbol

Delta ( not triangle but S) +

more electroneg symbol

Delta (S) -

Pauling scale of electronegativities

Developed by Linus Pauling, this scale assigns values to elements, with higher numbers indicating stronger electronegativity. The range typically goes from 0.7 (for cesium) to 4.0 (for fluorine), helping predict bond types and molecular behavior.

CONCEPT: greater diff in electroneg…

…more like ionic compound!

CONCEPT: a diff of 1.7 approc marks…

boundary betweeen predominately ionic or covalent

gen rule for expanded octet:

only avaible to those in the third period, Expanding the octet is possible whenever the molecule has a 3p subshell.

IF there is an extra ion when drawing LS…

… put it on the more ELECTRONEG element

If cannot determine central atom…

… usually least electroneg atom but NEVER hydrogen

non-bonding e-/e- pairs

any e- pairs that occur in valence shell of an atom but do not form a bond w another atom

dative/ co-ordinate bonding

(e- deficient species only)

a new shared pair/cov bond made up by using both e- from one species rather than one from each species as in a norm cov bond

What determines a substance’s polarity?

bonds w/in molecules must carry diff charges (dipole moment MUST exist) AND the dipoles that are present MUST NOT cancel out due to symmetry

how to indicate dipole moment

indicated by an arrow that points toward neg charge center, tail of arrow indicating pos charge center, or by using delta+/- to indicate areas of pos/neg charge

Valence Shell Electron Pair Repulsion theory

VSEPR,

shapes of cov bonded molecules and ions can be determines by considering number of e- pairs(e- domains) around CENTRAL atom

A non-bonding pair repels ___ stronglyu than a bonding pair

MORE

when predicting shape, triple and double bond=

= “one” bonding pair

2 0

linear

2 0 bond angle

180

3 0

Trigonal Planar

3 0 bond angle

120

2 1

bent

2 1 bond angle

slightly less than 120

4 0

tetrahedral

4 0 bond angle

109.5

3 1

trigonal pyramidal (lone pair on top, three on bottom

3 1 bond angle

107.5

2 2

Bent (the second one)

2 2 bond angle

104.5

5 0

trigonal byramidal (like a diamond)

5 0 bond angel

120 in plane, 90 perp to plane

4 1

SEESAW !!!!! (lone pair on top)

4 1 bond angle

complex (lol)

3 2 (Three to…)

T-shaped

(three to T)

3 2 bond angle

approx 90 for T

2 3

linear (second one)

2 3 bond angle

180

6 0

octahedral (6=8=oct)

6 0 bond angle

90 (oct)

5 1

square pyramidal (lone pair on bottom)

5 1 bond angle

approx 90 (sqPy)

4 2

square planar

4 2 bond angle

90 (sqPl)

# of e- domains (bond and lone pair)=

sum of s and p orbitals

weird not right but works rule for finding hybridization:

count totall number of e- domains then subtract one to get spX or sp3d (if 4 e- domains)

hybridize/hybridization

process of mixing

type of bonds used to form final molecule when terminal atom joins central atoms hybridizedd orbitals:

simple sigma bonds

hybdrization nummber tupes

sp, sp², sp³, sp³d

sigma covalent bond

when two dumbell 2p orbistals that are incomplete overlap their heads tgt

pi bond

when sideways overlap of other p orbitals

only sigma bonds…

…single bonds