2.1: atoms electronic structure and bonding

materials are made from

atoms

parts of an atom

• electron clouds

  • mostly empty space

• nucleus

  • protons and neutrons

  • most mass

electrons

primary atomic specise contributing to bonding

• mechanical properties

• crystal structure

• + more

electronic properties

optical properties (light is electromag wave)

magnetic properties

quantum #s

Principal (n)- distance of electrons from nucleus

Azimuthal (I)- shape of orbital\

Magnetic (m1)- orientation of orbital

spin (ms)- orientation of spin

Electron shells

principal quantum #

• higher n-value

  • further from nucleus

• valence sheels

  • shells furthest from nuclues

• core shells

  • inner shells

Shape

2nd Q#s

• s- sphere

• p - not a sphere

• d- not a sphere

Octet rule

atoms prefer to be in a state with access to 8 valance electrons wihch drive periodic and bonding trends

orbitals filled

highest energy last

orbital bonding

farther distance from nucleus you bond first

what are d and f shells good for

magnetism

• elemetns with unpaired electrons have high magnetic spin, which can result in higher saturation magnetiszation and higher remnance

fluorescence (immediate) & phosphoresence (sustained)

• d and f orbitals can have split energy levels due to atom-atom interactions. if light elevates an electron to a higher energy level it will relax back down and release light

• more atoms= more split

to have high saturation and higher remance

you need unpaired electrons

atomic bonding

determined by electronegativity difference

electronegativity

• increases from left ot right

• increases bottom to top

• attoms that want to reviece an electron are going to be more electronegative (want to be noble gas configuration)

• atoms that want to lose an electron to have noble gas configuration is less electronegative

pure covalent`

0 delta en

0% ionic

non-polar covalent

0-0.4 dellta en

0-4% ionic

polar covalent

0.4-2.0

4%-63%

ionic

>2.0

>63%

ionic bonds

• electrons transfered forming ions

• cation (+) attracting anion (-)— coulombic/electrostatic attraction

electrostatic in other bonds

primary driver in metallic and vanderwalls forces

partial role in all but 100% covalent bonds

coulombs law is used to

predict bond strength

repulsive forces

pauli exclusion

coulombic repulsion (e-e repulsion, nucleus-nucleus repulsion)

same for all bond types

ionic bonds have the same energy regardless of

orientation (it is non-directional)

plastic deformation of ionic bonding

like charges are lined up and they hate it

massive repulsion with higher energy

fracture with extreme repulsion

why ceramics fracture

covalent bond

• electrons shared between neighbor atoms

• result of orbital overlap between unfilled valence orbitals

  • can have partial overlap

• polymers and semi-conductors

• generally strong

hybridization

many common covalent rely on different types of orbitals overlapping to create hybrid orbitals

mixed orbitals have non-sphereical electron density

• directional bonds

• have fixed bond angles

covalent bonding is

directional

metallic bonds

• valance shell electrons are delocalized and shared among entire solid

• bonding is a result of atomic cores (nuclei + inner shells) floating in a jellium of valance electrons

• metals

metallic bonds are

non-directional

plastic deformation in metals

jellium doesnt care, it cant even tell if it was shifted

• atoms can slide past e/o to form bonds in new ares of jellium

• allows for it

• metals dont shatter when dropped- it bends

metallic solid density; pack spheres to

maximize space filling 74%

ionic solid density; pack spheres to _____ but

maximize space filling BUT limited efficiency due to size mismatch of cations and anions

67%

covalent soilid density

more complex open structures determined by fixed bond angle 34%

metallic and ionic are

both non-directional bonding

Van der waals forces

secondary bonding

MUCH WEAKER

due to electrostatic attraction

• london dispersion forces (two instantaneous/induced dipoles)

• dipole-diple (two permanent)

• dipole induced dipole

london dispersion forces (PET ex)

• weak bonds that form between two instantaneous/induced dipoles

• partial plus and minus

1. random flucuation in e- cloud create instantaneous dipole

2. indicuses dipole in other atom

3. weak electrostatic attraction formed

dipole-dipole

• paritail + and partial - alr present

• magnitute of pull is higher

• columbic attractino

• stronger than LDFs

dipole-induced bonding

• pvc and pet

• permanent dipole induces dipole in enighboring pet

• secondary bond is formed

polymers have such a low elastic moduli

connnected by weak-instantaneous van der walls attraction

polymers internal vs external bonds

internal bonds are covalent and strong internally

bonds between moleucles are extremely weak so they and weaker

permanent dipole is

stsiffer and stronger

less weak

elastic modulus of LDF and DD

• LDF- 0.8 GPA

• DD- 2.8 GPA

yeild strenght of LDF and DD

LDF- 28 MPa

DD- 52 MPa

strength of bonding strongest to weakest

strong

• covalent

• ionic

• metallic

weak

• hydrogen

• other van der waals

application of van der waals forces

gecko climbing on wall

graphene

selectivly break van der waals bonds