Nanoscale material

• Form– Nanoparticles

– Nanotube(strong)

– Nanofibre

Different behaviour than bulk form

melting pt lower/colour

Chemical reactivity

Electrical and thermal conductivity

Example from nature: Lotus effect(nano crystal on bumps of leave)

Cause of special property

- Quantum effect apparent at nano scale

tunneling effect

increase surface to volume ratio

• Application–Water repelling/water attracting=>self cleaning surfaces–Electronics = Quantum dot LED(QLED)–Nano-sized catalyst–Naosize drugs for easy absorbtion/through skin

Hazard-Can be very toxic due to reactivity

Easily enter body by penetrating skin/cell membrance

Nano-pollution to environment-difficult to remove/potential ecological impact

Atomic model• Thomson Plum Pudding model

– An atom is an uniform sphere of positive charge with electrons embedded in it so overall charge neutral• Rutherford’s model (deduced from Scattering experiment)

– Tiny core where most mass and all positive charge is concentrated.– Atom is mostlt empty space with –ve e orbiting the nucleus

Limitation: Stability of atom contradicts theory (accelarating e should loss energy by emitting radiation)

Line spectrum show discrete lines =>e can be only in certain orbits(not limited in Rutherford model)**other scattering experiment lead to discovery of proton & neutron

Bohr’s hydrogen ATOM Model-Assumption:

– Classical circular motion and electric force still applies– E can only orbit nucleus in certain orbits and do not radiate while accelerating– Angular momentum L is quantised and can only be multiple of h/2pi

mevrn = nh2π

- H atom absorbs or emits radiation in form of a photon when it jumps from one level to another

– rn n2

Photoelectric effect• Emission of electron from metal surface upon illumination by em wa

ve(usually UV)– KEmax= eVs

• Finding that wave theory cannot explain– No PE effect if frequency below a threshold– Immediate response (emission of e upon radiation)– Frequency of uv light ↑ KE↑; K independent of intensity– ***Wave Theory can only explain one observation:

• Intensity of light ↑ Photoelectric current↑

– =>dual particle and wave nature of light– Photon is an energy packet of em wave; – Power = nhf;– Ip =ne