Matter, Motion, and Entropy: A Review Answers will appear as you click. This is set up as a slide show so it will not print. CHM 102 Sinex

What is the difference between an atomic and molecular substance? Atomic single atom He Ar Fe Molecular multiple atoms N 2 CO 2 C 6 H 12

Describe the types of motion Translational Rotational Vibrational motion that changes the shape of the molecule – stretching, bending, and rotation of bonds whole atom or molecule changes its location in three dimensional space whole molecule spins around an axis in three dimensional space Motion of whole molecule  Motion within molecule

Which type of motion contributes the most to the entropy of a substance? Which type of motion is the cause of collisions? Which type of motion influences the orientation for an effective collision? Translational motion Rotational motion

MatterMode StateTypeTranslationRotationVibration Gas AtomicYesNo MolecularYes Liquid AtomicYesNo MolecularYes Solid AtomicNo Yes MolecularNo Yes Types of Motion and the States of Matter

Vibration Minimum number of atoms How atoms are connected What changes? Stretching2 Bond length Bending3Bond angle Internal rotation 4 Torsion angle Types of Vibrations

In solids such as the carbon tetrahedron from the diamond structure, how would you describe the motion of the atoms? As the carbon atoms vibrate, all the bond lengths vary about an average value.

Describe all the modes of vibration in each of the molecules. N2N2 CO 2 C 4 H 10 stretching only stretching, both symmetric and asymmetric, and bending stretching, bending, and internal rotation Which molecule has the highest entropy?

What hinders internal rotation in a molecule? Double or triple bonds Bulky groups in certain positions on some molecules Ring formation - cyclic molecules Sometimes hybrid orbitals (lone pairs of electrons) on single bonds such as hydrogen peroxide Molecules bound in a crystalline solid Examples are shown on the following three sides!

Twisting vibration around double bond in ethene, C 2 H 4 Two methyl groups (-CH 3 ) on biphenyl Click to view Chime structure of lowest energy stateChime structure Click to view a movie of the vibration movie Chime Guide

Restricted internal rotation or twisting vibration in ring Hydrogen peroxide, twisting motion along single bond C 6 H 12 Click here for Chime structure – you will need to right click on the Chime structure and click on animationChime structure Click here for Chime structure – you will need to right click on the Chime structure and click on animationChime structure H 2 O 2 has a permanent dipole moment  = 2.0 D

Molecules in solid CO 2 – note the tight packing of molecules How would larger molecules ever move around? Hexane, C 6 H 12, in the solid state – note the straight chain arrangement of the molecules Space- filled From: Roland Boese per. comm. Chime structure

Does the phase make a difference in biphenyl? Both rings in the same plane 40 o angle between rings still allows pi clouds to interact solidgas Chime structure

What is the cause of the entropy of solid carbon monoxide? Vibrations and arrangement of the molecules of CO

S total = S trans + S rot + S vib S trans > S rot >> S vib Why do solids have low entropies? How do impurities in a solid influence the solid’s entropy? Impurities cause an increase in entropy.

Here is a crystal of the mineral zircon. Click on the image, and radioactive decay will occur. How does entropy change? The decay particle causes a zirconium ion to recoil and it disrupts the structure which slowly recovers. In the end, the crystal structure becomes more disordered or  S > 0. Source: ZrSiO 4

Proteins – long chains of amino acids How does the entropy change as the chain takes the form of a helix? helix* chainchain*  S < 0 due to limited internal rotation in hydrogen-bonded helix (secondary structure of protein) coiling of 10 glycine chain *Chime structures