6. Atomic interactions Flashcards
What is the equilibrium distance?
internuclear distance at which Epot is the lowest : gives the bond length. It’s the distance at which Epot is the same as Ebinding
In what range is the bond energy for nuclear force?
MeV range
What is the dipole moment?
A measure of the separation of (+) and (-) charges. P=qd [Debye]
q : charge
d : distance of separation
What is a covalent bond?
Atoms are held together by electrons of molecular orbitals (especially valence e-). It can be single, multiple, triple, depending on the # of electrons shared.
What is a non-polar bond?
Electronegativity difference is lower than 0.6. Electrons are shared equally. Charge centers are symetrically arranged
What is a polar bond?
Elngtvty bw 0.6 and 2.1, electrons unequally shared, charge centers are not symmetrical, forming a dipole
What holds the atoms together in a metallic bond?
the interactions between the positive nucleus and the delocalized electron cloud.
What are 3 characteristics of the metallic bond?
Non transparent, ductile, electric conductivity
What holds the atoms together in the ionic bond?
coulombic forces of opposite charges
What is an ionic bond?
Engtivy difference is over 2.1, involves numerous atoms in a lattice structure
What is the lattice unit?
The minimum stoichiometric ratio of (+) and (-° charges that are periodically found in the crystalline structure
What is lattice energy?
energy required to break up 1 mole of a solid ionic compound into gaseous ionic constituents
Eb of dipole-dipole interactions
Eb = 0.003 - 0.02 eV
What are VDW interactions?
sum of attractive and repulsive interactions between 2 non polar participants. Caused by fluctuating polarizations (electron density)
Eb of VDW
Eb = 0.02 eV
Eb of H bonds
Eb = 0.2 eV
What is a hydrogen bond?
An interaction between a H atom covalently bound to a highly EN atom, and a lone pair of e- on another EN a tom
What is the typical bond distance for H bond?
0.23 to 0.35 nm
What does STM measure?
electric current between probe tip and sample
What is the role of the piezoelectric rod?
undergoes small changes in length when a current is applied to it
What is the feedback circuit for?
Amplifies signal coming from the tip and keeps the distance constant in cst height mode
What is electron tunnelling?
electron passing through a potential barrier : electron can go from A to B without extra E having been supplied
What are the 2 parts of the AFM probe?
cantilever and tip (radius 0.1nm)
Power of resolution of AFM
Depends on the tip.
Lateral : ~30nm
Vertical : up to 0.1nm
