ME115 - Interatomic Spacing

What is interatomic Spacing?

The natural spacing between the center of two atoms.

What is binding energy?

The energy required to separate two atoms from their equilibrium spacing to an infinite distance apart.

1: No interaction, energy is near 0
2: Attractive forces dominate, energy is dropping as the bonds are formed
3: Equilibrium spacing. Actual interatomic spacing
4: Atoms past equilibrium, repulsion pushes atoms away.

IAE GRAPH: What does a steep, narrow well mean?

High Young’s Modulus (E)
atoms strongly resist small changes in spacing

IAE GRAPH: What does a shallow, wide well mean?

Low Young’s Modulus (E)
atoms move more easily

What is the Coefficient of Thermal Expansion (CTE)?

How much a material changes in size per unit change in temperature.

IAE GRAPH: If the well is more asymmetric, what happens?

Higher CTE
atoms shift to larger average spacing when heated

more expansion

IAE GRAPH: If the well is more symmetric and steep, what happens?

Lower CTE
the average spacing changes less

less expansion

What is the derivative (slope) of the stress-strain curve?

Young’s Modulus

What is the derivative (slope) of the IAE graph?

Interatomic force

What is the derivative (slope) of the force-distance curve?

Bond stiffness (which is only related to young’s modulus close to the minimum of the IAE graph or the point of inflection of the bond stiffness graph)

What does strong bonding indicate?

High Binding Energy, Melting Point

Large force to stretch bond

Large slope

High modulus of elasticity

What does weak bonding indicate?

Low binding energy, melting point

Small force to stretch bond

Small slope

Low modulus of elasticity

Read the graph

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