CEM141 Recitation #9

Boiling and Melting Points Chart Observation
- The melting and boiling points can be categorized into two key groups based on their temperatures. There are elements with relatively low temperatures and those with relatively high temperatures.
Chart of Elemental Forms
Elemental Form
Melting Point (K)
Boiling Point (K)
H2
13.81
20.28
He
0.95
4.22
Li(s)
453.7
1615
Be(s)
1560
2744
B(s)
2348
4273
C(s)
3823
4098
N2
63.15
77.36
O2
54.36
90.20
F2
53.53
85.03
Ne
24.56
27.07

Elemental Forms with Low Melting and Boiling Points
- Elements: H2, He, N2, O2, F2, Ne
- Type of Element: All are nonmetals.
Bonding and Interactions During Phase Change
- Type of Interaction Overcome: London Dispersion Forces (LDF) are the interactions that are overcome during phase changes for the listed elemental forms.

Elemental Forms with High Melting and Boiling Points
- Elements: Li, Be (both are metals), B (nonmetal, metalloid), C (nonmetal).
Bonding and Interactions During Phase Change
- Types of Bonds/Interactions Overcome: Covalent bonds for B and C; metallic bonds for Li and Be.

Bonding and Intermolecular Forces Prediction Per Element

The table below summarizes the expected types of bonding and intermolecular forces (IMF) for each element.

Elemental Form	Melting Point (K)	Boiling Point (K)	Type of Interaction Overcome	Form of Matter
H2	13.81	20.28	LDF	Small molecules
He	0.95	4.22	LDF	Small molecules
Li(s)	453.7	1615	Metallic	Discrete atoms
Be(s)	1560	2744	Metallic	Discrete atoms
B(s)	2348	4273	Covalent	Extended network
C(s)	3823	4098	Covalent	Extended network
N2	63.15	77.36	LDF	Small molecules
O2	54.36	90.20	LDF	Small molecules
F2	53.53	85.03	LDF	Small molecules
Ne	24.56	27.07	LDF	Discrete atoms

Extended Network
- The term “extended network” refers to substances such as B, C, and the metals Li and Be where atoms are bonded in a continuous network, resulting in solid forms at room temperature.
- Liquid and/or Solid States - Do these elements have LDFs? Yes (for small molecules), No (for extended network or discrete atoms).

Identifying Patterns
- Elements with very high melting and boiling points are typically classified as extended network solids.
- The high melting and boiling points are attributed to strong interactions: metallic bonds and covalent bonds.
- Conversely, the lower melting and boiling points of certain elements correlate with their nature as discrete atoms or smaller molecules that are held together by relatively weak LDFs.
Explanation of Observed Patterns
- Extended network solids exhibit higher melting and boiling points because they are governed by strong metallic or covalent interactions that require significant energy to break.
- In contrast, LDFs are considered weak, resulting in less energy needed to overcome these forces when phase changes occur.
- Specifically, during the phase changes, it is LDFs that are broken, rather than the bonds holding the molecules together.

Comparison of Nitrogen and Carbon
- Nitrogen (N2): Exists as a gas at room temperature.
  - The intermolecular interactions are governed by LDFs, which arise from momentary fluctuating dipoles inducing dipoles in neighboring molecules.
- Carbon (C): Exists as a solid at room temperature.
  - Strong, localized interactions through covalent bonds bind the carbon atoms together.
- At room temperature, sufficient energy is available to overcome the LDFs holding the nitrogen molecules together; however, the energy is not adequate to break the covalent bonds in the carbon lattice, thus maintaining its solid state.