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Review of Basic Chemistry and Geology
Published in Arthur W. Hounslow, Water Quality Data, 2018
Covalent bonds result from the equal sharing of electrons. An example is two atoms of the same element such as Cl2, H2. As two hydrogen atoms are brought together there is a decrease in energy as the electrons approach one another until a minimum energy is attained. This distance of minimum energy is the bond distance. At closer distance the energy rises abruptly because of the repulsion between the nuclei. Covalent compounds are true molecules held together by strong intramolecular forces. These forces must be distinguished from the intermolecular forces, which hold the molecules together in either the liquid or solid states.
Introduction
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
Chemical bonds between two or more atoms in a molecule are referred to as intramolecular forces. They are generally categorized as ionic, covalent, or metallic. These are the bonds that are broken and reformed during a chemical reaction. Significantly lower in strength are intermolecular forces. Intermolecular forces are generally attractive forces that exist between and among molecules of all shapes, sizes, and masses. They exist in the gaseous, liquid, and solid phases, as well as in the solution phase, where water is acting as the solvent to hydrate the solute.
Molecular engineering activity for chemistry teacher education: An interactive simulation on cellulose dissolution in ionic liquids
Published in Yuli Rahmawati, Peter Charles Taylor, Empowering Science and Mathematics for Global Competitiveness, 2019
A. Mudzakir, Hernani, T. Widhiyanti, L. Lokollo
Intermolecular force is the force of attraction between molecules, and intra-molecular force is the force between atoms in a molecule. Intramolecular forces affect the chemical properties of a substance, while intermolecular forces affect the physical properties of a substance. In general, intermolecular forces are weaker than intramolecular forces. The types of intermolecular forces are Van der Waals forces, ion-dipole forces, and hydrogen bonds (Jesperson & Brady, 2012; Chang & Overby, 2011).
Diffusion characteristics of asphalt rejuvenators based on molecular dynamics simulation
Published in International Journal of Pavement Engineering, 2019
Meng Xu, Junyan Yi, Decheng Feng, Yudong Huang
It needs to be noticed that the diffusion coefficients of unaged and short-term aged asphalt have an abnormal decrease at 0 °C. As presented before, the molecular force and thermal motion were regarded as the main influencing factors to the diffusion behaviours of materials. There are two kinds of forces in a molecule: intramolecular and intermolecular forces. The intramolecular forces are defined as the interactions of holding together the atoms of a molecule, while the intermolecular forces describe the attractions between molecules and ions. It can be concluded from Figures 8–10 that the intermolecular forces mainly affect the diffusion process. Therefore, both of the molecular thermal motion and intermolecular forces were the key factors influencing the diffusion of asphalt and rejuvenator. When temperature increases, the molecules of the material could obtain enough energy to overcome/weaken the intermolecular forces, then move further apart and this may induce the phase change of material. However, the increase of temperature is able to improve the thermal motion of molecules. Therefore, the diffusion behaviours of asphalt binders with different ageing conditioning (unaged, short-term aged and long-term aged) are always combined effects of the intermolecular forces and thermal motions. When temperature is low (−25 °C for example), the thermal motions of molecules are weak. The diffusion behaviour of asphalt is determined by the intermolecular force. After the continual rise of temperature, the effect of intermolecular force is reduced, while the effect of thermal motion is improved. Because the unaged and short-term aged asphalt have the less asphaltenes molecules with strong chemical polarity, the intermolecular force is easily reduced along with the increase of temperature. At the same time, the asphalt still behaves like a mixture of solid and viscoelastic liquid at the temperature range from −25 to 0 °C, and the thermal motion of molecules caused by the increase of temperature for unaged and short-term aged asphalt may just have a limited increase. Therefore, when considered the combined effects of thermal motion and intermolecular force, the diffusion coefficients of unaged and short-term aged asphalt may decrease at 0 °C.