Search results: van der waals

Most of the theories describing dynamical processes at surfaces rely on the validity of the adiabatic Born-Oppenheimer approximation. What does this mean? We have already seen that adsorption commonly is understood as the reversible binding of molecules and atoms from the gaseous or liquid phase on surfaces, mostly of highly porous adsorbent media. In chemisorption […]

In ‘Chemistry Essentials for Dummies‘, John T. Moore writes: Matter is anything that has mass and occupies space. It can exist in one of three classic states: solid, liquid, and gas. When a substance goes from one state of matter to another, the process is called a change of state, or phase change. As he […]

We usually think of crystals as composed of different atoms in certain proportions, this proportion being the molecular fórmula that represents the crystal. However, it is not surprising that any molecule could be the basis of a crystal structure, whether a simple molecule such as methane, or a complicated molecule such as a protein or […]

Adsorption commonly is understood as the reversible binding of molecules and atoms from the gaseous or liquid phase on surfaces, mostly of highly porous adsorbent media. In chemisorption a single layer of molecules, atoms or ions is attached to the adsorbent surface by chemical bonds; in physisorption only van der Waals forces are involved. The […]

What only a decades ago seemed impossible for chemists, determining the chemical structure of molecules directly from experimental images, is now routinely done. Not only that, the information about bond order, intermediates, and products of on-surface chemical reactions or charge distribution within molecules can also be quantified from those images. Two main techniques have made […]

Beginning in 1928, Felix Bloch, an assistant to Werner Heisenberg in Leipzig, began to make some realistic assumptions in an attempt to formulate a more complete quantum mechanics of electrical conductivity. First, because he wanted to assign a definite momentum and energy to each of the electrons, but not a definite position or a time […]

A visionary perspective of molecular electronics is the use of single molecules as functional entities in electronic devices. In this context, some of the most important components are molecular switches, which are molecules that can be interconverted reversibly between at least two stable states, one for the OFF and one for the ON. In order […]

What more can be learnt from the chemistry of noble gases? Noble gases, the members of group 18 of the periodic table of elements (in previous terminology – group VIII) are known as monoatomic gases. The latter property is the result of their very low chemical reactivity thus, they do not form bonds between themselves […]

¨The chemical bond¨ is one of the most often used concepts in chemistry. It is also one of the eldest terms since the first definition of chemical bond comes from the studies of G.N. Lewis who published his classical paper on interactions between atoms in 1916 . Lewis stated that ¨ we shall say that […]

It is likely that you have read somewhere that gravity is much weaker than the electromagnetic interaction. And it is true: for the electron and the proton gravity is 39 orders of magnitude weaker. Still what governs the movement of moons, planets, stars and galaxies is gravity; even the existence of dark matter is deduced […]