Main-group element Main-group element In chemistry and atomic physics, the main group is the group of elements whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arranged in the periodic table of the elements. The main group includes the elements (except hydrogen, which is sometimes not included) in groups 1 and 2 (s-block), and groups 13 to 18 (p-block). The s-block elements are primarily characterised by one main oxidation state, and the p-block elements, when they have multiple oxidation states, often have common oxidation states separated by two units. Main-group elements (with some of the
Molecular solid interaction in TTF-TCNQ stems from the large partial negative charge (δ = -0.59) on the cyano- moiety on TCNQ at room temperature. For reference, a completely charged molecule δ = ±1. This partial negative charge leads to a strong interaction with the thio- moiety of the TTF. The strong interaction leads to favorable alignment of these functional groups adjacent to each other in the solid state. While π-π interactions cause the TTF and TCNQ to stack in separate columns. One form of an element may be a molecular solid, but another form of that same element may not be a