Which two climates have very low levels of precipitation?dry and polar

How is the way a mixture is combined different from how a compound is combined?

Use the drop-down menus to label each of the following changes p for physical change and c for chemical change. the substance changes to a new substance. the original substance can be recovered. the color changes. gas is produced and given off. the substance changes size, shape, or volume.

The allotropes of carbon include a variety of structures that include three-dimensional tetrahedral lattices, planes of hexagonal rings, cylindrical tubes of hexagonal rings, and spheres of five- and six-membered rings. similar shapes of network covalent atomic solids are possible with carbon nitride, boron, and pure silicon (e.g., silicene is a graphene-like allotrope of pure silicon). in contrast, silicates exist as either highly ordered or amorphous (more random) three-dimensional lattices. what could explain why there are there no naturally occurring sheets, stacked sheets, cylindrical tubes, or spheres of network covalent atomic solids composed of silicon and oxygen (sio2)? would pure silicate structures make good lubricants or good electrical conductors?