Answer:
The atomic theory has changed over time as new technologies have become available. Scientific knowledge builds on past research and experimentation. 400 B.C. Democritus, a philosopher in ancient Greece, began the search for a description of matter.
Explanation:
Soilds retain their shape because their particles (be they atoms or molecules) are locked in position by bonds or intermolecular forces of neighboring particles. When you heat a solid so that it changes phase to liquid form, the thermal energy put in serves to excite the particles of matter enough so that they are still held together but can now overcome the forces holding them rigidly in place and slides around each other. Liquids are virtually incompressible because the particles are still held together, but they can also flow and change shape because they're not fixed to the same arrangement.
A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms.
Answer:
Metals and non-metals are substances that can be differentiated on the basis of various physical and chemical properties. Metals are the elements that are generally hard as strong metallic bond exists between the atoms. As against non-metals are the elements which are usually soft.
Double displacement reaction I'd say