标签：atoms - 英国华人论坛

Each atom has a centre, called its nucleus. In this centre are one or more particles called protons. A proton is a particle that has a positive electrical charge. Revolving around this centre, or nucleus, are particles of negative electricit...英国华人论坛

For thousands of years,men have written and guessed about the nature of tiny particles likethese, but they did not have any real idea of what an atom is like.Thinking men in ancient Greece, including one named Democritus, 2,500years ago, ask...英国华人论坛