题目

 (1)第一电离能介于B、N之间的第二周期元素有________种。 (2)CH4中共用电子对偏向C，SiH4中硅元素为＋4价，则C、Si、H的电负性由大到小的顺序为____________。 (3)Fe3C晶体中碳元素为－3价，其中基态铁原子的价电子排布图为______________。 (4)甲醇(CH3OH)分子内的O—C—H键角________(填“大于”“等于”或“小于”)甲醛(H2C=O)分子内的O—C—H键角。 (5)BF3和NF3都是四个原子的分子，BF3分子的立体构型是平面三角形，而NF3分子的立体构型是三角锥形的原因是_______________  Daniel found some pictures of things that astronauts need from a magazine about space. He is showing them to Millie. Complete what Daniel says with the words in the box.gravity        helmet            oxygen     planetpower pack     sleeping bag        specially    uncomfortable    This digital camera helps the astronauts take high quality photos.   Astronauts can write their daily reports on a notebook computer.  Astronauts can't take off their (1) designed boots when they walk on the surface of the (2) because of the low (3). Astronauts have to wear a space (4) on their head when travelling in space. This is a (5) . Its fixed to the wall of the spacecraftwhen the astronauts sleep. Its not (6) to sleep in it.A (7) is very important because it provides energyfor the spacesuit. A spacecraft takes astronauts frorm the Earth to outer space. An air tank provides an astronaut with many hours of (8) .