chapter2- Atoms and Nuclei专用课件.pptVIP

NUCLEAR ENERGY PROFESSIONAL(SPECIAL) ENGLISH COURSE 2.1 ATOMIC THEORY（原子理论） The most elementary concept (元素概念) is that matter is composed of individual particles (单个粒子) – atoms – that retain their identity (同一性, 特性) as elements in ordinary physical and chemical interactions. Thus a collection of helium atoms (氦原子) that forms a gas has a total weight that is the sum of the weights of the individual atoms. Also, when two elements combine (结合) to form a compound (化合物) (e.g., if carbon atoms (碳原子) combine with oxygen atoms (氧原子) to form carbon monoxide molecules (一氧化碳分子)), the total weight of the new substance is the sum of the origin elements. There are more than l00 known elements. Each is given an atomic number (原子序数) in the periodic table of the elements (元素周期表)– examples are hydrogen (H) l, helium (He) 2, oxygen (O) 8, and uranium (U) 92. The symbol Z is given to the atomic number, which is also the number of electrons in the atom and determines its chemical properties (性质). The atomic weight (原子质量) M is the weight in grams of a definite (明确的) number of atoms, 6.02 ? 1023 , which is Avogadro’s number (阿佛伽德罗常数), Na. We can easily find the number of atoms per cubic centimeter (每立方厘米) in a substance if its density ? in grams per cubic centimeter is known. This procedure (程序, 手续) can be expressed as a convenient (便利的) formula for finding N, the number per cubic centimeter for any material 2.2 GASES (气体) Substances in the gaseous state (气态) are described approximately by the perfect gas law 理想气体规律(方程), relating pressure, volume, and absolute temperature (绝对温度), pV=nkT. An increase in the temperature of the gas due to heating causes greater molecular motion, which results in an increase of particle bombardment (n 炮击；轰击) of a container wall and thus of pressure on the wall. The particles of gas, each of mass m, have a variety of speeds v in accord with Maxwell’s gas theory (麦克斯韦气体理论) as shown in Fig. 2.1. The most probable speed(最概然速率), at the peak of Maxwellian di