table of Contents
- Chapter XVIII: atomic structure
- Chapter XIX: Nuclear
Chapter XVIII: atomic structure
A nucleus structure model
1, the discovery of the electron and atomic model Thomson:
⑴ electronic discovery: In 1897 the British physicist Thomson, cathode ray conducted a series of studies, leading to the discovery of electrons.
Electronic findings indicate that: the presence of the fine structure of atoms, the atom thus breaking the concept can not be divided.
⑵ Thomson atomic model: 1903 Thomson contemplated charged atoms is a ball, its positive charge evenly distributed throughout the sphere, negatively charged electrons embedded in the positive charge.
2, scattering experiment and nuclear structure model
⑴ particle scattering experiment: In 1909, Rutherford and Geiger and assistant Marston completed.
① Apparatus: FIG follows
② phenomenon:
a. After the majority of particles passing through the foil, still in the original direction, the deflection does not occur.
B. deflection angle of a few larger particles occurs.
C. There are very few particles deflection angle exceeds 90 °, and some nearly 180 °, i.e. reversing spring back.
⑵ nuclear structure model of the atom:
Since the mass of the particle is seven thousand times the mass of an electron, the electron motion direction of the particles is not changed obviously, only positive charge in the atom may have a significant impact on the movement of the particles.
If the positive charge distribution atoms, such as Thomson die model that uniform distribution of the particles passing through the foil suffered positive charge balanced by a force in all directions, the motion of the particles is not changed significantly. Scattering experiments demonstrate the phenomenon, atoms not evenly distributed positive charge atom.
1911, analysis and calculation of Rutherford scattering experiment nuclei proposed structure model: there is a small central atomic nucleus called nucleus, nucleus together all the positive charge and almost all of the mass of atoms, negatively charged electrons rotating around the nucleus space outside the core.
Nuclear radius is about at 10-15 \ (m \) , atomic orbital radius is about 10-10 of \ (m \) .
⑶ spectrum
① viewing instrument spectrum, beam splitter
② classification spectrum, and generating features
| Continuous spectrum | Line spectra | Absorption spectra | |
|---|---|---|---|
| produce | Spectrum hot solids, liquids and high pressure gas | Emission spectrum of rare gas or vapor of a metal | White (which includes all continuous wavelength distribution of light) emitted by the object through the high-temperature material, some wavelengths of light absorbed by the substance |
| phenomenon | All wavelengths of light from the continuous distribution of the composition | There is a section of the spectrum bright line - line | There exists a spectral region dark lines |
| Feature | The entire spectral region is bright | Characteristic lines | Each emission spectrum of a dark line in the absorption spectrum of each of the atoms are related to the type of atom in a bright line (line spectra), respectively. |
③ Spectrum:
An element, emits light at high temperatures characteristic of some wavelength, at low temperatures, but also absorbs light of these wavelengths, so the bright lines and bright lines in the absorption spectrum of light waves dark lines is called the characteristic lines of the elements, for spectral analysis.
Second, the spectrum of the hydrogen atom
Hydrogen atom is the simplest, most spectral simple.
In 1885, Balmer at that time known, in 14 lines were analyzed in the visible region, found that the wavelength spectrum can be represented by a formula:
\(1/\lambda=R(1/2^2-1/n^2) n=3，4，5……\)
Wherein R is called the Rydberg constant, this equation becomes Balmer formula.
In addition Balmer series, later found in other lines of the infrared spectrum of hydrogen and a purple zone are also satisfy formula Balmer similar relationship.
Spectral line spectrum is a hydrogen atom, with separate characteristics, can not be explained with the classical electromagnetic theory.
Third, the level atom
Bohr model of the atom:
1. The structural model and contradictions of Nuclear - classical electromagnetic theory (both)
a. electron around the nucleus in a circular motion is accelerated motion, according to the classical theory, the acceleration of the movement of charge, to constantly emit electromagnetic waves around the electron energy must continue to decrease, the last to fall on the electronic nucleus, which atoms are usually the facts contradict stable.
b. electromagnetic radiation when the electron around the nucleus should be equal to the rotational frequency of the rotational frequency of the nuclear electrons around, with continued rotation track becomes smaller, the frequency of electromagnetic waves radiated electrons should also be continuously changed, according to this reasoning and therefore should be atomic spectrometry continuous spectrum, the spectrum is a line spectrum such atoms fact contradict.
2. Bohr theory
上述两个矛盾说明，经典电磁理论已不适用原子系统，玻尔从光谱学成就得到启发，利用普朗克的能量量了化的概念，提了三个假设：
①定态假设：原子只能处于一系列不连续的能量状态中，在这些状态中原子是稳定的，电子虽然做加速运动，但并不向外在辐射能量，这些状态叫定态。
②跃迁假设：原子从一个定态（设能量为Em）跃迁到另一定态（设能量为En）时，它辐射成吸收一定频率的光子，光子的能量由这两个定态的能量差决定，即\(hv=Em－En\)
③轨道量子化假设，原子的不同能量状态，跟电子不同的运行轨道相对应。原子的能量不连续因而电子可能轨道的分布也是不连续的。
3.玻尔的氢原子模型：
①氢原子的能级公式和轨道半径公式：玻尔在三条假设基础上，利用经典电磁理论和牛顿力学，计算出氢原子核外电子的各条可能轨道的半径，以及电子在各条轨道上运行时原子的能量，（包括电子的动能和原子的热能。）
②氢原子的能级图：氢原子的各个定态的能量值，叫氢原子的能级。按能量的大小用图开像的表示出来即能级图。
其中n=1的定态称为基态。n=2以上的定态，称为激发态。
第十九章：原子核
一、原子核的组成
1、天然放射现象
⑴天然放射现象的发现：1896年法国物理学，贝克勒耳发现铀或铀矿石能放射出某种人眼看不见的射线。这种射线可穿透黑纸而使照相底片感光。
放射性：物质能发射出上述射线的性质称放射性。
放射性元素：具有放射性的元素称放射性元素。
天然放射现象：某种元素自发地放射射线的现象，叫天然放射现象。这表明原子核存在精细结构，是可以再分的。
⑵放射线的成份和性质：用电场和磁场来研究放射性元素射出的射线，在电场中轨迹，如下图
| 成分 | 速度 | 贯穿能力 | 电离能力 | |
|---|---|---|---|---|
| α射线 | 氦原子核 | 1/10光速 | 弱 | 很容易 |
| β射线 | 高速电子流 | 接近光速 | 较强 | 较弱 |
| γ射线 | 高能量电磁波 | 光速 | 很强 | 更小 |
2、原子核的组成
原子核的组成：原子核是由质子和中子组成，质子和中子统称为核子。
在原子核中有：质子数等于电荷数、核子数等于质量数、中子数等于质量数减电荷数。
二、原子核的衰变；半衰期
- 衰变：原子核由于放出某种粒子而转变成新核的变化称为衰变在原子核的衰变过程中，电荷数和质量数守恒
| 衰变类型 | 衰变方程 | 本质 |
|---|---|---|
| α衰变 | \({^M_Z}X\rightarrow {^{M-4}_{Z-2}}Y+{^4_2} He\) | 原子核内少两个质子和两个中子 |
| β衰变 | \({^M_Z}X\rightarrow {^M_{Z+1}}Y+^0_{-1}e\) | 原子核内的一个中子变成质子， 同时放出一个电子 |
2.γ 辐射：原子核的能量也跟原子的能量一样，其变化是不连续的，也只能取一系列不连续的数值，因此也存在着能级，同样是能级越低越稳定。
放射性的原子核在发生α衰变、β衰变时，往往蕴藏在核内的能量会释放出来，使产生的新核处于高能级，这时它要向低能级跃迁，能量以γ光子的形式辐射出来，因此，γ射线经常是伴随α射线和 β射线产生的，当放射性物质连续发生衰变时，原子核中有的发生α衰变，有的发生β衰变，同时就会伴随着γ辐射（没有γ衰变）。这时，放射性物质发出的射线中就会同时具有α、β和γ三种射线。
3.半衰期：放射性元素的原子核的半数发生衰变所需要的时间，称该元素的半衰期。
放射性元素衰变的快慢是由核内部自身因素决定的，跟原子所处的化学状态和外部条件没有关系。
三、放射性的应用与防护；放射性同位素
放射性同位素：有些同位素具有放射性，叫做放射性同位素。
同位素：具有相同的质子和不同中子数的原子互称同位素，放射性同位素：具有放射性的同位素叫放射性同位素。
正电子的发现：用粒子轰击铝时，发生核反应。
1934年，约里奥—居里夫妇发现经过α粒子轰击的铝片中含有放射性磷
，即：
反应生成物P是磷的一种同位素，自然界没有天然的
，它是通过核反应生成的人工放射性同位素。
与天然的放射性物质相比，人造放射性同位素：
①放射强度容易控制
②可以制成各种需要的形状
③半衰期更短
④放射性废料容易处理
放射性同位素的应用：
①利用它的射线
A.由于γ射线贯穿本领强，可以用来γ射线检查金属内部有没有砂眼或裂纹，所用的设备叫γ射线探伤仪。
B.利用射线的穿透本领与物质厚度密度的关系，来检查各种产品的厚度和密封容器中液体的高度等，从而实现自动控制。
C.利用射线使空气电离而把空气变成导电气体，以消除化纤、纺织品上的静电。
D.利用射线照射植物，引起植物变异而培育良种，也可以利用它杀菌、治病等
②作为示踪原子：用于工业、农业及生物研究等。
棉花在结桃、开花的时候需要较多的磷肥，把磷肥喷在棉花叶子上，磷肥也能被吸收。但是，什么时候的吸收率最高、磷在作物体内能存留多长时间、磷在作物体内的分布情况等，用通常的方法很难研究。
如果用磷的放射性同位素制成肥料喷在棉花叶面上，然后每隔一定时间用探测器测量棉株各部位的放射性强度，上面的问题就很容易解决。
放射性的防护：
①在核电站的核反应堆外层用厚厚的水泥来防止放射线的外泄
②用过的核废料要放在很厚很厚的重金属箱内，并埋在深海里
③在生活中要有防范意识，尽可能远离放射源
四、核反应方程
1.熟记一些实验事实的核反应方程式。
⑴卢瑟福用α粒子轰击氮核打出质子：
⑵贝克勒耳和居里夫人发现天然放射现象
α衰变：\({^{238}_{92}U}\rightarrow {^{234}_{90} Th}+{^4_2 He}\)
β衰变：\({^{234}_{90} Th}\rightarrow{^{234}_{91}Pa}+{^0_{-1}e}\)
⑶查德威克用α粒子轰击铍核打出中子：
⑷居里夫人发现正电子：
⑸轻核聚变：
⑹重核裂变：
\({^{235}_{92}U}+{^1_0 n}\rightarrow {^{136}_{54}Xe}+10{^1_0 n}+{^{90}_{38}Sr}\)
\({^{235}_{92}U}+{^1_0 n}\rightarrow {^{144}_{56}Ba}+{^{89}_{36} Kr}+3{^1_0 n}\)
2.熟记一些粒子的符号
3.注意在核反应方程式中，质量数和电荷数是守恒的。
Related topics dealing with the nuclear reaction equation, as long as the above points, you can fix the problem.
V. Significant nuclear fission; fusion
Way to release nuclear energy - fission and fusion
1. fission reaction:
Fission ①: two heavy nuclei change the nuclear medium quality under certain reaction conditions, called the nucleus fission reaction. E.g:
② chain reaction: fission neutrons produced by the reaction, and then by other uranium nuclei entrapped in the reaction to continue.
Chain reaction conditions: critical volume, extremely high temperatures.
③
2. fusion reaction:
Fusion reactions ①: light nuclei into the polymerization reaction heavier nuclei, called fusion reaction. E.g:
② a deuteron and a triton when combined into a helium nucleus (and release a neutron), release 17.6 (Mev \) \ energy, average energy per nucleon released 3 \ (Mev \) above. The average energy per nucleon reaction released 3-4 times larger than the column.
③ fusion reaction conditions; millions of degrees Celsius temperature.