## 物理代写|固体物理代写Solid-state physics代考|PHYSICS7544

2023年3月29日

couryes-lab™ 为您的留学生涯保驾护航 在代写固体物理Solid-state physics方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写固体物理Solid-state physics代写方面经验极为丰富，各种代写固体物理Solid-state physics相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础
couryes™为您提供可以保分的包课服务

## 物理代写|固体物理代写Solid-state physics代考|Covalent Bonding

In covalent bonding, stable electron configuration is assumed by the sharing of electrons between adjacent atoms. Two atoms that are covalently bonded will each contribute at least one electron to the bond, and the shared electron may be considered to belong to both atoms. The number of covalent bonds that is possible for a particular atom is determined by the number of valence electrons. In a covalent bond, the spins of the two electrons are antiparallel.

The elements $\mathrm{C}, \mathrm{Si}$ and Ge lack four electrons with respect to filled shell and thus these elements can have an attractive interaction associated with the charge overlap. Consider the case of diamond. The electron configuration of $C$ is $1 s^2 2 s^2 2 p^2$. Thus carbon can form two bonds. However, carbon forms four bonds. The reason why carbon does form four bonds can be understood when the energies of the $2 s$ and $2 p$ are considered. It turns out that the energy difference between $2 s$ and $2 p$ is very small so that one of the $2 s$ electron of the atom can be promoted to $2 p$ to make the configuration $1 s^2 2 s^1 2 p^3$ resulting in four unpaired electrons. This promotion of electron from the ground state require $4 \mathrm{eV}$ an amount more than regained when the bonds are formed. The orbital of these four electrons is disposed towards the four corners of the tetrahedral. The tetrahedral bond allows only four nearest neighbours, whereas a close packed structure has 12 . The covalent bonded solids are therefore less dense than the ionic solids. Characteristic properties of the covalent bond, which distinguished it from the bonds of other types are its saturability and directionality. Saturability means that each atom can form covalent bonds only with a limited number of neighbours. For example, each hydrogen atom can form covalent bonds only with one of its neighbours. The electron pair contributing such a bond has antiparallel spins. A third atom in this case instead of being attracted will be repelled.
Some common features of materials with covalent bonds are:
(i) covalent bond crystals are usually hard and brittle; (ii) binding energy is high so that their melting and boiling points are high, but low compared to ionic crystals; (iii) covalent bonds are highly directional in character; (iv) these bonds have saturation properties; (v) covalent substances are insoluble in water; (vi) these materials are soluble in non-polar solvents like benzene; (vii) the conductivity of covalent crystals varies over a wide range. Some are excellent insulators, others are medium conductors like Si and Ge, and some behave as poor metals like grey tin; (viii) the conductivity increases with increase in temperature; (ix) these are transparent for wavelength but opaque to shorter wavelength. Ge and Si are transparent for wavelength longer than the infrared radiation; (x) carbon and diamond structure is the hardest substance and has high melting point of $3820 \mathrm{~K}$. Compounds with covalent bonds may be solid, liquid or gas at room temperature depending on the number of atoms in the compound. The more atoms in each molecule, the higher a compound’s melting and boiling temperature will be. Since most covalent compounds contain only a few atoms and the forces between molecules are weak, most covalent compounds have low melting and boiling points. Examples of covalent crystals are: $\mathrm{CO}, \mathrm{N}_2, \mathrm{H}_2$, diamond, methane, silicon, germanium, rubber, etc.

## 物理代写|固体物理代写Solid-state physics代考|Metallic Bonding

The valence electrons in a metal are rather loosely bound and frequently the electronic shells are only partially filled, so that metals bond not to form covalent bonds. The basic structure of metals is a gas of approximately free electrons surrounding a lattice of positive ions. The metal is held together by the interaction of positive ions with the electron gas. The electrons moving between the ions compensate the repulsive forces existing between the positively charged ions and bring them closer together. As the distance between the ions becomes smaller the density of electron gas increases and this leads to an increase in force drawing the ions together. On the other hand, in this case the repulsive force acting between the ions tends to move them away from each other. When the distance between the ions become such that the force of attraction are compensated by the force of repulsion, a stable lattice is formed.

In metals, the outer valence electrons are removed from the ion cores. They are free to move between the remaining ion cores. These delocalized valence electrons are involved in the conduction of electricity and are therefore called conduction electrons. Thus the metals are expected to be formed from those elements for which the expenditure of energy for removing the electron is small. This expenditure of energy can be more than compensated by the bonding. The energy of the electron is kinetic plus potential energy. The kinetic energy $T$ is given by $T=-\frac{\hbar^2}{2 m} \nabla^2$. The quantum mechanical average kinetic energy is $\int \psi^* T \psi \mathrm{d} \tau$.

Where $\mathrm{d} \tau$ is volume element, and $\psi$ is wave function. $T \psi$ or $T=-\frac{\hbar^2}{2 m} \nabla^2 \psi$ is proportional to the second derivative of the wave function, that is the curvature. For an electron, localized to an atom the curvature is much higher than that for a nearly free electron in a metal. This result in a gain of energy. The potential energy gain comes mostly from Pauli exclusion principle which does not allow two electrons with the same spin direction to be at the same place and therefore the electron go out of each other way. Further, there is also Coulomb repulsion between the electrons themselves.

Consider sodium metal. It crystallizes in $b c c$ structure. In the structure each $\mathrm{Na}$ is surrounded by eight $\mathrm{Na}$ atoms. The electronic configuration of $\mathrm{Na}(Z=11)$ is $1 s^2 2 s^2 2 p^6 3 s^1$. Each atom has complete $K$ and $L$ shell and one unpaired $3 s$ electron in its outer shell. When $\mathrm{Na}$ atoms come together, the electrons in the $3 s$ atomic orbital of one sodium atom shares space with the corresponding electron on a neighbouring atom to form a molecular orbital. Each sodium atom is being touched by eight other sodium atoms and the sharing occurs between the central atom and the $3 s$ orbital on all of the eight other atoms.

# 固体物理代写

## 物理代写|固体物理代写Solid-state physics代考|Covalent Bonding

、C、Si 和 Ge 元素相对于填充壳缺乏四个电子，因此这些元素可以具有与电荷重叠相关的吸引相互作用。考虑钻石的情况。C 的电子排布是 1s22s22p2。因此碳可以形成两个键。然而，碳形成四个键。当考虑 2s 和 2p 的能量时，可以理解碳确实形成四个键的原因。事实证明，2s 和 2p 之间的能量差非常小，因此原子的 2s 电子之一可以提升到 2p 使构型 1s22s12p3 产生四个不成对的电子。这种从基态促进电子需要 4eV 的数量比形成键时重新获得的数量多。这四个电子的轨道朝向四面体的四个角。四面体键只允许四个最近邻，而密排结构有 12 个。因此，共价键合固体的密度低于离子固体。共价键区别于其他类型键的特征是它的饱和性和方向性。饱和性意味着每个原子只能与有限数量的邻居形成共价键。例如，每个氢原子只能与其相邻的一个原子形成共价键。形成这种键的电子对具有反平行自旋。在这种情况下，第三个原子不会被吸引，而是会被排斥。而密排结构有 12 。因此，共价键合固体的密度低于离子固体。共价键区别于其他类型键的特征是它的饱和性和方向性。饱和性意味着每个原子只能与有限数量的邻居形成共价键。例如，每个氢原子只能与其相邻的一个原子形成共价键。形成这种键的电子对具有反平行自旋。在这种情况下，第三个原子不会被吸引，而是会被排斥。而密排结构有 12 。因此，共价键合固体的密度低于离子固体。共价键区别于其他类型键的特征是它的饱和性和方向性。饱和性意味着每个原子只能与有限数量的邻居形成共价键。例如，每个氢原子只能与其相邻的一个原子形成共价键。形成这种键的电子对具有反平行自旋。在这种情况下，第三个原子不会被吸引，而是会被排斥。饱和性意味着每个原子只能与有限数量的邻居形成共价键。例如，每个氢原子只能与其相邻的一个原子形成共价键。形成这种键的电子对具有反平行自旋。在这种情况下，第三个原子不会被吸引，而是会被排斥。饱和性意味着每个原子只能与有限数量的邻居形成共价键。例如，每个氢原子只能与其相邻的一个原子形成共价键。形成这种键的电子对具有反平行自旋。在这种情况下，第三个原子不会被吸引，而是会被排斥。

(i) 共价键晶体通常又硬又脆；(ii) 结合能高，因此它们的熔点和沸点高，但与离子晶体相比较低；(iii) 共价键具有高度方向性；(iv) 这些债券具有饱和特性；(v) 共价物质不溶于水；(vi) 这些材料可溶于苯等非极性溶剂；(vii) 共价晶体的电导率在很宽的范围内变化。有的是极好的绝缘体，有的是Si、Ge等中等导体，有的像灰锡一样是不良金属；(viii) 电导率随温度升高而增加；(ix) 这些对于波长是透明的但对于较短的波长是不透明的。Ge和Si对波长大于红外线的辐射是透明的；(x) 碳和金刚石结构是最硬的物质，熔点高达 3820 K。具有共价键的化合物在室温下可以是固体、液体或气体，这取决于化合物中的原子数。每个分子中的原子越多，化合物的熔化和沸腾温度就越高。由于大多数共价化合物仅包含几个原子，分子间的作用力很弱，因此大多数共价化合物的熔点和沸点都较低。共价晶体的例子有：、、CO、N2、H2、金刚石、甲烷、硅、锗、橡胶等。化合物的熔化和沸腾温度越高。由于大多数共价化合物仅包含几个原子，分子间的作用力很弱，因此大多数共价化合物的熔点和沸点都较低。共价晶体的例子有：、、CO、N2、H2、金刚石、甲烷、硅、锗、橡胶等。化合物的熔化和沸腾温度越高。由于大多数共价化合物仅包含几个原子，分子间的作用力很弱，因此大多数共价化合物的熔点和沸点都较低。共价晶体的例子有：、、CO、N2、H2、金刚石、甲烷、硅、锗、橡胶等。

## 有限元方法代写

tatistics-lab作为专业的留学生服务机构，多年来已为美国、英国、加拿大、澳洲等留学热门地的学生提供专业的学术服务，包括但不限于Essay代写，Assignment代写，Dissertation代写，Report代写，小组作业代写，Proposal代写，Paper代写，Presentation代写，计算机作业代写，论文修改和润色，网课代做，exam代考等等。写作范围涵盖高中，本科，研究生等海外留学全阶段，辐射金融，经济学，会计学，审计学，管理学等全球99%专业科目。写作团队既有专业英语母语作者，也有海外名校硕博留学生，每位写作老师都拥有过硬的语言能力，专业的学科背景和学术写作经验。我们承诺100%原创，100%专业，100%准时，100%满意。

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。