0.1课程目标与定位在线视频

Chemistry from Microscopic Perspective

【0-1】Course Goal and Orientation

Hello, everyone！

Today we begin to learn a new course，

Chemistry from Microscopic Perspective.

The chemical microcosm refers to the

rational understanding formed by studying

the composition, structure, properties

and changing rules of chemical substances

at the level of individual atoms and molecules.

In general, what we call the microcosm

includes micro substances and micro phenomena.

That is to say,

the tiny matter and phenomena that

can't be directly observed by human senses.

Therefore,

the so-called chemical microcosm can be regarded as

a chemical understanding for the microcosm.

Although the object of chemical research is usually

a large number of atoms and molecules,

the knowledge of individual atoms and molecules are the

essential starting point for chemistry.

Our knowledge of matter is generally introduced by objects.

Matter is usually divided into objects and materials.

Matter has three states：gas, liquid and solid.

What does the so-called object mean?

It is a concrete substance.

For example,

we know water as a substance through

liquid water, gaseous water vapor or solid ice.

What do we mean by emphasizing a single atom or molecule?

For example,

for molecules consisting of three atoms, H₂O and CO₂ .

As matter, their physical properties vary greatly.

Water is liquid at normal temperature.

It will turn into steam at 100℃ and freeze at 0℃.

For carbon dioxide,

it is gaseous at normal temperature

and starts to liquefy at about -56℃

and solidifies to dry ice at about -78℃.

What makes the difference between the physical properties

of water and carbon dioxide?

The reason is that water molecule contains

two H-O polar bonds,

and the whole molecule has a V-shaped structure,

which is polar bond and polar molecule.

For carbon dioxide molecule,

although it also contains two polar C-O bonds,

the whole molecule is linearly symmetric,

so it is polar bond and nonpolar molecule.

This determines the interaction between water molecules

include what is commonly called dipole force,

induction force and dispersion force.

For carbon dioxide molecules,

only dispersion force exists between nonpolar molecules.

In other words,

from the perspective of intermolecular interaction,

the intermolecular interaction between water molecules

is much larger than that between carbon dioxide molecules.

Therefore, we can explain the difference between the

physical properties of water and carbon dioxide.

One of the aims of the study of chemical macro system

is to reduce macro phenomena to

atomic and molecular mechanisms

so as to grasp it more deeply and systematically.

These are the fundamental tasks and

highly focused questions of structural chemistry.

The material world we are facing

spans from 10²º meters to 10⁻²º meters.

The life of a substance, that is, its duration,

ranges from 10¹º years to 10⁻¹⁸ seconds.

The composition of matter is as many as

10²³ stars and as few as dozens of atoms.

Facing a world with

such large differences in physical scales,

can we use a unified theory to describe it?

Of course, the answer is no.

Different from the thinking mode of induction

based on facts in chemical macrocosm,

the chemical microcosm is mainly deduction

based on theory.

The modern chemical microcosm refers to a

chemical microscopic perspective formed by using

the laws of extra-nuclear electron motion

revealed by quantum mechanics theory

to explain the "structure-property" relationship

and their interaction properties of chemical particles

such as atoms, molecules and ions.

Chemical microcosm can be divided into two levels:

scale microcosmic and essence microcosmic.

The scale microcosmic refers to the rational judgment

based on the scale of micro particles.

The essence of micro is a theoretical exposition

based on the movement of micro particles.

They are different.

For example, later on,

the electron theory of chemical bonds is only based on

the particle characteristics of electrons themselves

to explain their interactions.

Modern covalent bond theory,

i.e. valence bond orbital and molecular orbital theory,

is based on the theoretical exposition of

wave-particle duality of microscopic particles,

and is a theoretical description of the interactions

generated in the movement process of microscopic particles.

Therefore, the two are different.

Let's look at the orientation of the course.

Chemistry from Microscopic Perspective is

a specialized elective course for chemistry majors

in colleges and universities,

especially normal colleges and universities.

It can be used as the advanced placement

for junior undergraduates

to learn the elementary course of “Structural Chemistry”.

It can also be used as a

subject thought expanding course

for senior undergraduates

and masters of chemistry education

to independently construct the

cognition picture of chemistry microcosm.

The theoretical basis of structural chemistry is highly

abstract and philosophical quantum mechanics.

For students who lack sufficient mathematical basis

and are accustomed to thinking in images,

quantum mechanics is often regarded as

a roadblock in their first study of structural chemistry.

Therefore, in the organization of teaching content,

we try to analyze some important scientific

historical facts in the history of quantum mechanics,

and then introduce new concepts such as

atomic orbit, molecular orbit,

electron cloud, energy level, etc.

On the premise of not going deep into the mathematics

jungle that may cause people to get lost,

students can make theoretical explanations and predictions

on chemical problems from a microscopic perspective.

The more important significance of the

thought of quantum mechanics lies in that

it completely reverses and changes

our usual thinking method and scientific attitude

based on classical mechanics.

In the process of understanding the

basic ideas of quantum mechanics,

students will inevitably experience the

collision of new and old ideas,

resulting in many "myth" concepts.

Through the discussion on the

origin of the chemical microcosm,

this course guides the students to be familiar with

and get used to the

chemical microscopic thinking mode gradually,

and promotes the abstract thinking ability,

modeling thinking,

scientific criticism and reflection spirit,

thus realizing the "double advancement" of

subject knowledge and subject thought.

For this course, the organized course content

is divided into the following five themes.

1. How to Reflect the Subject Guidance Function of Chemical Microscopic Perspective

2. How to Describe the Discontinuity of Microcosm with Energy Quantization

3. How to Describe the Uncertainty of Microcosm with Probability

4. How to Describe the Microscopic Picture of Chemical Particles Based on Orbital Thought

5. How to Understand the Language and Behavior of Molecules from Molecular Spectra

There is no fixed teaching material for this course.

You can refer to books on

material structure or structural chemistry.

For example,

G.X. Xu's Structure of Matter

B.R. Li’s Structural Chemistry.

Students with a good foundation in

mathematics and physics can look at the

J.Y. Zeng’s Quantum Mechanics.

For those students

who pay close attention to chemical problems,

they can see

Pauling's Nature of Chemical Bonds

and Coulson's Valence.

Of course, at the right time,

in order to cooperate with the promotion of this course,

we are going to compile two related teaching materials

while the course is on line,

of which one is

Subject Understanding of Chemistry

and the other is

Chemistry from Microscopic Perspective.

So much for this section.

Thank you for watching.