1.1化学微观世界的发展层次在线视频

Chemistry from Microscopic Perspective

【1-1】The Development Level of Chemical Microcosm

Hello, everyone！

Let's begin the discussion on the first theme.

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

There are four parts here.

【1-1】The Development Level of Chemical Microcosm

【1-2】 Interactions between Chemical Particles under Scale Microcosmic

【1-3】 Interaction between Chemical Particles under Essence Microcosmic

【1-4】The Status and Function of Microscopic Theory in Chemistry

Let's learn the first section of the first theme.

The Development Level of Chemical Microcosm

The formation of human micro-knowledge

begin with philosophy.

It can be traced back to the ancient Greek

philosopher Democritus.

He tried to understand the formation of all things

in the universe and the development and

change of nature from a rational perspective,

then put forward the thought of the "atom".

He believed that atoms and vanity were

the origin of the material world.

Atoms moved in the void and

combined with each other in different orders and positions

to produce all things in the universe.

About the change of matter,

from Democritus's atomic thought,

we can see that atoms were indivisible

and had no qualitative differences,

but only differenced in size and shape.

Atoms are separated from each other,

and objects change without disappearing.

This was the so-called material immortality.

However, this simple atomism is only

a general and vague philosophical speculation,

lacking experimental basis,

so it is difficult to apply it to explain

the development and changes of nature.

In natural science,

the understanding of the microcosm,

especially the chemical understanding of the microcosm

that we are concerned about,

begin with Dalton's atomic theory,

which is the beginning of modern chemistry.

In 1803, British physicist Dalton，

based on the series of achievements on

quantitative analysis of material composition

and scientific deduction,

put forward the atomic theory of chemical microcosm

in the sense of particle scale.

It considered that all materials were composed of

the smallest particles—atoms,

that couldn’t be further separated,

thus revealing the essence and internal connection of

the law of conservation of mass,

the law of equivalent,

the law of constant ratio composition

and law of multiple proportions.

We call Dalton's atomism scientific atomism,

this is a comparison with philosophical atomism.

In fact, as far as we know today,

in Dalton's atomic theory,

some conclusions are incorrect.

However,

Dalton's scientific thought of atomism had an

inexorable effect on the development of chemistry.

One aspect，

Dalton's atomism clearly pointed out that

atoms had the characteristics of weight.

That is, atomic mass.

Atom was no longer an abstract and fuzzy concept,

had quantitative characteristics that could be

directly measured by experiments.

Atomic weight had become the basic symbol

to distinguish atomic types.

Dalton's atomism clearly stated that

the essence of chemical reaction was

the process of atom recombination.

Moreover,

through the calculation of atomic weight,

the relationship between the composition of substances

and the mass of each substance in the reaction

could be accurately determined,

thus making Dalton's atomism truly operable.

This is one aspect of his thought.

On the other hand,

Dalton's atom concept was developed on the basis of

Lavoisier's element concept.

Element is a qualitative concept.

We say that matter was made up of elements.

For example,

water is composed of hydrogen and oxygen,

but cannot be quantified.

Dalton first linked elements and atoms into

a rigorous theoretical system.

Elements are abstractions and generalizations of atoms,

while atoms are concrete forms of existence of elements.

In other words, in Dalton's atomism，

elements truly find the objects they describe.

This not only raise people's understanding of elements

to a new level,

but also make Dalton's atomic concept clearer

and more specific,

thus laying the theoretical foundation

for the whole chemical development.

With the development of science and technology，

by the end of the 19th century, i.e. 1897,

British physicist J.J. Thomson discovered electrons

through his research on cathode rays,

proving that electrons are a basic

structural particle of matter,

thus ushering in a new era of chemical microcosm

based on scientific evidence.

Dalton's atomic theory mentioned earlier

was based on scientific speculation and

had not been confirmed by direct experiments.

It was based on the results of quantitative

chemical research obtained at that time.

Thomson's research work was to open the atom

and was based on scientific evidence.

During this period,

various cognitive models of different

levels of thought on atomic structure

had been produced successively,

For example,

Thomson's "raisin cake" model in 1904,

Rutherford's "nuclear atom" model in 1911,

and Bohr's atomic structure model in 1913.

Judging from the composition of chemical substances,

we say that a single atom or molecule is indeed

the most basic level.

The discovery of electrons makes it possible

for human beings to understand the relationship

between the structure of matter and its properties

at the microscopic level under the

essential attribute of wave-particle duality.

However, it is far from enough to regard

electrons as a structural particle.

We still need to clarify and reveal the

inevitable relationship between

the wave-particle duality of electrons

and its motion characteristics such as

quantization and probability.

Therefore, in this sense,

the modern scientific atomism in quantum mechanics

should belong to the chemical microcosm

under the “essence microcosmic".

Modern scientific atomism has overcome

the shortcomings of Dalton's atomism.

It not only proves that elements are variable

and atoms are separable,

but also establishes the dynamic model of atomic

structure under the quantum mechanics theory,

i.e. "electron cloud" model.

Modern scientific atomism is more dialectical

than Dalton's atomism.

The basic principles of quantum mechanics

not only reveal the nature of the binding force

between atoms in molecules,

but also establish modern chemical bond theory,

namely the valence bond theory

and molecular orbital theory,

which make people understand the motion images of

particles in atoms and molecules more and more lifelike.

This is the wisdom that quantum mechanics gives us.

Looking back on the history of the

development of human micro-cognition,

we can clearly see that scientific cognition

has gone through a difficult journey

from philosophical thinking to scientific speculation,

and finally transformed into scientific truth.

Of course, truth is always relative.

Although modern scientific atomism overcomes

many shortcomings of Dalton's atomism,

it is far from perfect.

In fact, so far,

we still know very little about the chemical microcosm.

The changes in nature are endless,

and the cognitive ability of human beings is infinite.

With the continuous development of

modern science and technology

and the continuous improvement of

experimental methods and research methods,

the scientific theories we are studying will be

continuously improved and developed with the

deepening of human understanding of objective things.

So much for this section.

Thank you for watching.