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Atom Emission Spectra

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化学基础：结构和溶解

4.7（94 個評分） | 11K 名學生已註冊

This is an introductory course for students with limited background in chemistry; basic concepts such as atomic and molecular structure, solutions, phases of matter, and quantitative problem solving will be emphasized with the goal of preparing students for further study in chemistry.

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4.7（94 個評分）

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TA

Sep 17, 2017

Skillful Quiz, the best understanding of chemistry. Although a little difficult to pass, U will be proficient in Introductory Chemistry.

L

Sep 16, 2017

Excellent presentation of the topics, easy to understand the instructor.

從本節課中

light

We will cover introduction to light, Bohr model of the hydrogen atom, atomic orbitals, electron configurations, valence versus core electrons. Don’t forget to use this week’s discussion forum for any questions and discussions.

Atom Emission Spectra8:55

Bohr Model Part I20:57

[Demo] Colored Flames5:46

Bohr Model Part II12:16

教學方

Prof. Dorian A. Canelas
Assistant Professor of the Practice

腳本

In this video, we will be viewing a demonstration of

the atomic emission spectra of three elements, hydrogen, helium, and neon.

We will be observing the different colors of light come out of tubes filled with the

different gases, when they are excited by applying an external electric charge.

We'll be able to separate each spectrum into its component

colors using a very simple diffraction grating.

Recall that a continuous spectrum of white light can

be separated into its component colors by a glass prism.

The prism bends the light and some colors of the light

are bent more than others due to differences in their wavelengths.

We are observing the same process when droplets of

water in the atmosphere separate sunlight into its component colors.

The sun

produces white light because it is an example of an incredibly hot object.

But what about the light produced here on Earth by the chemical elements?

For example, most of you are familiar with the term neon sign.

What color of light does neon produce? Do other elements produce

different colors of light?

Are all of these lights filled with neon? What about these?

Are these light tubes filled with the gas neon?

First, let's look at what we call white light using a simple light bulb.

When the tungsten filament light bulb is brightly lit,

we can see a continuous spectrum of visible colors.

Before we jump straight to neon lights,

let's start with the simplest element, hydrogen.

When hydrogen is given sufficient energy, it also produces visible light.

The light from hydrogen is especially important in astronomy, because

much of the matter in the universe is made from hydrogen.

Here is what a giant lit up hydrogen

gas discharge tube looks like.

As you can see, the lamp itself glows with a bright pinkish purple color.

This is an example of the smaller discharge

tube that we'll be using in this experiment.

At the end of each experiment, we will scan back so that you can see the

tube itself in the apparatus that we're using

to apply the electric charge to the tube.

In this case, they have little clamps, which are going to

electric source.

Here is some video footage we took of our small hydrogen lamp.

First is the lamp itself over on the right.

If we pass that light through a grading, we can separate that

pinkish purple composite light we observe with our eyes into its component colors.

You can see

some bright vertical lines of different colors separated by dark black spaces.

Other than the pinkish purple lamp itself, what colored lines are you observing?

It makes sense that we can see red and blue when we split colors apart.

Because red and blue mix together to make

purple, the composite color of the lamp light.

As you've reported, we don't see all colors of the rainbow.

Hydrogen spectral discharge tube does not

yield a continuous spectrum of visible light.

The lines are some of the visible spectral lines for hydrogen.

We see duplicated spectra here.

Because the diffraction grating gives us first order,

second order, and third order, et cetera, diffraction.

If we pan back with the camera, then we can see the apparatus itself, which is a

not very expensive cardboard box, was a piece

of grating film tapped over a hole in it.

As Dr. Lyle removes the box, you can see the light itself and its power supply.

Next, let's look at some video footage we took of our helium lamp.

This time we are starting with the lamp itself in the center.

To the naked eye, this helium light is

a different color than the hydrogen light was.

It's bright pink, and you can see the bottom of the lamp if you look carefully.

Again, there are duplicate spectra observable through the grating

on either side of the lamp. Please tell me what you are observing.

Is the helium lamp giving off more or less lines of color than the hydrogen lamp?

Yes, hopefully you realize that more lines can be seen

in the helium atomic emission spectrum than we saw for hydrogen.

Finally is the neon light, again, the lamp itself is in the center.

To the naked eye, the neon light is very bright red.

The spectrum that is showing up has lots of red and some magenta and yellow.

This is one that everyone is familiar with, vintage red neon signs.

In the United States, these signs are often used to advertise for the

beverage beer.

The camera has been panned back now, so you can see

the window we made in our cardboard box covered with the grating.

And finally, the block with the grating taped to it is

being pulled away, so that you can see the light apparatus again.

What we just watched was a demonstration of spectral tubes.

The study of atomic and molecular

spectra is a scientific specialty called spectroscopy.

The electrons of each element were excited in a discharge tube using electricity.

The energy from the electricity was converted to kinetic

energy that allowed the electron to move further away

from its atom's nucleus.

But this excited state is a temporary state.

As the excited electrons fell from this higher energy level back to another

lower energy level closer to the nucleus, they emitted photons of light.

That gave us the atomic emissions spectrum, and we could

see some of that spectrum in the visible light range.

Each element has its own set of allowed energy levels for the

electrons, and therefore, each element will have its own set of colored lines.

Tune in to the next lecture to learn more

about the energetics of this process for the hydrogen atom.

I can review what happened to the hydrogen atom using simple diagrams here.

If I draw a very curved picture of the hydrogen atom, with a dot in the center

for the positively charged nucleus, and a circle

to show the sphere where the electron is orbiting.

Here's the electron.

Initially, we put some energy into the

system using the electricity from the light apparatus.

When we did that, the electron had to respond by moving to higher energy.

So what it did was it moved further away from its nucleus.

So now the electron is in an excited state.

It's further away from the nucleus than it needs to be.

It then relaxed over time.

And when it relaxes, it emits light.

And it gets closer to its nucleus again, so that it's backward started from.

We will be reviewing this process in more detail

in the next lecture, so please check it out.

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