Name: line spectra from heated gases
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 39 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Physical Science

Matter and its Interactions

PS.PSc.1.4

Emission Spectra

Quando um átomo absorve energia, os elétrons ficam excitados e passam para um nível de energia mais elevado. Como os elétrons relaxam até um estado de energia mais baixa ou até ao estado do solo, o excesso de energia seja libertado como um fotão. O comprimento de onda da luz absorvida e emitida depende da diferença entre os níveis de energia elevada energia baixa.A luz de energia elevada emitida resulta dos elétrons a relaxar a partir de um nível de energia mais elevado, e a luz de baixa energia emitida resulta do relaxamento dos elétrons de um nível de energia mais baixo. Um espectro de emissão é uma medida da radiação emitida através de uma gama de comprimentos de onda. Com espécies elementares puras, o comportamento das emissões aparecem como linhas de comprimentos de onda específicos em vez de um largo espectro.Este é o espectro das emissões de hidrogênio. O conjunto de linhas espectrais na região da luz visível é conhecida como a série Balder. Ocorre quando a transição dos elétrons a partir de um nível de energia superior a n 3 de volta a n 2.O espectro de luz visível aparece como linhas espectrais a 410, 434, 486 e 656 nm, que correspondem a transições de nível de energia de n 3, 4, 5, e 6, respetivamente até n 2. Podem ser medidas linhas espectrais adicionais fora do alcance visível, como a série Lyman na região UV e a série Paschen na região do infravermelho. Os comprimentos de onda das linhas espectrais para o hidrogênio podem ser previstos utilizando uma expressão matemática, onde R-H é a constante de Rydberg, n1 é o número quântico principal do nível de energia inferior, e n2 é o número quântico principal para o nível de energia mais elevado.Para a série Balmer, n1 2. Uma vez que átomos diferentes têm níveis de energia diferentes, as linhas de emissão espectral variam de elemento para elemento e são utilizadas para identificar substâncias. O inverso de um espectro de emissões é o seu espectro de absorção.Olhando para o hidrogênio, as linhas no seu espectro de absorção estão localizadas nos mesmos comprimentos de onda da sua emissão mas são escuras. Estes são os comprimentos de onda de luz que são absorvidos por um átomo de hidrogênio quando é exposto ao espectro de uma luz branca contínua.

espectros de emissão

Quando sólidos, líquidos, ou gases condensados são suficientemente aquecidos, eles irradiam alguma energia em excesso na forma de luz. Os fotões produzidos desta forma têm uma gama de energias, produzindo assim um espectro contínuo no qual uma série de comprimentos de onda não quebrados está presente.

Ao contrário dos espectros contínuos, a luz também pode ocorrer como espectros discretos ou de linha com larguras de linha muito estreitas intercaladas ao longo das regiões espectrais. Excitar um gás a baixa pressão parcial utilizando uma corrente elétrica, ou o seu aquecimento, irá produzir espectros de linha. As lâmpadas fluorescentes e os sinais de néon funcionam desta forma. Cada elemento apresenta o seu próprio conjunto de linhas característico, tal como as moléculas, embora os seus espectros sejam geralmente muito mais complicados.

Cada linha de emissão consiste em um único comprimento de onda de luz, o que implica que a luz emitida por um gás consiste em um conjunto de energias discretas. Por exemplo, quando uma descarga elétrica passa através de um tubo que contém hidrogénio a baixa pressão, as moléculas H2 são divididas em átomos H separados e é observada uma cor azul-rosa. Passando a luz através de um prisma produz um espectro de linha, indicando que esta luz é composta por fotões de quatro comprimentos de onda visíveis.

A origem dos espectros discretos em átomos e moléculas foi extremamente intrigante para os cientistas no final do século XIX. De acordo com a teoria eletromagnética clássica, apenas espectros contínuos deveriam ser observados. Outras linhas discretas para o átomo de hidrogénio foram encontradas nas regiões UV e IV. Johannes Rydberg generalizou o trabalho de Balmer e desenvolveu uma fórmula empírica que previa todas as linhas de emissão do hidrogénio, não apenas as restritas à gama visível, onde , n1 e n2 são inteiros, n1 < n2

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/977/977_Equations-01.png" style="height: 40px;" />

Mesmo no final do século XIX, a espectroscopia era uma ciência muito precisa, pelo que os comprimentos de onda do hidrogénio foram medidos com uma precisão muito elevada, o que implicou que a constante Rydberg pudesse ser também determinada com muita precisão. Que uma fórmula tão simples como a fórmula de Rydberg poderia explicar tais medições precisas parecia surpreendente na altura, mas foi a eventual explicação para os espectros de emissões por Neils Bohr em 1913 que, em última análise, convenceu os cientistas a abandonarem a física clássica e estimulou o desenvolvimento da mecânica quântica moderna.

Este texto foi adaptado de <a href="https://openstax.org/books/chemistry-atoms-first-2e/pages/3-1-electromagnetic-energy">Openstax, Chemistry 2e, Section 3.1: Electromagnetic Energy</a>.

Espectros de Emissão

Quando sólidos, líquidos ou gases condensados são aquecidos o suficiente, eles irradiam parte do excesso de energia como luz. Os fótons produzidos dessa maneira têm um ...

Education

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Chemistry

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Electronic Structure of Atoms

Estrutura Eletrônica dos Átomos

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

line spectra from heated gases

Line spectra are produced when heated gases give off light at specific wavelengths. In contrast, hot solids, liquids, or condensed gases radiate excess energy as a continuous spectrum. That spectrum contains an unbroken range of wavelengths.

A gas at low partial pressure can produce a line spectrum when it is excited by an electric current or heated. Fluorescent light bulbs and neon signs work in this way. Each element has its own characteristic set of lines, and molecules can also produce line spectra, although their patterns are usually more complex.

Each emission line is a single wavelength of light. That means the light from a gas is made of discrete energies rather than a smooth spread of values. A good example is hydrogen gas in an electric discharge tube. The H2 molecules break apart into separate H atoms, and the gas gives off a blue-pink color.

When that light is passed through a prism, it separates into a line spectrum. For hydrogen, this shows four visible wavelengths. Scientists also found other hydrogen lines in the ultraviolet and infrared regions. In the late nineteenth century, these discrete spectra were hard to explain because classical electromagnetic theory predicted only continuous spectra.

Johannes Rydberg extended Balmer's work and wrote an empirical formula that predicted all of hydrogen's emission lines, not just the visible ones. The wavelengths of hydrogen were measured with high accuracy, so the Rydberg constant could also be determined very precisely. Later, Niels Bohr explained emission spectra in 1913. His explanation helped push scientists away from classical physics and toward modern quantum mechanics.

Line Spectra from Heated Gases

the wave nature of light

Measuring Light with Wavelength and Frequency

Light can be described as an electromagnetic wave, and its behavior helps explain many patterns seen in science. For centuries, scientists have tried to understand light. Newton used lenses and prisms to show that white light is made of the colors of the rainbow mixed together. He explained light as tiny particles moving at high speed. Other scientists, including Christiaan Huygens, showed that reflection and refraction could also be explained by treating light as a wave. At the time, people...

the electromagnetic spectrum

Electromagnetic Waves: Uses Across the Spectrum

The electromagnetic spectrum includes all electromagnetic radiation arranged by frequency and wavelength. Visible light is only a small part of it, and each color of visible light has its own frequency and wavelength. Different parts of the spectrum also use different units. Radio waves are usually measured in MHz, while the visible range is often measured in nm or angstroms. The spectrum is organized from radio waves to gamma rays as frequency increases and wavelength decreases. Radio waves...

interference and diffraction

Wave Patterns from Light and Slits

Light can form wave patterns through interference and diffraction. When two electromagnetic waves meet with their peaks and troughs lined up, they combine into a larger wave. This is constructive interference, and the waves are in phase. When a peak of one wave meets a trough of the other, the waves reduce each other. This is destructive interference, and the result has a much lower amplitude. Diffraction is another wave behavior. When light passes through a slit that is about the same size as...

photoelectric effect

Why Light Ejects Electrons from Metals

Light can eject electrons from a metal surface when it has the right frequency. This process is called the photoelectric effect. Each metal has its own threshold frequency, which is the minimum light frequency needed to free electrons. Light below the threshold frequency cannot cause emission, even if it is very bright. When the light frequency is above the threshold, electrons are ejected. In that case, the number of electrons released is directly proportional to the intensity, or brightness,...

the bohr model

Bohr’s Quantized Atomic Orbits

Bohr’s quantized atomic orbits explain why hydrogen atoms can stay stable. Early in the twentieth century, Ernest Rutherford and his colleagues described atoms as tiny dense nuclei with lighter electrons moving around them. This picture was called the planetary model because it compared the atom to a miniature solar system, with electrons orbiting the nucleus like planets around the sun. The simplest atom is hydrogen. It has one proton in the nucleus and one electron moving around it. In the...

emission spectra

Line spectra are produced when heated gases give off light at specific wavelengths. In contrast, hot solids, liquids, or condensed gases radiate excess energy as a continuous spectrum. That spectrum contains an unbroken range of wavelengths. A gas at low partial pressure can produce a line spectrum when it is excited by an electric current or heated. Fluorescent light bulbs and neon signs work in this way. Each element has its own characteristic set of lines, and molecules can also produce...

the de broglie wavelength

Electron Waves and Standing Orbits

Electron waves and standing orbits explain how tiny particles can behave like waves. Large objects in the macroscopic world, like a billiard ball on a table, follow classical physics. A ball keeps moving in a straight line unless it hits another ball or a force such as friction acts on it. It also has a well-defined position, velocity, and momentum, where momentum is mass times velocity. Waves behave differently from macroscopic particles. When waves interact, they can form interference...

the uncertainty principle

Electron Position and Momentum Limits

Heisenberg’s uncertainty principle sets a limit on how precisely we can know an electron’s position and momentum at the same time. Momentum is the motion of a particle, and the two measurements affect each other. If the momentum is known more accurately, the position becomes less certain, and the reverse is also true. Heisenberg described this limit with an equation that uses Planck’s constant. The equation shows the smallest possible uncertainty for position and momentum together. It explains...

the quantum-mechanical model of an atom

Electron Orbitals in Quantum Mechanics

Quantum mechanics explains how electrons behave in atoms using waves and probability. Erwin Schrödinger built on de Broglie’s idea that an electron in hydrogen could act like a circular standing wave instead of moving in fixed circular paths. He then derived the Schrödinger equation, which became a major step in modern atomic theory. When Schrödinger applied his equation to hydrogen-like atoms, it matched Bohr’s energy expression and the Rydberg formula for hydrogen spectra. He described...

quantum numbers

Electron Orbitals and Spin

Electron orbitals are described by quantum numbers that show where an electron is most likely to be found around the nucleus. These numbers come from the quantum mechanical model, which is based on solutions of the Schrödinger equation. They also help explain why electron energy comes in set values instead of changing smoothly. The principal quantum number, n, labels the energy level. It can be 1, 2, 3, and so on, and higher n values usually mean higher electron energy. This number also tells...

atomic orbitals

Electron Regions in Atomic Orbitals

Electron regions in atomic orbitals show where an electron is most likely to be found in an atom. These three-dimensional regions are often drawn as boundary surfaces around the densest part of the cloud. The shape of an orbital depends on the angular momentum quantum number, l. This value can range from 0 to n - 1, where n is the principal quantum number. For n = 1, only l = 0 is allowed. For n = 2, both l = 0 and l = 1 are allowed. Orbitals with the same value of l form a subshell. The l =...

the pauli exclusion principle

Electron Spin and Orbital Pairing

Electron spin and orbital pairing explain why only two electrons can fit in one atomic orbital. Electron configuration describes how electrons are arranged in an atom’s orbitals. It is written with three parts: the principal quantum number, n, the orbital type, or subshell, and a superscript that shows how many electrons are in that subshell. For example, 2p4 means four electrons in a p subshell with n = 2, and 3d8 means eight electrons in a d subshell with n = 3. The three quantum numbers...

the energies of atomic orbitals

Shielding and Orbital Penetration

Shielding and orbital penetration help explain why electrons in an atom have different energies. Electrons are attracted to the positive nucleus, but they also repel one another in atoms with more than one electron. The strength of these forces depends on the charge and the distance between the particles. Opposite charges attract, like charges repel, and the force gets weaker as the particles move farther apart. An electron that stays closer to the nucleus is held more tightly. That means...

the aufbau principle and hund's rule

Electron Filling Order in Atomic Orbitals

Electron filling order in atomic orbitals follows the aufbau principle and Hund's rule. To write an electron configuration, we build atoms in order of atomic number. Starting with hydrogen and moving across the periods of the periodic table, one proton is added to the nucleus and one electron is placed into the correct subshell. This process describes the ground-state electron configurations of the elements. The aufbau principle comes from the German word aufbau, which means "to build up." It...

electron configuration of multielectron atoms

electron-configuration-of-multielectron-atoms

Valence Electrons and Noble Gas Shorthand

Valence electrons and noble gas shorthand help show how electrons are arranged in multielectron atoms. Sodium, the alkali metal with atomic number 11, has one more electron than neon. That extra electron goes into the lowest-energy subshell available, the 3s orbital, so sodium has the configuration 1s2 2s2 2p6 3s1. Electrons in the outermost shell, where n is highest, are called valence electrons. Electrons in the inner shells are called core electrons. Because core electrons often match a...

key terms and concepts

Explore how heated gases produce line spectra, why hydrogen shows discrete wavelengths, and how Rydberg and Bohr helped explain emission lines.

Line Spectra from Heated Gases | JoVE K12

chemistry

JoVE Core - Química dá vida a conceitos gerais de química usando vídeos de animação fáceis de entender. Além disso, nos vídeos Cientistas em ação, demonstramos experimentos de pesquisa clássicos e originais realizados atualmente por cientistas em laboratórios em todo o mundo.

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Earth Science

Earth’s Place In The Universe

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Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
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Solution Formation

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Phase Transitions

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Phase Transitions: Vaporization and Condensation

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Vapor Pressure

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally ...

Clausius-Clapeyron Equation

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Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

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Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

Use models to compare the phases of matter and the physical changes they undergo.

PS.PSc.1.2

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Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

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Molecular Comparison of Gases, Liquids, and Solids

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

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Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

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Carry out investigations to compare physical and chemical properties of matter.

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The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

Use models to interpret the data presented in Bohr diagrams and electron dot diagrams for neutral atoms of elements 1 through 18.

Understand types, properties, and structure of matter.

Line Spectra from Heated Gases

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