Name: absorbance spectra and beer-lambert analysis
Uploaded: 2020-03-26T07:22:26.000Z
Duration: 2 min 53 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

Beer's Law

Многие химические реакции протекают в двух направлениях: прямом и обратном. Со временем прямые и обратные реакции будут происходить с одинаковой скоростью, а концентрация реагентов и продуктов уже не будет меняться. Это известно как химическое равновесие.
При химическом равновесии концентрации каждого компонента связаны друг с другом константой равновесия K, которая представляет собой отношение концентраций продуктов к концентрациям реагентов, каждая из которых приводится в степень их стехиометрических коэффициентов.
Но как определить равновесные концентрации? Один из методов измеряет интенсивность длины волны света, которую продукт поглощает до и после прохождения через образец. Разница интенсивностей называется абсорбцией, и она соответствует количеству поглощающего соединения в образце.
Возможно, вы помните, что электроны в основном находятся в основном в основном состоянии. Когда они поглощают определенное количество энергии, они возбуждаются до более высокого энергетического уровня. Эта энергия соответствует определенной длине волны света. Вы можете найти эту длину волны и измерить поглощение с помощью спектрофотометра, который направляет луч света через образец и измеряет изменение интенсивности на одной или нескольких длинах волн.
Поглощение равно отрицательному логарифму интенсивности ослабленного света по отношению к интенсивности падающего света. Построив графики значений поглощения нескольких растворов с различными известными концентрациями продуктов, мы наблюдаем линейную зависимость между поглощением и концентрацией. Это пример закона Пива.
Закон Бира математически выражается следующим уравнением, где A — поглощение, эпсилон — молярный коэффициент затухания, константа, которая варьируется для каждого соединения, l — длина пути света через образец, а c — концентрация соединения.
Определив линейную функцию для данного соединения на определенной длине волны и длине пути, вы можете использовать данные об поглощении решения в равновесном состоянии для определения равновесной концентрации продукта. Исходя из этого, вы можете рассчитать равновесные концентрации реагентов и рассчитать константу равновесия. В этой лаборатории вы будете готовить растворы изотиоцианата железа (III) и использовать спектрофотометр для определения его поглощения в различных концентрациях.

Закон о пиве

Абсорбция и флуоресценция
Когда свет попадает на вещество, оно либо поглощается, либо пропускается, либо отражается. Как правило, вещество взаимодействует с диапазоном длин волн света, каждая из которых взаимодействует с молекулами или атомами по-разному. Вещество может поглощать определенный диапазон длин волн, отражать другой диапазон длин волн и пропускать другие длины волн света.
Когда молекула поглощает свет, энергия используется четырьмя различными способами: (1) перемещение, которое заставляет молекулу изменять свою молекулярную скорость; (2) вибрация, которая приводит к быстрому изменению расстояния между молекулами; (3) вращение, которое заставляет атомы вращаться вокруг связей в молекуле; и (4) возбуждение электронов, которое заставляет электроны переходить на более высокие энергетические уровни.
<h4>Уровни энергии</h4>
В 1913 году Нильс Бор предложил модель атома водорода, в которой электроны движутся вокруг ядра по фиксированным круговым орбитам, называемым стационарными состояниями. Энергия, связанная с каждой орбитой, или стационарным состоянием, существует только при фиксированных, дискретных энергиях. Только когда электрон переходит на другую орбиту, энергия поглощается или испускается. Электрон никогда не находится между промежуточными состояниями. Это изменение происходит только в том случае, если поглощенная или излучаемая энергия равна разнице между двумя энергетическими состояниями.
В модели Бора квантовое число n представляет собой энергию электрона. Когда электрон занимает минимально возможное энергетическое состояние, говорят, что он занимает основное состояние, которое равно n = 1. Когда электрон поглощает фотон, энергия которого равна разности между первым и вторым состояниями, электрон возбуждается и переходит из основного состояния в возбужденное, где n = 2. Если энергия фотона равна разности между первым и третьим состояниями, электрон переходит в третье состояние, или n = 3, и т. д.
Электроны могут самопроизвольно возвращаться в основное состояние или в любое другое более низкое, возбужденное состояние. Когда это происходит, избыточная энергия, полученная от возбуждения, высвобождается в виде испускаемого фотона. Энергия фотона равна разнице между двумя энергетическими состояниями и соответствует разным длинам волн света.
<h4>Спектры поглощения и излучения</h4>
В то время как большинство веществ поглощают или излучают максимальное количество света на одной длине волны, они также имеют тенденцию поглощать или излучать свет в диапазоне длин волн. Этот диапазон длин волн называется спектром. Энергия поглощенного света количественно определяется и визуализируется с помощью спектра поглощения, в то время как энергия излучаемого света количественно измеряется и визуализируется с помощью спектра излучения.
Спектры поглощения и излучения измеряются с помощью спектрофотометра, который представляет собой устройство, пропускающее свет через образец, а затем измеряющее как длину волны, так и интенсивность света, проходящего через него. Внутри спектрофотометра находится либо дифракционная решетка, либо призма, которая разделяет входящий свет на составляющие его длины волн. Затем различные длины волн пропускаются через образец, а интенсивность регистрируется на детекторе устройства с линейной зарядовой связью (ПЗС). ПЗС-матрица представляет собой интегральную схему, выгравированную на кремниевой поверхности, которая образует светочувствительные элементы, называемые пикселями. ПЗС-матрица собирает и сортирует дифрагированный свет и считывает его обратно на длине волны поглощения.
При измерении абсорбционной способности образца растворенное вещество обычно растворяют в растворителе и помещают в контейнер, известный как кювета. Затем образец помещают внутрь спектрофотометра, и измеряют интенсивность проходящего света вместе с длинами волн света для получения спектров поглощения. Как и ожидалось, интенсивность проходящего света ниже, чем при отсутствии образца внутри спектрофотометра.
Это связано с тем, что проходящий свет поглощается образцом, кюветой и растворителем. Перед измерением образцов спектрофотометр должен быть откалиброван с «заготовкой». Бланк — это кювета, которая содержит только растворитель, используемый для растворения растворенного вещества. Спектрофотометр откалиброван таким образом, что общая поглощающая способность, обусловленная кюветой и растворителем, вычитается из измеренной абсорбции образца. Это позволяет нам регистрировать поглощение, которое приписывается только интересующему нас виду.
Поглощение часто измеряется на одной длине волны, максимальной длине волны поглощения. Тем не менее, поглощение также может быть измерено в диапазоне длин волн для получения спектра поглощения. Для этого образец подвергается воздействию падающего света в диапазоне длин волн, и поглощение регистрируется на каждой длине волны. Если образец излучает свет, спектр излучения измеряется аналогичным образом, за исключением того, что длина падающей волны фиксируется на длине волны максимального поглощения. Затем прибор измеряет интенсивность излучаемого света в диапазоне длин волн.
<h4>Закон Бир-Ламберта</h4>
Поглощение образца на длине волны максимального поглощения дает информацию о образце, а именно о его концентрации. Закон Бера-Ламберта — это уравнение, которое связывает коэффициент пропускания с концентрацией образца. Коэффициент пропускания, или интенсивность проходящего света, представляет собой долю исходного света, проходящего через образец I, деленную на интенсивность падающего света I0.
<img src="/CDNSource/lm/labs/49/49_Concepts_1.jpg" alt="Уравнение пропускания \(T = \frac{I}{I_0}\), диаграмма для анализа оптической плотности." data-altupdatedat="1754907201000">
Закон Бера-Ламберта гласит, что оптическое поглощение А вещества в растворе связано с отрицательным логарифмом пропускания.
<img src="/CDNSource/lm/labs/49/49_Concepts_2.jpg" alt="Формула поглощения A=-log(T), уравнение для анализа оптического поглощения в спектроскопических исследованиях." data-altupdatedat="1754907201000">
Альтернативная версия закона Бера-Ламберта гласит, что оптическое поглощение A вещества в растворе линейно пропорционально концентрации c этого вещества, когда длина волны λ и длина пути l остаются постоянными.
<img src="/CDNSource/lm/labs/49/49_Concepts_3.jpg" alt="Уравнение закона Бера-Ламберта, A=εcl, концепция поглощения, спектроскопический анализ данных, физическая диаграмма." data-altupdatedat="1754907201000">
Молярный коэффициент затухания, ε, является мерой того, насколько сильно вещество поглощает свет на данной длине волны. Чем больше коэффициент затухания моляров, тем больше поглощение. Длина пути, l, — это расстояние, на которое свет проходит через образец, то есть ширина кюветы. Стандартные кюветы имеют длину пути 1 см.
Эта линейная зависимость между поглощением и концентрацией является мощным инструментом, который используется для определения концентрации неизвестного образца на основе его поглощения. Для этого строится стандартная кривая с использованием градиента известных концентраций растворенного вещества. Поглощение на пиковой длине волны поглощения, λmax, измеряется для каждой концентрации.
При построении графика зависимости концентрации от поглощения наблюдается линейная зависимость, которая соответствует уравнению Бира-Ламберта. Наклон этой линии равен произведению длины пути на молярный коэффициент затухания. Используя эту рассчитанную линейную функцию, если известна поглощающая способность неизвестного образца, можно легко определить концентрацию.
Если анализируемый образец представляет собой реакцию в равновесии, закон Бира может быть использован для определения равновесной концентрации продукта или реагента, если поглощение измеряется при λmax, специфичном для этого продукта или реагента. После того, как концентрация известна, можно определить равновесные концентрации остальных реагентов и продуктов, а затем рассчитать константу равновесия Keq.
<h4>Ссылки</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Химия и химическая реакционная способность. Бельмонт, Калифорния: Брукс/Коул, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). Химия: молекулярная природа материи и изменения. Бостон, Массачусетс: Макгроу Хилл, Бостон.</li>
	<li style="font-size:17px">Harris, D.C. (2015). Количественный химический анализ. Нью-Йорк, Нью-Йорк: W.H. Freeman and Company.</li>
</ol>

Абсорбция и флуоресценция
Когда свет попадает на вещество, оно либо поглощается, либо пропускается, либо отражается. Как правило, вещество взаимодействует с целым рядом ...

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JoVE Lab Manual

Chemistry

Химия

absorbance spectra and beer-lambert analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way.

When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it moves an electron to a higher energy level. In Niels Bohr’s model, electrons in the hydrogen atom move in fixed circular orbits called stationary states, and each state has a discrete energy. An electron can move only when it absorbs or emits energy equal to the difference between two states.

The lowest energy state is the ground state, or n = 1. If a photon has the right energy, the electron can move to a higher state such as n = 2 or n = 3. When the electron returns to a lower state, it releases the extra energy as an emitted photon. The photon energy matches the energy gap between the two states and corresponds to specific wavelengths of light.

Most substances absorb or emit most strongly at one wavelength, but they usually interact with a range of wavelengths. That range is called a spectrum. An absorption spectrum shows how much light a sample absorbs at different wavelengths, and an emission spectrum shows the light a sample gives off. These spectra are measured with a spectrophotometer, which sends light through a sample and records the wavelength and intensity of the light that passes through.

Inside the spectrophotometer, a diffraction grating or a prism separates incoming light into its component wavelengths. The light then passes through the sample, and a linear charge-coupled device, or CCD, detector records the intensity. A CCD is an integrated circuit on silicon that contains light-sensitive pixels. It collects and sorts the diffracted light and reads it back at an absorption wavelength.

For absorbance measurements, the solute is usually dissolved in a solvent and placed in a cuvette, which is the container used in the instrument. The sample is then placed in the spectrophotometer, and the intensity of transmitted light is measured along with wavelength to produce an absorbance spectrum. The transmitted light is lower than when no sample is present because light is absorbed by the sample, the cuvette, and the solvent. Before samples are measured, the spectrophotometer is calibrated with a blank, which is a cuvette that contains only the solvent. This step removes the absorbance from the cuvette and solvent so the reading reflects only the species of interest.

Absorbance is often measured at the wavelength of maximum absorbance, but it can also be recorded across a range of wavelengths. For emission spectra, the incident wavelength is fixed at the wavelength of maximum absorbance, and the instrument measures emitted light over a range of wavelengths. The Beer-Lambert Law then connects absorbance to sample concentration. Transmittance is the fraction of light that passes through the sample, I divided by I0, and absorbance is related to the negative log of transmittance.

A second form of the Beer-Lambert Law shows that absorbance is directly proportional to concentration when wavelength and pathlength stay constant. The molar attenuation coefficient, ε, describes how strongly a species absorbs light at a given wavelength. The pathlength, l, is the distance the light travels through the sample, which is the width of the cuvette. Standard cuvettes have a 1 cm pathlength. This linear relationship makes it possible to find the concentration of an unknown sample from its absorbance.

To do that, a standard curve is made with known concentrations of the solute. The absorbance at λ max is measured for each standard, and the results are plotted as concentration versus absorbance. The line that appears matches the Beer-Lambert equation, and its slope equals the product of the pathlength and the molar attenuation coefficient. Once that line is known, the concentration of an unknown sample can be calculated from its absorbance.

Beer’s Law can also be used for reactions at equilibrium. If absorbance is measured at the λ max of a specific product or reactant, the equilibrium concentration of that species can be found. The concentrations of the other reactants and products can then be determined, and the equilibrium constant K eq can be solved.

Absorbance Spectra and Beer-Lambert Analysis

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Reaction Rate, Arrhenius, and Catalysts

Chemical kinetics explains how fast a reaction happens and why that speed changes. The reaction rate is the speed of a chemical reaction. It is defined as the change in concentration of a reactant or product over time. Reaction speed depends on several factors, including the concentration of the reactants and the temperature of the reaction. Each reactant affects the rate in a specific way. That relationship is described by the rate law. The rate law is an equation that connects the...

galvanic cells

Battery Power from Redox Reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The...

electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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Explore how spectrophotometers measure absorbance spectra, how blank calibration works, and how Beer-Lambert Law is used to find concentration and equilibrium values.

Absorbance Spectra and Beer-Lambert Analysis | JoVE K12

Louisiana Student Standards for Science

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Motion And Stability: Forces And Interactions

HS-PS2-6

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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 ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Ions and Ionic Charges

In ordinary chemical reactions, the nucleus &mdash; which contains the protons and neutrons of each atom and thus identifies the element &mdash; remains ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Model basic atomic structure and relate an element's atomic structure to its bonding, reactivity, and placement on the Periodic Table.

IPC.7.A

physical-and-chemical-properties-of-matter

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 ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Use patterns within the Periodic Table to predict the relative physical and chemical properties of elements.

IPC.7.B

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
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

phase-transitions-vaporization-and-condensation

Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

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 ...

Explain how physical and chemical properties of substances are related to their usage in everyday life such as in sunscreen, cookware, industrial applications, and fuels.

IPC.7.C

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Absorbance Spectra and Beer-Lambert Analysis

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