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

Viele chemische Reaktionen verlaufen in zwei Richtungen, vorwärts und rückwärts. Im Laufe der Zeit laufen die Vorwärts- und Rückwärtsreaktionen mit der gleichen Geschwindigkeit ab, und die Konzentration der Reaktanten und Produkte ändert sich nicht mehr. Dies wird als chemisches Gleichgewicht bezeichnet.
Im chemischen Gleichgewicht sind die Konzentrationen der einzelnen Komponenten durch die Gleichgewichtskonstante K miteinander verbunden, die das Verhältnis der Produktkonzentrationen zu den Reaktantenkonzentrationen darstellt, die jeweils hoch ihren stöchiometrischen Koeffizienten erhöht werden.
Doch wie bestimmt man Gleichgewichtskonzentrationen? Eine Methode misst die Intensität einer Wellenlänge des Lichts, die das Produkt vor und nach dem Durchgang durch eine Probe absorbiert. Die Intensitätsdifferenz wird als Absorption bezeichnet und entspricht der Menge der absorbierenden Verbindung in der Probe.
Sie erinnern sich vielleicht, dass Elektronen hauptsächlich den Grundzustand einnehmen. Wenn sie eine bestimmte Menge an Energie absorbieren, werden sie auf ein höheres Energieniveau angeregt. Diese Energie entspricht einer bestimmten Wellenlänge des Lichts. Sie können diese Wellenlänge ermitteln und die Absorption mit einem Spektralphotometer messen, das einen Lichtstrahl durch die Probe lenkt und die Intensitätsänderung bei einer oder mehreren Wellenlängen misst.
Die Absorption ist gleich dem negativen Logarithmus der Intensität des abgeschwächten Lichts über die Intensität des einfallenden Lichts. Durch die Darstellung der Absorptionswerte mehrerer Lösungen mit unterschiedlichen bekannten Produktkonzentrationen beobachten wir eine lineare Beziehung zwischen Absorption und Konzentration. Dies ist ein Beispiel für das Biersche Gesetz.
Das Beersche Gesetz wird mathematisch durch diese Gleichung ausgedrückt, wobei A die Absorption, Epsilon der molare Dämpfungskoeffizient, eine Konstante, die für jede Verbindung variiert, l die Weglänge des Lichts durch die Probe und c die Konzentration der Verbindung ist.
Durch die Identifizierung der linearen Funktion für eine gegebene Verbindung bei einer bestimmten Wellenlänge und Weglänge können Sie die Absorptionsdaten einer Lösung im Gleichgewicht verwenden, um die Gleichgewichtskonzentration des Produkts zu bestimmen. Von dort aus können Sie die Gleichgewichtskonzentrationen der Reaktanten berechnen und nach der Gleichgewichtskonstante auflösen. In diesem Labor bereiten Sie Lösungen von Eisen(III)-isothiocyanat vor und verwenden ein Spektralphotometer, um dessen Extinktion bei verschiedenen Konzentrationen zu bestimmen.

das gesetz des bieres

Absorption und Fluoreszenz
Wenn Licht auf eine Substanz trifft, wird es entweder absorbiert, durchgelassen oder reflektiert. Typischerweise interagiert eine Substanz mit einer Reihe von Wellenlängen des Lichts, wobei jede anders mit den Molekülen oder Atomen interagiert. Eine Substanz kann einen bestimmten Wellenlängenbereich absorbieren, einen anderen Wellenlängenbereich reflektieren und die anderen Wellenlängen des Lichts übertragen.
Wenn ein Molekül Licht absorbiert, wird die Energie auf vier verschiedene Arten genutzt: (1) Translation, die das Molekül dazu bringt, seine Molekülgeschwindigkeit zu ändern; (2) Vibration, die dazu führt, dass sich der Abstand zwischen den Molekülen schnell ändert; (3) Rotation, die dazu führt, dass sich die Atome um die Bindungen in einem Molekül drehen; und (4) Elektronenanregung, die dazu führt, dass Elektronen auf höhere Energieniveaus übergehen.
<h4>Energieniveau</h4>
Im Jahr 1913 schlug Niels Bohr ein Modell für das Wasserstoffatom vor, in dem sich Elektronen in festen, kreisförmigen Umlaufbahnen, den sogenannten stationären Zuständen, um den Kern bewegen. Die Energie, die mit jedem Umlauf oder stationären Zustand verbunden ist, existiert nur bei festen, diskreten Energien. Erst wenn sich ein Elektron auf eine andere Umlaufbahn bewegt, wird Energie absorbiert oder abgegeben. Das Elektron befindet sich nie zwischen den Zuständen. Diese Änderung tritt nur dann ein, wenn die aufgenommene oder abgegebene Energie gleich der Differenz zwischen den beiden Energiezuständen ist.
In Bohrs Modell repräsentiert die Quantenzahl n die Energie des Elektrons. Wenn ein Elektron den geringstmöglichen Energiezustand einnimmt, spricht man davon, dass es den Grundzustand einnimmt, der n = 1 ist. Wenn ein Elektron ein Photon absorbiert, dessen Energie der Differenz zwischen dem ersten und dem zweiten Zustand entspricht, wird das Elektron angeregt und geht vom Grundzustand in den angeregten Zustand über, wobei n = 2 ist. Wenn die Energie des Photons gleich der Differenz zwischen dem ersten und dritten Zustand ist, geht das Elektron in den dritten Zustand über, oder n = 3, und so weiter.
Elektronen können spontan in den Grundzustand oder einen anderen niedrigeren, angeregten Zustand zurückkehren. In diesem Fall wird die überschüssige Energie, die durch die Anregung gewonnen wurde, in Form eines emittierten Photons freigesetzt. Die Energie des Photons ist gleich der Differenz zwischen den beiden Energiezuständen und entspricht unterschiedlichen Wellenlängen des Lichts.
<h4>Absorptions- und Emissionsspektren</h4>
Während die meisten Substanzen die maximale Lichtmenge bei einer Wellenlänge absorbieren oder emittieren, neigen sie auch dazu, Licht bei einem Bereich von Wellenlängen zu absorbieren oder zu emittieren. Dieser Wellenlängenbereich wird als Spektrum bezeichnet. Die Energie des absorbierten Lichts wird mit Hilfe eines Absorptionsspektrums quantifiziert und visualisiert, während die Energie des emittierten Lichts mit Hilfe eines Emissionsspektrums quantifiziert und visualisiert wird.
Absorptions- und Emissionsspektren werden mit einem Spektralphotometer gemessen, einem Gerät, das Licht durch eine Probe durchlässt und dann sowohl die Wellenlänge als auch die Intensität des Lichts misst, das sie durchdringt. Im Inneren des Spektralphotometers befindet sich entweder ein Beugungsgitter oder ein Prisma, das das einfallende Licht in seine einzelnen Wellenlängen trennt. Die verschiedenen Wellenlängen werden dann durch die Probe übertragen, und die Intensität wird auf einem CCD-Detektor (Linear Charge-Coupled Device) aufgezeichnet. Der CCD ist ein integrierter Schaltkreis, der auf eine Siliziumoberfläche geätzt ist und lichtempfindliche Elemente bildet, die als Pixel bezeichnet werden. Der CCD sammelt und sortiert das gebeugte Licht und liest es mit einer Absorptionswellenlänge zurück.
Bei der Messung der Extinktion einer Probe wird der gelöste Stoff in der Regel in einem Lösungsmittel gelöst und in einen Behälter gegeben, der als Küvette bekannt ist. Dann wird die Probe in das Spektralphotometer gelegt, und die Intensität des durchgelassenen Lichts wird zusammen mit den Wellenlängen des Lichts gemessen, um ein Absorptionsspektrum zu erhalten. Erwartungsgemäß ist die Intensität des durchgelassenen Lichts geringer als wenn sich keine Probe im Spektralphotometer befindet.
Dies liegt daran, dass das durchgelassene Licht von der Probe, der Küvette und dem Lösungsmittel absorbiert wird. Vor der Messung von Proben muss das Spektralphotometer mit einem "Rohling" kalibriert werden. Ein Rohling ist eine Küvette, die nur das Lösungsmittel enthält, das zum Auflösen des gelösten Stoffes verwendet wird. Das Spektralphotometer ist so kalibriert, dass die Gesamtextinktion durch Küvette und Lösungsmittel von der gemessenen Extinktion der Probe abgezogen wird. Dies ermöglicht es uns, die Absorption zu erfassen, die nur der interessierenden Art zugeschrieben wird.
Die Extinktion wird oft bei einer Wellenlänge gemessen, der maximalen Absorptionswellenlänge. Die Absorption kann jedoch auch bei einer Reihe von Wellenlängen gemessen werden, um das Absorptionsspektrum zu erfassen. Zu diesem Zweck wird die Probe einem Bereich von Wellenlängen des einfallenden Lichts ausgesetzt, und die Absorption wird bei jeder Wellenlänge aufgezeichnet. Wenn die Probe Licht emittiert, wird das Emissionsspektrum auf ähnliche Weise gemessen, mit der Ausnahme, dass die einfallende Wellenlänge auf die Wellenlänge der maximalen Absorption festgelegt ist. Das Instrument misst dann die Intensität des emittierten Lichts über einen Bereich von Wellenlängen.
<h4>Bier-Lambert-Gesetz</h4>
Die Extinktion einer Probe bei der Wellenlänge der maximalen Extinktion gibt Aufschluss über die Probe, nämlich ihre Konzentration. Das Beer-Lambert-Gesetz ist eine Gleichung, die die Durchlässigkeit mit der Probenkonzentration in Beziehung setzt. Die Durchlässigkeit oder Intensität des durchgelassenen Lichts ist der Anteil des ursprünglichen Lichts, der durch die Probe fällt, I, geteilt durch die Intensität des einfallenden Lichts, I0.
<img src="/CDNSource/lm/labs/49/49_Concepts_1.jpg" alt="Transmissionsgleichung \(T = \frac{I}{I_0}\), Diagramm für die optische Dichteanalyse." data-altupdatedat="1754907201000">
Das Beer-Lambert-Gesetz besagt, dass die optische Absorption A einer Spezies in Lösung mit dem negativen Logarithmus der Durchlässigkeit zusammenhängt.
<img src="/CDNSource/lm/labs/49/49_Concepts_2.jpg" alt="Absorptionsformel A=-log(T), Gleichung für die optische Absorptionsanalyse in Spektroskopiestudien." data-altupdatedat="1754907201000">
Eine alternative Version des Beer-Lambert-Gesetzes besagt, dass die optische Absorption A einer Spezies in Lösung linear proportional zur Konzentration c dieser Spezies ist, wenn die Wellenlänge λ und die Weglänge l konstant gehalten werden.
<img src="/CDNSource/lm/labs/49/49_Concepts_3.jpg" alt="Beer-Lambert-Gesetz-Gleichung, A=εcl, Absorptionskonzept, spektroskopische Datenanalyse, physikalisches Diagramm." data-altupdatedat="1754907201000">
Der molare Abschwächungskoeffizient (ε) ist ein Maß dafür, wie stark eine Spezies Licht bei einer bestimmten Wellenlänge absorbiert. Je größer der molare Dämpfungskoeffizient, desto größer die Absorption. Die Weglänge l ist die Entfernung, die das Licht durch die Probe zurücklegt, was der Breite der Küvette entspricht. Standardküvetten haben eine Schichtdicke von 1 cm.
Diese lineare Beziehung zwischen Extinktion und Konzentration ist ein leistungsfähiges Werkzeug, mit dem die Konzentration einer unbekannten Probe anhand ihrer Extinktion bestimmt werden kann. Zu diesem Zweck wird eine Standardkurve unter Verwendung eines Gradienten bekannter Konzentrationen des gelösten Stoffes erzeugt. Die Extinktion bei der maximalen Absorptionswellenlänge λmax wird für jede Konzentration gemessen.
Durch die Darstellung von Konzentration und Absorption wird eine lineare Beziehung beobachtet, die der Beer-Lambert-Gleichung entspricht. Die Steigung dieser Linie ist gleich dem Produkt aus der Weglänge und dem molaren Dämpfungskoeffizienten. Mit dieser berechneten linearen Funktion kann die Konzentration leicht bestimmt werden, wenn die Extinktion der unbekannten Probe bekannt ist.
Wenn es sich bei der zu analysierenden Probe um eine Gleichgewichtsreaktion handelt, kann das Biersche Gesetz zur Bestimmung der Gleichgewichtskonzentration eines Produkts oder Reaktanten verwendet werden, wenn die Extinktion bei λmax gemessen wird, die für dieses Produkt oder diesen Reaktanten spezifisch ist. Sobald die Konzentration bekannt ist, können Sie die Gleichgewichtskonzentrationen der verbleibenden Reaktanten und Produkte bestimmen und dann nach der Gleichgewichtskonstante Keq auflösen.
<h4>Referenzen</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr., P.M., Townsend, J.R. (2012). Chemie und chemische Reaktivität. Belmont, Kalifornien: Brooks/Cole, Cengage Lernen.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). Chemie: Die molekulare Natur von Materie und Veränderung. Boston, MA: McGraw Hill, Boston.</li>
	<li style="font-size:17px">Harris, D.C. (2015). Quantitative chemische Analyse. New York, NY: W.H. Freeman und Company.</li>
</ol>

Das Gesetz des Bieres

Absorption und Fluoreszenz
Wenn Licht auf eine Substanz trifft, wird es entweder absorbiert, durchgelassen oder reflektiert. Typischerweise interagiert eine Substanz mit einem Bereich ...

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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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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

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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

Bereiten Sie den Unterricht zu Das Gesetz des Bieres mit diesem 7-minütigen Leitfaden für Lehrkräfte vor. Behandelt die wichtigsten Vorbereitungsschritte für das Chemistry-Labor auf JoVE Lab Manual.

Das Gesetz des Bieres Lehrervorbereitung in Chemistry - 4.7K+ Aufrufe | JoVE Lab Manual

Folgen Sie den Schritt-für-Schritt-Verfahren von Das Gesetz des Bieres in diesem 17-minütigen Studentenprotokoll-Video. Teil der Chemistry-Sammlung auf JoVE Lab Manual.

Das Gesetz des Bieres Studentenprotokoll in Chemistry - 40K+ Aufrufe | JoVE Lab Manual

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 ...

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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