Name: hydrogen emission lines
Uploaded: 2020-03-26T07:22:25.000Z
Duration: 3 min 53 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

Balmer Series

אטומים ומולקולות מפגינים התנהגות מעניינת מאוד כאשר הם סופגים ומשחררים אנרגיה. האלקטרונים באטום קיימים באופן מסורתי במצב האנרגיה הנמוך ביותר שלהם, הנקרא מצב הקרקע, ומסומנים כ-n שווה לאחד. עם זאת, כאשר אטום סופג אנרגיה, האלקטרונים נעשים נרגשים ונעים לרמת אנרגיה גבוהה יותר. כאשר האלקטרונים נרגעים למצב אנרגיה נמוך יותר או למצב הקרקע, האנרגיה העודפת משתחררת כאור הנפלט.
ייתכן שאתם מכירים את מצבי האנרגיה האלה, כפי שהם מתוארים במודל בוהר, המתאר אטום כגרעין עם אלקטרונים המקיפים קונכיות או אורביטלים. קליפות אלה זהות לרמות האנרגיה ומסומנות על ידי n. אורך הגל של האור הנפלט תלוי בהפרש בין רמות האנרגיה הגבוהות והנמוכות. אור הנפלט באנרגיה גבוהה נובע מכך שאלקטרונים נרגעים מרמת אנרגיה גבוהה יותר, ואור הנפלט באנרגיה נמוכה נובע מכך שאלקטרונים נרגעים מרמת אנרגיה נמוכה יותר.
ספקטרום הפליטה הוא מדד לקרינה הנפלטת על פני טווח של אורכי גל. אצל מיני יסודות טהורים, התנהגות הפליטה מופיעה כקווים באורכי גל ספציפיים ולא כספקטרום רחב. מאחר שלאטומים שונים יש רמות אנרגיה שונות, קווים ספקטרליים אלה משתנים מיסוד ליסוד ותלויים במעברים שאלקטרונים אלה מבצעים בין מצבי אנרגיה כאשר הם מעוררים. לדוגמה, ישנן שש סדרות בעלות שם של קווים ספקטרליים עבור מימן, אחת מהן היא סדרת Balmer.
סדרת Balmer של קווים ספקטרליים מתרחשת כאשר אלקטרונים עוברים מרמת אנרגיה גבוהה מ-n = 3 בחזרה ל-n = 2. ספקטרום האור הנראה של סדרת Balmer מופיע כקווים ספקטרליים ב-410, 434, 486 ו-656 ננומטר. קו אלפא h הוא הקו האדום ב 656 ננומטר ומתרחש עקב המעבר מ n = 3 ל n = 2. קווי הציאן, הכחול והסגול מתאימים למעברי רמת האנרגיה מ-n = 4, 5 ו-6, בהתאמה, בחזרה ל-n = 2. קווים ספקטרליים נוספים ניתנים למדידה מחוץ לטווח הנראה לעין.
יוהאן באלמר כימת את הקווים הגלויים באמצעות נוסחת באלמר. כאן, למדא הוא אורך הגל הנצפה, c הוא קבוע, n היא רמת האנרגיה הנמוכה יותר של שתיים, ו-m היא רמת האנרגיה הגבוהה יותר. השילוב של משוואת באלמר ומודל בוהר נותן לנו את משוואת רידברג, המתארת את הקווים הספקטרליים של אלמנטים רבים ושונים. במשוואה זו, למדא הוא אורך הגל המוקלט, ו-RH הוא קבוע רידברג. הרמות ההתחלתיות המסומנות על ידי n-initial מייצגות את רמת האנרגיה הגבוהה יותר שהאלקטרונים מעוררים אליה, ו-n סופית היא רמת האנרגיה הנמוכה יותר שהאלקטרונים נרגעים אליה בחזרה. עבור סדרת Balmer, nfinal = 2.
במעבדה זו תמדוד ותצפה בספקטרום הפליטה של מימן, הליום וניאון ותשתמש במשוואת רידברג כדי לקבוע את מיקום הקווים הספקטרליים.

סדרת balmer

מודל בוהר
נילס בוהר הציע מודל לאטום המימן בשנת 1913 שתיאר מצבי אנרגיה בדידים הקשורים למסלול אלקטרונים קבוע סביב הגרעין. חשוב לציין, אטום אינו יכול לפרוק אנרגיה כאשר האלקטרונים שלו נמצאים במצב נייח. אלקטרון יכול לפלוט אנרגיה רק על ידי שינוי מצבי אנרגיה. כדי לשנות מצבי אנרגיה, אלקטרון חייב לעבור ממסלול אחד לאחר על ידי בליעה או פליטה של אנרגיה. שינוי זה יכול להתרחש רק אם האנרגיה הנבלעת או הנפלטת שווה להבדל בין שני המצבים. אלקטרונים אינם יכולים להתקיים בין מסלולים.
המספר הקוונטי, n, משמש לסימון מצבי האנרגיה השונים. מצב האנרגיה הנמוך ביותר הוא מצב הקרקע, שהוא n שווה לאחד. המצבים הנרגשים מסומנים n שווה ל- 2, 3, 4 וכן הלאה. כאשר אלקטרון במצב הקרקע בולע פוטון שהאנרגיה שלו שווה להפרש בין מצב הקרקע למצב השני, האלקטרון נעשה נרגש ועובר ממצב הקרקע למצב n=2 מעורר. אם האנרגיה של הפוטון שווה להפרש בין מצב הקרקע למצב השלישי, האלקטרון עובר למצב n=3.
על פי המודל של בוהר, ניתן לחשב את האנרגיה הפוטנציאלית של אלקטרון ברמהn באמצעות המשוואה הבאה:
<img src="/CDNSource/lm/labs/54/54_Concepts_1.jpg" alt="נוסחת רמת האנרגיה של מודל בוהר, En=-Rhc/n², הקשורה למעברי אלקטרונים, משוואה." data-altupdatedat="1754907201000">
כאשר En היא האנרגיה הפוטנציאלית, R הוא קבוע רידברג (1.0974 × 107 m-1), h הוא קבוע פלאנק (6.62607004 × 10-34 m2·kg/s), ו- c היא מהירות האור (~ 3 × 108 m/s). אלקטרונים יכולים גם לחזור באופן ספונטני למצב הקרקע או לכל מצב מעורר נמוך אחר. כאשר זה קורה, האנרגיה העודפת משתחררת בצורה של פוטון שנפלט. האנרגיה של הפוטון שווה להפרש האנרגיה בין מצבי האנרגיה הגבוהים והנמוכים. אנרגיה זו מתאימה לאורכי גל של אור. מכיוון שלכל סוג אטום יש רמות אנרגיה שונות, האור הנפלט מכל מעבר משתנה עבור כל אטום. עבור דגימה של מולקולות מעורבות, האור הנפלט מכיל טווח של אורכי גל במה שנקרא ספקטרום רציף. עבור דגימה המכילה אטומים של יסוד יחיד, האור הנפלט מכיל רק אורכי גל מסוימים, שניתן לראותם כקווים בדידים המופרדים פעם על ידי מנסרה.
<h4>אטום המימן</h4>
בהסתכלות ספציפית על אטום המימן, עירור האלקטרונים שלו דורש ספיגה של אנרגיה מספקת כדי לפצל את הקשר במולקולה הדיאטומית H2. מכיוון שיותר אנרגיה משמשת לפיצול המולקולה מהנדרש, האלקטרונים באטום המימן סופגים את האנרגיה העודפת ומעוררים לרמת אנרגיה גבוהה יותר. כאשר האלקטרונים חוזרים באופן ספונטני לרמת אנרגיה נמוכה יותר, נפלט אור, המתאים להפרש האנרגיה בין הרמה הנרגשת לרמה הנמוכה יותר.
כאשר דנים בפליטת אנרגיה, רמת האנרגיה הגבוהה יותר נחשבת לרמה הראשונית, או ni, ואילו הרמה הנמוכה יותר נחשבת לרמה הסופית, או nf. אורכי הגל של האור הנפלט תלויים בסופו של דבר בהפרש האנרגיה בין שתי הרמות.
בדגימה טהורה של גז מימן, ספקטרום הפליטה מופיע כקווים נפרדים של אורכי גל בדידים הספציפיים ליסוד מימן. חלק מהקווים הללו נמצאים בטווח הנראה לעין של הספקטרום האלקטרומגנטי, בעוד שחלקם נמצאים בתחום האולטרה סגול או האינפרא אדום.
<h4>סדרת Balmer</h4>
סדרת הקווים הנראים בספקטרום אטומי המימן נקראת סדרת באלמר. סדרה זו של קווי פליטה ספקטרליים מתרחשת כאשר האלקטרון עובר מרמת אנרגיה גבוהה לרמת אנרגיה נמוכה יותר של n=2. יוהאן באלמר צפה בקווים ספקטרליים אלה ברמות 410.2 ננומטר, 434.1 ננומטר, 486.1 ננומטר ו-656.3 ננומטר, המתאימים למעברים מרמות האנרגיה n=6, n=5, n=4 ו-n=3 לרמה n=2, בהתאמה.
באלמר הצליח לקשר בין אורכי גל אלה של האור הנפלט באמצעות נוסחת באלמר.
<img src="/CDNSource/lm/labs/54/54_Concepts_2.jpg" alt="נוסחת חישוב אורך גל λ=C(m²/(m²-n²)), משוואה לניתוח ספקטרוסקופיה." data-altupdatedat="1754907201000">
כאן, λ הוא אורך הגל הנצפה, C הוא קבוע (364.50682 ננומטר), n היא רמת האנרגיה הנמוכה יותר עם ערך של 2, ו- m היא רמת האנרגיה הגבוהה יותר, שיש לה ערך גדול מ -3. תצפית זו שוכללה אז על ידי יוהנס רידברג, כאשר R הוא קבוע רידברג.
<img src="/CDNSource/lm/labs/54/54_Concepts_3.jpg" alt="משוואת נוסחת רידברג; מחשב קווים ספקטרליים בספקטרוסקופיה אטומית." data-altupdatedat="1754907201000">
זכור כי משוואה זו מתארת את האור הנפלט, ולכן רמת האנרגיה הגבוהה יותר נחשבת לרמה הראשונית, או ni, ואילו הרמה הנמוכה יותר נחשבת לרמה הסופית, או nf. במקרה של סדרת Balmer, nf שווה ל-2. משוואה זו שולבה עם מודל בוהר כדי לחשב את האנרגיה הדרושה להעברת אלקטרון בין רמת האנרגיה הראשונית והסופית שלו, ΔE.
<img src="/CDNSource/lm/labs/54/54_Concepts_4.jpg" alt="משוואת מעבר רמת אנרגיה \(\Delta E = Rhc(\frac{1}{n_f^2} - \frac{1}{n_i^2})\); נוסחה פיזיקלית." data-altupdatedat="1754907201000">
מאוחר יותר התגלו סדרות ספקטרליות נוספות של אטום המימן. לדוגמה, סדרת ליימן מכילה קווי פליטה עם אנרגיות באזור האולטרה סגול.
<h4>הפניות</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). כימיה ותגובתיות כימית. בלמונט, קליפורניה: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). כימיה: הטבע המולקולרי של חומר ושינוי. בוסטון, מסצ'וסטס: מקגרו היל.</li>
</ol>

סדרת Balmer

מודל בוהר
נילס בוהר הציע מודל לאטום המימן בשנת 1913 שתיאר מצבי אנרגיה בדידים הקשורים למסלול אלקטרונים קבוע ...

Education

JoVE Lab Manual

Chemistry

כימיה

hydrogen emission lines

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them.

These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between two levels. A photon with the right energy can move an electron from one orbit to another.

Bohr’s model also links each energy level to a specific amount of potential energy. That value can be calculated with an equation that uses the Rydberg constant, Planck’s constant, and the speed of light. When an electron returns to the ground state or another lower excited state, it releases the extra energy as a photon. The photon energy matches the gap between the two states, so it also determines the wavelength of the emitted light.

Because each atom has its own energy levels, each element gives off its own pattern of light. A mixed sample can produce a continuous spectrum with many wavelengths. A pure sample of one element produces only certain wavelengths. When that light passes through a prism, it appears as separate lines instead of one smooth band.

Hydrogen shows this pattern clearly. Exciting hydrogen atoms requires enough energy to split the H2 molecule, and the extra energy excites the hydrogen electrons to higher levels. When those electrons drop back down, they emit light at wavelengths set by the energy difference between the initial level, n i, and the final level, n f. In pure hydrogen gas, this emission spectrum contains distinct visible, ultraviolet, and infrared lines that are unique to hydrogen.

The visible lines in hydrogen are called the Balmer series. They occur when an electron falls to n = 2 from a higher level. Johann Balmer observed lines at 410.2 nm, 434.1 nm, 486.1 nm, and 656.3 nm, which match transitions from n = 6, 5, 4, and 3 to n = 2. He described these wavelengths with the Balmer formula, where λ is the observed wavelength, C is a constant of 364.50682 nm, n is the lower level, and m is the higher level.

Later, Johannes Rydberg refined this idea using the Rydberg constant. For the Balmer series, the final level n f equals 2. The same relationship, combined with the Bohr model, can be used to calculate the energy change, ΔE, for electron transitions. Other hydrogen spectral series were later identified as well, including the Lyman series, which lies in the ultraviolet region.

Hydrogen Emission Lines

lab techniques

Measuring with Accuracy in the Lab

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

scientific measurement and lab skills

Graphs, Curve Fit, and Standard Deviation

Two-dimensional graphs help students compare an independent variable with a dependent variable in science data. In a chemistry example, temperature is the independent variable and volume is the dependent variable. After data are collected, the relationship between the two measurements must be quantified so it can be evaluated and compared with other relationships. A graph can also show when no relationship exists between the two variables. To make a two-dimensional graph, each data point needs...

stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

Chemical equations show how reactants change into products during a reaction. Stoichiometry is the study of the relative amounts of reactants and products. It is based on the Law of Conservation of Mass, which says matter is neither created nor destroyed. Because atoms are only rearranged, the number and identity of atoms must match on both sides of a reaction. That is why a chemical equation must be balanced. A balanced equation has the same number of atoms for each element in the reactants...

redox reactions

Oxidation States in Redox Reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number. Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding...

ideal gas law

Gas Laws Behind the Ideal Gas Equation

The ideal gas equation brings together the main gas laws used in chemistry. Gases have molecules that are far apart, so their behavior is described with four measurable variables: pressure, volume, number of moles, and temperature. The ideal gas law links these variables with the gas constant, R, which equals 8.314 J·K−1 mol−1. Boyle’s law describes the link between pressure and volume. When temperature and the number of moles stay constant, pressure and volume change in opposite directions.

acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

Buffer solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

Reaction heat is explained through enthalpy, Hess’s law, and calorimetry. These ideas show how heat moves during chemical reactions and how scientists measure it. Thermodynamics is the study of heat energy and other forms of energy, such as work. Its laws are used across science, from biology to physics. The first law says energy is conserved in an isolated system. Energy can change form, such as thermal energy becoming work, but it cannot be created or destroyed. The second law of...

solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

metal flame emission

Flame Test Metal Color Clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors. The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron...

balmer series

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them. These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between...

beer's law

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...

concentration dependence

Reaction Order and Rate Constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate. In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is...

temperature dependence

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.

https://cloudfront.jove.com/files/banners/scicat/labbio.jpg

Explore how hydrogen electrons jump between energy levels and produce discrete emission lines, including the visible Balmer series and other hydrogen spectra.

Hydrogen Emission Lines | JoVE K12

Louisiana Student Standards for Science

motion-and-stability-forces-and-interactions

Motion And Stability: Forces And Interactions

HS-PS2-6

Tennessee Academic Standards

waves-and-their-applications-in-technologies-for-information-transfer

Waves and Their Applications in Technologies for Information Transfer

CHEM1.PS4.1

Next Generation Science Standards

Earth and Space Science

Earth’s Place in the Universe

HS-ESS1-2

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

Matter and Its Interactions

C-PS1-4

Georgia Standards of Excellence

9-12

SC1.

Light Emission and Electron Movement

התכוננו ללמד את סדרת Balmer עם מדריך מדריכים זה באורך 1 דקות. כולל שלבי הכנה מרכזיים עבור מעבדת Chemistry ב-JoVE Lab Manual.

הכנת מדריך עבור סדרת Balmer ב-Chemistry - 2.0K+ צפיות | JoVE Lab Manual

עקבו אחר הנהלים של סדרת Balmer שלב אחר שלב בסרטון פרוטוקול סטודנטים זה באורך 4 דקות. חלק מאוסף Chemistry ב-JoVE Lab Manual.

פרוטוקול סטודנטים עבור סדרת Balmer ב-Chemistry - 5.1K+ צפיות | 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. ...

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

IPC.7.B

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

Hydrogen Emission Lines

Description

Transcript

More videos by Standards