Name: reading molecular, empirical, and structural formulas
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 52 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.3

Chemical Formulas

תרכובות כימיות הן חומרים המורכבים משני יסודות או יותר ביחס מסוימם. כדי לתאר במדויק תרכובות אלה פותחו הנוסחאות כימיות. הנוסחה הכימית מספקת מידע על היסודות ועל מספר היונים או האטומים המעורבים בתרכובת.יסודות אלה מיוצגים על ידי סימולים הכימי, בעוד המספר היחסי של היונים או האטומים מיוצג במספר תחתי. לדוגמה, סוכר או סוכרוז הוא תרכובת המכילה את היסודות פחמן, מימן וחמצן המיוצגים על ידי הסמלים C, H ו-O. המספרים 12, 22 ו-11 מצביעים על המספר הכולל של אטומי פחמן, מימן וחמצן המרכיבים את התרכובת.באופן כללי, היסודות לא רשומים בסדר אלפביתי, אלא מתחילים בבעלי המטען החיובי הגדול ביותר או יסודות מתכתיים, ואחריהם בעלי מטען שלילי, או יסודות פחות מתכתיים, כמו אשלגן הידרוקסידי. נוסחאות כימיות מתחלקות לנסוחאות מולקולריות, אמפיריות ומבניות. נוסחאות מולקולריות מתארות תרכובת באמצעות רישום של כל יסוד והמספר המדויק של האטומים בתרכובת.הנוסחה המולקולרית של גלוקוז היא C-6H-12O-6, כלומר גלוקוז מורכז משישה אטומי פחמן, 12 אטומי מימן ושישה אטומי חמצן. הנוסחה האמפירית מציגה באופן הפשוט ביותר, במספרים שלמים, יחס מספרי בין אטומי היסודות בתרכובת. בגלוקוז, היחס המספרי בין פחמן, מימן וחמצן הוא 1:2:1, הנותן את הנוסחה האמפירית CH-20.הנוסחה המולקולרית של תרכובת היא גם מספר שלם כפול הנוסחה האמפירית. בגלוקוז, המכפלה של הנוסחה האמפירית עם המספר השלם שש נותנת את הנוסחה המולקולרית. לעומת זאת, הנוסחה המבנית מציגה את היחסים בין האטומים הבודדים באופן גרפי.הסימנים הכימיים מייצגים את האטום והקווים הקצרים מתארים את הקשרים הכימיים. קווים יחידים מייצגים קשרים יחידים בעוד שני קווים או שלושה מתארים קשרים כפולים או משולשים, בהתאמה. מודלים מוגדלים של נוסחאות מבניות כגון ציור פרספקטיבה, מודל מקלות וכדורים״או מודל מילוי המרחב, מספקים מגוון של פרספקטיבות תלת ממדיות על הצורה המולקולרית.בין שלוש הנוסחאות הכימיות, הנוסחה המבנית מספקת את מרב המידע בנוגע לחומר הכימי, ולאחריה הנוסחה המולקולרית. הנוסחה האמפירית מספקת הכי פחות מידע.

נוסחאות כימיות

<div style="direction:rtl">נוסחה כימית מציגה מידע על הפרופורציות של האטומים המהווים תרכובת או מולקולה כימית מסוימת, בעיקר באמצעות סמלים של יסודות ומספרים. לפעמים נעשה שימוש גם בסמלים אחרים, כגון מקפים, סוגריים, פסיקים, סימני פלוס ומינוס. נוסחה כימית יכולה להיות אחד משלושה סוגים - מולקולרית, אמפירית ומבנית. <h4>נוסחה מולקולרית</h4> הנוסחה המולקולרית מייצגת מולקולה או תרכובת כימית באמצעות סמלים כימיים (כדי לציין את סוגי האטומים) ומספרי תחתית (כדי להראות את מספר האטומים מכל סוג במולקולה). נוסחאות מולקולריות משמשות גם כקיצורים לשמות של תרכובות. יסודות מסוימים מורכבים מאטומים נפרדים, כמו הגזים האצילים הליום, ניאון וארגון. יסודות כאלה נקראים גזים מונאטומיים ויש להם נוסחאות מולקולריות He, Ne ו-Ar, בהתאמה. יסודות מעטים קיימים כמולקולות המורכבות משני או יותר אטומים הקשורים כימית של אותו יסוד. לדוגמה, יסודות כמו מימן, חמצן וחנקן קיימים כמולקולות דו-אטומיות המכילות שני אטומים כל אחת ולכן יש להם את הנוסחאות המולקולריות H2, O2 ו-N2, בהתאמה. באופן דומה, יסודות כמו זרחן וגופרית קיימים כמולקולות פוליאטומיות עם נוסחאות מולקולריות P4 ו-S8, בהתאמה. חשוב לציין שסמל ומספר מול סמל אינו מייצג את אותו הדבר; לדוגמה, H2 ו-2H מייצגים מינים שונים באופן מובהק. H2 היא נוסחה מולקולרית; היא מייצגת מולקולה דו-אטומית של מימן, המורכבת משני אטומים של היסוד הקשורים זה לזה בצורה כימית. הביטוי 2H, לעומת זאת, מציין שני אטומי מימן נפרדים שאינם משולבים כיחידה. הביטוי 2H2 מייצג שתי מולקולות של מימן דו-אטומי. <h4>נוסחה אמפירית</h4> תרכובות נוצרות כאשר שני יסודות או יותר מתאחדים כימית, וכתוצאה מכך נוצרים קשרים. לדוגמה, מימן וחמצן יכולים להגיב ליצירת מים, ונתרן וכלור יכולים להגיב ליצירת נתרן כלורי או מלח שולחן. לעיתים אנו מתארים את הרכב התרכובות הללו בנוסחה אמפירית, המציינת את סוגי האטומים הקיימים ואת היחס הפשוט ביותר בין מספר האטומים (או היונים) בתרכובת. לדוגמא, טיטניום דו-חמצני (המשמש כפיגמנט בצבע לבן ובסוג קרם ההגנה העבה, הלבן והחוסם) הוא בעל נוסחה אמפירית של TiO2. זה מזהה את היסודות טיטניום (Ti) וחמצן (O) כמרכיבים של טיטניום דו-חמצני ומצביע על נוכחותם של פי שניים יותר אטומים של היסוד חמצן מאשר אטומים של היסוד טיטניום. במקרים רבים, הנוסחה המולקולרית של חומר נגזרת מקביעה ניסיונית של הנוסחה האמפירית והן של המסה המולקולרית שלו (סכום המסות האטומיות של כל האטומים המרכיבים את המולקולה). לדוגמה, ניתן לקבוע בניסוי שבנזן מכיל שני יסודות, פחמן (C) ומימן (H), ושלכל אטום פחמן בבנזן, יש אטום מימן אחד. לפיכך, הנוסחה האמפירית היא CH. קביעה ניסיונית של המסה המולקולרית מגלה שמולקולה של בנזן מכילה שישה אטומי פחמן ושישה אטומי מימן, ולכן הנוסחה המולקולרית לבנזן היא C6H6. <h4>נוסחה מבנית</h4> נוסחת המבנה של תרכובת נותנת את אותו מידע כמו הנוסחה המולקולרית שלה (סוגי ומספרי האטומים במולקולה) אך גם מראה כיצד האטומים מחוברים במולקולה. במילים אחרות, נוסחת המבנה מייצגת את המבנה המולקולרי של תרכובת באופן גרפי. זה מראה את הסידור הסביר של האטומים וכיצד האטומים מחוברים במרחב 3d אמיתי, נותן מידע נוסף על הגיאומטריה המולקולרית. קווים משמשים לייצג קשרים הקיימים בין האטומים. הנוסחה עשויה גם לתאר את זוויות הקשר המשוערות, לתת תחושה של צורת המולקולה. טקסט זה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/2-4-chemical-formulas">Openstax Chemistry 2e, Section 2.4: Chemical Formulas.</a></div>

נוסחה כימית מציגה מידע על הפרופורציות של אטומים המרכיבים תרכובת כימית או מולקולה מסוימת, בעיקר באמצעות סמלים של ...

Education

Book

כימיה

Molecules, Compounds, and Chemical Equations

מולקולות, תרכובות ומשוואות כימיות

molecules-compounds-and-chemical-equations

reading molecular, empirical, and structural formulas

Chemical formulas show the types and proportions of atoms in a compound or molecule. They use element symbols and numbers. Some formulas also use dashes, parentheses, brackets, commas, plus signs, and minus signs.

A molecular formula shows a molecule or compound with chemical symbols and subscript numbers. The symbols tell which atoms are present, and the subscripts show how many of each atom are in the molecule. Molecular formulas can also serve as short names for compounds.

Some elements exist as separate atoms. The noble gases helium, neon, and argon are monatomic gases, so their molecular formulas are He, Ne, and Ar. Other elements form molecules with two or more bonded atoms of the same element. Hydrogen, oxygen, and nitrogen are diatomic and have the formulas H2, O2, and N2. Phosphorus and sulfur are polyatomic and have the formulas P4 and S8.

It is important to tell the difference between a subscript and a number in front of a symbol. H2 means one diatomic hydrogen molecule. The expression 2H means two separate hydrogen atoms. The expression 2H2 means two hydrogen molecules.

An empirical formula shows the types of atoms present and the simplest whole-number ratio of those atoms or ions in a compound. Compounds form when two or more elements chemically combine and make bonds. Water and sodium chloride are common examples of compounds. Titanium dioxide has the empirical formula TiO2, which shows titanium and oxygen and means there are twice as many oxygen atoms as titanium atoms.

In many cases, a molecular formula is found from the empirical formula and the molecular mass. Molecular mass is the sum of the atomic masses of all atoms in a molecule. Benzene is one example. Experiments show that benzene contains carbon and hydrogen in a 1:1 ratio, so its empirical formula is CH. Its molecular mass shows that one molecule contains six carbon atoms and six hydrogen atoms, so its molecular formula is C6H6.

A structural formula gives the same atom count information as a molecular formula, but it also shows how the atoms are connected. It draws the molecular structure in a way that helps show the probable arrangement of atoms in three-dimensional space. Lines represent bonds between atoms. Structural formulas may also show approximate bond angles, which gives a sense of molecular shape.

Reading Molecular, Empirical, and Structural Formulas

reading-molecular-empirical-and-structural-formulas

chemical formulas

Chemical formulas show the types and proportions of atoms in a compound or molecule. They use element symbols and numbers. Some formulas also use dashes, parentheses, brackets, commas, plus signs, and minus signs. A molecular formula shows a molecule or compound with chemical symbols and subscript numbers. The symbols tell which atoms are present, and the subscripts show how many of each atom are in the molecule. Molecular formulas can also serve as short names for compounds. Some elements...

molecules and compounds

Atomic Elements, Molecules, and Bonds

Matter is made of elements, and elements are built from atoms. An atom is the smallest unit of an element that still keeps that element’s properties. A silver coin, for example, is made of silver atoms. Each atom keeps the unique properties of silver. Elements are pure substances made of identical atoms. They cannot be broken down into simpler substances by chemical changes. Most elements are atomic elements, which use single atoms as their basic unit. Carbon and sodium are examples of atomic...

classification of elements and compounds

Atomic vs Molecular Substances and Bonding

Pure substances are made of only one kind of matter. A pure substance can be an element or a compound. An element contains only one type of atom. A compound contains two or more types of atoms joined by a chemical bond. Elements are classified as atomic or molecular based on their basic units. Compounds are classified as ionic or molecular, also called covalent, based on the bonds they contain. Molecular compounds form when two or more different nonmetal atoms share electrons. Their basic...

ionic compounds: formulas and nomenclature

ionic-compounds-formulas-and-nomenclature

Ionic Charges, Formulas, and Naming Rules

Ionic compounds form when metals transfer electrons to nonmetals and create oppositely charged ions. The electrostatic attraction between the ions, called an ionic bond, holds the compound together. Many nonmetals gain electrons by moving toward the electron count of the next noble gas. Group 17 atoms usually gain one electron and form 1− ions, while group 16 atoms usually gain two electrons and form 2− ions. Oxygen is a clear example. A neutral oxygen atom has 8 protons and 8 electrons. When...

molecular models

Molecular Model Types in Chemistry

Molecular models help chemists and students visualize the structures and shapes of atoms and molecules. They represent the molecular architecture of chemical compounds in a way that is easier to study than formulas alone. Skeletal models are simple two-dimensional drawings of compounds. They show the molecular framework, or the bonds, without drawing every atom. In this model, many carbon and hydrogen atoms are not shown directly. Their positions are implied by the ends and junctions of the...

molecular compounds: formulas and nomenclature

molecular-compounds-formulas-and-nomenclature

Naming Covalent Compounds and Acids

Molecular compounds are covalent compounds made when atoms share electrons. Because there is no electron transfer, they do not contain ions. They are made of separate, neutral molecules. Since covalent compounds usually form from nonmetals, the periodic table can help students recognize many of them. In many cases, the positions of the elements can also help predict whether a compound is ionic or covalent, although there are exceptions. Molecular compounds are named differently from ionic...

organic compounds

Organic Molecules in Everyday Chemistry

Organic molecules are carbon-based compounds found in living things and in many everyday products. Most organic compounds have carbon as the main element, bonded to hydrogen and other carbon atoms. Some carbon-containing substances, such as carbonates, cyanides, and simple oxides like CO and CO2, are not classified as organic. Carbon can form up to four strong bonds, which helps explain why organic compounds can make chains and rings of many sizes and shapes. These molecules appear in...

formula mass and mole concepts of compounds

formula-mass-and-mole-concepts-of-compounds

Chemical Formula Mass and Percent Composition

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance. For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses. Ionic...

experimental determination of chemical formula

experimental-determination-of-chemical-formula

Finding Empirical and Molecular Formulas

Chemical formulas show the elemental makeup of a compound. When a formula is unknown, scientists often start by measuring the masses of the elements in the sample. Those mass data are then used to find the simplest whole-number ratio of atoms, which gives the empirical formula. To get from mass to atom ratio, the masses of the elements are first converted to moles using molar masses. Chemical formulas describe numbers of atoms, not masses, so this step is necessary. In one example, 1.71 grams...

chemical equations

Reading Chemical Equations and Balancing Them

Chemical equations show the identities and relative amounts of substances in a chemical reaction. The substances that react are called reactants, and their formulas are written on the left side of the equation. The substances formed are called products, and their formulas are written on the right side. A plus sign (+) separates formulas on the same side, and an arrow (→) shows the change from reactants to products. The numbers in a chemical equation are shown with coefficients. A coefficient...

scientists in action

מדענים בעבודה

key terms

מונחים מרכזיים

key relationships & equations

קשרים ומשוואות מרכזיים

chapter exercises

תרגילי פרק

appendices

נספחים

molecules, compounds, and chemical equations

Learn how molecular, empirical, and structural formulas show atom counts, ratios, and bonds. See examples like H2, TiO2, and C6H6.

Reading Molecular, Empirical, and Structural Formulas | JoVE K12

chemistry

PS.Chm.4.3

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Structure And Properties Of Matter

Representing compounds

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.a

Texas Essential Knowledge and Skills

High School

CHEM.8

CHEM.8.D

Florida Department of Education

Physical Science

SC.912.P.8

SC.912.P.8.7

Georgia Standards of Excellence

SPS2.

Chemical Names and Chemical Formulas

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

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 ...

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 ...

Use models to explain how the scientific understanding of atomic structure has evolved.

PS.Chm.1.1

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

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 ...

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, ...

Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

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 ...

Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

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 ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

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 ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

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, ...

Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

molecular-comparison-of-gases-liquids-and-solids

Molecular Comparison of Gases, Liquids, and Solids

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

Intermolecular vs Intramolecular Forces

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

Intermolecular Forces

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

comparing-intermolecular-forces-melting-point-boiling-point

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

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

surface-tension-capillary-action-and-viscosity

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded ...

Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Reading Molecular, Empirical, and Structural Formulas

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