Name: alkali metals: reactivity trends
Uploaded: 2020-09-03T13:38:28.000Z
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Alkali Metals

מתכות אלקליות הן יסודות מקבוצה 1, וכוללות ליתיום, נתרן, אשלגן, רובידיום, צזיום ופרנציום. פרנציום הוא רדיואקטיבי ואין לו איזוטופים יציבים. כל המתכות האלקליות בדרך כלל רכות במיוחד ובעלות תכונות מתכתיות משותפות, כגון מוליכות חשמל וחום גבוהה.כשממשיכים למטה בקבוצה, המסה, הצפיפות והרדיוס האטומי גדלים, בעוד נקודות ההתכה ואנרגיות היינון קטנות. תצורת האלקטרונים של יסודות אלה מעידה על כך שבקליפת הערכיות יש רק אלקטרון אחד. אנרגיות היינון הנמוכות שלהם מעידות על כך שמתכות אלקליות גורעות בקלות אלקטרונים והופכות לקטיונים עם תצורת גז אצילי.זה מסביר גם מדוע מתכות אלקליות הן חומרי חיזור מצוינים, כשליתיום הוא הכי פחות פעיל וצזיום הפעיל ביותר. מתכות אלקליות מגיבות ברצון עם לא מתכות כגון הלוגנים, ליצירת מלחים. תגובת מתכת הנתרן עם גז כלור היא אקסותרמית ביותר ומשחררת ניצוצות וחום.עוצמת התגובה עולה במורד הקבוצה ככל שאנרגיות היינון של המתכות האלקליות קטנה. מתכות אלקליות מגיבות בעוצמה עם מים ומייצרות גז מימן ותמיסה של מתכת הידרוקסיד אלקלית כמו אשלגן הידרוקסיד, שהוא בסיס המשמש לעיתים קרובות בייצור סבון. התגובה הופכת לאלימה יותר במקרים של מתכות אלקליות כבדות יותר בהתחשב באנרגיות היינון הנמוכות יותר שלהן.החום שנוצר במהלך התגובה עשוי אפילו להצית את גז המימן המשתחרר ולהוביל לשרפה או לפיצוץ. מתכות אלקליות יכולות גם להגיב עם מימן כדי ליצור הידרידים אלקליים מתכתיים, המשמשים לעיתים קרובות כבסיסים חזקים. בתגובה זו, אטום המימן צובר אלקטרון ומתפקד כיון ההידריד.בשל הפעילות הגבוהה שלהם, מתכות אלקליות מתחמצנות בקלות עם חשיפה לאוויר ולכן נשמרות בשמנים מינרליים. כאשר מציתים מלחי מתכות אלקליות ומחזרים אותם למתכת הגזית שלהם, הם פולטים צבעים אופייניים. החום מעורר את אלקטרון הערכיות לרמת אנרגיה גבוהה יותר.כשהאלקטרונים המעוררים חוזרים אל מצב היסוד, אנרגיה נפלטת בצורה של קרינה באזור הנראה. ספקטרום הפליטה של כל יסוד הוא ייחודי ומשמש לזיהוי איכותני של היסוד.

מתכות אלקליות

<div style="direction:rtl">יסודות מקבוצה 1 הם מוצקים מתכתיים רכים ומבריקים. הם גמישים, רקיעים ומוליכים טובים של חום וחשמל. נקודות ההיתוך של המתכות האלקליות נמוכות בצורה יוצאת דופן עבור מתכות ויורדות במורד הקבוצה, בעוד שהצפיפות עולה במורד הקבוצה למעט אשלגן (טבלה 1). טבלה 1: תכונות של המתכות האלקליות <table style="margin-left: auto; margin-right: auto;"> <tbody style="border: 1px solid black;"> <tr> <td style="color: black; border: 1px solid black; text-align: center;">Element</td> <td style="color: black; border: 1px solid black; text-align: center;">Electron Configuration</td> <td style="color: black; border: 1px solid black; text-align: center;">Atomic Radius (pm)</td> <td style="color: black; border: 1px solid black; text-align: center;">IE1 (kJ/mol)</td> <td style="color: black; border: 1px solid black; text-align: center;">Melting Point (°C)</td> <td style="color: black; border: 1px solid black; text-align: center;">Density at 25 °C (g/cm3)</td> </tr> <tr> <td style="color: black; border: 1px solid black; text-align: center;">Li</td> <td style="color: black; border: 1px solid black; text-align: center;">[He] 2s1</td> <td style="color: black; border: 1px solid black; text-align: center;">152</td> <td style="color: black; border: 1px solid black; text-align: center;">520</td> <td style="color: black; border: 1px solid black; text-align: center;">181</td> <td style="color: black; border: 1px solid black; text-align: center;">0.53</td> </tr> <tr> <td style="color: black; border: 1px solid black; text-align: center;">Na</td> <td style="color: black; border: 1px solid black; text-align: center;">[Ne] 3s1</td> <td style="color: black; border: 1px solid black; text-align: center;">186</td> <td style="color: black; border: 1px solid black; text-align: center;">496</td> <td style="color: black; border: 1px solid black; text-align: center;">98</td> <td style="color: black; border: 1px solid black; text-align: center;">0.97</td> </tr> <tr> <td style="color: black; border: 1px solid black; text-align: center;">K</td> <td style="color: black; border: 1px solid black; text-align: center;">[Ar] 4s1</td> <td style="color: black; border: 1px solid black; text-align: center;">227</td> <td style="color: black; border: 1px solid black; text-align: center;">420</td> <td style="color: black; border: 1px solid black; text-align: center;">64</td> <td style="color: black; border: 1px solid black; text-align: center;">0.86</td> </tr> <tr> <td style="color: black; border: 1px solid black; text-align: center;">Rb</td> <td style="color: black; border: 1px solid black; text-align: center;">[Kr] 5s1</td> <td style="color: black; border: 1px solid black; text-align: center;">248</td> <td style="color: black; border: 1px solid black; text-align: center;">400</td> <td style="color: black; border: 1px solid black; text-align: center;">39</td> <td style="color: black; border: 1px solid black; text-align: center;">1.53</td> </tr> <tr> <td style="color: black; border: 1px solid black; text-align: center;">Cs</td> <td style="color: black; border: 1px solid black; text-align: center;">[Xe] 6s1</td> <td style="color: black; border: 1px solid black; text-align: center;">265</td> <td style="color: black; border: 1px solid black; text-align: center;">380</td> <td style="color: black; border: 1px solid black; text-align: center;">29</td> <td style="color: black; border: 1px solid black; text-align: center;">1.93</td> </tr> </tbody> </table> בתנועה במורד הקבוצה, המספר הקוונטי העיקרי, n, גדל באחד עבור כל יסוד. לפיכך, האלקטרונים החיצוניים מתרחקים מהגרעין, והרדיוס האטומי גדל מליתיום לצסיום. תצורת האלקטרונים של יסודות אלה מראה שלקליפת הערכיות יש רק אלקטרון אחד (טבלה 1). אובדן האלקטרון הזה מייצר קטיון עם תצורת הגז האציל. לפיכך, למתכות אלקליות יש נטייה גדולה למסור את האלקטרון הזה ולהן אנרגיות יינון ראשונות נמוכות, אשר יורדות במורד הקבוצה. היכולת שלהם לאבד אלקטרון בקלות הופכת אותם לחומרים מצמצמים מאוד, תגובתיים ומעולים. המתכות האלקליות מגיבות בעוצמה עם לא מתכות, כגון הלוגנים. התגובה של נתרן וכלור לייצור נתרן כלורי היא אקסותרמית. המתכות האלקליות גם מגיבות באלימות עם מים, כמו כן, נוצר גז מימן ומתכת אלקלית הידרוקסיד. החום שנוצר במהלך התגובה יכול להצית את גז המימן המשתחרר, ולהוביל לפיצוץ. שתי התגובות הללו הופכות לאקסותרמיות יותר עבור מתכות האלקליות הכבדות יותר בגלל אנרגיות היינון הנמוכות שלהן. חשיפה לאוויר, כפי שהם מגיבים עם חמצן ליצירת תחמוצות, מפחיתה את הברק המתכתי של המתכות האלקליות. ליתיום מגיב עם חמצן כדי לתת תחמוצת ליתיום, בעוד שמתכות אלקליות אחרות כמו נתרן יוצרות תחמוצות ופרוקסידים. ליון החמצן יש קשר קוולנטי חמצן-חמצן יחיד והוא קולט יוני מימן רבי עוצמה, מה שהופך את החמצנים של המתכות האלקליות לבסיסים חזקים. המתכות האלקליות כמו אשלגן, רובידיום וצסיום מייצרות גם סופראוקסיד. סופראוקסידים מאופיינים בנוכחות של O2−. אשלגן סופראוקסיד הוא מוצק צהוב שמתפרק ב-560 מעלות צלזיוס. טקסט זה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">Openstax, Chemistry 2e, Section 6.5: Periodic Variations in Element Properties.</a></div>

אלמנטים מקבוצה 1 הם מוצקים מתכתיים רכים ומבריקים. הם גמישים, רקיעים ומוליכים טובים של חום וחשמל. נקודות ההיתוך של ...

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alkali metals: reactivity trends

Alkali metals are Group 1 elements with one valence electron. They are soft, shiny metallic solids that are malleable, ductile, and good conductors of heat and electricity. Their melting points are unusually low for metals and drop as you move down the group. Density generally increases down the group, except for potassium.

The trend in atomic size helps explain their behavior. Moving from lithium to cesium, each element has a higher principal quantum number, so the outer electron is farther from the nucleus and the atomic radius increases. Their electron configurations show a single electron in the valence shell. When that electron is lost, the atom forms a cation with a noble gas configuration.

Because they give up that outer electron so easily, alkali metals have low first ionization energies and are highly reactive. Their first ionization energies decrease down the group, which makes the heavier elements even more reactive. They are also strong reducing agents. In reactions with nonmetals such as halogens, they react vigorously. A common example is sodium reacting with chlorine to form sodium chloride, and the reaction releases heat.

Alkali metals also react violently with water. These reactions produce hydrogen gas and an alkali metal hydroxide. The heat can ignite the hydrogen gas, which may lead to an explosion. The reactions become more exothermic for the heavier alkali metals because their ionization energies are lower.

Exposure to air causes alkali metals to react with oxygen and lose their metallic luster. Lithium forms lithium oxide. Other alkali metals such as sodium can form oxides and peroxides. A peroxide contains a single oxygen-oxygen covalent bond and acts as a strong base because it strongly accepts hydrogen ions. Potassium, rubidium, and cesium can also form superoxides, which contain O2- . Potassium superoxide is a yellow solid that decomposes at 560 °C.

Alkali Metals: Reactivity Trends

periodic classification of the elements

How Valence Electrons Shape the Periodic Table

The periodic table organizes elements by increasing atomic number, and it also shows why elements in the same group behave alike. As the electron configurations are placed into the table, a repeating pattern appears in the outer shells of atoms. These outer electrons are called valence electrons, and they play the biggest role in chemical reactions. They are the highest-energy electrons in an atom, so they are easier to lose or share than core electrons. Valence electrons also help determine...

ionization energy

Ionization Energy Trends in the Periodic Table

Ionization energy is the energy needed to remove an electron from a gaseous atom or ion in its ground state. The first ionization energy, or IE1, removes the most loosely bound electron and forms a 1+ cation. The second ionization energy, IE2, removes the next electron, and each later ionization energy removes another electron from the atom or ion. Ionization always requires energy, so these processes are endothermic. That means ionization energy values are always positive. In general, larger...

atomic radii and effective nuclear charge

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Periodic Trends in Atomic Size

Periodic trends in atomic size help explain why atoms get larger or smaller across the periodic table. Elements in the same group show similar chemical behavior because they have the same number and arrangement of valence electrons. Across a period, each new element adds one proton to the nucleus and one electron to the valence shell. Down a group, the number of valence electrons stays the same, but the principal quantum number increases by one. Atomic radius is not easy to define with perfect...

ionic radii

How Ionic Charge Changes Ion Size

Ionic radius describes the size of an ion. It changes when an atom gains or loses electrons. Cations are positive ions with fewer electrons than the parent atom, and they are smaller than the atoms they come from. Aluminum shows this pattern clearly. A neutral aluminum atom has a covalent radius of 118 pm, while Al3+ has an ionic radius of 68 pm. When electrons are removed from the outer valence shell, the remaining core electrons feel a stronger effective nuclear charge, or Zeff. That pull...

electron affinity

Electron Affinity Trends on the Periodic Table

Electron affinity is the energy change that happens when a gaseous atom gains an electron and becomes a negative ion, or anion. For many elements, this process releases energy, so the electron affinity value is negative. For some elements, energy must be added instead, so the value is positive. Electron affinity also applies when more than one electron is added. The second electron affinity is the energy change for adding an electron to an anion to make a 2− ion. Later electron affinities...

alkali metals

Alkali metals are Group 1 elements with one valence electron. They are soft, shiny metallic solids that are malleable, ductile, and good conductors of heat and electricity. Their melting points are unusually low for metals and drop as you move down the group. Density generally increases down the group, except for potassium. The trend in atomic size helps explain their behavior. Moving from lithium to cesium, each element has a higher principal quantum number, so the outer electron is farther...

halogens

Halogens: Trends and Reactions

Halogens are Group 17 nonmetals that show clear trends in structure and reactivity. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine is highly unstable and radioactive, so most of its properties are still unknown because it has a very short half-life. Tennessine is a synthetic element that is also predicted to belong to this group. These elements do not usually exist as single atoms. Instead, they form diatomic molecules, which means...

noble gases

Noble Gases: Sources, Uses, and Reactions

Noble gases are the group 18 elements helium, neon, argon, krypton, xenon, and radon. They were called “noble” because they were once thought to be nonreactive. That idea changed in 1962, when Dr. Neil Bartlett at the University of British Columbia showed that this assumption was not fully correct. These gases occur in very small amounts in the atmosphere. Some natural gas contains 1–2% helium by mass. Helium is separated from natural gas by removing the condensable components, which leaves...

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Explore how alkali metals change down Group 1, from atomic size and ionization energy to reactions with water, oxygen, and halogens.

Alkali Metals: Reactivity Trends | JoVE K12

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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, ...

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

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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 ...

Vapor Pressure

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

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Phase Transitions: Melting and Freezing

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Phase Transitions: Sublimation and Deposition

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

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

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Physical and Chemical Properties of Matter

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Physical Properties of Matter

A physical property is ...

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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 ...

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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 ...

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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 ...

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 ...

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 ...

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 the Periodic Table as a model to predict the relative properties (metallic/nonmetallic character, ionic charge, and reactivity) and arrangement of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

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 ...

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 ...

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 ...

Construct an explanation to classify the type of chemical bond that occurs (covalent, ionic, or metallic) in a given substance.

PS.PSc.2.1

Nomenclature of Alkanes

In the late 19th-century, the number of new chemical compounds discovered increased tremendously. Hence, the necessity arose to develop a naming system ...

Use models to apply International Union of Pure and Applied Chemistry (IUPAC) conventions to name and write formulas for simple compounds.

PS.PSc.2.2

Understand types, properties, and structure of matter.

Alkali Metals: Reactivity Trends

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