Name: alkali metals: reactivity trends
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 3 min 6 s
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Physical Science

Matter and its Interactions

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Alkali Metals

Los metales alcalinos son los elementos del grupo 1, incluyendo el litio, el sodio, el potasio, el rubidio, el cesio, y el francio. El francio es radiactivo y no tiene isótopos estables. Todos los metales alcalinos son inusualmente blandos y comparten propiedades metálicas, como una alta conductividad eléctrica y térmica.Descendiendo por el grupo, la masa, la densidad y los radios atómicos aumentan, mientras que los puntos de fusión y las energías de ionización disminuyen. La configuración electrónica de estos elementos implica que la capa de valencia tiene un solo electrón. Sus bajas energías de ionización indican que los metales alcalinos pierden fácilmente electrones para convertirse en cationes con una configuración de gas noble.Esto también explica por qué los metales alcalinos son excelentes agentes reductores, siendo el litio el menos reactivo y cesio el más reactivo. Los metales alcalinos reaccionan vigorosamente con los no metales, como los halógenos, para formar sales. La reacción del sodio metálico con el cloro gaseoso es altamente exotérmica y libera chispas y calor.La intensidad de la reacción aumenta hacia abajo en el grupo al mismo tiempo que las energías de ionización de los metales alcalinos disminuyen. Los metales alcalinos reaccionan vehementemente con el agua para generar gas hidrógeno y una solución de hidróxido de metal alcalino como el hidróxido de potasio, que es una base de uso frecuente en la fabricación de jabón. La reacción se vuelve más violenta para los metales alcalinos más pesados en vista de sus energías de ionización más bajas.El calor producido durante la reacción incluso puede encender el gas hidrógeno liberado produciendo fuego o una explosión. Los metales alcalinos también pueden reaccionar con el hidrógeno para formar hidruros de metales alcalinos, que a menudo se utilizan como bases fuertes. En esta reacción, el átomo de hidrógeno gana un electrón y está presente como ion hidruro.Debido a su alta reactividad, los metales alcalinos se oxidan fácilmente al exponerse al aire y, por tanto, se almacenan en aceites minerales. Cuando las sales de metales alcalinos se colocan en una llama y se reducen a sus átomos metálicos gaseosos, emiten colores característicos. El calor excita el electrón de valencia a un nivel de energía superior.Cuando los electrones excitados regresan al estado base, la energía se emite en forma de radiación en la región visible. El espectro de emisión de cada elemento es único y se utiliza para identificar cualitativamente el elemento.

metales alcalinos

Los elementos del grupo 1 son sólidos metálicos suaves y brillantes. Son maleables, dúctiles y buenos conductores del calor y la electricidad. Los puntos de fusión de los metales alcalinos son inusualmente bajos para los metales y disminuyen al descender por el grupo. La densidad también disminuye en la misma dirección, con la excepción del potasio (Tabla 1).
 
 Tabla 1: Propiedades de los metales alcalinos
 
 <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;">Elemento</td>
 <td style="color: black; border: 1px solid black; text-align: center;">Configuración electrónica</td>
 <td style="color: black; border: 1px solid black; text-align: center;">Radio atómico (pm)</td>
 <td style="color: black; border: 1px solid black; text-align: center;">EI1 (kJ/mol)</td>
 <td style="color: black; border: 1px solid black; text-align: center;">Punto de fusión (°C)</td>
 <td style="color: black; border: 1px solid black; text-align: center;">Densidad a 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>
 
 Al descender por un grupo, el número cuántico principal, n, aumenta en uno para cada elemento. Así, los electrones externos se alejan del núcleo, y el radio atómico aumenta del litio al cesio.
 
 La configuración electrónica de estos elementos muestra que la capa de valencia tiene sólo un electrón (Tabla 1). La pérdida de este electrón produce un catión con la configuración de gases nobles. Por lo tanto, los metales alcalinos tienen una gran tendencia a entregar este electrón y tienen bajas energías de primera ionización, que disminuyen al descender en el grupo. Su capacidad de perder un electrón fácilmente los hace altamente reactivos y excelentes agentes reductores.
 
 Los metales alcalinos reaccionan vigorosamente con los no metales, como los halógenos. La reacción del sodio y el cloro para producir cloruro de sodio es exotérmica. Los metales alcalinos también reaccionan violentamente con el agua y se produce gas hidrógeno y un hidróxido de metal alcalino. El calor producido durante la reacción puede encender el gas hidrógeno liberado, lo que puede provocar una explosión. Ambas reacciones se vuelven más exotérmicas para los metales alcalinos más pesados debido a sus energías de ionización más bajas.
 
 La exposición al aire, al reaccionar con el oxígeno para formar óxidos, reduce el brillo metálico de los metales alcalinos. El litio reacciona con el oxígeno para dar óxido de litio, mientras que otros metales alcalinos como el sodio forman óxidos y peróxidos. El ion peróxido tiene un enlace covalente de oxígeno-oxígeno y es un poderoso aceptor de iones hidrógeno, haciendo que los peróxidos de los metales alcalinos sean bases fuertes. Los metales alcalinos como el potasio, el rubidio y el cesio también producen superóxidos. Los superóxidos se caracterizan por la presencia de O2−. El superóxido de potasio es un sólido amarillo que se descompone a 560 °C. 
 
 Este texto es adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">Openstax, Química 2e, Sección 6.5: Variaciones Periódicas en las Propiedades de los Elementos.</a>

Metales Alcalinos

Los elementos del grupo 1 son sólidos metálicos blandos y brillantes. Son maleables, dúctiles y buenos conductores del calor y la electricidad. Los puntos de fusión de la ...

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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

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Periodic Trends in Atomic Size

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How Ionic Charge Changes Ion Size

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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...

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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.

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Phase Transitions: Sublimation and Deposition

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Ions and Ionic Charges

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The Periodic Table

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Periodic Classification of the Elements

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Atomic Radii and Effective Nuclear Charge

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Ionic Radii

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Ionization Energy

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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 ...

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Halogens

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Noble Gases


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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

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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.

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Alkali Metals: Reactivity Trends

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