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

Physical Science

Matter and its Interactions

PS.PSc.1.6

Alkali Metals

Os metais alcalinos são elementos do grupo 1, incluindo o lítio, sódio, potássio, rubídio, césio e frâncio. O frâncio é radioativo e não tem isótopos estáveis. Todos os metais alcalinos são invulgarmente macios e partilham propriedades metálicas, tal como a elevada condutividade elétrica e térmica térmica Descendo no grupo, a massa, a densidade e os raios atómicos aumentam, enquanto os pontos de fusão e as energias de ionização diminuem.A configuração de elétrons destes elementos implica que a camada da valência tem apenas um elétron. As suas baixas energias de ionização indicam que os metais alcalinos perdem facilmente elétrons para se tornarem cátions com uma configuração de gás nobre. Isto também explica porque é que os metais alcalinos são excelentes agentes redutores, sendo o lítio o menos reativo e o césio o mais reativo.Os metais alcalinos reagem vigorosamente com metais não metálicos, tal como o halogêneo, para formar sais. A reação do metal de sódio com gás de cloro é altamente exotérmico e liberta faíscas e calor. A intensidade da reação aumenta ao baixarmos no grupo à medida que as energias de ionização dos metais alcalinos diminuem.Os metais alcalinos reagem veementemente com a água para gerar hidrogênio gasoso e uma solução de metal alcalino como o hidróxido de potássio, que é uma base frequentemente utilizada no fabrico do sabão. A reação torna-se mais violenta para os metais álcalinos mais pesados, dadas as suas energias de ionização mais baixas. O calor produzido durante a reação pode até incendiar o gás de hidrogênio libertado originando fogo ou uma explosão.Os metais alcalinos também podem reagir com o hidrogênio para formarem hidretos de metais alcalinos, muitas vezes utilizados como bases fortes. Nesta reação, o átomo de hidrogênio ganha um elétron e está presente como o íon de hidreto. Devido à sua elevada reatividade, os metais alcalinos oxidam facilmente após exposição ao ar e estão, portanto, armazenados nos óleos minerais.Quando os sais alcalinos metálicos são colocados numa chama e reduzidos aos seus átomos de metal gasoso, emitem cores características. O calor desperta o elétron de valência a um nível de energia mais elevado. Quando os elétrons despertados regressam ao estado de sólido, a energia é emitida sob a forma de radiação na região visível.O espectro de emissão de cada elemento é único e utilizado para identificar qualitativamente o elemento.

metais alcalinos

Os elementos do grupo 1 são sólidos metálicos macios e brilhantes. São maleáveis, dúcteis, e bons condutores de calor e eletricidade. Os pontos de fusão dos metais alcalinos são invulgarmente baixos para os metais e diminuem ao descer no grupo. A densidade também diminui na mesma direção, com excepção do potássio (Tabela 1).

Tabela 1: Propriedades dos metais 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;">Configuração Eletrónica</td>
<td style="color: black; border: 1px solid black; text-align: center;">Raio Atómico (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;">Ponto de Fusão (°C)</td>
<td style="color: black; border: 1px solid black; text-align: center;">Densidade 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>

Descendo um grupo, o número quântico principal, n, aumenta por um para cada elemento. Assim, os eletrões exteriores ficam mais longe do núcleo e o raio atómico aumenta do lítio para o césio.

A configuração eletrónica desses elementos mostra que a camada de valência tem apenas um eletrão (Tabela 1). A perda deste eletrão produz um catião com a configuração de gás nobre. Assim, os metais alcalinos têm uma grande tendência a dar este eletrão e têm primeiras energias de ionização baixas, que diminuem ao descer o grupo. A sua capacidade de perder um eletrão torna-os facilmente altamente reativos e excelentes agentes de redução.

Os metais alcalinos reagem vigorosamente com não metais, como halogénios. A reação do sódio e do cloro na produção de cloreto de sódio é exotérmica. Os metais alcalinos também reagem violentamente com a água, sendo produzidos hidrogénio gasoso e um hidróxido de metal alcalino. O calor produzido durante a reação pode incendiar o hidrogénio libertado, levando a uma explosão. Ambas as reações tornam-se mais exotérmicas para os metais alcalinos mais pesados devido às suas energias de ionização mais baixas.

A exposição ao ar, à medida que reagem com oxigénio para formar óxidos, reduz o brilho metálico dos metais alcalinos. O lítio reage com o oxigénio para fornecer óxido de lítio, enquanto que outros metais alcalinos, como sódio formam óxidos e peróxidos. O ião peróxido tem uma ligação covalente simples oxigénio-oxigénio e é um potente aceitador de iões de hidrogénio, tornando os peróxidos das dos metais alcalinos bases fortes. Os metais alcalinos como potássio, rubídio, e césio também produzem superóxidos. Os superóxidos são caracterizados pela presença de O2−. O superóxido de potássio é um sólido amarelo que se decompõe a 560 °C. 

Este texto é adaptado de <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>

Metais Alcalinos

Os elementos do grupo 1 são sólidos metálicos macios e brilhantes. Eles são maleáveis, dúcteis e bons condutores de calor e eletricidade. Os pontos de fusão do ...

Education

JoVE Core

Chemistry

Química

Periodic Properties of the Elements

Propriedades Periódicas dos Elementos

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

atomic-radii-and-effective-nuclear-charge

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...

key terms and concepts

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

chemistry

JoVE Core - Química dá vida a conceitos gerais de química usando vídeos de animação fáceis de entender. Além disso, nos vídeos Cientistas em ação, demonstramos experimentos de pesquisa clássicos e originais realizados atualmente por cientistas em laboratórios em todo o mundo.

Pennsylvania State Academic Standards

Chemical Reactions

3.2.9-12.C

Structure and Properties of Matter

3.2.9-12.A

Louisiana Student Standards for Science

High School

Matter And Its Interactions

HS-PS1-1

HS-PS1-2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Periodic trends of the elements

Structure And Properties Of Matter

Periodic Table

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.12

Virginia  Standards of Learning

HIgh School

PS.2

PS.2.b

PS.4

PS.4.b

Arizona Science Standards

HS.P1

HS.P1U1.1

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Texas Essential Knowledge and Skills

CHEM.5

CHEM.5.B

Alabama Course of Study Science

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

9-12.C.2.2.f

9-12.PS.3.4.b

Next Generation Science Standards

Chemistry and Physics

IPC.7

IPC.7.B

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-2.

Georgia Standards of Excellence

SPS1.

Periodic Table Trends

SC1.

electron-configuration-and-chemical-properties

Electron Configuration and Chemical Properties

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 ...

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 ...

Molecules and Compounds

Atoms and Molecules

Everything in the universe is made up of matter, and matter is composed of a combination of elements. An atom is the smallest unit of ...

Solution Formation

There is no one solvent that can dissolve every type of solute. Some substances that readily dissolve in a certain solvent might be insoluble in a ...

Colloids

Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera ...

Construct an explanation to classify matter as a pure substance or mixture; homogeneous or heterogeneous; element or compound; solution, colloid or suspension.

PS.PSc.1.1

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

phase-transitions-vaporization-and-condensation

Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

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 ...

Clausius-Clapeyron Equation

The equilibrium between a liquid and its vapor depends on the temperature of the system; a rise in temperature causes a corresponding rise in the vapor ...

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

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 ...

Heating and Cooling Curves

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

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

Use models to compare the phases of matter and the physical changes they undergo.

PS.PSc.1.2

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 ...

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, ...

Carry out investigations to compare physical and chemical properties of matter.

PS.PSc.1.3

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 ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

Emission Spectra

When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a ...

The de Broglie Wavelength

In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a ...

The Uncertainty Principle

Werner Heisenberg considered the limits of how accurately one can measure properties of an electron or other microscopic particles. He determined that ...

Use models to interpret the data presented in Bohr diagrams and electron dot diagrams for neutral atoms of elements 1 through 18.

PS.PSc.1.4

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 ...

Use models to compare representations of atoms, ions, and isotopes.

PS.PSc.1.5

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

Description

Transcript

Tags

More videos by Standards