Name: alkali metals: reactivity trends
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Alkali Metals

Alkali metals are group 1 elements, including lithium, sodium, potassium, rubidium, cesium, and francium. Francium is radioactive and has no stable isotopes.
All alkali metals are unusually soft and share metallic properties, such as high electrical and thermal conductivity. Moving down the group, the mass, density, and atomic radii increase, while the melting points and ionization energies decrease.
The electron configuration of these elements implies that the valence shell has only one electron.
Their low ionization energies indicate that alkali metals readily lose electrons to become cations with a noble gas configuration. This also explains why alkali metals are excellent reducing agents, with lithium being the least reactive and cesium the most.
Alkali metals react vigorously with nonmetals, such as halogens, to form salts. The reaction of sodium metal with chlorine gas is highly exothermic and releases sparks and heat. The intensity of the reaction increases down the group as the ionization energies of the alkali metals decrease.
Alkali metals react vehemently with water to generate hydrogen gas and a solution of alkali metal hydroxide like potassium hydroxide, which is a base often used in soap making.
The reaction becomes more violent for the heavier alkali metals given their lower ionization energies. The heat produced during the reaction may even ignite the released hydrogen gas leading to fire or an explosion.&nbsp;
Alkali metals can also react with hydrogen to form alkali metal hydrides, often used as strong bases. In this reaction, the hydrogen atom gains an electron and is present as the hydride ion.&nbsp;
Due to their high reactivity, alkali metals oxidize easily upon exposure to air and are therefore stored in mineral oils.&nbsp;
When alkali metal salts are placed in a flame and reduced to their gaseous metal atoms, they emit characteristic colors. &nbsp;
The heat excites the valence electron to a higher energy level. When the excited electrons return to the ground state, energy is emitted in the form of radiation in the visible region. The emission spectrum of each element is unique and used to identify the element qualitatively.

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 alkali metals are unusually low for metals and decrease going down the group, while the density increases going down the group with the exception of potassium (Table 1).
Table 1: Properties of the alkali metals
<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 (&deg;C)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Density at 25 &deg;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>
Moving down a group, the principal quantum number, n, increases by one for each element. Thus, the outer electrons get farther from the nucleus, and the atomic radius increases from lithium to cesium.
The electron configuration of these elements shows that the valence shell has only one electron (Table 1). The loss of this electron produces a cation with the noble gas configuration. Thus, alkali metals have a great tendency to give away this electron and have low first ionization energies, which decrease down the group. Their ability to lose an electron readily makes them highly reactive and excellent reducing agents.
The alkali metals react vigorously with nonmetals, such as halogens. The reaction of sodium and chlorine to produce sodium chloride is exothermic. The alkali metals also react violently with water, also, and hydrogen gas and an alkali metal hydroxide are produced. The heat produced during the reaction can ignite the hydrogen gas released, leading to an explosion. Both of these reactions become more exothermic for the heavier alkali metals due to their lower ionization energies.
Exposure to air, as they react with oxygen to form oxides, reduces the metallic luster of the alkali metals. Lithium reacts with oxygen to give lithium oxide, while other alkali metals like sodium form oxides and &nbsp;peroxides. The peroxide ion has a single oxygen-oxygen covalent bond and is a powerful hydrogen ion acceptor, making the peroxides of the alkali metals strong bases. The alkali metals such as potassium, rubidium, and cesium also produce superoxides. Superoxides are characterized by the presence of O2&minus;. Potassium superoxide is a yellow solid that decomposes at 560 &deg;C.&nbsp;
This text is adapted from <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>

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 ...

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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

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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...

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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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Alkali Metals: Reactivity Trends

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