Metals are typically highly reactive chemically, especially with nonmetals. They have a tendency to lose electrons and form cations, which makes them good reducing agents. This means that they have a high affinity for electrons and will readily react with other substances to gain them.
| IA | IIA | IIIA | IVA | VA |
|---|---|---|---|---|
| Li | Be | |||
| Na | Mg | Al | ||
| K | Ca | Ga | ||
| Rb | Sr | In | Sn | |
| Cs | Ba | Ti | Pb | Bi |
| Fr | Ra |
Electropositivity is a chemical property of an element that describes its tendency to lose electrons and form cations, which are positively charged ions. Elements with low electronegativity and high ionisation energy tend to be more electropositive, as they require less energy to lose an electron and become a cation.
Metals such as sodium (Na) and magnesium (Mg) have a low electronegativity and high ionisation energy, making them highly electropositive. When these metals react with nonmetals such as chlorine (Cl) or oxygen (O), they tend to lose electrons and form cations such as Na+ and Mg2+. These cations have a positive charge and are attracted to negatively charged species such as anions.
In general, elements on the left side of the periodic table tend to be more electropositive than those on the right side. The most electropositive element is francium (Fr), which is located in the bottom-left corner of the periodic table. However, francium is extremely rare and radioactive, so it is not commonly used in everyday applications.
It is important to understand the concept of electropositivity and how it relates to the formation of cations in chemical reactions. Some common examples of cations that are formed due to electropositivity include Na+, K+, Ca2+, and Mg2+.
Ionisation energy is the energy required to remove an electron from an atom or a cation. Alkali metals and alkaline earth metals are two groups of elements in the periodic table that have low ionisation energies, meaning they require less energy to lose an electron compared to other elements.
Alkali metals, including elements such as lithium, sodium, and potassium, have relatively low ionization potentials. This means that they tend to lose their outermost electron easily, forming positively charged ions.
On the other hand, alkaline earth metals, such as beryllium, magnesium, and calcium, have higher ionization potentials compared to alkali metals. This is because alkaline earth metals possess two valence electrons in their outermost energy level.
| Alkali Metals | Alkaline Earth Metals |
|---|---|
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Reactivity with water: Alkali metals, such as sodium (Na), react vigorously with water, releasing hydrogen gas and forming metal hydroxides. For example: 2Na + 2H2O → 2NaOH + H2 |
Reactivity with water: Alkaline earth metals, like calcium (Ca), also react with water, but their reactivity is relatively lower compared to alkali metals. They form metal hydroxides and release hydrogen gas. For instance: Ca + 2H2O → Ca(OH)2 + H2 |
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Ionization potential: Alkali metals have relatively low ionization potentials due to their large atomic size and presence of a single valence electron. This makes them highly reactive. For example, when sodium (Na) reacts with chlorine (Cl), it loses its valence electron to form sodium cation (Na+) and combines with chloride anion (Cl-) to form sodium chloride (NaCl): 2Na + Cl2 → 2NaCl |
Ionization potential: Alkaline earth metals, such as calcium (Ca), have higher ionization potentials compared to alkali metals due to the increased nuclear charge and stronger electron-nucleus attraction. They typically form ions with a +2 charge by losing their two valence electrons. For instance: Ca → Ca2+ + 2e- |
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Reactivity with oxygen: Alkali metals readily oxidize in air or react with oxygen to form metal oxides. For example, when lithium (Li) reacts with oxygen (O2), it forms lithium oxide (Li2O): 4Li + O2 → 2Li2O |
Reactivity with oxygen: Alkaline earth metals, such as magnesium (Mg), also react with oxygen but at higher temperatures compared to alkali metals. They form metal oxides. For instance: 2Mg + O2 → 2MgO |
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Reactivity with acids: Alkali metals, such as potassium (K), react vigorously with acids, displacing hydrogen gas. For example: 2K + 2HCl → 2KCl + H2 |
Reactivity with acids: Alkaline earth metals, like calcium (Ca), also react with acids but generally exhibit a slower and less vigorous reaction compared to alkali metals. They also displace hydrogen gas. For instance: Ca + 2HCl → CaCl2 + H2 |
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Density: Alkali metals, such as lithium (Li), sodium (Na), and potassium (K), have relatively low densities. For example, potassium has a density of 0.86 g/cm³. |
Density: Alkaline earth metals, such as beryllium (Be), magnesium (Mg), and calcium (Ca), have higher densities compared to alkali metals. For example, calcium has a density of 1.54 g/cm³. |