Introduction:
The properties of alkali metals are similar because they belong to the same group in the periodic table and possess similar electronic configuration. A few of these properties are discussed below.
1) Size: Atomic radius increases as we move down the alkali metal group because an extra shell of electrons is added down the group. Hence, lithium is the smallest atom and francium is the largest atom among alkali metals. Francium is an unstable element.
2) Electronic configuration: All alkali metals have a similar electronic configuration with only one electron in the outermost s-orbital. The electronic configuration of alkali metals are given by:
3) Density: Alkali metals are the light metals. Their density is low because of larger atomic volumes. However, the density goes on increasing down the group because an increase in mass predominates over increase in volume down the group. Li, Na, K are lighter than water. Density of sodium and potassium are 0.972 g/cm3 and 0.867 g/cm3 respectively. The density of potassium is less than that of sodium because of unusual increase in atomic size of potassium. The density of cesium is 1.67 g/cm3.
4) Ionization energy: Alkali metals have low ionization energies because the last electron is present in the outermost s-orbital and the removal of electron is easy. As we move down the group, there is decrease in the ionization energy.
5) Electropositive character: Due to low ionization energy, alkali metals are highly electropositive. They have a tendency to lose electrons readily and change to M+ ion.
M → M+ + e-
As ionization energy decreases down the group, electropositive character increases from lithium to cesium. Metals like Cs and Rb lose electrons even they expose to light. This property is known as photoelectric effect.
6) Oxidation states: All alkali metals exhibit an oxidation state of +1 because they have only one electron in the outermost shell which is lost during the reactions. +2 state is not observed because the second ionization of alkali metals is very high than the first ionization energy.
7) Metallic properties: The metallic character of alkali metals increases from Li to Cs due to low ionization energy. They show strong metallic character. Hence , They show strong metallic character. Hence they are highly electropositive and less electronegative. As they have only one unpaired electron, metallic bond is weak. Hence they are soft metals and can be easily deformed.
8) Flame test: When cesium metal is heated strongly in a non-luminous flame, the salts are ionized. Cesium ions are later excited and the electrons jumps to high energy levels. When these electrons return back, they emit radiations which fall on the visible region. Periodic test cesium emits pale violet color to the flame.
9) Reducing property: Alkali metals are powerful reducing agents because they have very low reduction potentials. This indicates that electrons can be released from them very easily.
Where R.P. = Reducing potential.
Lower the R.P. Greater the reducing potential. Hence alkali metals react readily with water to liberate hydrogen.
2Cs + 2H2O → 2CsOH + H2↑
10) Reaction of periodic table cesium with air: When alkali metals are exposed to air, they tarnish rapidly due to formation of oxides on the surface. Hence they are kept under kerosene to protect from the action of air.
When Cesium metal are heated in air they burn vigorously to form cesium superoxide.
Cs + O2 → CsO2
11) Diagonal relationship between periodic table Cesium and radium: The diagonal element relationship is the similarity between the first elements of a group with the second element in the next higher group.
- Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr) constitutes Group 1 of the periodic table.
- Robert Wilhelm Bunsen and Gustav Robert Kirchhoff found the metal cesium in the year 1860.
- Cesium has chemical symbol ‘Cs’.
- Periodic table cesium has atomic number 55 and mass number 132.9054
- Periodic table cesium belongs to Group 1 and Period 6
- Group 1 elements are called alkali metals because their oxides and hydroxides dissolve in water to produce strong alkali’s.
- Group1 elements are highly reactive and highly electropositive elements.
- Francium is a radioactive element.
- Electron configuration cesium:
- Electrons per energy level: 2, 8, 18, 18, 8, 1
- Shell model:
Properties of periodic table cesium:
The properties of alkali metals are similar because they belong to the same group in the periodic table and possess similar electronic configuration. A few of these properties are discussed below.
1) Size: Atomic radius increases as we move down the alkali metal group because an extra shell of electrons is added down the group. Hence, lithium is the smallest atom and francium is the largest atom among alkali metals. Francium is an unstable element.
| Element | Li | Na | K | Rb | Cs |
| Atomic radius (pm) | 134 | 154 | 196 | 211 | 235 |
2) Electronic configuration: All alkali metals have a similar electronic configuration with only one electron in the outermost s-orbital. The electronic configuration of alkali metals are given by:
- Li: [He] 2s1
- Na: [Ne] 3s1
- K: [Ar] 4s1
- Rb: [Kr] 5s1
- Cs: [Xe] 6s1
- Fr: [Rn] 7s1
3) Density: Alkali metals are the light metals. Their density is low because of larger atomic volumes. However, the density goes on increasing down the group because an increase in mass predominates over increase in volume down the group. Li, Na, K are lighter than water. Density of sodium and potassium are 0.972 g/cm3 and 0.867 g/cm3 respectively. The density of potassium is less than that of sodium because of unusual increase in atomic size of potassium. The density of cesium is 1.67 g/cm3.
4) Ionization energy: Alkali metals have low ionization energies because the last electron is present in the outermost s-orbital and the removal of electron is easy. As we move down the group, there is decrease in the ionization energy.
| Elements | Li | Na | K | Rb | Cs |
| Atomic radius (pm) | 520 | 495 | 418 | 403 | 376 |
5) Electropositive character: Due to low ionization energy, alkali metals are highly electropositive. They have a tendency to lose electrons readily and change to M+ ion.
M → M+ + e-
As ionization energy decreases down the group, electropositive character increases from lithium to cesium. Metals like Cs and Rb lose electrons even they expose to light. This property is known as photoelectric effect.
6) Oxidation states: All alkali metals exhibit an oxidation state of +1 because they have only one electron in the outermost shell which is lost during the reactions. +2 state is not observed because the second ionization of alkali metals is very high than the first ionization energy.
7) Metallic properties: The metallic character of alkali metals increases from Li to Cs due to low ionization energy. They show strong metallic character. Hence , They show strong metallic character. Hence they are highly electropositive and less electronegative. As they have only one unpaired electron, metallic bond is weak. Hence they are soft metals and can be easily deformed.
8) Flame test: When cesium metal is heated strongly in a non-luminous flame, the salts are ionized. Cesium ions are later excited and the electrons jumps to high energy levels. When these electrons return back, they emit radiations which fall on the visible region. Periodic test cesium emits pale violet color to the flame.
9) Reducing property: Alkali metals are powerful reducing agents because they have very low reduction potentials. This indicates that electrons can be released from them very easily.
| Elements | Li | Na | K | Rb | Cs |
| R.P. (volts) | -3.05 | -2.71 | -2.93 | -2.99 | -2.99 |
Lower the R.P. Greater the reducing potential. Hence alkali metals react readily with water to liberate hydrogen.
2Cs + 2H2O → 2CsOH + H2↑
10) Reaction of periodic table cesium with air: When alkali metals are exposed to air, they tarnish rapidly due to formation of oxides on the surface. Hence they are kept under kerosene to protect from the action of air.
When Cesium metal are heated in air they burn vigorously to form cesium superoxide.
Cs + O2 → CsO2
11) Diagonal relationship between periodic table Cesium and radium: The diagonal element relationship is the similarity between the first elements of a group with the second element in the next higher group.
Uses of periodic table Cesium:
- Cs is used as a catalyst in the hydrogenation of few organic compounds.
- Cs metal can be used in ion propulsion systems. Although not usable in the earth’s atmosphere.
- Periodic table cesium is used in atomic clocks.
- Cs has high electron affinity. Therefore it is used in electron tubes.
- Cs is used in photoelectric cells and vaccum tubes.
- Periodic table cesium is used in Infra red lamps.
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