Tag: anomalous properties of lithium

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Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Which of the following carbonate is not stable to heat.

  1. $Li _2CO _3$
  2. $Na _2CO _3$
  3. $K _2CO _3$
  4. $Rb _2CO _3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Li2CO3 is unstable to heat and decomposes to Li2O + CO2 at lower temperatures. Other alkali metal carbonates (Na2CO3, K2CO3, Rb2CO3) are thermally stable due to larger cation size. This is a unique property of lithium carbonate.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Which one of the alkali metals,forms only,the normal oxide $M _2O$ on heating in air?

  1. $Li$
  2. $Na$
  3. $Rb$
  4. $K$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Lithium forms only the normal oxide Li2O on heating in air. Sodium forms Na2O2 (peroxide), and potassium/rubidium form superoxides (KO2, RbO2) under similar conditions. This is due to the small size of Li+ ion.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Li has chemical properties most similar to :

  1. Al

  2. Ca

  3. Mg

  4. Ti
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Li has chemical properties most similar to Mg due to diagonal relationship.
Both exhibits same properties like
(i).

$MgCO _3\, \overset{\Delta}{\rightarrow}\, MgO\, +\, CO _2$
$Li _2CO _3\, \overset{\Delta}{\rightarrow}\, Li _2O\, +\, CO _2$

(ii).
$3Mg\, +\, N _2\, \rightarrow Mg _3N _2$ 
$6Li+ N _2 \rightarrow 2Li _3N$

Hence option C is correct answer.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Li resembles to element X which is not the member of alkali metals. The group of X is?

  1. II

  2. III

  3. IV

  4. I
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Li resembles to element X which is not a member of alkali metals. The group of X must be II group, because certain elements of 2nd period show similarity with their diagonal elements in the 3rd period as shown below : Thus, Li resembles Mg, Be resembles Al and B resembles Si. This is called diagonal relationship and is due to the reason that these pairs of element have almost identical ionic radii and polarizing power (i.e. charge/size ratio). Element of second period are known as bridge elements.

So Li is I st group element and the diagonal element Mg is II nd group element.
Hence option A is correct.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

$Mg$ and $Li$ and similar in their properties due to:

  1. same $\dfrac {e}{m}$ ratio

  2. same electron affinity

  3. same group

  4. same radius
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$Li$ and $Mg$ show diagonal relationship due to the similarity in size (radius), electronegativity, ionisation enthalpy and charge/radius ratio.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Li resembles to element X which is not the member of alkali metals.
The element X is :

  1. Mg

  2. Be

  3. Ca

  4. B
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Li resembles to element X which is not the member of alkali metals. The element X is Mg. This is due to diagonal relationship. Certain elements of 2nd period show similarity with their diagonal elements in the 3rd period as shown below : Thus, Li resembles Mg, Be resembles Al and B resembles Si. 


This is called diagonal relationship and is due to the reason that these pairs of element have almost identical ionic radii and polarizing power (i.e. charge/size ratio). Element of second period are known as bridge elements.   
Hence option A is correct.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Lithium borohydride, $LiB{H} _{4}$, crystallizes in an orthorhombic system with four molecules per unit cell. The unit cell dimensions are $a=6.0\mathring { A } ,b=4.4\mathring { A } ,c=7.5\mathring { A } $. The density of crystals is
$\left( Li=7,B=11,{ N } _{ A }=6\times { 10 }^{ 23 } \right) $

  1. $0.74g/{cm}^{3}$
  2. $1.48g/{cm}^{3}$
  3. $0.37g/{cm}^{3}$
  4. $0.90g/{cm}^{3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using the density formula: d = (Z × M) / (NA × a × b × c). With Z=4, M=22 g/mol (7+11+4), NA=6×10^23, dimensions in Angstroms (1 Å = 10^-8 cm): volume = 6×4.4×7.5 × 10^-24 cm^3 = 198×10^-24 cm^3. Mass = (4 × 22)/(6 × 10^23) g = 1.47×10^-22 g. Density = 1.47×10^-22 / 198×10^-24 = 0.74 g/cm^3.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Lithium shows similarities with magnesium in its chemical behaviour because :

  1. similar size, greater electronegativity and lower polarising power

  2. similar size, same electronegativity, and lower polarising power

  3. similar size, same electronegativity and similar high polarising power

  4. none of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Lithium shows similarities with magnesium in its chemical behaviour because they have similar size and charge/size ratio. They have similar electronegativity.


This type of diagonal similarity is commonly referred to as diagonal relationship in the periodic table.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

In certain matters, lithium differs from other alkali metals; the main reason for this is :  

  1. small size of lithium atom and $Li^+$.
  2. extremely high electropositivity of $Li$.
  3. greater hardness of $Li$.
  4. hydration of $Li^+$ ion.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In certain matters, lithium differs from other alkali metals(anamalous property); the main reason for this is small size of lithium atom and $Li^+$ and high polarizing power.

Hence option A is correct.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

In certain matters, lithium differs from other alkali metals, the main reason for this is:

  1. Small size of lithium atom and $Li^+$ ion
  2. Extremely high electro positivity of $Li$
  3. Greater hardness of $Li$
  4. Hydration of $Li^+$ ion
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The chemistry of lithium shows several differences from that of the rest of the group as the small lithium cation polarises anions and gives its compounds as the more covalent character.