Which of these pairs of elements have the same number of valence electrons?
2 answers:
Answer : The correct option is, (B) sodium and potassium
Explanation :
Valence electrons : Valence electrons are those electrons which are present in the outermost shell of the element.
As we know that,
<u>Option (A) :</u>
Element = Hydrogen
Atomic number = Number of electrons = 1
The electronic configuration is,
The number of valence electrons = 1
Element = Helium
Atomic number = Number of electrons = 2
The electronic configuration is,
The number of valence electrons = 2
<u>Option (B) :</u>
Element = Sodium
Atomic number = Number of electrons = 11
The electronic configuration is,
The number of valence electrons = 1
Element = Potassium
Atomic number = Number of electrons = 19
The electronic configuration is,
The number of valence electrons = 1
<u>Option (C) :</u>
Element = Carbon
Atomic number = Number of electrons = 6
The electronic configuration is,
The number of valence electrons = 4
Element = Oxygen
Atomic number = Number of electrons = 8
The electronic configuration is,
The number of valence electrons = 6
<u>Option (D) :</u>
Element = Boron
Atomic number = Number of electrons = 5
The electronic configuration is,
The number of valence electrons = 3
Element = Beryllium
Atomic number = Number of electrons = 4
The electronic configuration is,
The number of valence electrons = 2
From this we conclude that, the sodium and potassium are the elements have the same number of valence electrons.
Hence, the correct option is, (B)
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Answer: a. A solid melts:
b. a vapor is converted to solid:
c. a liquid freezes:
d. A solid sublimes:
e. a vapor condenses to liquid :
f. a liquid boils:
g. dissolving a tablespoon of salt in water:
h. combustion of gasoline:
Explanation:
Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy change is negative and vice versa.
a. A solid melts: The solid is converting to liquid, thus the randomness is increasing as the molecules are moving away and the intermolecular forces are getting weaker. Thus the entropy change is positive.
b. a vapor is converted to solid: The gas is converting to solid, thus the randomness is decreasing as the molecules are moving close and the intermolecular forces are getting stronger Thus the entropy change is negative.
c. a liquid freezes: The liquid is converting to solid, thus the randomness is decreasing as the molecules are moving close and the intermolecular forces are getting stronger. Thus the entropy change is negative.
d. A solid sublimes: The solid is converting to gas, thus the randomness is increasing as the molecules are moving away and the intermolecular forces are getting weaker. Thus the entropy change is positive.
e. a vapor condenses to liquid : The gas is converting to liquid, thus the randomness is decreasing as the molecules are moving close and the intermolecular forces are getting stronger. Thus the entropy change is negative.
f. a liquid boils: The liquid is converting to gas, thus the randomness is increasing as the molecules are moving away and the intermolecular forces are getting weaker. Thus the entropy change is positive.
g. dissolving a tablespoon of salt in water: The solid is converting to ions , thus the randomness is increasing as the ions can move freely. Thus the entropy change is positive.
h. combustion of gasoline: The liquid is converting to gas, thus the randomness is increasing as the molecules are moving away and the intermolecular forces are getting weaker. Thus the entropy change is positive.