J's answer to Anonymous's Secondary 3 A Maths Singapore question.
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http://www.dynamicscience.com.au/tester/solutions1/chemistry/chemicalequations/valency.html
" Group 6 elements, have 6 valence electrons and will tend to take 2 electrons and have a valency of -2. "
This is for people who are grossly unaware of different conventions used in chemistry :D
" Group 6 elements, have 6 valence electrons and will tend to take 2 electrons and have a valency of -2. "
This is for people who are grossly unaware of different conventions used in chemistry :D
Date Posted:
3 years ago
Just take note. Certain 'tutors' are blind to different conventions and only insist on their way.
Especially those unknown ones who claim to be professional and quote some websites.
For this qn, you don't really need to know Valency.
Even at the highest level, scientists often debate which is wrong or right.
The IUPAC definition of valency is not used universally, just like we don't see the IUPAC nomenclature being used in many industries.
Especially those unknown ones who claim to be professional and quote some websites.
For this qn, you don't really need to know Valency.
Even at the highest level, scientists often debate which is wrong or right.
The IUPAC definition of valency is not used universally, just like we don't see the IUPAC nomenclature being used in many industries.
https://www.thoughtco.com/definition-of-valence-in-chemistry-604680
By Anne Marie Helmenstine, Ph.D.
Updated January 24, 2019
Valence is typically the number of electrons needed to fill the outermost shell of an atom. Because exceptions exist, the more general definition of valence is the number of electrons with which a given atom generally bonds or number of bonds an atom forms. (Think iron, which may have a valence of 2 or a valence of 3.)
Common Valences
Atoms of elements in the main group of the periodic table may display a valence between 1 and 7 (since 8 is a complete octet).
Group 1 (I) - Usually displays a valence of 1. Example: Na in NaCl
Group 2 (II) - Typical valence is 2. Example: Mg in MgCl2
Group 13 (III) - Usual valence is 3. Example: Al in AlCl3
Group 14 (IV) - Usual valence is 4. Example: C in CO (double bond) or CH4 (single bonds)
Group 15 (V) - Usual valences are 3 and 5. Examples are N in NH3 and P in PCl5
Group 16 (VI) - Typical valences are 2 and 6. Example: O in H2O
Group 17 (VII) - Usual valences are 1 and 7. Examples: Cl in HCl
Valence vs Oxidation State
There are two problems with "valence". First, the definition is ambiguous. Second, it's just a whole number, without a sign to give you an indication of whether an atom will gain an electron or lose its outermost one(s). For example, the valence of both hydrogen and chlorine is 1, yet hydrogen usually loses its electron to become H+, while chlorine usually gains an additional electron to become Cl-.
The oxidation state is a better indicator of the electronic state of an atom because it has both magnitude and sign. Also, it's understood an element's atoms may display different oxidation states depending on the conditions. The sign is positive for electropositive atoms and negative for electronegative atoms. The most common oxidation state of hydrogen is +8. The most common oxidation state for chlorine is -1.
By Anne Marie Helmenstine, Ph.D.
Updated January 24, 2019
Valence is typically the number of electrons needed to fill the outermost shell of an atom. Because exceptions exist, the more general definition of valence is the number of electrons with which a given atom generally bonds or number of bonds an atom forms. (Think iron, which may have a valence of 2 or a valence of 3.)
Common Valences
Atoms of elements in the main group of the periodic table may display a valence between 1 and 7 (since 8 is a complete octet).
Group 1 (I) - Usually displays a valence of 1. Example: Na in NaCl
Group 2 (II) - Typical valence is 2. Example: Mg in MgCl2
Group 13 (III) - Usual valence is 3. Example: Al in AlCl3
Group 14 (IV) - Usual valence is 4. Example: C in CO (double bond) or CH4 (single bonds)
Group 15 (V) - Usual valences are 3 and 5. Examples are N in NH3 and P in PCl5
Group 16 (VI) - Typical valences are 2 and 6. Example: O in H2O
Group 17 (VII) - Usual valences are 1 and 7. Examples: Cl in HCl
Valence vs Oxidation State
There are two problems with "valence". First, the definition is ambiguous. Second, it's just a whole number, without a sign to give you an indication of whether an atom will gain an electron or lose its outermost one(s). For example, the valence of both hydrogen and chlorine is 1, yet hydrogen usually loses its electron to become H+, while chlorine usually gains an additional electron to become Cl-.
The oxidation state is a better indicator of the electronic state of an atom because it has both magnitude and sign. Also, it's understood an element's atoms may display different oxidation states depending on the conditions. The sign is positive for electropositive atoms and negative for electronegative atoms. The most common oxidation state of hydrogen is +8. The most common oxidation state for chlorine is -1.
https://www.thoughtco.com/what-is-valence-or-valency-606459
https://www.ibchem.com/IB16/03.22.htm
"To find whether an atom takes a positive or negative valency consider the electronegativity of the atom to which it is attached.
In nitrogen dioxide, NO2, oxygen is MORE electronegative than the nitrogen and so the nitrogen takes a positive valency (in this case = +4).
In ammonia, NH3, nitrogen is MORE electronegative than the hydrogen, so it is the nitrogen that takes the negative valency (in ths case -3)."
"To find whether an atom takes a positive or negative valency consider the electronegativity of the atom to which it is attached.
In nitrogen dioxide, NO2, oxygen is MORE electronegative than the nitrogen and so the nitrogen takes a positive valency (in this case = +4).
In ammonia, NH3, nitrogen is MORE electronegative than the hydrogen, so it is the nitrogen that takes the negative valency (in ths case -3)."
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