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    Which electron configuration represents the elements with the smallest first ionisation energy?
    1) 1s2
    2)1s2 2s2
    3)1s2 2s2 2p1
    4)1s2 2s2 2p2

    Is the answer 2?
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    its 3
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    Why, please explain Does ionisation energy increase across a period
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    3 is boron, when the outermost 2p electron is removed, the result is [He]2s2, the complete 2s electron shell is stable. The others leave incomplete electron shells if the outermost electron is removed therefore less stable.

    1 is hydrogen, the electron is next to the proton and has no shielding from other electrons so the ionisation energy is high.

    Can't remember about the latter bit.
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    it’s 3 because in the first two options, the outermost electron is in the s sub shell which means it’s closer to the nucleus and there’s a stronger attraction and therefore larger ionization energy is needed. now between 3, and 4 it’s its 3 because 4 has more electrons and therefore a stronger attraction and more energy is needed to remove that electron. this is my best guess, i’m not entirely sure.
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    (Original post by 1234123456785678)
    it’s 3 because in the first two options, the outermost electron is in the s sub shell which means it’s closer to the nucleus and there’s a stronger attraction and therefore larger ionization energy is needed. now between 3, and 4 it’s its 3 because 4 has more electrons and therefore a stronger attraction and more energy is needed to remove that electron. this is my best guess, i’m not entirely sure.
    also theres a greater shielding effect in 3 and 4
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    (Original post by 1234123456785678)
    it’s 3 because in the first two options, the outermost electron is in the s sub shell which means it’s closer to the nucleus and there’s a stronger attraction and therefore larger ionization energy is needed. now between 3, and 4 it’s its 3 because 4 has more electrons and therefore a stronger attraction and more energy is needed to remove that electron. this is my best guess, i’m not entirely sure.
    The difference between 3 and 4 is not accounted for by stronger attraction, attraction to what?
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    (Original post by 1234123456785678)
    also theres a greater shielding effect in 3 and 4
    You would expect 4 to have more electron shielding than 3 but that does not account for the fact 3 has lower ionisation energy than 4. Its about completed electron shells.
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    (Original post by Maker)
    The difference between 3 and 4 is not accounted for by stronger attraction, attraction to what?
    as the number of electrons increases, the number of protons (positive charge) increases as well making the attraction between the electrons and the positive charge stronger (again, im not sure so please correct me if im mistaken)
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    (Original post by Maker)
    You would expect 4 to have more electron shielding than 3 but that does not account for the fact 3 has lower ionisation energy than 4. Its about completed electron shells.
    not really since both 3 and 4 have the same number of shells so the shielding effect is the same. however, it is larger than in 1 and 2.
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    (Original post by 1234123456785678)
    not really since both 3 and 4 have the same number of shells so the shielding effect is the same. however, it is larger than in 1 and 2.
    If you look at the actual first ionisation energy of 3 which is boron and 4 which is carbon, you will see why you are incorrect.
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    (Original post by 1234123456785678)
    as the number of electrons increases, the number of protons (positive charge) increases as well making the attraction between the electrons and the positive charge stronger (again, im not sure so please correct me if im mistaken)
    The attraction between protons and electrons decrease rapidly with atomic number so the first ionisation energy of potassium is less than sodium. If you are right sodium would be more reactive than potassium but the reverse is true.
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    (Original post by Maker)
    If you look at the actual first ionisation energy of 3 which is boron and 4 which is carbon, you will see why you are incorrect.
    i’m award that boron has a lower ionization energy than carbon which is why my answer was 3, which is boron. however this is not due to the shielding the effect. it is due to other factors
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    (Original post by 1234123456785678)
    i’m award that boron has a lower ionization energy than carbon which is why my answer was 3, which is boron. however this is not due to the shielding the effect. it is due to other factors
    aware*
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    (Original post by Maker)
    The attraction between protons and electrons decrease rapidly with atomic number so the first ionisation energy of potassium is less than sodium. If you are right sodium would be more reactive than potassium but the reverse is true.
    That is incorrect. The reason why sodium has a higher ionization energy than potassium is the increased shielding effect (K has 4 principal shells, Na has 3)which overcomes the increased positive charge. Otherwise, the attraction between protons and electrons increases as the atomic number increases, which is why the ionization energy increases across a period.
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    (Original post by 1234123456785678)
    i’m award that boron has a lower ionization energy than carbon which is why my answer was 3, which is boron. however this is not due to the shielding the effect. it is due to other factors
    What other factors?
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    (Original post by 1234123456785678)
    That is incorrect. The reason why sodium has a higher ionization energy than potassium is the increased shielding effect (K has 4 principal shells, Na has 3)which overcomes the increased positive charge. Otherwise, the attraction between protons and electrons increases as the atomic number increases, which is why the ionization energy increases across a period.
    The shielding between 3 and 4 is the same, why are the ionisation energies different?
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    (Original post by Maker)
    What other factors?
    (Original post by Maker)
    The shielding between 3 and 4 is the same, why are the ionisation energies different?
    the increased attraction between the positive charge and the electrons (due to the increased numbers of electrons present)
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    (Original post by 1234123456785678)
    the increased attraction between the positive charge and the electrons (due to the increased numbers of electrons present)
    How would attraction between electrons and protons account for the high first ionisation energy of noble gases?
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    (Original post by Maker)
    How would attraction between electrons and protons account for the high first ionisation energy of noble gases?
    again, this just only adds to what i’ve mentioned. The noble gases have the largest number of electrons and protons across a period which is they they,predictably, have high ionization energies. However, this isn’t the only factor playing a role here. They also have a stable structure making the ionization energy even higher.
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