Mastina asked in 科學化學 · 1 decade ago

AL chemistry Question

1. Which oxide is more basic ? MgO or BaO? Why?

2.Why do noble gases have negative electron affinity values?

3.The H ions and the He atom have two 1s electrons each, Which of the two species is larger? Explain .

4 Oxygen forms double bonds in O2 , but sulfur forms single bonds inS8 .Explain.

5.Tranisition metal complexs containing CN – ligands are often yellow in colour , whereas those containg H2O ligands are often green or blue . Explain

3 Answers

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  • 1 decade ago
    Favorite Answer

    1)

    如果比小弟答嘅

    我捻我會加埋difference in solubility in aqueous solution

    BaO is much more soluble than MgO

    therefore theoretically more -OH could be released

    2)

    我相信設題者系想學生用stable octet structure黎解釋

    而唔係用wiki嘅知識去反問個問題

    仲有

    One of the EA definitions is the energy released when a neutral atom accepts an electron to become an anion.

    So, if an atom really does not like to become an anion, its EA will take a negative value(energy has to be supplied), not a zero value.

    EA can be taken as the result of a combination of 2 factors:

    a) the repulsion between existing e- within an atom and the added e-

    b) the effective nuclear charge

    In short, noble gases have stable octet e- config which leads to a relatively large amount of energy required to overcome the e- repulsion and such energy input is greater in magnitude than the energy released due to the attraction by nucleus.

    其他嘅樓上個位都答得幾精準架喇

  • 冷風
    Lv 5
    1 decade ago

    So, if an atom really does not like to become an anion, its EA will take a negative value(energy has to be supplied), not a zero value.

    呢句錯喎

    EA應該係positive value (exothermic) if the atom is unwilling to accept an incoming electron.

  • 1 decade ago

    1.

    BaO is more basic.

    Ba2+ ion has a greater ionic size than O2- ion. Therefore, Ba2+ has a smaller charge density, and thus a smaller polarizing power. In BaO, the O2- ion is less polarized by the cation, and thus its lone pair of electrons is more available to accept a proton.

    2.

    Generally, the values of electron affinity (E.A.) are negative or close to zero. The noble gases have E.A. close to zero, and this indicates that they do not like to become anions. However, the electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values of E.A.

    3.

    H- ion is larger in size.

    The nuclear charges of H- ion and He atom are +1 and +2 respectively. The H- ion has a large size, because its 1s electron pair experiences a much weaker nuclear attraction.

    4.

    O atom is very small in size. Comparing with the case of O-O single bond, O=O double bond leads to a weaker repulsion between the lone pair electrons on the two atoms, because the lone pair electrons are further apart.

    S atom is large in size, and bond lengths of SS bonds are long. It is difficult to form S=S double bond, because the π overlapping is ineffective due to the long bond length.

    5.

    CN- is a stronger ligand than H2O.

    In a complex with CN- ligands, the CN- ligands split the valence d subshell of the central metal ion/atom to two energy levels with a greater energy difference. Therefore, visible light of higher frequency (higher energy, e.g. green, blue or violet) is absorbed, and thus visible light of lower frequency (e.g. yellow or orange) is observed.

    In a complex with H­2O ligands, the H2O ligands split the valence d subshell of the central metal ion/atom to two energy levels with a smaller energy difference. Therefore, visible light of lower frequence (lower energy, e.g. red, orange or yellow) is absorbed, and thus visible light of higher frequency (e.g. green or blue) is observed.

    =

    2009-06-26 01:07:04 補充:

    To wahyanlingbibi:

    1) BaO reacts with water more readily to give OH^- ions. This is due to its stronger basicity, but NOT an explanation for its stronger basicity.

    2009-06-26 01:07:12 補充:

    2) Firstly, E.A. involves gasesous atoms and anions, and the amount is 1 mole. Secondly, a negative E.A. indicates that the process is thermodynamically feasible, but NOT "does not like to become an anion" as you stated.

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