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The first ionzation energy generally increases from left to right across a period. However, there are some exceptions to this trend. For example, boron has a smaller ionization energy than beryllium even though it lies to the right of it in the same period. Select the statement that explains this exception to the trend in ionization energy. Beryllium has a noble gas electron configuration, whereas boron is one electron away from achieving a noble gas configuration. Consequently, it takes much less energy to remove one electron from boron and achieve a noble gas configuration than it does to remove an electron from beryllium which is already in a noble gas configuration. Boron has an electron in a 2p orbital which is higher in energy than the 2s orbital. Consequently, it is easier to remove an electron from the 2p orbital in boron than from the 2s orbital in beryllium. The 2p electron in boron experience a greater effective nuclear charge than the 2s electrons in beryllium, meaning it is easier to remove the 2p electron from boron than it is to remove a 2s electron from beryllium. O Boron has an electron in a 2p orbital, whereas beryllium only has electrons in the 2s orbital. Both 2s electrons must be removed at the same time, so it takes less energy to remove the one electron from the 2p orbital in boron than to remove both electrons from the 2s orbital in beryllium.
Another exception occurs between nitrogen and oxygen. Oxygen has a smaller ionization energy than nitrogen even though it lies to the right of it in the same period. Select the statement that explains this exception to the trend in ionization energy. Oxygen has one more electron than nitrogen in its outer shell. This extra electron decreases the shielding of the other electrons in the outer shell and makes it easier to remove an electron from oxygen. O Nitrogen has three unpaired electrons in the 2p orbitals, whereas oxygen has two unpaired electrons and two paired electrons in the 2p orbitals. The repulsion between the paired 2p electrons in oxygen increases their energy, making one of them easier to remove. Nitrogen has three unpaired electrons in the 2p orbitals, whereas oxygen has two unpaired electrons and two paired electrons in the 2p orbitals. When an electron is removed from nitrogen, it causes the remaining two 2p electrons to pair. The combined energy of these two processes is greater than the energy needed to remove a 2p electron from oxygen. An electron is removed from the 2s orbital in oxygen, whereas an electron is removed from the 2p orbitals in nitrogen. It is easier to remove a 2s electron than a 2p electron.