In reality, the effective nuclear charge is approximately one point nine, and that's because beryllium has another electron in its two s orbital over here, which does effect this electron a little bit. It repels it a little bit, and so it actually deceases the effective nuclear charge to about, one point nine.
But again, for a quick calculation, positive two works.
So, the outer electron for beryllium, let's just choose this one again, is feeling an effective nuclear charge of positive two, which means that, it's going to be pulled closer to the nucleus, there's a greater attractive force on this outer electron for beryllium, as compared to this outer electron for lithium. The effective nuclear charge is only plus one for this outer electron, and because of this, the beryllium atom is smaller, right?
The two s orbital gets smaller, and the atom itself is smaller.
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Beryllium is smaller than lithium. So this outer electron here, let me switch colors again, this outer electron for beryllium is closer to the nucleus than the outer electron for lithium. It feels a greater attractive force, and therefore it takes more energy to pull this electron away from the neutral beryllium atom, and that's the reason for the higher ionization energy. So beryllium has an ionization energy of positive kilojoules per mole, compared to lithium's of kilojoules per mole. So it has to do with the effective nuclear charge.
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So far we've compared lithium and beryllium and we saw that the ionization energy went from positive kilojoules per mole to kilojoules per mole, and we said that was because of the increased effective nuclear charge for beryllium, but as we go from beryllium to boron, there's still an increased effective nuclear charge, but notice our ionization energy goes from kilojoules per mole for beryllium to only kilojoules per mole for boron, so there's a slight decrease in the ionization energy.
And let's look at the electron configuration of boron to see if we can explain that. Boron has five electrons, so the electron configuration is one s two, two s two, and two p one.
So that fifth electron goes into a two p orbital, and the two p orbital is higher in energy than a two s orbital, which means the electron in the two p orbital is on average, further away from the nucleus that the two electron in the two s orbital. So if we just sketch this out really quickly, let's say that's my two s orbital, I have two electrons in there, and this one electron in the two p orbital is on average further away from the nucleus. So, those two electrons in the two s orbital actually can repel this electron in the two p orbital. So, there's a little bit extra shielding there of the two p electron from the full attraction of the nucleus, right?
So, even though we have five protons in the nucleus, and a positive five charge for boron, the fact that these two s electrons add a little bit of extra shielding means it's easier to pull this electron away. So, it turns out to be a little bit easier to pull this electron in the two p orbital away due to these two s electrons.
And that's the reason for this slight decrease in ionization energy. As we go from boron to carbon, we see an increase in ionization energy, from carbon to nitrogen, an increase in ionization energy. Again, we attribute that to increased effective nuclear charge, but when we go from nitrogen to oxygen, we see a slight decrease again. From about kilojoules per mole, down to about kilojoules per mole for oxygen. So, let's see if we can explain that by writing out some electron configurations for nitrogen and oxygen.
The chilling effect of asteroid impacts and volcanic eruptions — like those which helped wipe out the dinosaurs — is mostly down to the emission of sulphur, generated by vaporising sulphur-rich rock. The particles stick around for years, increasing the density of the atmosphere and reflecting sunlight back into space.
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It happened as recently as , when the eruption of Mount Pinatubo unleashed thousands of tonnes of sulphur dioxide gas. In the following years, Earth cooled by a few tenths of a degree. In a global warming emergency, an artificial super-volcano might be just what the planet needs. Whether it would work in practice is not quite so clear-cut. How quickly would the Earth cool down and by how much?
Would it shade the planet evenly? After all, just a few degrees more cooling than expected could be catastrophic. Dr Matthew Watson, a volcanologist at the University of Bristol, has other concerns. We know what volcanoes do to global temperatures pretty well.
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According to Watson, the real risks lie in the unintended consequences. Take ozone, the chemical which shields the Earth from cancer-causing ultraviolet rays. The Montreal Protocol banned the use of ozone-eating chemicals, called chlorofluorocarbons CFCs , which were once widely used in refrigerators and spray cans.
And yet every spring, a hole appears in ozone layer over the Antarctic, as ice clouds provide a surface on which left over chlorine compounds can destroy it.
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