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AS chemistry help

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Reply 20

username2752874

Original post by mynameisno123

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?

Worth noting that ionisation generally increases across a period due to more protons, therefore resulting in general increase in greater effective nuclear charge.

Option 1 has outer electron in a shell closer to a nucleus, so less shielding and stronger electrostatic attraction

Option 2 has electrons in a new energy level, so they face shielding from the inner electrons in the first energy level. so far we know 2 is lower than 1

Option 3 has an extra proton, but its new electron is in a new sub shell that faces shielding from the 2s sub shell.

Option 4 would definitely be higher than 3 since it has an extra proton, and has no extra shielding or repulsion in orbitals due to electron pairing.

You're left with option 2 or 3, and in practice, chemists would use maths to calculate the net effect of having an extra proton, along with an extra electron in a new sub shell. However, from periodicity study, you should know anomalies, such as N and O, or Be and B. It happens that the electron in a new sub shell bucks the trend in ionisation energy, and so 3 has a lower ionisation energy than 2.

In a degree, you'll have to mathematically prove for example that 3 is lower than 2, and not just base it off qualitative explanation (this explanation would've been derived from calculations too).

Reply 21

Maker

Original post by 1234123456785678

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.

What stable structure?

Reply 22

1234123456785678

Original post by Maker

What stable structure?

Original post by Maker

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.
.

you literally mentioned it here?

(edited 6 years ago)

Reply 23

username2752874

Original post by 1234123456785678

you literally mentioned it here?

Why would a full octet affect ionisation energy?

Distance, effect of nuclear charge and shielding are the main factors.

A full octet is often a characteristic of a high ionisation energy, but it's not the cause of it.

Reply 24

1234123456785678

Original post by Kyber Ninja

Okay well even if that weren’t true then you can consider the effect of nuclear charge, that’s why noble gases have high ionization energies across a period.

Reply 25

username2752874

Original post by 1234123456785678

Okay well even if that weren’t true then you can consider the effect of nuclear charge, that’s why noble gases have high ionization energies across a period.