Ionisation Energies

Question 1

When had an atom or molecule been ionised?

Answer 1

• when electrons have been removed from it

Question 2

What is the first ionisation energy?

Answer 2

• the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Question 3

What are the important parts of ionisation energies?

Answer 3

• you must use the gas state symbol (g) because ionisation energies are measured for gaseous atoms
• always refer to 1 mole of atoms, as stated in the definition, rather than to a single atom
• the lower the ionisation energy, the easier it is to form a positive ion

Question 4

What does a high ionisation energy mean?

Answer 4

• there’s a high attraction between the electron and the nucleus, so more energy is needed to remove the electron

Question 5

What are the three things that affect ionisation energies?

Answer 5

• nuclear charge
• distance from the nucleus
• shielding

Question 6

describe how the nuclear charge affects the ionisation energy

Answer 6

• the more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for electrons

Question 7

describe how the distance from the nucleus affects the ionisation energy

Answer 7

• attraction fall off very rapidly with distance, an electron close to the nucleus will be much more strongly attracted than one further away

Question 8

describe how shielding affects the ionisation energy

Answer 8

• as the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction to the nucleus, this lessening of the pull of the nucleus thanks to the inner electron shells is called shielding

Question 9

what is the second ionisation energy?

Answer 9

• the energy needed to remove an electron from each ion in one mole of gaseous 1+ ions

Question 10

describe the second ionisation energy

Answer 10

• just like the first ionisation energy, the value of the second ionisation energy depends on nuclear charge, the distance of the electron from the nucleus and the shielding effect of inner electrons
• second ionisation energies are greater than first ionisation energies because the electron is being removed from a positive ion and not an atom, which will require more energy
• the electron configuration of the atom will also play a role in how much larger the second ionisation energy is from the first

Question 11

describe successive ionisation energies

Answer 11

• you can remove all the electrons from an atom, leaving only the nucleus, each time you remove an electron, there’s a successive ionisation energy
• the general equation for the nth ionisation energy is: x^(n-1)+ (g) > x^n+ (g) +e^-

Question 12

describe the ionisation trends down group 2

Answer 12

• first ionisation energy decreases down group 2
• this provides evidence that electron shells really exist
• if each element going down group 2 has one or more electron shell than the one above, the extra shell will shield the outer electrons from the attraction of the nucleus, the extra shell also means that the outer electrons will be further from the nucleus, so the nucleus’s attraction will be reduced, this results in lower activation energies

Question 13

describe the ionisation trends across periods?

Answer 13

• as you move across a period, the general trend is for the ionisation energies to increase, it gets harder to remove the electrons, this can be explained by the fact that the number of protons is increasing, which means a stronger nuclear attraction
• all the extra electrons are roughly at the same energy level, even if the outer electrons are in different orbital types, this means theres generally little extra shielding effect or distance to lessen the attraction from the nucleus, but there are small drops between groups 2 and 3, and 5 and 6
• the drop between group 2 and 3 shows shell structure
• the drop between group 5 and 6 is due to electron repulsion

Question 14

what happens within each shell?

Answer 14

• successive ionisation energies increase, this is because electrons are removed from an increasingly possitive ion, theres less repulsion amongst the remaining electrons, so they’re held more strongly by the nucleus

Question 15

when does the big jumps within ionisation energy happen?

Answer 15

• when a new shell is broken into, an electon is being removed from a shell closer to the nucleus

Question 16

how are graphs used to tell you which group of the periodic table and element belongs to?

Answer 16

• count how many electrons are removed before the big jump to find the group number

Question 17

how are the graphs used to predict the electronic structure of an element?

Answer 17

• working right to left, count how many points there are before each big jump, to find out how many electrons are in each shell, starting with the first