Atomic basics and ionisation energy

Question 1

Define atomic number

Answer 1

The number of protons in the nucleus of an atom

Question 2

Define isotope

Answer 2

An atom of the same element with a different number of neutrons and therefore a different mass

Question 3

Define mass number

Answer 3

The sum of the number of protons and neutrons in the nucleus

Question 4

Define relative atomic mass

Answer 4

The weighted mean mass of an atom compared with the 1/12 th the mass of an atom of carbon 12

Question 5

Define relative isotopic mass

Answer 5

The weighted mean mass of an isotope compared with 1/12th the mass of an atom of carbon-12

Question 6

What are the axis on a mass spectrum?

Answer 6

x- mass to charge ratio (m/z) y- relative abundance

Question 7

What does the number of lines on a mass spectrum represent?

Answer 7

The number of different isotopes of an element

Question 8

How do you work out the % abundance of an isotope of an element from a mass spectrum?

Answer 8

-Add up all the heights to find the total -Divide the height of the isotope you want by the total height -x100

Question 9

What are atoms converted to in a mass spectrometer? Therefore what does the mass to charge ratio represent?

Answer 9

1+ The relative isotopic mass

Question 10

Suggest 3 reasons carbon-12 is the standard for relative atomic mass

Answer 10

1) it is abundant 2) it is unreactive 3) it is easily found in an isotopically pure state

Question 11

Define 1st ionisation energy

Answer 11

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 12

What are the 3 factors that affect ionisation energy?

Answer 12

1) Nuclear charge 2) Atomic radius 3) Shielding (no. inner electron shells)

Question 13

Explain what is meant by the term ‘shielding’

Answer 13

The electrons in the inner shell ‘protect’ the outer electrons from the attraction of the positive charge of the nucleus

Question 14

Why is 2nd ionisation energy always greater than 1st ionisation energy?

Answer 14

• once the 1st electron is removed the attraction of the nucleus on the remaining electrons is greater -so electrons are pulled closer to the nucleus -so more energy is required

Question 15

Why is the 3rd ionisation energy of magnesium much greater than the 2nd ionisation energy?

Answer 15

• the 3rd electron is taken from the next electron shell in which is closer to the nucleus -less shielding is experienced - the nuclear attraction is therefore greater -so a lot more energy needed

Question 16

What can graphs of successive ionisation energy show about an atom?

Answer 16

• the number of electrons in each shell

Question 17

What are the axis of graphs for successive ionisation energies?

Answer 17

x- number of electrons y- log of ionisation energy

Question 18

Which element has the greatest ionisation energy and why?

Answer 18

Helium because: -atoms higher up the group have fewer electron shells so less shielding - atoms to the right of a period have a higher nuclear charge for their number of electron shells -helium is the highest up and furthest right element so has the highest effective nuclear charge -so the electron is hardest to remove

Question 19

Why does neon have a greater 1st ionisation energy than lithium?

Answer 19

• neon has a greater nuclear charge than lithium -electrons are pulled closer to the nucleus - the atomic radius therefore is decreased -the shielding in both atoms in similar

Question 20

Why does sodium have a smaller 1st ionisation energy than lithium?

Answer 20

-more electron shells -more shielding -so the sodium atom has the greater atomic radius -the outer electron is further from the nucleus and so there is reduced attraction between the nucleus and the outer electron -this outweighs the greater nuclear charge