The periodic table and energy

Question 1

What does the modern periodic table arrange elements by?

Answer 1

Their atomic (proton) number.

Question 2

What did Dmitri Mendeleev do with his table that made it different to those before his?

Answer 2

He left gaps in the table where the next element didn’t seem to fit. This allowed him to predict properties of undiscovered elements that he expected to fill these gaps. Examples of gaps he left are germanium, scandium and gallium.

Question 3

The periodic table is arranged into _______ (columns) and ______ (rows)

Answer 3

Groups

Periods

Question 4

All the elements in a period have the same number of ________ ______.

Answer 4

Electron shells

Question 5

What is the name for the repeating trends in the physical and chemical properties of the elements across a period?

Answer 5

Periodicity

Question 6

All the elements within a group have the same number of _________ in their _____ _____. This means they have similar ________ properties.

Answer 6

Electrons
Outer shell
Chemical

Question 7

What part of the periodic table is the s-block?

Answer 7

Groups 1-2

Question 8

What part of the periodic table is the p-block?

Answer 8

Groups 3-8

Question 9

What part of the periodic table is the d-block?

Answer 9

The transition metals

Question 10

Define first ionisation energy

Answer 10

The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.

Question 11

Is ionisation exothermic or endothermic?

Answer 11

Endothermic, because energy has to be put in to ionise the atom or molecule.

Question 12

What is the equation for the first ionisation of oxygen?

Answer 12

O(g) ——>O+(g) + e-

Question 13

How does nuclear charge affect ionisation energy?

Answer 13

The more protons there are in the nucleus, the stronger the positive charge of the nucleus and so the stronger the attraction for the electrons.

Question 14

How does atomic radius affect ionisation energy?

Answer 14

Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away.

Question 15

How does electron shielding affect ionisation energy?

Answer 15

As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge. This lessening of the pull of the nucleus by inner shells of electrons is called shielding.

Question 16

What does a high ionisation energy mean?

Answer 16

A high ionisation energy means there’s a strong attraction between the electron and the nucleus, so more energy is need to overcome the attraction and remove the electron.

Question 17

Why does ionisation energy decrease down a group?

Answer 17

Elements down a group have extra electron shells, which mean that the atomic radius is larger, so the outer electrons are farther from the nucleus and the attraction between them is greatly reduced.
Also, the extra inner shells shield the outer electrons from the attraction of the nucleus.

Question 18

Why does ionisation energy increase across a period?

Answer 18

Across period, the number of protons in the nucleus increases, so the positive charge of the nucleus increases. This causes the electrons to be pulled closer to the nucleus, decreasing the atomic radius. There is no increased electron shielding as electrons are added to the outer shell.

Question 19

Why is there a drop in ionisation energy between group 2 and 3?

Answer 19

The drop is due to sub-shell structure. The outer electron in group 3 is in a p-orbital rather than an s-orbital. A p-orbital has a slightly higher energy than an s-orbital in the same shell, so the electron is, on average, to be found further from the nucleus. The p-orbital also has additional shielding provided by the s electrons. These factors override the effect of the increased nuclear charge, so the ionisation energy drops slightly.

Question 20

Why is there a drop in ionisation energy between group 5 and 6?

Answer 20

The drop is due to p-orbital repulsion. In the group 5 elements, the electron is being removed from a singly-occupied orbital. In group 6 elements, the electron is being removed from an orbital containing two electrons. The repulsion between these two electrons makes the removal of an electron easier and therefore the ionisation energy lower.