Topic 1- atomic structure and periodic table

Question 1

What is a mass spectrometer?

Answer 1

A massspectrometer measures the masses of atoms and molecules, it produces positive ions that are deflected by a magnetic field according to their mass to charge ratio. It also calculates the relative abundance of each positive ions and displays this as a percentage.

Question 2

What is first ionisation energy?

Answer 2

Ionisation energy is a measure of the energy required to completely remove an electron from each atom in one mole of atoms in gaseous state

Question 3

Why does successive ionisation energy increases?

Answer 3

Because the first electron is considerably easier to remove than the second. This is because electrons closer to the nucleus have a higher energy and therefore require more energy to remove.

Question 4

What if an electron is in a high-energy quantum shell?

Answer 4

If an electrons already has a high energy then the energy it needs to gain in order to be removed will not be large.

Question 5

What if the electron is in a lower energy quantum shell?

Answer 5

If it is in a lower energy quantum shell then it will need to gain considerably more energy to be removed.

Question 6

What factors affect the energy of an electron?

Answer 6

The orbital in which the electron exists.
The nuclear charge of the atoms.
The repulsion(shielding) experienced by the electron from all other electrons present.

Question 7

What happens to ionisation energy across a period?

Answer 7

Across a period ionisation energy increases this is because the nuclear charge increases as the number of protons increases. This leads to an increases attraction between the nucleus and the electron, and therefore a decrease in the energy of the outermost electron and increase in first ionisation energy.
However to counteract this an electron is added to same quantum shell on each occasion and this increases electron repulsion and decreases the ionisation energy.
But the increases in nuclear charge is more significant than the electron- electron repulsion. So there is a general increase.

Question 8

What happens to ionisation energy down a group?

Answer 8

Down a group nuclear charge increases and so do the number of protons. This leads to an increase in ionisation energy. However one new quantum shell is added on each occasion, this is increases the energy of the outermost electrons.
So on this occasion the combined effect of adding an extra shell and increasing the shielding is more significant than the increase in nuclear charge. So the first ionisation energy decreases.

Question 9

Why is the first ionisation energy of beryllium higher than boron?

Answer 9

Although the nuclear charge of the boron atom is greater the outer electron has more energy since it is in a 2p orbital as opposed to the 2s orbital for beryllium. So energy required to remove that is less than the 2s for beryllium.
In addition the 2p electron in boron experiences greater electron -electron repulsion (greater shielding)

Question 10

Why is the first ionisation energy of magnesium higher than that of aluminium?

Answer 10

The outer electron in the aluminium atom has higher energy it is in a 3p orbital as opposed to the 3s orbital for magnesium. In addition, the 3p electron in aluminium experiences greater electronelectron repulsion (i.e. greater shielding) since there are three inner electron shells as opposed to only two in the magnesium atom

Question 11

Why is the first ionisation energy of sodium lower than that of magnesium?

Answer 11

The sodium atom has a lower nuclear charge than the magnesium atom

The orbital energy of the electron in the 3s orbital in the sodium atom is therefore lower than that in the magnesium atom

Question 12

Why does Si have a greater boiling point than Na to Al?

Answer 12

Si is a giant covalent structure with many covalent bonds between the atoms. These covalent bonds a very high amount of energy to break these bonds, hence they have a very high mp, bp.

Question 13

Why is there a dip in ionisation between phosphorus and sulfur? (group 5 and 6).

Answer 13

Sulfur has 4 electrons in the 3p sub shell. The fourth electron fully fills the first 3p orbital. The electron pair in this orbital slightly repel each other due to opposite spin, making it easier to remove an electron. Hence first ionisation energy decreases between them.

Question 14

Trend in melting points for Na to Al

Answer 14

Metallic bonding increases as proton number increases. This means that more electrons are released into the sea of electrons, and with decrease in ionic radii, the metallic bonding gets stronger. Hence melting points increase

Question 15

explain the trend in first ionisation energy from end of period to start of new period.

Answer 15

• although nuclear charge increases
• atomic radius increases due to 1 more shell.
• electron shielding effect increases
• force of attraction between outermost electrons and nucleus decreases
• first ionisation energy decreases.

Question 16

why does atomic radii decrease across a period?

Answer 16

• nuclear charge increases
• number of shells stay the same
• shielding effect stays the same
• force of attraction between outer electrons and nucleus increases.
• outer electrons are pulled in closer towards the nucleus.
• atomic radii decreases across a period.

Question 17

What is second ionisation energy?

Answer 17

The energy required to remove an electron from each single charged positive ion in one mole of a positive ions in gaseous state. To make 2+ ions

Question 18

periodicity?

Answer 18

is a regularly repeating pattern of atomic,phyiscal and chemical properties with increasing atomic number.