Alevel Chemistry - Topic 1

Question 1

Define Atomic Number

Answer 1

Atomic number: The number of protons in the nucleus of an atom of that element

Question 2

Define mass number

Answer 2

Mass number: The sum of the number of protons and number of neutrons in the nucleus of that atom

Question 3

Isotopes

Answer 3

Isotopes: Atoms of the same element with the same number of protons but differ in the number of neutrons

Question 4

Define Relative atomic mass

Answer 4

Relative atomic mass: The weighted mean mass of an atom of an element compared to 1/12th the mass of an atom of Carbon-12

Question 5

Define Relative isotopic mass

Answer 5

Relative isotopic mass: The mass of an atom of an isotope compared to 1/12th the mass of an atom of Carbon-12

Question 6

What is effective nuclear charge?

Answer 6

effective nuclear charge is the actual amount of positive charge experienced by an electron in a multi-electron atom

Question 7

What is the relative mass and charge of a neutron, proton, and electron?

Answer 7

Neutron: 1, 0 charge
Proton: 1, +1 charge
Electron: 1/1840, -1 Charge

Question 8

What are isoelectronic species?

Answer 8

Isoelectronic species are elements or ions that have the same, or equal number of electrons. E.g. Na+, F- both have 10 electrons.

Question 9

What are the two exceptions in electronic configurations?

Answer 9

Copper and chromium, will fill their 4s sub shell with an electron so that the 3d Sub shell is either half or completely full since this is the most stable state.

Question 10

What is the maximum number of electrons that can occupy each shell?

Answer 10

Number of electrons = 2n^2

E.g. 2,8,18,32

Question 11

What is Hunds law?

Answer 11

Electrons will occupy orbitals singly before pairing takes place

Question 12

What is paulis exclusion principle?

Answer 12

Electrons cannot occupy the same orbital unless they have opposite spins

Question 13

What is an orbital?

Answer 13

Region within the atom than can hold up to two electrons with opposite spins

Question 14

What is the shape of a S-Orbital

Answer 14

Sphere

Question 15

What is the shape of a P-Orbital

Answer 15

Dumbbell

Question 16

What is Periodicity?

Answer 16

the repeating chemical and physical properties across different periods

Question 17

What is the general trend of Atomic Radii across a period?

Answer 17

-Atomic radius decreases
-Proton number increases
-Increasing effective charge on electrons
-Greater effect that the electron-electron repulsion
-Pulling the electron cloud inwards
-Decreasing the radius of the atom

Question 18

Explain why an atom or an +ion of the same element is larger in atomic radii?

Answer 18

• Both same the proton number since they belong to the same element
• +Ion has a fewer electrons than its atom version
• This results in less shielding effect or reduced electron-electron repulsion
• Increase the effective nuclear charge on electrons
• Pulling the electron cloud closer to the nucleus
• And decreasing radii

Question 19

Explain why an atom or an -ion of the same element is larger in atomic radii?

Answer 19

• Both same the proton number since they belong to the same element
• -Ion has a more electrons than its atom of the same element
• This results in greater shielding effect or larger electron-electron repulsion
• Decreases the effective nuclear charge on electrons
• the electron cloud is further from the nucleus
• Increasing radii

Question 20

What is First ionization energy?

Answer 20

First ionization energy is the energy needed to remove one mole of electrons from one mole of atoms in their gaseous state to from one mole of 1+ ions also in their gaseous state.

Question 21

What is successive ionization energy?

Answer 21

Successive ionization energy is the energy needed to remove a mole of electrons from a mole of IONS in their gaseous state to form one mole of greater charged IONS also in their gaseous state.

Question 22

What is the formula for ionization energy?

Answer 22

Doesn’t have to be diatomic:

I(g) -> I+ (g) + e-

Question 23

What is ionization energy affected by?

Answer 23

Number of protons, electron shielding, and the electron sub-shell from which the electron is removed from

Question 24

How does the proton number affect electron shielding? (Mg vs Na)

Answer 24

-Mg has a greater number of protons than Na
-This results in greater effective nuclear charge on Mg valence electrons than Na
-This is more significant than added electron-electron repulsion
-Hence greater energy needed to remove an electron from Mg than Na

Question 25

How does electron-shielding affect ionization energy? (K vs Na)

Answer 25

- K and Na are in the same group so both have a single valence electron - K has more quantum shells than Na - Greater electron shielding of inner core electrons on valence electrons - Reducing effective nuclear charge from nucleus on K outer electron - Hence less energy needed to remove outer electron - ionization energy decreases from Na, to K

Question 26

How does the Sub shell by which an electron is removed from affect ionization energy?

Answer 26

In a multi electron atom, if an electron were to be removed from a 2p sub shell , it requires less energy than if it was from a 2s sub shell . This is because 2p sub shells are higher than 2s, so less additional energy required to remove valence electron. 2s orbital is closer to the ground state.

Question 27

Explain the general trend for Ionisation across a period?

Answer 27

-From Left to right, the number of protons in a period increase per atom -This results in greater effective nuclear charge across on valence electrons -This is more significant than added electron-electron repulsion -Hence greater energy needed to remove an electron from Mg than Na

Question 28

Explain the trend of ionisation energy down a group?

Answer 28

- Elements in the same group have the same number of valence electrons - Down a group, the number of quantum shells increases - Greater electron shielding of inner core electrons on valence electrons - Reducing effective nuclear charge from nucleus on outer electrons down a group - Hence less energy needed to remove outer electron - ionization energy decreases down the group

Question 29

What does a graph of LOG successive ionisation energies tell us?

Answer 29

- Tell us how many quantum shells of an element - Can tell us its electronic configuration - Big jumps can denote a change of shell - Small jumps can denote a change of sub shell (but minute so we ignore this)

Question 30

Explain the two anatomies in the ionization energies across a period?

Answer 30

The first Dip is from group 2 to group 3 elements. This is because the valence electron in group 2 elements is removed from the Xs orbital whereas group 3 elements have their electron removed from its Xp orbital. Xp orbitals are higher in energy than Xs orbital so less energy required to overcome electrostatic forces of attraction from the positive nucleus. The second dip is between group 5 and 6 elements. Due to Hunds law, electrons occupy orbitals singly before pairing takes place. In group 5 elements electrons occupy the p orbitals singly, and it is in group 6 elements where pairing first takes place. The pairing results in greater shielding due to electron-electron repulsion of electrons in the same orbital, reducing the energy needed to overcome the electrostatic forces of attraction of the positive nucleus.

Question 31

Why do isotopes have the same chemical properties?

Answer 31

Isotopes of the same element have identical chemical properties because their electronic configuration is still the same.