Atomic Structure And Periodic Table

Question 1

Electron Shells

Answer 1

-Electron Shells are made from sub-shells (s,p,d and f), which are made from orbitals
-An s Sub-shell has one orbital
-A p Sub-shell has 3 orbitals
-A d Sub-shell can have five orbitals
-An orbital is a region around the nucleus which can hold up to 2 electrons with opposite spins
-A-level studies shells 1-4 (hydrogen-Krypton)

Question 2

S-orbitals

Answer 2

-Can hold 2 electrons
-have spherical shape
-Each shell contains one s-sub shell
-s-sub shells are made from one s-orbital
-s-sub shells can hold 2 electrons

Question 3

P-orbitals

Answer 3

-can hold 2 electrons
-Have dumbbell shape
-shells 2-4 contain one p sub-shell
-p-sub shells are made from 3 p-orbitals
-p-sub shells can hold 6 electrons

Question 4

D-orbitals

Answer 4

-Can hold 2 electrons
-shells 3 and 4 contain one d-sub shell
-Clover shape
-d-sub shell are made from 5 d-orbitals
-d-sub shells can hold 10 electrons

Question 5

F-orbitals

Answer 5

-Can hold 2 electrons
-Shell 4 contain one f-sub shell
-f-sub shells are made from 7 f-sub shells
-f-sub shells can contain maximum 14 electrons

Question 6

Electron spin/ Pauli exlusion principle

Answer 6

-in a single atom, no two electrons will have an identical set or the same quantum numbers
-Therefore, if two electrons share and orbital they will be spinning i opposite directions (antiparallel)

Question 7

Aufbau Principle

Answer 7

-The Aufbau Principle gives the order in which orbitals are filled up.
-It states that each electron occupies the orbital whose energy is the lowest available to it

Question 8

Hund’s rule

Answer 8

-Every orbital in a sub shell is singly occupied with one electron before any one orbital is doubly occupied
-All electrons in singly occupied orbitals have the same spin.

Question 9

What is Mass Spectra

Answer 9

-Mass spectrometry is a form of molecular analysis
-There are many types of mass spectrometry including; time of flight (TOF) and Low resolution
-However, they all follow the same steps- Ions are formed from the sample, the ions are separated and the ions are detected
-Mass spectrometry is used to provide structural information, identifying unknown compounds and determining the relative abundance (%) of each isotope of an element

Question 10

Describe the Steps of Time of flight Mass spectra

Answer 10

-In a Time of Flight Mass spectrometer, the apparatus is under a vacuum to prevent ions colliding with air (particles)
-The steps of TOF mass spectrometry is:
1. Ionisation: the sample is dissolved in a volatile solvent and forced through a hollow needle (which is connected to the +ve terminal of a high voltage supply)
-This produces tiny positively charged droplets, which have now lost electrons
-Therefore, these droplets are reduced in size to a 1+ ion and the solvent evaporates
-Alternatively, an electron gun can be used to fire electrons at the substance, knocking elections of the outer shell, forming ions (electron impact ionisation)
2. Acceleration: the positively charged ions are attracted towards a negatively charged electric plate
-This caused the ions to accelerate with the same kinetic energy
-Hence the larger, heavier particles will have a lower speed and vice versa
3. Ion drift: The ions pass through a hole(s) in the negatively charged plate forming a beam of ions
-This beam travel along a flight tube
4. Detection: the ions arrive at the detector where their time of flight is recorded
-The positive ions gain an electron, causing current to flow
5. Data analysis: the detector passes a signal to the computer, forming a mass spectrum

Question 11

Low resolution mass spectra

Answer 11

-Isotopes are atoms with the same number of protons and different number of neutrons e.g Cl-35 and Cl-37
-Each isotope has different masses
-Therefore the isotopes will have a different M/Z ratio (mass over charge) and therfore will be detected differently
-mass spectrometry can be carried out to 5 decimal places, but when done to one its described as low resolution mass spectra

Question 12

Define relative isotopic mass

Answer 12

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

Question 13

Define Relative atomic mass

Answer 13

The weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of Carbon-12

Question 14

Define Periodicity

Answer 14

Periodicity is the study of repeating patterns/trends of physical or chemical properties as we move around the periodic table (A level focuses on period 3)
-Periodicity looks at trends and differences in : atomic radius, 1st Ionisation energy and melting/boiling point

Question 15

Atomic Radius (periodicity)

Answer 15

Across the period, we remain in the same outer shell, therefore the shielding throughout remains the same (for we have the same amount of inner shells)
-However, the proton number increases hence the nucleus having a stronger positive charge, hence there being a stronger force of attraction
-So, across the period, atomic radius decreases

Question 16

Ionisation energy (periodicity)

Answer 16

-Energy required to remove one more of electrons from one mole of an atom in its gaseous state to produce one mole of 1+ ions
-Generally the ionisation increases across a period, however, in period 2 as example it decreases twice- once in boron as there is one electron in the p subshell, undergoing great shielding and with a far radius from the nucleus hence having a lower first ionisation energy than the element before
-In the case of oxygen, The election is removed from a single doubly occupied orbital, hence having strong repulsion

Question 17

Melting and BP (periodicity)

Answer 17

-The changed in MP and BP changes across the period based on the types of bonding in the elements
-Generally there is an increase across the highest MP and BP metals at the start of the period as they are metallically bonded.
-After this it generally decreases as it goes too covalent and monoatomic bonds

Question 18

Define Ionisation energy (1st )

Answer 18

-The first ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in their gaseous state to form a mole of 1+ ions (also in their gaseous state)

Question 19

Successive ionisation energies

Answer 19

Once one electron is removed, we can continue to remove more electrons and measure the ionisation energy required each time
-For example, the definition is very similar to definition of the first ionisation energies: The second ionisation energy is the energy needed to remove one mole of electrons from one mole of 1+ ions in their gaseous state to form one mole of 2+ ions (also in their gaseous state)
-This definition can be altered for each successive ionisation energy, changing the charge however each time ( as example, in the third ionisation energy, the ions will be 2+ -> 3+)

Question 20

Give the three factors affecting ionisation energies

Answer 20

• The distance between the nucleus and the outermost electrons (the atomic radius). As the atomic radius increases, the force of attraction between the oppositely charged nucleus and electrons decreases, therefore requiring less ionisation energy.
• The second factor is the charge on the nucleus,with more positively charged protons in the nucleus having a greater force of attraction on the negatively charged outermost electrons, thus requiring more ionisation energy to overcome
• The final factor is shielding- electrons in the outer shell are repelled by the like charges in the inner shells therefore reducing the attraction between the outer electrons and the nucleus

Question 21

Ionisation energy down a group

Answer 21

-Ionisation energy decreases down a group due to 2 factors;
• Firstly, moving down a group increases the atomic radius, so the outer electrons are further from the nucleus hence requiring less ionisation energy
• Secondly, shielding increases, for there are more inner shells, repelling the outer shell, increasing distance between the outer shell and nucleus
-It is important to note that despite there being a higher nuclear charge of the nucleus, this is offset by the two factors above