Chemistry Topic One - Atomic Structure

Atomic number

Number of protons in the nucleus which defines the element which is equal to the number of electrons

Calculation for relative atomic mass with percentages

(% x mass number of first isotope) + (% x mass number of second isotope)

Electrons location

Energy levels

Electrons relative charge

-1

Electrons relative mass

1

Explain atomic radius

Electrons closer to the nucleus experience stronger electrostatic forces of attraction = higher IE , further away = lower IE

Explain nuclear charge

The number of protons in the nucleus, the more protons the stronger the electrostatic forces of attraction between the electrons = more protons = higher IE

Explain shielding

The inner electron shells repel outer electrons, shielding them from the full electrostatic force of attraction from the nucleus, the more inner shells the stronger the shielding is and the lower the IE

Explain the exception from group 2 to 3

-Mg has its outer electron in a S subshell -Al has its outer electron in a P subshell - The P subshell is of higher energy and further away from the nucleus, therefore the electrostatic force of attraction between the positive nucleus and the negative electrons is weaker therefore it is easier to lose the P subshell electron. Alongside this shielding also increases due to the S subshells therefore even less energy is required

Explain the exception from group 5 to 6

• P has 3 electrons in its 3p subshell therefore each orbital is half full, there is one electron in each - S has 4 electrons in its 3- subshell this means that one of the orbitals must now have two and the electrons are sharing - Since they must be of opposite spin in each orbital a mutual repulsion means that less energy is required to remove the outer shell electron

How is electron impact carried out

• Sample is vapourised - High energy electrons are fired at it using an electron gun - This knocks off one electron from each particle - This forms 1+ ions - X(g) --> X+(g) + e- - Used for elements with a lower Mr

How is electrospray ionisation carried out

• Sample is dissolved in a volatile solvent - Sample is passed through a small nozzle under high pressures and high voltages - The particle gains a proton (H+) - This increases the mass - X(g) + H+ --> XH+(g)

How many electrons can go in each orbital

2 (must be of opposite spin)

How many orbitals in D subshell

5

How many orbitals in P subshell

3

How many orbitals in S subshell

1

How to calculate relative atomic mass using relative abundance

(Isotope mass number x relative abundance) + (same) + (same)

Isotopes

Atoms of the same element with the same number of protons but different number of neutrons

Isotopes properties

Isotopes have the same number of electrons therefore their chemical properties will be the same, however they have a different number of neutrons and therefore a different mass number so will have different physical properties

Mass number

Number of protons and neutrons in the nucleus

Neutrons location

Nucleus

Neutrons relative charge

0

Neutrons relative mass

1

Protons location

Nucleus

Protons relative charge

+1

Protons relative mass

1

Relative atomic mass

The average mass of an atom of an element relative to 1

Relative isotopic mass

The mass of a single isotope of an element relative to 1

What 3 things dictate ionisation energy

Nuclear charge, Distance from nucleus (atomic radius), sheilding

What are the 3 subshells

S,P,D

What are the exceptions in IE

Exception from group 2 to 3 (Mg to Al) and Exception from group 5 to 6 (P to S) where the ionisation energy drops

What are the two types of ionisation TOF

Electrospray and Electron Impact

What atoms are exceptions when it comes to subshells and orbitals

Chromium and copper

What happens at ion detection

The positive ions hit a negatively charged detector plate When they hit the plate they gain an electron to become neutral which generates a current The size of the electric current generated is proportional to the abundance of that specific isotope

What happens during acceleration

An electric field is applied so that all the positive ions are given the same constant kinetic energy Kinetic energy = 1

What happens during ion drift

The ions enter a region with no electric field (flight tube) Here the ions are separated based on their velocity All ions have the same KE, therefore velocity depends on their mass Lighter ions travel faster and have a shorter time of flight Heavier ions travel slower and take longer to reach the detector

What happens when d block elements become ions (positive ions losing electrons)

They must lose their 4s electrons before their 3d electrons

What is a mass spectrum

A graph which shows the trace from the mass spectrometer

What is chromium expected to be vs what it actually is

[Ar] 4s2 3d4 vs [Ar] 4s1 3d5 as a half filled d subshell is more stable

What is copper expected to be vs what it actually is

[Ar]4s2 3d9 vs [Ar]4s13d10 as a full d subshell is more stable

What is on the X axis of a mass spectrum

Mass to charge ratio (m

What is on the Y axis of a mass spectrum

Relative abundance

What is the definition of 1st ionisation energy

The amount of energy required to remove an electron from one mole of gaseous atom to from one mole of gaseous ion

What is the definition of isoelectronic

Chemical species (atoms,ion,molecules) that have the same number of electrons and identical electron configurations

What is the equation for 1st ionisation energy

Na(g) --> Na(g)+ +e-

What is the general trend across a period

IE increase: - nuclear charge increases = higher efoa -shielding stays constant - atomic radius decreases = outer shell electrons have higher efoa

What is the general trend in IE down a group

The IE decreases (electrons get easier to lose): - Atomic radius increases meaning that electrons are further away from the nucleus = less efoa - Shielding increases - These override the increase in nuclear charge

What is the general trend in successive IE's

It always increases due to the fact that you are removing and electron from an increasingly positive ion (therefore an electron is harder to lose) Also because as electrons are being lost there is less electron to electron repulsion and a stronger efoa from the nucleus

What is the order of subshells

1s 2s 2p 3s 3p 4s 3d 4p

What is the order on a TOF mass spectrometer

Ionisation (Electrospray, electron impact) Acceleration Ion drift Detection

Where are the d block elements located

Group 3 to Group 12 transition metals

Where is the P block located

Group 13 to 18 main group elements (except He)

Where is the s block located on the periodic table

Group 1 (alkali metals) Group 2 (Alkaline earth metals)

Why are all ionisation energies positive

Because they all require energy to remove an electron therefore they are endothermic , the higher the value the more energy required

Why are the copper and chromium exceptions doable

The 4s and 3d subshells are very close in energy levels, making this single electron promotion energetically favourable (energy levels get closer together as they go on)

Why is a TOF mass spectrometer done under high vacuum conditions

To prevent the generated positive ions reacting with air molecules