1.1 Atomic Structure Flashcards
What is the symbol for atomic number?
Z
What is the symbol for mass number?
A
Define atomic number
The number of protons in an atom
Define mass number
The amount of protons plus neutrons in an atom
Define relative atomic mass
Average mass of an atom compared to 1/12th the mass of a carbon-12 atom
What is an isotope?
An atom of the same element with the same number of protons but a different number of neutrons
Why do isotopes have the same chemical properties?
Because they have the same electronic configurations
What is mass spectrometry used to determine?
Ar of elements and isotopes/relative abundance of isotopes/Mr of covalent compounds
What is ionisation?
High energy electrons fired from an electron gun knock off an electron from a gaseous atom, forming a positive ion
What is acceleration?
Positive ions are accelerated using negatively charged plates as opposite charges attract- positive ions are attracted and accelerated by these negatively charged plates
What is ion drift?
As all ions have a different mass but have the same kinetic energy so they have different velocities. ToF depends on the mass of the ions, and the lighter ions travel faster so reach the detector first
What is detection?
When positively charged ions hit the detector, electrons flow from the detector plate to the positive ions, providing a current. The greater the current, the greater the abundance of the ion
How do you know the Mr from a mass spectra graph?
The highest (furthest along the x-axis) m/z value is equal to the Mr (with electron impact ionisation)
Why is it necessary to ionise the atoms?
-particles need to have a positive charge to be accelerated with the negative plates
-neutral particles cannot generate a current in order to be detected at the detector plates
Why might the Ar be slightly different on the periodic table than to what you work out?
Because the relative abundance of isotopes varies/differs in different parts of the world
What will always generally happen when you have a peak of C-12 on a mass spectra graph?
There will be another very small peak of C-13 that is roughly 100x smaller
What are the two isotopes of Br and the relative ratio they’re found in?
79Br and 81Br, in a relative ratio of 1:1
What are the two isotopes of Cl and the relative ratio they’re found in?
35Cl and 37Cl, in a relative ratio of 3:1
What are the two types of ionisation and what are they each used for?
Electron impact ionisation - used for atoms/elements/small molecules
Electron spray ionisation - used for very large molecules like proteins/DNA
What are the steps to electron spray ionisation?
-sample is dissolved in a volatile solvent
-this is injected through a fine hypodermic needle giving a fine mist
-the tip of the needle has a high voltage
-each molecule gains a proton (H+)
What is the general formula for electron spray ionisation?
M + H^+ –> [MH^]+
How do you find out the Mr from a mass spectra graph of an electron spray ionisation?
Find the highest m/z value and -1 (to take into account the proton it gained during ionisation)
What is the formula for KE?
KE=1/2 m v²
What is the formula for mass?
Mass = (Ar/ Avogadros)/1000
What is the formula for distance?
D= t sr.root 2KE/mass
What is the formula for time?
T= d sr.root mass/2KE OR t2= sr.root m2/m1 (t1)
What is the formula for mass given the time/distance/mass?
mass = 2KE t²/ d² OR m1= t1² (m2/t2²)
What groups are in the s block?
1 and 2
What groups are in the d block?
All the middle parts of the periodic table
What groups are in the p block?
3-0
What groups are in the f block?
Lanthanides and Actinides
How many orbitals on the energy levels 1-4 and how many electrons can they each hold in total?
1st- 1 (2 electrons)
2nd- 4 (8 electrons)
3rd- 9 (18 electrons)
4th- 16 (32 electrons?
What is the order of the electronic configuration?
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰
What subshell loses electrons first when filled?
4s
Why are chromium and copper different and why?
They have 3d⁵ and 3d¹⁰ filled subshells as that is more stable than having a full 4s subshell
What is Hund’s rule?
Electrons will go in different orbitals with the same spin if the orbitals are degenerate (same energy level)
Name each sub level and the number of orbitals it has, along with how many electrons it can hold
S- 1 orbital, 2 electrons
P- 3 orbitals, 6 electrons
D- 5 orbitals, 10 electrons
F- 7 orbitals, 14 electrons
What is an orbital?
A volume of space with a 95% chance of finding an electron
What is a subshell?
A collection of orbitals, all of the same energy
What is ionisation energy and what is it measured in?
The minimum amount of energy required to remove 1 mole of electrons from 1 mole of gaseous atoms. Measured in kJmol-¹
Give the equation for the 1st IE of Na
Na(g) –> Na(g)^+ + e^-
What four factors affect the first IE?
-size of nuclear charge
-size of nuclear radius
-shielding
-spin-pair repulsion
Describe and explain the pattern of successive IE’s
Increase every time, due to the fact that it’s harder to remove an electron from an increasingly positive ion so consistently requires more energy
Describe and explain the trend of the 1st IE down a group
Decreases due to an increasing atomic radius and greater shielding which reduces the effect of the electrostatic forces of attraction between the nucleus and the electron = less energy needed
Describe and explain the trend in 1st IE across a period
Increases due to a greater nuclear charge and similar shielding so more energy is needed to overcome the greater electrostatic forces of attraction between the nucleus and the electron = more energy needed
Explain why there is a decrease in the 1st IE of Mg-Al / groups 2–>3
Al’s outer electron is in a higher energy 3p subshell so requires less energy to overcome the weaker attraction between the nucleus and the electron, whereas in Mg the electron is being removed from an s subshell, which requires more energy to remove
Explain why there is a decrease in the 1st IE of N–>O / groups 5/6
O has a pair of electrons in it’s p orbital that repel
Group 6 elements have one full p orbital, the paired electrons repel each other which increases their energy and makes them easier to remove
Explain why there are very large increases from some IEs to the next
Because the electron is being removed from a much closer energy level which is closer to the nucleus with less shielding, so requires much more energy to overcome the strong attraction between the nucleus and the electron
Why is the 1st IE of neon greater than the 1st IE of sodium?
Because neon’s outer electron is in a closer energy level to sodium’s so is more strongly attracted to the nucleus
Why is the 1st IE of sodium less than the 1st IE of magnesium?
Due to sodium having fewer protons but similar shielding to magnesium
Describe the trend in the graph as the IE increases among the same elements
The pattern shifts to the right by 1 spot every time the IE goes up
Why must you specify gaseous when defining 1st IE?
As if you don’t it could potentially then be a solid or a liquid, and this would mean that the value of the 1st IE wouldn’t be enough to remove an electron, as some of the energy would be used instead to break bonds
Why must the ToF mass spectrometer be a vacuum?
To stop the chance of the ions colliding with the air molecules and them slowing down
How does the successive IE graph give evidence for shells?
Big jumps on graph = caused by an electron being removed from a different, closer inner shell which requires much more energy
How does the graph of 1st IEs across a period give evidence for subshells?
Drop between Mg and Al = expect Al to have a higher 1st IE than Mg but it doesn’t as it’s outer electron is lost from a higher energy 3p subshell, so requires less energy
How does the graph of 1st IEs across a period give evidence that electrons paired in the same orbital repel more?
Drop between P and S = expect S to have a higher 1st IE but it doesn’t, it has two electrons in the same p orbital that repel so requires less energy
