1.1 - Atomic Structure Flashcards
What is the mass number (A)?
The total number of protons and neutrons in the nucleus of an atom
What is the atomic (proton) number (Z)?
The total number of protons in the nucleus of an atom and identifies the element
What is an isotope?
An isotope of an element are atoms with the same number of protons but a different number of neutrons
Do isotopes have different chemical properties?
No, they have the same chemical properties as they have the same configuration of electrons
Do isotopes have different physical properties?
Isotopes have slightly different physical properties e.g. densities and rates of diffusion. This is because these properties tend to depend more on the mass of the atom
How did John Dalton describe atoms as?
He described atoms as solid spheres and that different spheres made up different elements
What is the plum pudding model and who hypothesised it?
Once electrons were discovered, scientists believed that electrons surrounded a positively charged ‘pudding’.
What is Rutherford’s model?
Rutherford’s model contained lots of empty space (as shown by the gold foil experiment), with a tiny positively charged nucleus surrounded by a ‘cloud’ of negative electrons
What is Bohr’s model?
Bohr’s model has a small, positively charged nucleus with electrons in fixed shells orbiting the nucleus
What is the definition of relative atomic mass?
The relative atomic mass, Ar, is the average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12
What is the definition of relative isotopic mass?
Relative isotopic mass is the mass of an isotope of an element on a scale where an atom of carbon-12 is exactly 12
How is the relative atomic mass calculated?
Multiply the atomic mass of each isotope by its relative percentage abundance and then divide by 100
What is the definition of relative molecular mass?
The relative molecular mass, Mr, is the average mass of a molecule on a scale where an atom of carbon-12 is exactly 12
How is the relative molecular mass calculated?
Relative molecular mass is calculated by adding up all the relative atomic masses of all the atoms in the molecule
What is the definition for relative formula mass?
Relative formula mass is the average mass of a formula unit on a scale where an atom of carbon-12 is exactly 12. It is used for compounds that are ionic or giant covalent.
What are the four steps for Time of Flight Mass Spectroscopy?
Ionisation, acceleration, ion drift and detection
What happens in electrospray ionisation?
The sample is dissolved in a solvent and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing each particle to gain an H+ ion. The solvent is then removed, leaving a gas made up of positively charged ions
What happens in electron impact ionisation?
The sample is vaporised and an ‘electron gun’ is used to fire high energy electrons at it. This knocks one electron off each particle so that they become +1 ions
Describe the ‘acceleration’ stage in ToF MS
The positive ions are accelerated by an electric field that gives the same kinetic energy to all of the ions
At what speed does lighter ion travel compared to a heavier ion?
A lighter ion travels faster as they have less mass
Describe the ‘Ion Drift’ stage in ToF MS
The ions enter a region with no electric field and they drift through at a constant speed
Describe the ‘Detection’ stage in ToF MS
The detector detects the current created when the ions hit it and records how long they took to pass through the mass spectrometer. The data is then used to calculate mass/charge values
What is a mass spectrum?
A chart that is produced by a mass spectrometer shows information about the sample. It has the relative isotopic abundance on the y-axis and mass/charge ratio on the x-axis.
What is different about mass spectra produced by ‘electron impact ionisation’ compared to ‘electrospray ionisation’?
In ‘electron impact ionisation’, an electron is lost and therefore no significant mass is lost. However, in ‘electrospray ionisation’, an H+ ion is added and so the mass/charge values are one less than the mass spectra shows
What does the number of lines show on mass spectra?
The different number of isotopes
How is relative atomic mass calculated from mass spectra?
Multiply the mass/charge value by the percentage abundance for each isotope. Add these totals up and divide by 100 (or the total abundance depending on whether percentages were used or not)
What is the principal quantum number?
The number of which electron shell it is in
What are different shells divided into?
Shells are divided into sub-shells
How many electrons does an orbital hold?
Orbitals hold a maximum of 2 electrons
How many orbitals are in an ‘s’ sub-shell?
One
How many orbitals are in a ‘p’ sub-shell?
Three
How many orbitals are in a ‘d’ sub-shell?
Five
How many orbitals are in an ‘f’ sub-shell?
Seven
What is electron configuration?
Electron configuration is the number of electrons that an atom or an ion has and how they are arranged
How does the ‘arrow in boxes’ work for showing sub-shells?
Each box represents one orbital. Each arrow represents one electron. The arrows are drawn in opposite directions if there are two electrons in one box to show the electrons spinning in opposite directions
How are electron configurations worked out?
Electrons fill up the lowest energy sub-shell first, and electrons fill up orbitals singly before they start sharing. Finally, for the configuration of ions from the s and p blocks of the periodic table, just add or remove electrons to or from the highest energy occupied shell
What are shortened electron configurations?
Noble gas symbols in square brackets e.g. [Ar] are shortened versions of electron configurations. Only the electrons after the noble gas are needed
How many electrons are in the 4s and 3d sub-shells in Chromium?
There is one electron in the 4s sub-shell and 5 in the 3d sub-shell
Hom many electrons are in the 4s and 3d sub-shells in Copper?
There is one electron in the 4s sub-shell and 10 in the 3d subshell
Why do Copper and Chromium have anomalous electron configurations?
They are more stable with half-filled or fully-filled sub-shells
Which electrons are lost first in transition metals?
Transition metals lose their 4s electrons before their 3d electrons
What is the definition for ‘first ionisation energy’?
The energy needed to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
How does the value of the ionisation energy compare to the formation of a positive ion?
The lower the ionisation energy, the easier it is to form a positive ion
What three factors affect ionisation energy?
Nuclear charge, distance from the nucleus and the amount of shielding
How does nuclear charge affect ionisation energy?
The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction to the electrons
How does the distance from the nucleus affect the ionisation energy?
Attraction falls off very rapidly with distance; an electron closer to the nucleus will be much more strongly attracted than one further away
How does the amount of shielding affect ionisation energy?
As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction to the nucleus
What is the definition for ‘second ionisation energy’?
The energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
Why are second ionisation energies always greater than first ionisation energies?
The electron is being removed from a 1+ ion instead of an atom, meaning that more energy is needed to remove the electron
What is the general equation for ionisation energies?
X^(n-1)+ (g) → X^n+ (g) + e-
What is the trend in ionisation energies down a group?
There is a decrease as the atomic radius and shielding is much larger
What is the general trend in ionisation energies across a period?
Generally, the ionisation energy increases across a period. This is due to the nuclear charge increasing
Why does Aluminium have a lower ionisation than Magnesium?
Aluminium’s outer electron is in a 3p orbital rather than a 3s orbital. The 3p orbital has slightly higher energy and is further from the nucleus. Also, the 3p electron is being shielded by the 3s electrons
Why does Sulphur have a lower ionisation than Phosphorous?
Both are taken from the 3p orbital, but with sulphur, it is taken from a fully-filled p orbital instead of a half-filled p orbital. The repulsion between these electrons means that the electron is easier to be removed
With a graph of successive ionisation energies, how is it possible to tell which group it is in?
The big jump is when an electron is being taken from a shell closer to the nucleus. The group number is how many electrons were removed before the first big jump
