Atomic Structure Flashcards
What is an element’s mass number?
The total number of protons and neutrons in its nucleus
What is an element’s atomic number?
Number of protons it has in its nucleus
What are isotopes?
Atoms of the same element with different numbers of neutrons
What are electrons arranged into?
Electron shells/ energy levels
What are electrons divided up into?
Sub-shells/ sub-levels
What are sub-shells divided up into?
Orbitals
What are orbitals?
The area of space that electrons occupy - area which we are most likely to find electron in.
How many electrons can an orbital hold up to?
2
What is on an atom’s 1st energy level?
1 sub-shell
s sub-shell: 1 orbital
total electrons: 2
What is on an atom’s 2nd energy level?
2 sub-shells
s sub-shell: 1 orbital
p sub-shell: 3 orbitals
total electrons: 8
What is on an atom’s 3rd energy level?
3 sub-shells
s sub-shell: 1 orbital
p sub-shell: 3 orbitals
d sub-shell: 5 orbitals
total electrons: 18
What are the rules for determining the electron configuration?
Lowest energy is filled first (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p)
Electrons should occupy orbitals on their own, only sharing an orbital if there are no empty orbitals of the same energy level
Why is hydrogen difficult to place on the periodic table?
It is an s-block element with 1 electron in the s sub-level but has different properties to Group 1 elements
Why is helium difficult to place on the periodic table?
It is NOT a p-block element but is placed with other noble gases because they share properties.
When an ion forms,are the 3d or 4s electrons lost first?
4s
Why would the electrons in the last orbital in an atom be the easiest to lose?
Has the weakest attraction to nucleus:
Has the furthest distance from nucleus
Positive charge of nucleus shielded by inner electrons
What is the definition of ionisation energy?
Ionisation energy (IE) is the energy required to remove one mole of electrons from one mole of atoms in the gaseous state.
What is ionisation energy measured in?
kJ mol−1
What is magnesium’s first ionisation energy equation?
Mg (g) –> Mg+ (g) + e-
Are ionisation energies always increasing?
Yes.
What factors affect ionisation energies?
Distance from nucleus
Nuclear charge
Shielding (repulsion) by electrons in inner shells between nucleus and outer electron
What is the trend in 1st ionisations as we go down group 2?
Ionisation energies decrease
Why do 1st ionisation energies generally decrease down groups?
-Increase in size of atom (more energy levels occupied by electrons)
-‘Outer electrons further away from nucleus’
-‘Additional inner electrons shield the positive charge of nucleus’
‘ ‘ = Reduced attraction between electron + nucleus - less energy required to remove
What trend would you expect to see in 1st IE’s across period 3?
General increase in IE
Why do 1st IEs generally increase across periods?
An increased nuclear charge but no/little difference in shielding so there is a stronger attraction between the electron being removed and the nucleus
Describe the Aluminium anomaly.
Aluminium has a lower 1st IE than Magnesium.
The electron being removed from Al is in a 3p orbital whereas for Mg the electron is in a 3s orbital.
The 3p orbital is higher in energy than 3s, so requires less energy to remove an electron from 3p
Describe the Sulfur anomaly.
Sulfur has a lower 1st IE than Phosphorus.
In S, there are a pair of electrons in a 3p orbital. These electrons repel each other, which makes it easier to remove one of them than P.
What is Mass Spectrometry?
An analytical technique which allows us to determine the mass of molecules and elements.
What are the four stages of Time of Flight mass spectrometry?
Ionisation
Acceleration
Drift region
Detection
What are the two types of ionisation in ToF?
Electron impact method
Electrospray method
What is the electron impact method used for?
Elements and low Mr compounds
What is the electrospray method used for?
Used for elements and high Mr compounds (e.g. proteins)
What is the equation for electron impact method?
X (g) –> X+ (g) + e-
X (g) +e- –> X+ (g) + 2e-
What is the equation for electrospray method?
X (g) + H+ –> XH+ (g)
What happens in electron impact?
Substances lose an e-
Mass remains the same
What happens in electrospray?
Substances gain a H+
Mass increases by 1
How do atoms form ions?
By gaining or losing electrons
Why do isotopes have the same chemical properties?
They have the same electron configuration
Why do isotopes have different physical properties?
Physical properties tend to depend more on the mass of the atom.
Describe Dalton’s model of the atom.
At the start of the 19th century, he described atoms as solid spheres and said that different spheres made up the different elements
Describe Thomson’s model of the atom.
In 1897, he discovered that an atom must have even smaller, negatively charged particles - electrons.
Plum pudding model.
Describe Rutherford’s model of the atom.
Discovered that there was a tiny, positively charged nucleus at the centre, surrounded by a ‘cloud’ of negative electrons. Most of the atom is empty space.
What are the factors affecting ionisation energy?
- Nuclear charge
- Distance from nucleus
- Shielding
Define the relative atomic mass.
The relative atomic mass is the average mass of an atom of an element compared to 1/12th of an atom of Carbon-12
