Atomic Structure Flashcards
What is the mass number of an element?
Protons + neutrons
What is the atomic number of an element
Number of protons
What are the relative charges for a proton neutron and electron?
Proton = +1
Neutron =0 neutral
Electron =-1
What is the structure of an atom?
Central nucleus with protons and neutrons surrounded by shells of orbiting electrons
What is an isotope?
An element with the same number of protons and electrons it different mass number as there are a different number of neutrons
What is mass spectrometry? And how does it generally work?
Form of molecular chemical analysis.
- Forms ions
- Ions are separated according to their mass/charge ratio
- Ions are detected
What are the uses of mass spectrometry?
Provide structural information
Identify unknown compounds
To determine the relative abundance of each isotope of an element
How would you do an isotopic mass and abundance calculation for chlorine?
Isotope 35 =75%
Isotope 37= 25%
Therefore
(35 x 75) + (37 x 25) / 100 gives the average mass number
=35.5
Why is a time of flight mass spectrometer in a vacuum?
Prevents ions colliding with air.
What are he steps in a time of flight mass spectrometer?
- Ionisation
- Acceleration
- Ion drift
- Detection
- Data analysis
What happens during ionisation in a ToF?
An electron gun fires high energy electrons at the sample causing an electron to be knocked off forming a positive ion
What happens during the acceleration stage in a ToF
The ions are attracted to a negatively charged plate
This causes the ions to accelerate towards the plate so all ions have the same kinetic energy.
Therefore the larger, heavier particles have a lower velocity.
What happens during the ion drift stage of a ToF?
The ions pass through a hole in the negatively charged plate forming a beam of ions. This then travels along a tube (flight tube).
What happens during he detection stage in a ToF?
When the ions arrive at the detector their flight times are recorded.
Positive ions pick up an electron causing a current to flow.
Since the ions have a different mass some with arrive at a different time and therefore have a different mass spec reading.
What happens during the data analysis stage of a ToF?
The detector passes a signal to a computer once the current is available.
This generates a mass spectrum for that particular ion which then can be collated forming the overall structure of the element/ compound.
What is the S orbital?
The first orbital (closest to the nucleus) in a shell containing a max of two electrons
Spherical shape
What is the p orbital?
Each shell has 3 p orbitals holding a maximum of 6 electrons.
Dumbbell shape
What are the d and f orbitals?
A shell has 5 d orbitals holding upto 10 electrons and there are 7 f orbitals
What is the aufbau principle?
Electrons fill orbitals from the lowest energy levels first.
What is hund’s rule?
Orbitals are filled up singularly in a shell before the electrons pair up each with an opposite spin.
What is the order of orbitals?
1s 2s 2p 3s 3p 4s 3d
The 4s orbital has a lower energy level than the 3d and therefore fills up first. However once electrons are in the 3d orbital, this orbital now has a lower energy level and therefore the 4s orbital will also lose electrons first.
What are the exceptions to the rules when filling up electron orbitals?
Chromium and copper.
Chromium 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Has one electrons promoted to the 3d orbital as this is more electronically stable than having a half filled 3d orbital and fully filled s orbital.
Copper 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Has one electron promoted to the 3 d orbital as it is more electronically stable to have a fully filled d orbital than s orbital.
