Atomic structure and bonding Flashcards
(44 cards)
What is an atom?
The smallest particle of a chemical element
Ionisation Energy
The amount of energy needed to remove 1 mole of electrons from a mole of atoms, in the gaseous state
Factors that affect ionisation energy
Nuclear charge, shielding and distance from nucleus
Successive ionisation energies
The energy required to remove each electron in turn
What can a mass spectrometer be used for?
To find the relative abundance and mass/charge ratio of an element or compound
Why is the mass spectrometer a vacuum?
Prevent any particles being tested from colliding with molecules in the air
What is electrospray ionisation?
Sample dissolved in a volatile substance
Injected through a fine hypodermic needle
The tip of the needle is connected to the positive terminal of a high voltage power supply
The particles gain a proton and are ionised
What is electron impact ionisation?
The sample is vaporised
High energy electrons are fired at it from an electron gun
This will knock off an electron from each particle to form a positive ion
What is acceleration in a mass spectrometer?
Positive ions are attracted towards a negatively charged plate and accelerate towards it
Once accelerated, all ions have the same kinetic energy
The amount they accelerate depends on the mass to charge ratio of an ion
What is ion drift in a mass spectrometer?
Particles travel at different speeds due to their mass and start to drift apart
How are ions detected in a mass spectrometer?
Ions hit the detector and gain electrons which generates a current
The size of the current is proportional to the abundance of the ion
Why are sample particles ionised?
So they can be accelerated towards a negatively charged plate and gain electrons to generate a current when they hit the detector
How are ions accelerated in a mass spectrometer?
Positive ions attracted to negatively charged plate
All ions have the same kinetic energy
How are ions separated in a mass spectrometer?
Ions travelling at higher speeds (slower m/z ratio) move ahead of those travelling more slowly (large m/z ratio)
What is the relative atomic mass?
Average weighted mass of an atom relative to carbon 12
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond
How to work out if a molecule is polar?
Partial charges around the molecule change
So, asymmetrical
Dipoles do not cancel out
Permanent dipole
Polar
How to work out if a molecule is non-polar?
Partial charges around the molecule remain the same
So, symmetrical
Dipoles cancel out
No permanent dipole
Non-polar
How does hydrogen bonding arise?
Large difference in electronegativity between the oxygen atom and the hydrogen atom of the OH bond
This polarises the OH bond
There is a strong attraction between the lone pair of Oxygen atom and partially positive hydrogen atom on another molecule
How do permanent dipole-dipole forces arise?
There is a difference in electronegativity between the chlorine atom and hydrogen atom
This polarises the HCL bond forming a dipole
The dipoles do not cancel out as the molecule is asymmetrical
There is an attraction between the partial positive hydrogen atom and partial negative chlorine on another molecule
How do induced dipole-dipole forces arise?
Random movement of electrons in a molecule causes an uneven distribution of electrons
This forms a temporary dipole
This induces a dipole in another molecule
There is an attraction between dipoles on neighbouring molecules
What are the 4 properties of metals and why?
Good conductors of heat because delocalised electrons help transfer energy through the metal efficiently
Good conductors of electricity because delocalised electron can flow easily
Strong - strong electrostatic attraction between positive metal ions and delocalised electron
Malleable and ductile - rows of metal ions can slide past one another
High melting and point
What is ionic bonding?
Strong electrostatic attraction between oppositely charged ions
What is a covalent bond?
Shared pair of electrons between 2 atoms
