Atomic structure Flashcards
What is the relative mass and charge of a proton?
Relative mass=1
Relative charge=+1
What is the relative charge and mass of a neutron ?
Relative charge=0
Relative mass=1
What is the relative mass and charge of an electron?
Relative charge=-1
Relative mass=1/1840
What are isotopes?
Isotopes are atoms with the same number of protons, but different number of neutrons
Why do isotopes have similar chemical properties ?
Because they have the same electronic structure.
What can a mad spectrometer be used for?
It can be used to determine all the isotopes present in a sample of an element and to therefore identify elements
What are the two techniques in which a sample can be ionised?
- electron spray
- electron impact
What is electron impact used for?
It is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment
What is electron spray used for?
It used preferably for larger organic molecules . The ‘softer’ conditions of this technique mean fragmentation does not occur
Electron impact:
- a vaporised sample is injected at low pressure
- an electron gun fires high energy electrons at the sample
- this knocks out an outer electron
- forming positive ions with different charges
Electro spray ionisation:
- the sample is dissolved in a volatile, polar solvent
- injected through a fine needle giving aerosol
- the tip of the needle has a high voltage
- at the tip of the needle the sample molecule, M, gains a proton from the solvent forming MH+
- the solvent evaporated away while the MH+ ions move towards a negative plate
Definition of 1at ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form a positive ion
Factors that affect ionisation energy:
- the attraction of the nucleus
- atomic radii
- shielding
