Atomic Structure Flashcards
(29 cards)
What are protons and neutrons held together by
Strong nuclear forces,
They are much stronger than electrostatic forces but only act over a very short distance
What are electrons and protons held together by
Electrostatic forces
Why are atoms neutral
Because the number of protons and electrons are the same so their charges cancel out
What is the atomic number
The number of protons, atoms of the same element have the same atomic number
What is the mass number
The total number of protons plus neutrons in the nucleus, electrons weight virtually nothing
What is an isotope
Atoms with the same number of protons but different number of neutrons, different isotopes of the same element react chemically in the same way as they have the same electrons configuration
What does a mass spectrometer do
It accurately determines relative atomic masses
What is the vacuum stage of a tof mass spectrometer
The whole apparatus is kept under a high vacuum to prevent the ions that are produced colliding with molecules from the air
What is electrospray ionisation
The sample is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply,
This produces tiny positively charged droplets into the vacuum and the droplets get smaller and smaller until they may contain no more than a single positively charged ion
What is electron impact ionisation
The sample is vaporised and high energy electrons are fired at it from an electron gun, which is a hot wire filament with a current running through it that emits a beam of high energy electrons,
This usually knocks off one electron from each particle forming a 1+ ion
What happens during the acceleration stage of tof
The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed
What happens during the ion drift stage of tof
The ions pass through a hole in the negatively charged plate, forming a beam and travel along a tube, called a flight tube, to a detector,
What happens during the detection stage of tof
When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities, the flight times are recorded, the positive ions pick up an electron from the detector, which causes a current to flow
What happens during the data analysis stage of tof
The signal from the detector is passed to a computer which generates a mass spectrum
How many electrons can be held in each shell
Use the formula 2n^2 where n is the number of the main level. so 2, 8, 18 etc
What is an atomic orbital
The volume of space an electron fills
What does the orbital shape represent
The volume of space in which there is a 95% probability of finding an electron, they influence the shapes of molecules
How many electrons
can a s-orbital hold
2
How many electrons can a p-orbital hold
6, as they always come in groups of three
How many electrons can a d-orbital hold
10, they come in groups of five
What is ionisation energy
They energy it takes to remove electrons from atoms
What is the ionisation energy trend
The first electron needs the least energy to remove it, the second needs more, the third needs even more etc..
Why do the ionisation energy’s change
As you remove more electrons the ion becomes more and more charged to it is harder each time
Why does ionisation energy increase across a period
Because there are more protons in the nucleus but the shielding stays the same so the attraction of the outer electrons to the nucleus increases
