The atomic structure Flashcards
What are proton and neutrons also called and why?
Nucleons because they are found in the nucleus
What forces are protons and neutrons held together by?
strong nuclear force
Compare nuclear forces and electrostatic forces
- Nuclear forces are stronger = Because it’s stronger than electrostatic forces, nuclear forces can overcome the repulsion between protons in the nucleus.
- Nuclear forces act between protons and neutrons instead of electrons and protons. Nuclear forces act only over very short distances, that is, within the nucleus.
Instead of particles, what are electrons considered to be?
A cloud of negative charge
What volume of space does an electron fill?
atomic orbital
What is the importance of an atomic orbital?
it influences the shape of molecules
What determines the chemical properties (how it reacts) of an element?
The number of electrons in the outer shell of an atom
What do all atoms of the same element have?
The same atomic number
Why do different isotopes of the same element react chemically in the exact same way?
Because they have the same electron configuration
What happens when isotopes are unstable?
The nucleus of the atom breaks down giving off bits of the nucleus or energetic rays. This causes radioactivity.
The rate of radioactive isotope decaying is measured by what?
half life
What is the half-life?
the time taken for half of its radioactivity to decay
What idea did Niels Bohr put forward about the atom?
- That the atom consisted of a tiny positive nucleus orbited by electrons to form an atom like a tiny solar system.
- Electrons orbited in shells of fixed size
- The movement of electrons from one shell to the next explained how atoms absorbed and gave out light
- This was the beginning of quantum theory.
What did Erwin Schrodinger discover about the atom?
He worked out an equation that used the idea that electrons had some of the properties of waves as well as particles = quantum mechanics, which predicts the behaviour of sub atomic particles
What did James Chadwick discover about the atom?
Neutron
What did Gilbert Lewis discover about bonding?
- The inertness of the noble gases was related to their having full out shells of electrons
- Ions were formed by atoms losing or gaining electrons to attain full out shells
- Atoms could also bond by sharing electrons to form full out shells
What is the formula for the number of electrons in each shell?
2n^2
What does a mass spectrometer do?
gives accurate information about the relative isotopic mass and also about the relative abundance of isotopes. It determines the mass of separate atoms
How are relative atomic masses measured and why is it measured this way?
They are measured on a scale on which the mass of an atom of C(12) is defined as exactly 12. This is because no other isotope has a relative atomic mass that is exactly a whole number due to the proton and the neutron both not having an exact mass of 1
What is a mass spectrometer used for?
Mass spectrometry can be used :
- to identify elements.
- to determine relative molecular mass.
Give an outline of what happens in a time of flight mass spectrometer
the substances in the sample are converted to positive ions, accelerated to high speed (which depend on their mass to charge ratio), and arrive at a detector
What are the 5 steps in TOF mass spectrometer?
1) ionisation
2) acceleration
3) ion drift
4) Detection
5) data analysis
Why are mass spectrometers kept in a Vacuum?
the whole apparatus is kept under a high vacuum to prevent the ions that are reduced colliding with molecules from the air