Ar, Atomic Strcuture, Nuclear Fusion Flashcards
Where is most of the mass of an atom concentrated?
The nucleus
What are the relative charges and masses of protons, neutrons and electrons?
P - 1, +1
N - 1, 0
E - 1/2000, -1
What does the mass number of an element tell you?
The total number of protons and neutrons in the nucleus
What does the atomic (proton) number tell you?
The number of protons in the nucleus - this is the same for all atoms of the same element
What are isotopes?
Isotopes are atoms of the same element with different numbers of neutrons
What dictates the chemical properties of an element?
The number and arrangement of electrons
Do isotopes have different chemical or physical properties and why?
Isotopes of the same element have the same chemical properties because they have the same configuration of electrons, but different physical properties (such as densities and rate of diffusion) because they often depend more on the mass of the atom
What makes up most of the volume in an atom?
The electron shells
How did John Dalton describe atoms?
Solid spheres
How did John Dalton describe atoms?
Solid spheres
What did JJ Thompson suggest?
The plum pudding model
Describe the plum pudding model
A positively charged sphere with negative electrons embedded into it
What is the Geiger-Marsden experiment?
Rutherford, Geiger and Marsden fired alpha particles at a thin sheet of gold
What happened during the Geiger-Marsden experiment and what did this mean?
They expected most of the alpha particles to be deflected very slightly by the positive ‘pudding’ of the atom, but most particles travelled straight through the gold and a very small number were deflected backwards (more than 90 degrees) - this showed the plum pudding model was incorrect, and so Rutherford created the nuclear model of the atom
What is the nuclear model?
- Tiny, positively charged nucleus at the centre of the atom where most of the mass is concentrated
- the nucleus is surrounded by a ‘cloud’ of freely orbiting negative electrons
- most of the atom is empty space
How was Rutherford’s nuclear model modified?
- Mosley discovered that the charge of the nucleus increased from one element to another in units of one
- Rutherford then investigated further and discovered protons
- Chadwick discovered the neutron
What 4 principles did Bohr propose in his model of the atom?
- electrons can only exist in fixed orbits, or shells, and not anywhere in between
- each shell has a fixed energy
- when an electron moves between shells, electromagnetic radiation is emitted or absorbed
- because the energy of the shells is fixed, the radiation will always have a fixed frequency
What else did the Bohr model explain?
Why some elements (the noble gases) are inert - shells of an atom can only hold a fixed number of electrons, and an elements reactivity is due to its electrons. So when it has a full shell, it is stable and does not react
Is only one atomic model in use?
No, scientists use whichever model is relevant to what they’re investigating
What is the relative atomic mass (Ar)?
The average mass of an atom of an element on a scale where an atom on carbon-12 is 12
What is the relative isotopic mass?
The mass of an atom of an isotope of an element on a scale where carbon-12 is 12
What is the relative molecular/formula mass (Mr)?
The average mass of a molecule or formula unit on a scale where an atom of carbon-12 is 12
What types of compounds are Mr used for?
Ionic or giant covalent
Are Ar and relative isotopic masses usually whole numbers?
Ar is an average, so is not usually a whole number
Relative isotopic mass will always be a whole number
What information can you get from a mass spectrometer?
Relative atomic mass, relative molecular mass, relative isotopic abundance and molecular structure
Explain the 4 steps when a sample is squirted into a mass spectrometer
- Vaporisation - the sample is turned into gas (vaporised) using an electric heater
- Ionisation - the gas particles are bombarded with high energy electrons to ionise them. Electrons are knocked off of particles, leaving positive ions
- Acceleration - the positive ions are accelerated by an electric field
- Detection - the time taken for the positive ions to reach the detector is measured. This depends on an ion’s mass and charge - light, highly charged ions will reach the detector first, while heavier ions with a smaller charge will take longer. For each sample analysed a mass spectrum is produced
What goes on the x and y axes of a mass spectrum?
The y axis gives the abundance of ions (often as a percentage). For an element, the height of each peak gives the relative isotopic abundance
The x axis units are given to a mass/charge ratio. Since the charge on ions is mostly 1+ you can often assume the x axis is simply the relative mass
What are the 3 steps for calculating the Ar of an element from the mass spectrum?
- For each peak, read the % relative isotopic abundance from the y axis and multiply it with the relative isotopic mass from the x axis to get the total mass for each isotope
- Add up these totals
- Divide by 100 (because percentages were used)
What do you need to change about mass spectrum calculations if the relative abundance is not given as a percentage?
Divide by the total relative abundance instead of 100
What is the formula for % relative isotopic abundance?
% relative isotopic abundance = (relative abundance/total relative abundance) x 100
