Flashcards in A level Chemistry OCR A- Module 2 Deck (22)
Atoms of the same element with different number of neutrons and the same number of protons.
Why do isotopes have the same chemical properties?
They have the same configuration of electrons.
Why do isotopes have different physical properties?
Physical properties depend on the mass of the atom. They have the different masses.
What is the relative mass of an electron?
What is the relative mass of a neutron?
What is the relative mass of a proton?
What is the mass number?
The total number of protons and neutrons in the nucleus of an atom.
What is the atomic number?
The number of protons in the nucleus of an atom.
What does Thomson's model explain.
Atoms are not solid and indivisible, an atom contains even smaller, negatively charged particles- electrons
What was JJ Thomson's model called?
The plum pudding model- a positively charged sphere with negative electrons embedded in it.
What does Rutherford's model explain?
That the plum pudding model isn't right; there's a tiny positively charged nucleus at the centre of the atom surrounded by a 'cloud' of negative electrons.
How did Ernest Rutherford prove his theory?
He conducted the famous gold foil experiment; they fired alpha particles (positively charged) at an extremely thin sheet of gold. Most of the alpha particles passed straight through the gold atoms and a small number were deflected backwards through more than 90*.
Name the scientists who conducted the gold foil experiment?
Ernest Rutherford, Hans Geiger and Ernest Marsden.
What modifications were made to Rutherford's model?
Describe the main features of Bohr's model?
*Electrons only exist in fixed shells, nowhere in between
*Each shell has a fixed energy
*When an electron moves between shells electromagnetic radiation is emitted or absorbed
*Because the energy of shells is fixed, the radiation will have a fixed frequency
What does Bohr's model explain?
Some elements are inert- noble gases.
Shells of an atom can only hold fixed numbers of electrons, and that an element's reactivity is due to its electrons.
How is evidence used to accept or reject particular models?
Define the relative atomic mass
The weighted mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom
Define the relative isotopic mass
The weighted mean mass of an isotope compared to 1/12 the mass of an atom of carbon-12
How do you calculate the relative isotopic mass of an element?
1. Multiply each relative isotopic mass by its % relative isotopic abundance and add up the results
2. Divide by 100
How do you calculate the relative atomic mass from mass spectra?
1. Multiply each relative isotopic mass by its relative abundance and add up the results
2. Divide by the sum of the relative abundances