Atoms, ions and compounds Flashcards
What is relative mass and charge of subatomic particles?
Protons: relative charge, +1, relative mass, 1.
Neutrons: relative charge, 0, relative mass, 1.
Electrons: relative charge, -1, relative mass, 1/2000.
What is the mass number?
The total number of protons and neutrons in the nucleus of an atom.
It is the larger, bottom, number.
What is the atomic number?
The number of protons in the nucleus of an atom.
All atoms of the same element have the same number of protons.
It is the smaller, top number.
What are ions?
Ions are atoms with different numbers of protons and electrons.
Negative ions (anions) have more electrons.
Positive ions (cations) have fewer electrons.
What are isotopes?
Isotopes of an element are atoms with the same number of protons and electrons but different numbers of neutrons.
E.g. Cl35 and Cl37.
Isotopes have the same configuration of electrons, so they have the same chemical properties, but different physical properties, e.g. density, melting point, mass.
What is Dalton’s atomic model?
He described atoms as solid spheres, and said that different types of sphere made up different elements.
What is Thomson’s model?
Thomson concluded that atoms weren’t solid and indivisible.
He showed that an atom must contain even smaller, negatively charged particles - corpuscles.
The new model was the plum pudding model, a positively charged sphere with negative electrons embedded in it.
What is Rutherford’s model?
The gold foil experiment. They fired alpha particles (positive charge) at an extremely thin sheet of gold.
Most of the particles passed straight through, and a small number were deflected backwards through more than 90°.
Nuclear model of the atom - tiny, positively charged nucleus surrounded by a cloud of electrons.
Most of the mass is concentrated at the centre.
What are the modifications to Rutherford’s model?
After Moseley discovered that the charge of the nucleus increased from one element to another, Rutherford experimented more.
He discovered it contained protons, and predicted there were other particles in the nucleus with no charge, Chadwick so discovered neutrons.
What is Bohr’s model?
Electrons only exist in fixed orbits and not anywhere inbetween.
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.
When an atom has full shells of electrons, it’s stable and doesn’t react.
What is relative atomic mass?
The weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12.
What is weighted mean mass?
Weighted mean mass takes account of the % abundance of each isotope, and the relative isotopic mass of each.
What is relative isotopic mass?
The mass of an atom of an isotope of an element relative to 1/12th of the mass of an atom of carbon-12.
How does mass spectrometry work?
It finds the % abundance of isotopes by:
A sample is placed in the mass spectrometer.
The sample is vaporised and then ionised to form positive ions.
The ions are accelerated. Heavier ions move slower and are more difficult to deflect, so the ions of each isotope are separated.
The ions are detected on a mass spectrum as a mass to charge ratio, the greater the abundance the larger the signal.
What is mass to charge ratio?
Mass to charge ratio m/z = relative mass of an ion / relative charge of an ion.
