Carbon and hydrogen are the only two elements in a hydrocarbon. When a hydrocarbon combusts completely in excess oxygen, the products would be and . The and would come from the hydrocarbon, while the atoms would come from oxygen.
Look up the relative atomic mass of these three elements on a modern periodic table:
: .
: .
: .
Calculate the molar mass of and :
.
Calculate the number of moles of molecules in of :
.
Similarly, calculate the number of moles of molecules in of :
.
Note that there is one carbon atom in every molecule. Approximately of molecules would correspond to the same number of atoms. That is: .
On the other hand, there are two hydrogen atoms in every molecule. approximately of molecules would correspond to twice as many atoms. That is: .
The ratio between the two is: .
The empirical formula of a compound gives the smallest whole-number ratio between the elements. For this hydrocarbon, the empirical formula would be .
Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron.
Electron Affinity of Lithium is 59.6 kJ/mol.
Electron Affinity of Caesium is 45.5 kJ/mol.
Electron Affinity of Lithium is 59.6 kJ/mol. Electronegativity of Lithium is 0.98. ... Electron affinities are more difficult to measure than ionization energies. An atom of Lithium in the gas phase, for example, gives off energy when it gains an electron to form an ion of Lithium.
Trends
The ionization energy of the elements within a period generally increases from left to right. This is due to valence shell stability.
The ionization energy of the elements within a group generally decreases from top to bottom. This is due to electron shielding.
The noble gases possess very high ionisation energies because of their full valence shells as indicated in the graph. Note that helium has the highest ionization energy of all the elements.