Atoms, molecules, quantum theory and electron configuration

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Atoms

Atomic number- Elements differ from each other by the number of protons they contain in the nucleus. The number of protons is the atomic number of an element.

Atomic Mass number- Is the total number of protons and neutrons within an atom and so differs for Isotopes.

Isotope- Atoms of the same element and so a fixed number of protons, with different numbers of neutrons in their nuclei, are known as Isotopes.

Atom composition

Protons- equal to the atomic number

Electrons- In a neutral atom, this is equal to the number of protons. For ions electrons gained or lost result in the atom being negatively or positively charged.

Neutrons- Number can be calculated from the Mass number - the atomic number

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The mole

Mole- SI unit used to describe an amount. By definition is 1 mol of C^12 atoms weigh exactly 12.00g, this contains 6022^23 atoms of carbon. Hence Avogadro's Number=6.022E^23 mol/L.

Relative molar mass- The sum of all the relative molar masses of the atoms in a molecule.

Number of moles = mass / Molar mass

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Quantum numbers

Quantum theory- Electrons in an atom orbital can only exist in certain allowed states. Each state is fully described by a set of four quantum numbers.

The Principal quantum number, n- determines the energy level orbital radius. (n=1,2,...)

The Orbital quantum number, l- determines the name and the shape of the orbital. (l=0,1,...n-1) where the s orbital is described by l=0, the p orbital is described by l=1, the d orbital is described by l=2 and so on.

The Magnetic quantum number, ml- determines the number of each type of orbital. 1 S orbital ( ml= 0), 3 P orbitals (ml=-1,0,1), 5 D orbitals (ml=-2,-1,0,1,2) and so on.

The Spin quantum number, ms- determines the total angular momentum associated with electron spin. (ms=+1/2 or -1/2)

Pauli exclusion principle-no two electrons in an atom n have the same set of four quantum numbers.

Shell- electrons with the same value of n

Subshell- electrons with the same values of n and l

Orbital- electrons with the same values of n, l and ml are in the same orbital. Within each orbital, the two electrons will have opposite ms values.

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Orbital shapes

ns orbital- As n increases, the orbital radius increases.

np orbitals- have a nodal plane where the electrons do not spend time. As n increases, the orbitals become larger.

nd orbitals- have two nodal planes separating the four lobes. As n increases, the orbitals become larger.

orbitals that are degenerate have the same energy.

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Electron configuration

Aufbau's Principle- Electrons occupy the lowest-energy levels first.

Hund's rule- The most stable arrangement of electrons within an orbital level has the greatest number of parallel spins.

Inert gases- are exceptionally stable due to filled orbital levels.

Cations- are positively charged and so have lost electrons, these are firstly removed from the highest number orbital level.

Anions- are negatively charged and so have gained electrons, these are firstly added to the highest number orbital level.

Exceptions

Chromium- 3d and 4s orbitals are half filled in order to gain a more stable configuration.vhk

Copper- 4s orbital is half filled and 3d completely filled in order to gain a more stable configuration.