Chemistry - Mole Concept And Atomic Structures Revision

Mole Concept & Atomic Structures Revision Mole Concept 1.

Definitions:

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Relative Isotopic Mass – The mass of an atom of a specific isotope as compared with 1/12 the mass of a carbon12 atom.

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Relative Atomic Mass – The weighted average of the mass of an atom of an element compared with 1/12 the mass of a carbon-12 atom. And other similar terms, eg. RMM, RFM

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No units as they are ratios

3.

Other terms to remember: molar mass, molar volume, limiting reagent

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Points to note: • A balanced equation or at least the molar ratio of relevant species is needed.

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If the reacting species are gaseous, apply pV=nRT. This means that the amount is proportionate to the volume provided the temperature and pressure remain unchanged or amount is proportionate to the pressure provided temperature and volume remain unchanged.

Atomic Structures 1.

Recall the subatomic particles, their masses, their charges and their behaviour in an electric field. • Atomic number/proton number – Number of protons (also the number of electrons in an atom) • Nucleon number – Number of protons + number of neutrons

2.

Electronic configuration • Higher principle quantum numbers generally have higher energy levels; exception 4s and 3d. • Fill up the lower energy levels first, electrons fill up orbitals of equivalent energy levels before pairing up (minimise repulsion of like charges). An exception occurs in transition metals, chromium and copper.

• • 3.

Ground state – electrons in the atom occupy the lowest energy levels. Excited state – When one or more electrons absorbed enough energy to become promoted to a higher energy level, the atom is unstable and is said to be in an excited state.

Ionisation energies

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The first ionisation energy of an element is defined as the amount of energy (in kJ mol-1) required to remove one electron from each atom in a mole of gaseous atoms, producing one mole of gaseous cations.

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Trends across a period and down a group (1st I.E.)

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Factors affecting 1st I.E. i. Magnitude of the positive nuclear charge ii. Atomic and ionic radii iii.Screening (shielding) effect of inner electrons Uses:

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2 | Page i. Prediction of the group an element belongs to in the Periodic Table and the electronic configuration of the valence shell ii. Prediction of the number of quantum shells