![]() By convention, the negative sign shows a release of energy. This affinity is known as the first electron affinity, and these energies are negative. When an electron is added to a neutral atom, energy is released. To use electron affinities properly, it is essential to keep track of signs. Sn + e – → Sn – – ∆H = Affinity = 107.3 kJ/mol Electron affinities are more difficult to measure than ionization energies.Īn atom of Tin in the gas phase, for example, gives off energy when it gains an electron to form an ion of Tin. Note that ionization energies measure the tendency of a neutral atom to resist the loss of electrons. In other words, it can be expressed as the neutral atom’s likelihood of gaining an electron. The change in energy (in kJ/mole) of a neutral atom or molecule (in the gaseous phase) when an electron is added to the atom to form a negative ion. In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as: The Standard English unit is pounds mass per cubic foot ( lbm/ft 3).Įlectron Affinity and Electronegativity of TinĮlectron Affinity of Tin is 107.3 kJ/mol. The standard SI unit is kilograms per cubic meter ( kg/m 3). ![]() In other words, the density (ρ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance. It is an intensive property, which is mathematically defined as mass divided by volume: Typical densities of various substances at atmospheric pressure.ĭensity is defined as the mass per unit volume. For 63Cu, the atomic mass is less than 63, so this must be the dominant factor. A nucleus with greater binding energy has lower total energy, and therefore a lower mass according to Einstein’s mass-energy equivalence relation E = mc 2.
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