The electron affinity of metals is lower than that of nonmetals. Metals: Metals like to lose valence electrons to form cations to have a fully stable shell.This affinity is known as the second electron affinity, and these energies are positive.Īffinities of Nonmetals vs. However, more energy is required to add an electron to a negative ion which overwhelms any release of energy from the electron attachment process. 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.

Electron affinities are more difficult to measure than ionization energies.Īn atom of Caesium in the gas phase, for example, gives off energy when it gains an electron to form an ion of Caesium.Ĭs + e – → Cs – – ∆H = Affinity = 45.5 kJ/mol 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 CaesiumĮlectron Affinity of Caesium is 45.5 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.

The nuclear binding energy varies between nuclei.

This increases the mass of nuclei with more neutrons than protons relative to the atomic mass unit scale based on 12C with equal numbers of protons and neutrons.

The neutron is slightly heavier than the proton.

There are two reasons for the difference between mass number and isotopic mass, known as the mass defect: For example, 63Cu (29 protons and 34 neutrons) has a mass number of 63, and an isotopic mass in its nuclear ground state is 62.91367 u. The isotopic mass usually differs for other isotopes and is usually within 0.1 u of the mass number.

One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.įor 12C, the atomic mass is exactly 12u since the atomic mass unit is defined from it. One atomic mass unit is equal to 1.66 x 10 -24 grams. The unit of measure for mass is the atomic mass unit (amu). Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance.

See also: Properties of Caesium Atomic Mass of Caesium Caesium has physical and chemical properties similar to those of rubidium and potassium.Ĭaesium – Properties Element Caesium Atomic Number 55 Symbol Cs Element Category Alkali Metal Phase at STP Solid Atomic Mass 132.9055 Density at STP 1.879 Electron Configuration 6s1 Possible Oxidation States +1 Electron Affinity 45.5 Electronegativity 0.79 1st Ionization Energy 3.8939 Year of Discovery 1860 Discoverer Kirchhoff, Gustav & Bunsen, Robert Thermal properties Melting Point 28.4 Boiling Point 669 Thermal Conductivity 36 Specific Heat 0.24 Heat of Fusion 2.092 Heat of Vaporization 67.74 The chemical symbol for Caesium is Cs.Ĭaesium is a soft, silvery-gold alkali metal with a melting point of 28.5 ☌, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium is a chemical element with atomic number 55 which means there are 55 protons and 55 electrons in the atomic structure.

Caesium physical properties