A chemical element, often simply called an element, is a type of atom which has the same number of protons in its atomic nucleus (i.e., the same atomic number, or Z). This is a list of the 118 chemical elements that have been identified as of 2023. The Standard English unit is pounds mass per cubic foot ( lbm/ft 3).Ĭhromium – Properties Summary Element Chromium Atomic Number 24 Symbol Cr Element Category Transition Metal Phase at STP Solid Atomic Mass 51.9961 Density at STP 7.14 Electron Configuration 3d5 4s1 Possible Oxidation States +2,3,6 Electron Affinity 64.3 Electronegativity 1.66 1st Ionization Energy 6.7666 Year of Discovery 1797 Discoverer Vauquelin Thermal properties Melting Point 1907 Boiling Point 2671 Thermal Conductivity 93.7 Specific Heat 0.45 Heat of Fusion 16.9 Heat of Vaporization 344.List of the 118 identified chemical elements 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. How does the atomic mass determine the density of materials? Density of Chromium

The atomic mass number determines especially the atomic mass of atoms. The mass number is different for each different isotope of a chemical element. 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. For other isotopes, the isotopic mass usually differs 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).

Therefore this resulting atomic mass is calculated from naturally-occurring isotopes and their abundance. Note that each element may contain more isotopes. How does the atomic number determine the chemical behavior of atoms? Atomic Mass of Chromium Since the number of electrons is responsible for the chemical behavior of atoms, the atomic number identifies the various chemical elements. Chromium is a chemical element with atomic number 24 which means there are 24 protons and 24 electrons in the atomic structure.

Periodic table atomic number cr