In the periodic table, the elements are listed in order of increasing atomic number Z. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. The configuration of these electrons follows from the principles of quantum mechanics. The chemical properties of the atom are determined by the number of protons, in fact, by number and arrangement of electrons. See also: Atomic Number – Does it conserve in a nuclear reaction? Atomic Number and Chemical PropertiesĮvery solid, liquid, gas, and plasma is composed of neutral or ionized atoms. It is the electrons that are responsible for the chemical bavavior of atoms, and which identify the various chemical elements. In a neutral atom there are as many electrons as protons moving about nucleus. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10 -19 coulombs. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The nucleus is composed of protons and neutrons. The atom consist of a small but massive nucleus surrounded by a cloud of rapidly moving electrons. K) 0.8 Thermal Conductivity 129 Specific Heat 0.71 Heat of Fusion - Heat of Vaporization 355.8 Atomic Number of CarbonĬarbon is a chemical element with atomic number 6 which means there are 6 protons and 6 electrons in the atomic structure.Carbon – Properties Element Carbon Atomic Number 6 Symbol C Element Category Non Metal Phase at STP Solid Atomic Mass 12.0107 Density at STP 2.26 Electron Configuration 2s2 2p2 Possible Oxidation States -4 -3 … + 4 Electron Affinity 153.9 Electronegativity 2.55 1st Ionization Energy 11.2603 Year of Discovery unknown Discoverer unknown Thermal properties Melting Point 4099 Boiling Point 4527 Thermal Expansion µm/(m In such cases, chemists usually define a standard by arbitrarily assigning a numerical value to one of the quantities, which allows them to calculate numerical values for the rest.įigure 1.6.2 Determining Relative Atomic Masses Using a Mass Spectrometer. We will encounter many other examples later in this text. It is actually rather common in chemistry to encounter a quantity whose magnitude can be measured only relative to some other quantity, rather than absolutely. Thus it is not possible to calculate absolute atomic masses accurately by simply adding together the masses of the electrons, the protons, and the neutrons, and absolute atomic masses cannot be measured, but relative masses can be measured very accurately. By measuring the relative deflection of ions that have the same charge, scientists can determine their relative masses (Figure 1.6.2). The extent of the deflection depends on the mass-to-charge ratio of the ion. When an electric field is applied, the ions are accelerated into a separate chamber where they are deflected from their initial trajectory by a magnetic field, like the electrons in Thomson’s experiment. First, electrons are removed from or added to atoms or molecules, thus producing charged particles called ions. The technique is conceptually similar to the one Thomson used to determine the mass-to-charge ratio of the electron. Scientists can measure relative atomic masses very accurately, however, using an instrument called a mass spectrometer. We can easily calculate the binding energy from the mass difference using Einstein's formula E=mc 2.īecause atoms are much too small to measure individually and do not have a charge, there is no convenient way to accurately measure absolute atomic masses. Although the difference in mass is small, it is extremely important because it is the binding energy of the nucleus. For example, the ratio of the masses of 1H (hydrogen) and 2H (deuterium) is actually 0.500384, rather than 0.49979 as predicted from the numbers of neutrons and protons present. Br\) or, more commonly, 79Br and 81Br.Īlthough the masses of the electron, the proton, and the neutron are known to a high degree of precision (Table 1.5.1), the mass of any given atom is not simply the sum of the masses of its electrons, protons, and neutrons.
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