Most of the elements whose chemistry and valence we have discussed so far fall into this category. The representative elements are those in which the distinguishing electron enter an s or p subshell. The type of subshell ( s, p, d, f)into which the distinguishing electron is placed is very closely related to the chemical behavior of an element and gives rise to the classification shown by the color-coding on the periodic table seen here. This last electron is called the distinguishing electron because it distinguishes an atom from the one immediately preceding it in the periodic table. Since it is the outermost (valence) electrons which are primarily involved in chemical interactions between atoms, the last electron added to an atom in the building-up process is of far more interest to a chemist than the first. The commonly used long form of the periodic table is designed to emphasize electron configurations. You should memorize the symbol and atomic number for the elements H through Ne.\): Electron Configuration.For example: H 2O and H 2S, NH 3 and PH 3. Because they have the same valence shell electronic configuration, adjacent elements in any column make similar compounds.The opposite of electronegative is electropositive. It also increases as you go from bottom to top in any column. If you ignore the noble gases (column including He, Ne, Ar.), electronegativity increases as you go from left to right across any row.It is in a row corresponding to n=4 so its electronic configuration as a neutral atom is 4s 24d 2. Titanium is 4 elements from the left and has 4 valence electrons. Counting along a row from the left gives the number of valence electrons.The row beginning with H has n=1 the row beginning with Li has n=2 etc. Each row in the periodic table corresponds to one principle quantum number, n.Many of the properties of elements and their reactivity relate to their position in the periodic table. The periodic table is a device that helps us classify elements according to their electronic configuration. There is a different ordering of orbital energies for neutral atoms and for those same atoms in ions or molecules where there can be a partial charge on the atom.ġs < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 5dġs < 2s < 2p < 3s < 3p < 3d < 4s < 4p < 4d < 5s < 5p < 5d Reduction = gain of one or more electrons Oxidation = loss of one or more electrons Only when there are unpaired electrons in orbitals does the atom or molecule have a net electron spin. When there are 2 electrons in an orbital, their spins (1/2, -1/2) cancel. The 1s orbital has 0 radial nodes, 2p orbitals each have 1 node, 3d orbitals have 2 nodes, etc. This orbital has a nodal plane, a plane where the electron density is zero, at the nucleus. The curve below the baseline encloses the mathematically negative part of the electron density function. The part of the line above the base line encloses the mathematically positive part of the electron density function. Think of this as a 2 dimensional representation of a p orbital. A nodal plane is a plane where electron density is exactly zero. The orbitals differ in the number of nodes. The shapes of the simplest s, p, and d orbitals are shown below. Two electrons at most can occupy each orbital with a spin quantum number of 1/2 or -1/2. For l= 2, there are 5 kinds of d orbitals (m= -2, -2, 0, 1, 2). For l= 1, p, there are 3 kinds of orbitals (m= -1, 0, 1) that we know as the p x, p y, and p z orbitals. s, spin quantum number, value= -1/2 or 1/2įor l= 0, there is only one kind of orbital (m= 0), the s orbital.m, magnetic quantum number, integral values between -l and l.l, orbital quantum number, value= 0, 1, 2.(n-1).n, principle quantum number, value= 1, 2, 3.For hydrogen, the isotope 1H has the highest natural abundance.Įach electron in an atom is described by a unique quantum number. Different isotopes have different natural abundance. These are atoms of the same element that differ in the number of neutrons. The number of electrons in a neutral atom is equal to the number of protons in the nucleus, or the atomic number. atomic number: Count the number of protons in the nucleus for the atomic number.The most common isotope of carbon has a mass of 12, 12C. We write the atomic mass as a superscript in front of the atomic symbol. atomic mass: Count the number of neutrons protons for the atomic mass.Elements and the Periodic Table Elements and the Periodic Table
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