![]() 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 Neon ![]() Since the number of electrons is responsible for the chemical behavior of atoms, the atomic number identifies the various chemical elements. Which would mean that, of the three p orbitals, one is filled, one is half-filled, and one is empty.Neon is a chemical element with atomic number 10 which means there are 10 protons and 10 electrons in the atomic structure. Notice that the 2p electrons are shown as Using a box diagram, we show the electron configuration of nitrogen as: Two arrows, one pointing up and the other down. Their axes.) Therefore, if an orbital contains two electrons, its box will contain Section 5.3B that two electrons in an orbital spin in opposite directions on The direction of the arrow represents the spin of the electron. Of electrons by using box diagrams, where each box representsĪn orbital and the arrows within the boxes represent the electrons in that orbital. Orbitals than with some filled and some empty. The energy of the electrons in a sublevel would then be lower with half-filled Lower energy configuration than are paired electrons (two electrons in an orbital). Has shown that unpaired electrons (a single electron in an orbital) are in a The electrons of that sublevel are distributed among the orbitals. If an atom has a partially filled sublevel, it may be important to know how TABLE 5.2 Electron configurations of the first 18 elementsĪ. The electron configurations of elements with higher atomic number can be written by following the orbital-filling chart in Figure 5.9. Table 5.2 shows the electron configurations of the elements with atomic numbers 1 through 18. The fifth electron is added to a 2p orbital, the sublevel next higher in energy (Figure 5.9). Four electrons fill both the 1s and 2s orbitals. Therefore, the electron configuration of lithium is:īoron (atomic number 5) has five electrons. In order to write its electron configuration, we must first determine (from Figure 5.9) that the 2s sublevel is next higher in energy after the 1s sublevel. The element lithium (atomic number 3) has three electrons. Because the helium nucleus is different from the hydrogen nucleus, neither of the helium electrons will have exactly the same energy as the single hydrogen electron, even though all are in the 1s sublevel. Two electrons completely fill the first energy level. Therefore, the electron configuration of hydrogen is written:įor helium (atomic number 2), which has two electrons, the electron configuration is: The single electron is assigned to the 1s sublevel, the lowest-energy sublevel in the lowest-energy level. The order is summarized under the diagram.įIGURE 5.9 The arrow shows a second way of remembering the order in which sublevels fill.Īn atom of hydrogen (atomic number 1) has one proton and one electron. To use this figure, read along the diagonal lines in the direction of the arrow. The principal energy levels are listed in columns, starting at the left with the 1s level. This order is difficult to remember and often hard to determine from energy-level diagrams such as Figure 5.8Ī more convenient way to remember the order is to use Figure 5.9. The first sublevel filled will be the 1s sublevel, then the 2s sublevel, the 2p sublevel, the 3s, 3p, 4s, 3d, and so on. Each added electron is assigned to the lowest-energy sublevel available. To determine the electron configuration of a particular atom, start at the nucleus and add electrons one by one until the number of electrons equals the number of protons in the nucleus. The electron configuration of an atom shows the number of electrons in each sublevel in each energy level of the ground-state atom.
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