Beryllium, Atomic Number

Each atom of beryllium. Be—atomic number 4, atomic mass 9.01218— contains 4 protons and 5 neutrons in its nucleus. The beryllium atom has two iimer 

Beryllium can react chemically by losing 2 electrons from the beryllium atom. This occurs according to the half-reaction 

Beryllium is an environmentally and toxicologicaUy important element because it causes berylliosis, a disease marked by lung deterioration. Inhalation of beryllium is particularly hazardous, and atmospheric standards have been set at very low levels. 

has an atomic number of 5 and an atomic mass of 10.81. Most boron atoms have 6 neutrons in addition to 5 protons in their nuclei a less common isotope has 5 protons. Two of boron s 5 electrons are in a helium core and 3 are outer electrons, as shown by the Lewis symbol 

Atoms of carbon, C, have 2 inner and 4 outer electrons, the latter shown by the Lewis symbol 

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Physical and Chemical Properties Beryllium, atomic number 4, is the first element in Group 2 (formerly called Group IIA) of the Periodic Table of the Elements. It has an atomic mass of 9.012, and is a steel-gray metal with a density of 1.846 gmL a melting point of 1287-1292°C, a boiling point of 2970°C, and a valence of +2. Some of the physical properties of beryllium metal and common beryllium salts are outlined in Table 2.1-1 (Agency for Toxic Substances and Disease Registry 1988). 

Beryllium, atomic number 4, has 2 inner electrons in the l orbital and 2 outer electrons in the 2s orbital. Therefore, beryllium has a helium core, plus 2 valence electrons. Its electron configuration is sP-2iP-. 

Magnesium [7439-95-4] atomic number 12, is in Group 2 (IIA) of the Periodic Table between beryllium and calcium. It has an electronic configuration of 1T2T2 3T and a valence of two. The element occurs as three isotopes with mass numbers 24, 25, and 26 existing in the relative frequencies of 77, 11.5, and 11.1%, respectively. 

With modern detectors and electronics most Enei -Dispersive X-Ray Spectroscopy (EDS) systems can detect X rays from all the elements in the periodic table above beryllium, Z= 4, if present in sufficient quantity. The minimum detection limit (MDL) for elements with atomic numbers greater than Z = 11 is as low as 0.02% wt., if the peaks are isolated and the spectrum has a total of at least 2.5 X 10 counts. In practice, however, with EDS on an electron microscope, the MDL is about 0.1% wt. because of a high background count and broad peaks. Under conditions in which the peaks are severely overlapped, the MDL may be only 1—2% wt. For elements with Z < 10, the MDL is usually around 1—2% wt. under the best conditions, especially in electron-beam instruments. 

Atomic weights are known most accurately for elements which have only 1 stable isotope the relative atomic mass of this isotope can be determined to at least 1 ppm and there is no possibility of variability in nature. There are 20 such elements Be, F, Na, Al, P, Sc, Mn, Co, As, Y, Nb, Rh, I, Cs, Pr, Tb, Ho, Tm, Au and Bi. (Note that all of these elements except beryllium have odd atomic numbers — why )... 

Electrons are not only charged, they also have a characteristic physicists call spin. Pairing two electrons by spin, which has two possible values, up or down, confers additional stability. Bei yllium (Be, atomic number 4) has two spin-paired electrons in its second shell that are easily given up in chemical reactions. Beryllium shares this characteristic with other elements in column two, the alkaline earth metals. These atoms also generally form ionic bonds. Boron... 

From Figure 6.8 it is possible to predict the electron configurations of atoms of elements with atomic numbers 1 through 36. Because an s sublevel can hold only two electrons, the Is is filled at helium (Is2). With lithium (Z = 3), the third electron has to enter a new sublevel This is the 2s, the lowest sublevel of the second principal energy level. Lithium has one electron in this sublevel (ls s1)- With beryllium (Z = 4), the 2s sublevel is filled (ls22s2). The next six elements fill the 2p sublevel. Their electron configurations are... 

Alternative methods are based on the pioneering work of Hylleraas ([1928], [1964]). In these cases orbitals do not form the starting point, not even in zero order. Instead, the troublesome inter-electronic terms appear explicitly in the expression for the atomic wavefunction. However the Hylleraas methods become mathematically very cumbersome as the number of electrons in the atom increases, and they have not been very successfully applied in atoms beyond beryllium, which has only four electrons. Interestingly, one recent survey of ab initio calculations on the beryllium atom showed that the Hylleraas method in fact produced the closest agreement with the experimentally determined ground state atomic energy (Froese-Fischer [1977]). 

Beryllium i s a strong and light metal with useful nuclear character-istics (its atomic number is 4). It oxidizes readily and the oxide is toxic. Its properties are li sted in Tabl e 6.2. It i s produced by C VD on an experimental basis. 

The next atoms of the periodic table are beryllium and boron. You should be able to write the three different representations for the ground-state configurations of these elements. The filling principles are the same as we move to higher atomic numbers. Example shows how to apply these principles to aluminum. 

Ans. Onlv hvdrogen. Lithium and beryllium arc metals, which tend to lose electrons (and form ionic bonds) rather than share. The resulting configuration of two electrons in the first shell, with no other shells occupied, is stable, and therefore is also said to satisfy the octet rule. Second-period elements of higher atomic number tend to acquire the electron configuration of neon. If the outermost shell of an atom is the first shell, the maximum number of electrons in the atom is 2. 

Figure 1. The first-order shell correction SiE of the total binding energy of atoms (squares), cations (circles) and airions (triangles) from beryllium to calcium, as a function of the atomic number Z.

Atomic numbers are like name tags They identify an element as carbon, nitrogen, beryllium, and so on by telling you the number of protons in the nucleus of that element. Atoms are known by the numbers of their protons. Adding a proton or removing one from the nucleus of an atom changes the elemental identity of an atom. 

Let us consider au atom with two s electrons, with different total quantum numbers for example, a beryllium atom with one valence electron in a 2s orbital and the other in a 3s orbital, in addition to the two electrons in the K shell. The orbital angular momenta of the two valence electrons are zero (h = 0, k = 0), and accordingly the resultant angular momentum is zero (L = 0). Each of the two electrons has spin quantum number (si = sz = ), and each spin angular mo-... 

The window material is beryllium (approximately 0.9-mm thick), the material of choice for low-energy x- and y-radiation. Aluminum windows can be used but must be strong enough to withstand a vacuum hence a significant sacrifice in transparency must be made. Suitable plastic windows, restricted to low atomic number materials, leak slightly, and the presence of any oxygen or water will reduce the resolution performance of a detector of this kind. It is essential that the gas fill used be of the highest possible purity and that it remain so. 

ALKALINE EARTHS. The elements of group 2 of the periodic classification. In order of increasing atomic number, they are beryllium,... 

The critical choice was made of a CASSCF(4,4)/6-31G calculation the active space is thus the degenerate filled 2s + 2s and 2s 2s pair of MOs, and the degenerate empty 2px + 2px and 2px — 2px pair of MOs. CASSCF(4,4) was chosen because it corresponds to the CASSCF(2,2) calculation on one beryllium atom in the sense that we are doubling up the number of electrons and orbitals in our noninteracting system. This calculation gave an energy of 29.1709451 hartree. We can compare this with twice the energy of one beryllium atom, 2 x — 14.5854725 hartree = —29.1709450 hartree. 

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