Essential Elements

Essential Elements Elements in organic matter H He Major minerals Li 1 He 2 Major minerals Li 3 Be 4 B 5 C 6 N 7 O 8 F 9 Ne 10 Trace elements Na 11 Mg 12 Al 13 Si 14 P 15 S 16 Cl 17 Ar 18 K 19 Ca 20 Sc 21 Ti 22 V 23 Cr 24 Mn 25 Fe 26 Co 27 Ni 28 Cu 29 Zn 30 Ga 31 Ge 32 As 33 Se 34 Br 35 Kr 36 Rb 37 Sr 38 Y 39 Zr 40 Nb 41 Mo 42 Tc 43 Ru 44 Rh 45 Pd 46 Ag 47 Cd 48 In 49 Sn 50 Sb 51 Te 52 I 53 Xe 54 Minerals are considered the inorganic elements of the body. Minerals fall into two categories – the major minerals and the trace minerals, or trace elements, as they are sometimes called. Trace elements are minerals with dietary daily requirements of 100 mg or less. They are found in foods derived from both plants and animals. Though these elements are present in very small quantities, they perform a variety of essential functions in the body. Elements that are absolutely required in the diets of humans are called essential elements (highlighted in purple). Essential elements are restricted to the first four rows of the periodic table with only two exceptions (Mo and ). An essential element is one that is required for life and whose absence results in death. An element is considered to be essential if a deficiency consistently causes abnormal development or functioning and if dietary supplementation of that element and only that element prevents this adverse effect. Cs 55 Ba 56 La 57 Hf 72 Ta 72 W 74 Re 75 Os 76 Ir 77 Pt 78 Au 79 Hg 80 Tl 81 Pb 82 Bi 83 Po 84 At 85 Rn 86 Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 748

Trace Elements in Biological Systems Of the 100 known elements, 28 are known to be essential for the growth of at least one biological species, and only 19 are essential to humans. The following makes some elements essential: 1. The element must have some unique chemical property that an organism can use to its advantage and without which it cannot survive. 2. Adequate amounts of the element must be available in the environment in an easily accessible form. • Many of the elements essential to life are necessary in only small amounts (trace elements). Elements that are present in trace amounts can exert large effects on the health of an organism. Elements function as part of an amplification mechanism, in which a molecule containing a trace element is an essential part of a larger molecule that acts in turn to regulate the concentrations of other molecules. Essential trace elements in mammals have four general roles: 1. They can behave as macrominerals. 2. They can participate in the catalysis of group transfer reactions. 3. They can participate in oxidation-reduction reactions. 4. They can serve as structural components. The macrominerals (sodium, magnesium, potassium, calcium, chlorine, and phosphorus) are found in large amounts in biological tissues. • Macrominerals are present as inorganic compounds, either dissolved or precipitated. • All form monatomic ions except phosphorus. • Body fluids of all multicellular organisms contain high concentrations of these ions. • Substantial energy is required for transport of these ions across cell membranes — selection of ion pumps based on differences in ionic radius. • It is important to maintain optimum levels of macrominerals because temporary changes in their concentrations within a cell affect biological functions. Trace metal ions play crucial roles in many biological group transfer reactions. In these reactions, a recognizable functional group is transferred from one molecule to another. To neutralize the negative charge on the molecule that is undergoing the reaction, many biological reactions of this type require the presence of metal ions. Effectiveness of a metal ion depends on its charge and radius. The third important role of trace elements is to transfer electrons in biological oxidation-reduction reactions. Because most transition metals have multiple oxidation states separated by only one electron, they are uniquely suited to transfer multiple electrons one at a time. Many of the p-block elements are suited for transferring two electrons at once. Trace elements act as essential structural components of biological tissues or molecules. The trace element stabilizes a particular three-dimensional structure of the biomolecule in which it is found. Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Classification of the Essential Elements Most living matter consists primarily of bulk elements—oxygen, carbon, hydrogen, nitrogen, and sulfur. They are the building blocks of the compounds that make up our organs and muscles; they also constitute the bulk of our diet. Six elements—sodium, magnesium, potassium, calcium, chlorine, and phosphorus—are called macrominerals and provide essential ions in body fluids and form the major structural components of the body. Remaining essential elements called trace elements and are present in small amounts. Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

The Trace Elements It is difficult to detect low levels of some of the essential elements, so the trace elements were relatively slow to be recognized. Many compounds of trace elements are toxic. Dietary intakes of elements range from deficient to optimum to toxic with increasing quantities; the optimum levels differ greatly for the essential elements. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Amplification How can elements present in small amounts have such large effects on the health of an organism? Trace elements participate in an amplification mechanism—they are essential components of larger biological molecules that are capable of interacting with or regulating the levels of relatively large amounts of other molecules. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Oxidation State of Elements The most stable atom will be one that has a completely filled outer valence region (complete octet with the exception of Hydrogen Group 1=lose 1 electron = +1 ion Group 2 = lose 2 electrons = +2 ion Group 13 = lose 3 electrons = +3 ion Group 14 = lose 4 electrons = +4 ion Group 15= gain 3 electrons = -3 ion Group 16 = gain 2 electrons = -2 ion Group 17 = gain 1 electron = -1 ion Group 18 = gain 0 electrons = no charge

Various Ions Group 16 = gain 2 electrons = -2 ion The most stable atom will be one that has a completely filled outer valence region (complete octet with the exception of Hydrogen Group 1=lose 1 electron = +1 ion Group 2 = lose 2 electrons = +2 ion Group 13 = lose 3 electrons = +3 ion Group 14 = lose 4 electrons = +4 ion Group 15= gain 3 electrons = -3 ion Group 16 = gain 2 electrons = -2 ion Group 17 = gain 1 electron = -1 ion Group 18 = gain 0 electrons = no charge

Oxidation States of Elements 1 8 Groups 2 3 4 5 6 7 Li1+ Be2+ F1- O2- Cl1- Na1+ Te2- Al3+ S2- Br1- K1+ Te2- Zn2+ Ga3+ Se2- I1- Rb1+ Te2- Ag1+ In3+ Te2- Many elements have a tendency to gain or lose enough electrons to attain the same number of electrons as the noble gas closest to them in the periodic table. Monatomic ions contain only a single atom. Charges of most monatomic ions derived from the main group elements are predicted by simply looking at the periodic table and counting how many columns an element lies from the extreme left or right. Transition metals form cations with various charges. Cs1+ Te2-

Chemical Bonding Ionic Covalent Metal (cation) with non-metal (anion) Transfer of electron(s) Strong bond…high melting point Covalent Non-metal with non-metal Sharing of electron(s) Non-polar (equal distribution of electrons) Polar (uneven electron distribution) Weak bonds…low melting points Single, double and triple bonds Metallic (nuclei in a “sea” of shared electrons)

First Four Energy Levels Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 334

Modern Atomic Structure 2p 3p 4p 3d 4d 4f Sublevel designation n = 1 n = 2 n = 3 n = 4 An orbital for a hydrogen atom. The intensity of the dots shows that the electron spends more time closer to the nucleus. The first four principal energy levels in the hydrogen atom. Each level is assigned a principal quantum number n. The types of orbitals on each of the first four principal energy levels. Hein, Arena, Foundations of College Chemistry, 2000, page 202

Sublevels Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 334

Principal Level 2 Divided Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 334

s,p, and d-orbitals

Element Sublevels