DOCSLIB.ORG

3.2 Periodic Trends Mrs

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

3.2 Periodic Trends Mrs. Page – IB Chemistry SL – 2015-2016 Essential Idea • Elements show trends in their physical and chemical properties across periods and down groups. Understandings • Vertical and horizontal trends in the periodic table exist for atomic radius, ionic radius, ionization energy, electron affinity, and electronegativity. • Trends in metallic and non-metallic behavior are due to the trends above. • Oxides change from basic through amphoteric to acidic across a period. Application and Skills • Prediction and explanation of the metallic and non-metallic behavior of an element based on its position in the periodic table. • Discussion of the similarities and differences in the properties of elements in the same group, with reference to alkali metals (group 1) and halogens (group 17). • Construction of equations to explain the pH changes for reactions of Na2O, MgO, P4O10, and the oxides of nitrogen and sulfur with water. Nature of Science • Looking for patterns – the position of an element in the periodic table allows scientists to make accurate predictions of its physical and chemical properties. This gives scientists the ability to synthesize new substances based on the expected reactivity of elements. Trends in Electron Configuration • As we have already seen, there is a pattern when looking at the electron configuration and the periodic table. • Valence electrons – electrons in the highest main energy level (outer shells s and p orbitals) • Valence electrons for the main group elements are related to their group (1 valence for alkali metals, 2 for alkaline earth 7 for halogens and 8 for noble gases) • The period number indicates the number of shells (main energy levels) Trends in Atomic Radius • Used to describe the size of an atom larger radius = larger atom • The electron cloud doesn’t have a definite edge • Get around this by measuring diatomic molecules and measuring the distance between their nuclei half of this measure is the radius of each atom (this is sometimes called the covalent radius) • Trends: • atomic radius increases down group • atomic radius decreases across period Atomic Radius H Li • Increases down a group • More electron shells Na • More electrons so more repulsion K Rb Atomic Radius • Decreases across period • nuclear charge increases (more protons), more attraction to electrons pulls shells closer to nucleus • (Note: the e- are in same energy level so there is no additional shielding) Na Mg Al Si P S Cl Ar Trends in Atomic Radius • Note: it is not possible to measure the atomic radius for the noble gases because the do not form covalent bonds (unreactive) • Therefore there is another measure atomic radius – the van der Waals’ radius • The van der Waals’ radius assumes that when two atoms collide, there is little penetration in the electron clouds of each atom, therefore if frozen the atomic radius would be ½ the diameter between the nuclei of the non-bonded atoms • Bond length can be estimated from the atomic radii Effective Nuclear Charge & Shielding • Shielding (S): Core electrons (those in inner shell) repel the outer shell electrons creating a smaller electrostatic force between the outer electrons and the nucleus. • The outer shell electrons are pushed away from the nucleus being held less tightly. • The net charge experienced by an electron is called the effective nuclear charge, Zeff http://wps.prenhall.com/ Trends in Ionic Radius • Cations form by losing electrons (+ charge) • Metals form cations • Cations of an element have noble gas configuration. • Cations are smaller than the atom they come from • Lost electrons therefore the same number of protons are attracting fewer electrons • Less repulsion between electrons due to fewer electrons Trends in Ionic Radius • Anions are form by gaining electrons (- charge) • Non-metals form anions • Anions of an element have noble gas configuration. • Anions are larger than the atom they come from • More electrons means more repulsion between them so increases electron cloud • Number of protons remained the same and more electrons so attractive force weakened Trends in Ionic RadiI -3 B+3 N O-2 F-1 Li+1 Be+2 C+4 First Ionization Energy • The energy required to remove one electron from each atom in one mole of gaseous atoms under standard conditions. + - • X(g) X (g) + e First Ionization Energy • Down groups first ionization energy decreases • Size of atom increases down group so outer electrons are further from nucleus and so less strongly attracted to the nucleus • Increased shielding First Ionization Energy • Across a period first ionization energy increases • Larger nuclear charge w/out adding energy levels attracts electrons more strongly • Atom is smaller so electrons are more strongly held First Ionization Energy •EXCEPTIONSBoron has a lower ionization energy than beryllium • Be 1s2 2s2 B 1s2 2s2 2p1 • 2p sub level is higher energy so less energy is needed to remove the electron from B First Ionization Energy •EXCEPTIONSOxygen has a lower ionization energy than nitrogen • N 1s2 2s2 2p3 O 1s2 2s2 2p4 • Oxygen has two electrons paired in same p orbital making it easier to remove an electron due to the repulsive force between electrons in the same shell. Electron Affinity Eea • The change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. - - • X(g) + e X (g) • See data book Section 8 • Negative signs indicate energy is released (exothermic) • More negative = greater attraction for the electron Electron Affinity Down Group 17 • Not same clear trend as others • General trend is that Eea decreases down a group • Atoms larger so weaker attraction to electrons • In smaller atoms electron repulsion force is greater (less exothermic when electrons are added to smaller atoms) Electron Affinity Across period • General trend is that Eea becomes more exothermic (increases) • Increased nuclear charge & smaller atomic radii electrons more strongly attracted Electronegativity • A measure of the attraction of an atom in a molecule for the electron pair in the covalent bond of which it is a part. • In a covalent bond atoms do not share the pair of bonding electrons equally Electronegativity – Across Period • Increases across period • Increased nuclear charge & no additional shielding Electronegativity – DOWN Group • Decreases down a group • Bonding electrons far from nucleus – less attraction, more shielding Trends in metallic and Non-metallic properties • Metallic properties decrease across period • Metallic properties increase down a group • Metals lose electrons – get oxidized • Non-metals gain electrons – get reduced Melting Points • Depends on the type of bonding and structure of compound • Down a group – elements bond in a similar way • For metals – melting point decreases down a group (elements held together by delocalized electrons and positive ions), attraction decreases with distance • Nonmetals – melting points increase down a group (more in topic 4) • Generally increase across a period until group 14 and then decrease to group 18. (more in topic 4) Group Trends – Alkali Metals • Group 1 Elements: Alkali Metals • Highly reactive – not found in nature (1 valence electron) • Reactivity increases down the group (ionization energies decrease) • Soft silvery metals • Low melting points (decreasing down group) • Form M+ ions • React vigorously with oxygen (tarnish quickly) • 4M(s) + O2(g) 2M2O(s) Group Trends – Alkali Metals • Group 1 Elements: Alkali Metals • React rapidly with water (stored in oil) • Good conductors • Reactivity with water increases down a group • 2M(s) + H2O(l) MOH(aq) + H2(g) • Forms an alkali metal hydroxide (strong base), which ionizes completely in aqueous solution • Ex: 2K(s) + H2O(l) 2KOH(aq) + H2(g) Group Trends – Halogens • Group 17 Elements: Halogens • Nonmetals • Most diatomic molecules (X2) • Melting points increase down the group • 7 valence electrons react by gaining an electron or forming covalent bonds • Reactivity decreases down the group (F is most reactive element) • React with alkali metals to form salts • 2M(s) + X2(g) 2MX(s) Group Trends – Halogens • Displacement Reactions of Halogens • Reaction of halogen with a solution containing halide ions • K, Cl, Br, and I solutions are colorless KCl(aq) KBr(aq) KI(aq) • Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq) No Orange Dark red/ • Cl2(aq) + 2KI(aq) 2KCl(aq) + I2(aq) Cl2(aq) reaction solution brown • Br2(aq) + 2KI(aq) 2KBr(aq) + I2(aq) solution No No Dark red Br2(aq) reaction reaction /brown Color change to brown due to iodine solution Color change to orange due to bromine No No No reaction I2(aq) reaction reaction Group Trends – Noble Gases • Colorless gases • Monoatomic • Least reactive elements – full valence shell (stable octet) • Highest ionization energies Trends in metal & Non-metal Oxides • Oxides when element combines with oxygen • Oxygen forms on O2- ion • Ex: Na2O, CaO, Al2O3 • Metal oxides form giant ionic structures • Metal oxides are basic & react with water to form metal hydroxides • Ex: Na2O(s) + H2O(l) 2NaOH(aq) Trends in metal & Non-metal Oxides • Non-metal oxides are formed by covalent bonding and form giant covalent structures • Non-metal oxides are acidic and react with water to form acidic solutions • CO2(g) + H2O(l) H2CO3(aq) carbonic acid • SO3(l) + H2O(l) H2SO4(aq) sulfuric acid • SO2(g) + H2O(l) H2SO3(aq) sulfurous acid • P4O10(s) + H2O(l) 4H3PO4(aq) phosphoric acid Trends in metal & Non-metal Oxides • Non-metal oxides are acidic and react with water to form acidic solutions • CO2(g) + H2O(l) H2CO3(aq) carbonic acid • SO3(l) + H2O(l) H2SO4(aq) sulfuric acid • SO2(g) + H2O(l) H2SO3(aq) sulfurous acid • P4O10(s) + H2O(l) 4H3PO4(aq) phosphoric acid Interesting Oxides • Silicon dioxide does not dissolve in water but is an acidic oxide • SiO2(s) + 2NaOH(aq) Na2SiO3(aq) + H2O(l) • Aluminum oxide is amphoteric (reacts as both an acid and a base) • Al2O3(s) + 2NaOH(aq) + 3H2O(l) 2NaAl(OH)4(aq) • Al2O3(s) + 6HCl(aq) 2AlCl3(aq) + 3H2O(l) Polyatomic Ions to KNOW - p.
Recommended publications
  • ATOMIC RADII of the ELEMENTS References

    ATOMIC RADII of the ELEMENTS References

    ATOMIC RADII OF THE ElEMENTS The simple model of an atom as a hard sphere that can approach The Cambridge Crystallographic Data Center also makes use only to a fixed distance from another atom to which it is not bond- of a set of “covalent radii” to determine which atoms in a crystal ed has proved useful in interpreting crystal structures and other are bonded to each other . Thus two atoms A and B are judged to molecular properties . The term van der Waals radius, rvdw, was be connected by a covalent bond if their separation falls within a originally introduced by Pauling as a measure of this atomic size . tolerance of ±0 .4 Å of the sum rcov (A) + rcov (B) . The covalent radii Thus in a closely packed structure two non-bonded atoms A and are given in the fourth column of the table . B will be separated by the sum of their van der Waals radii rvdw (A) and rvdw (B) . The set of van der Waals radii proposed by Pauling References was refined by Bondi (Reference 1) based on crystallographic data, gas kinetic collision cross sections, and liquid state properties . The 1 . Bondi, A ., J. Phys. Chem. 68, 441, 1964 . non-bonded contact distances predicted from the recommended 2 . Rowland, R . S . and Taylor, R ., J. Phys. Chem. 100, 7384, 1996 . 3 . Cambridge Crystallographic Data Center, www .ccdc .cam .ac .uk/prod- r of Bondi have been compared with actual data in the collec- vdw ucts/csd/radii/ tion of the Cambridge Crystallographic Data Center by Rowland and Taylor (Reference 2) and modified slightly .
  • Modeling the Shape of Ions in Pyrite-Type Crystals

    Modeling the Shape of Ions in Pyrite-Type Crystals

    Crystals 2014, 4, 390-403; doi:10.3390/cryst4030390 OPEN ACCESS crystals ISSN 2073-4352 www.mdpi.com/journal/crystals Article Modeling the Shape of Ions in Pyrite-Type Crystals Mario Birkholz IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany; E-Mail: [email protected]; Tel.: +49-335-56250 Received: 13 April 2014; in revised form: 22 August 2014 / Accepted: 26 August 2014 / Published: 3 September 2014 Abstract: The geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point groups, however, the ionic radius must be assumed to be an anisotropic quantity. An appropriate modelling of p valence ions then has to be performed by ellipsoids. The approach is tested for pyrite-structured dichalcogenides MX2, with chalcogen ions X = O, S, Se and Te. The latter are found to exhibit the shape of ellipsoids being compressed along the <111> symmetry axes, with two radii r|| and describing their spatial extension. Based on this ansatz, accurate interatomic M–X distances can be derived and a consistent geometrical model emerges for pyrite-structured compounds. Remarkably, the volumes of chalcogen ions are found to vary only little in different MX2 compounds, suggesting the ionic volume rather than the ionic radius to behave as a crystal-chemical constant. Keywords: ionic radius; ionic shape; bonding distance; ionic volume; pyrite-type compounds; di-chalcogenides; di-oxides; di-sulfides; di-selenides; di-tellurides 1.
  • A Study of the Hydration of the Alkali Metal Ions in Aqueous Solution

    A Study of the Hydration of the Alkali Metal Ions in Aqueous Solution

    Article pubs.acs.org/IC A Study of the Hydration of the Alkali Metal Ions in Aqueous Solution Johan Mahler̈ and Ingmar Persson* Department of Chemistry, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden *S Supporting Information ABSTRACT: The hydration of the alkali metal ions in aqueous solution has been studied by large angle X-ray scattering (LAXS) and double difference infrared spectroscopy (DDIR). The structures of the dimethyl sulfoxide solvated alkali metal ions in solution have been determined to support the studies in aqueous solution. The results of the LAXS and DDIR mea- surements show that the sodium, potassium, rubidium and cesium ions all are weakly hydrated with only a single shell of water molecules. The smaller lithium ion is more strongly hydrated, most probably with a second hydration shell present. The influence of the rubidium and cesium ions on the water structure was found to be very weak, and it was not possible to quantify this effect in a reliable way due to insufficient separation of the O−D stretching bands of partially deuterated water bound to these metal ions and the O−D stretching bands of the bulk water. Aqueous solutions of sodium, potassium and cesium iodide and cesium and lithium hydroxide have been studied by LAXS and M−O bond distances have been determined fairly accurately except for lithium. However, the number of water molecules binding to the alkali metal ions is very difficult to determine from the LAXS measurements as the number of distances and the temperature factor are strongly correlated.
  • CHEM 1A03 UNIT 3: Periodic Trends Introduction

    CHEM 1A03 UNIT 3: Periodic Trends Introduction

    CHEM 1A03 UNIT 3: Periodic Trends Introduction Hey! Thanks for opening up this Chemistry Periodic Trends Review! The education team at WebStraw McMaster has put together a comprehensive breakdown for you that covers all the key concepts for Chemistry Periodic Trends Members of our team have taken the course in previous years, and we understand better than anyone else what specific ideas and concepts tend to trip students up throughout the semester. We are essentially offering you the key takeaways from the course, after having completed the course ourselves. Before you read further, also keep in mind that these review packages are not meant to be a tool for you to learn the course from scratch. The content presented below was designed with the assumption that you already have a preliminary understanding of Periodic Trends. Our goal is to help give you a more in-depth understanding of key outcomes, as well as to help you see how concepts relate/connect to one another within the scope of the course as a whole. We do our best to cover every topic within the unit; however, some testable outcomes may not be discussed. With that said, best of luck in your studying! Remember to make good use of your time, but to also take breaks as well. Yousef Abumustafa & Julia Ma The WebStraw McMaster Chemistry team WebStraw McMaster Periodic properties of elements The periodic table is divided into called columns called groups that group elements with similar chemical/physical properties together and rows called periods that group elements with the same
  • Atomic and Ionic Radii of Elements 1–96 Martinrahm,*[A] Roald Hoffmann,*[A] and N

    Atomic and Ionic Radii of Elements 1–96 Martinrahm,*[A] Roald Hoffmann,*[A] and N

    DOI:10.1002/chem.201602949 Full Paper & Elemental Radii Atomic and Ionic Radii of Elements 1–96 MartinRahm,*[a] Roald Hoffmann,*[a] and N. W. Ashcroft[b] Abstract: Atomic and cationic radii have been calculated for tive measureofthe sizes of non-interacting atoms, common- the first 96 elements, together with selected anionicradii. ly invoked in the rationalization of chemicalbonding, struc- The metric adopted is the average distance from the nucleus ture, and different properties. Remarkably,the atomic radii where the electron density falls to 0.001 electrons per bohr3, as defined in this way correlate well with van der Waals radii following earlier work by Boyd. Our radii are derived using derived from crystal structures. Arationalizationfor trends relativistic all-electron density functional theory calculations, and exceptionsinthose correlations is provided. close to the basis set limit. They offer asystematic quantita- Introduction cule,[2] but we prefer to follow through with aconsistent pic- ture, one of gauging the density in the atomic groundstate. What is the size of an atom or an ion?This question has been The attractivenessofdefining radii from the electron density anatural one to ask over the centurythat we have had good is that a) the electron density is, at least in principle, an experi- experimental metricinformation on atoms in every form of mental observable,and b) it is the electron density at the out- matter,and (more recently) reliable theory for thesesame ermost regionsofasystem that determines Pauli/exchange/ atoms. And the momentone asks this question one knows same-spinrepulsions, or attractive bondinginteractions, with that there is no unique answer.Anatom or ion coursing down achemical surrounding.
  • ARC: an Open-Source Library for Calculating Properties of Alkali Rydberg Atoms

    ARC: an Open-Source Library for Calculating Properties of Alkali Rydberg Atoms

    ARC: An open-source library for calculating properties of alkali Rydberg atoms N. Šibalic´a,∗, J. D. Pritchardb, C. S. Adamsa, K. J. Weatherilla aJoint Quantum Center (JQC) Durham-Newcastle, Department of Physics, Durham University, South Road, Durham, DH1 3LE, United Kingdom bDepartment of Physics, SUPA, University of Strathclyde, 107 Rottenrow East, Glasgow, G4 0NG, United Kingdom Abstract We present an object-oriented Python library for computation of properties of highly-excited Rydberg states of alkali atoms. These include single-body effects such as dipole matrix elements, excited-state lifetimes (radiative and black-body limited) and Stark maps of atoms in external electric fields, as well as two-atom interaction potentials accounting for dipole and quadrupole coupling effects valid at both long and short range for arbitrary placement of the atomic dipoles. The package is cross-referenced to precise measurements of atomic energy levels and features extensive documentation to facilitate rapid upgrade or expansion by users. This library has direct application in the field of quantum information and quantum optics which exploit the strong Rydberg dipolar interactions for two-qubit gates, robust atom-light interfaces and simulating quantum many-body physics, as well as the field of metrology using Rydberg atoms as precise microwave electrometers. Keywords: Alkali atom, Matrix elements, Dipole-dipole interactions, Stark shift, Förster resonances PROGRAM SUMMARY They are a flourishing field for quantum information process- Program Title: ARC: Alkali Rydberg Calculator ing [1, 2] and quantum optics [3, 4, 5] in the few to single exci- Licensing provisions: BSD-3-Clause tation regime, as well as many-body physics [6, 7, 8, 9, 10, 11], Programming language: Python 2.7 or 3.5, with C extension in the many-excitations limit.
  • Periodic Trends and the S-Block Elements”, Chapter 21 from the Book Principles of General Chemistry (Index.Html) (V

    Periodic Trends and the S-Block Elements”, Chapter 21 from the Book Principles of General Chemistry (Index.Html) (V

    This is “Periodic Trends and the s-Block Elements”, chapter 21 from the book Principles of General Chemistry (index.html) (v. 1.0M). This book is licensed under a Creative Commons by-nc-sa 3.0 (http://creativecommons.org/licenses/by-nc-sa/ 3.0/) license. See the license for more details, but that basically means you can share this book as long as you credit the author (but see below), don't make money from it, and do make it available to everyone else under the same terms. This content was accessible as of December 29, 2012, and it was downloaded then by Andy Schmitz (http://lardbucket.org) in an effort to preserve the availability of this book. Normally, the author and publisher would be credited here. However, the publisher has asked for the customary Creative Commons attribution to the original publisher, authors, title, and book URI to be removed. Additionally, per the publisher's request, their name has been removed in some passages. More information is available on this project's attribution page (http://2012books.lardbucket.org/attribution.html?utm_source=header). For more information on the source of this book, or why it is available for free, please see the project's home page (http://2012books.lardbucket.org/). You can browse or download additional books there. i Chapter 21 Periodic Trends and the s-Block Elements In previous chapters, we used the principles of chemical bonding, thermodynamics, and kinetics to provide a conceptual framework for understanding the chemistry of the elements. Beginning in Chapter 21 "Periodic Trends and the ", we use the periodic table to guide our discussion of the properties and reactions of the elements and the synthesis and uses of some of their commercially important compounds.
  • Periodic Activity of Metals Periodic Trends and the Properties of the Elements SCIENTIFIC

    Periodic Activity of Metals Periodic Trends and the Properties of the Elements SCIENTIFIC

    Periodic Activity of Metals Periodic Trends and the Properties of the Elements SCIENTIFIC Introduction Elements are classified based on similarities, differences, and trends in their properties, including their chemical reactions. The reactions of alkali and alkaline earth metals with water are pretty spectacular chemical reactions. Mixtures bubble and boil, fizz and hiss, and may even smoke and burn. Introduce the study of the periodic table and periodic trends with this exciting demonstration of the activity of metals. Concepts • Alkali and alkaline earth metals • Periodic table and trends • Physical and chemical properties • Metal activity Materials Calcium turnings, Ca, 0.3 g Beaker, Berzelius (tall-form), Pyrex®, 500-mL, 4 Lithium metal, Li, precut piece Forceps or tongs Magnesium ribbon, Mg, 3-cm Knife (optional) Sodium metal, Na, precut piece Petri dishes, disposable, 4 Phenolphthalein, 1% solution, 2 mL Scissors Water, distilled or deionized, 600 mL Safety Precautions Lithium and sodium are flammable, water-reactive, corrosive solids; dangerous when exposed to heat or flame. They react violently with water to produce flammable hydrogen gas and solutions of corrosive metal hydroxides. Hydrogen gas may be released in sufficient quantities to cause ignition. Do NOT “scale up” this demonstration using larger pieces of sodium or lithium! These metals are shipped in dry mineral oil. Store them in mineral oil until immediately before use. Do not allow these metals to stand exposed to air from one class period to another or for extended periods of time. Purchasing small, pre-cut pieces of lithium and sodium greatly reduces their potential hazard. Calcium metal is flammable in finely divided form and reacts upon contact with water to give flammable hydrogen gas and corrosive calcium hydroxide.
  • CHEMISTRY 130 Periodic Trends

    CHEMISTRY 130 Periodic Trends

    CHEMISTRY 130 General Chemistry I Periodic Trends Elements within a period or group of the periodic table often show trends in physical and chemical properties. The variation in relative sizes of the halogens is shown above. DEPARTMENT OF CHEMISTRY UNIVERSITY OF KANSAS 1 Periodic Trends Introduction In the modern periodic table (shown below in Figure 1), elements are arranged according to increasing atomic number in horizontal rows called “periods.” In Figure 1, atomic numbers, which represent the number of protons in an atom of a given element, are listed directly above the element symbols. Figure 1: The modern periodic table. Elements in boxes shaded blue, orange, and purple are characterized as metals, metalloids, and nonmetals, respectively. The structure of the periodic table is such that elements with similar properties are aligned vertically in columns called “groups” or “families.” As indicated in Figure 1, each group has a number (1-18) associated with it. Select groups have also been assigned special names. For instance, the elements in Group 1 (hydrogen excluded) are called the alkali metals. These metallic elements react with oxygen to form bases. They also form alkaline (basic) solutions when mixed with water. Elements in other columns of the periodic table have also been given special “family” names. For instance, the elements in Groups 2, 11 (Cu, Ag, and Au), 16, 17, and 18 are commonly referred to as the alkaline earth metals, the coinage metals, the chalcogens, the halogens, and the noble gases, respectively. Many of these names reflect, unsurprisingly, the reactivity (or the lack thereof) of the elements found within the given group.
  • Chalcogen-Nitrogen Bond: Insights Into a Key Chemical Motif

    Chalcogen-Nitrogen Bond: Insights Into a Key Chemical Motif

    Proceedings Chalcogen-nitrogen Bond: Insights into A Key Chemical Motif Marco Bortoli,1 Andrea Madabeni,1 Pablo Andrei Nogara,2 Folorunsho B. Omage,2 Giovanni Ribaudo,3 Davide Zeppilli,1 Joao Batista Teixeira Rocha,2* Laura Orian1* 1 Dipartimento di Scienze Chimiche Università degli Studi di Padova Via Marzolo 1 35131 Padova, Italy; [email protected] (M.B.); [email protected] (A.M..); [email protected] (D.Z.) 2 Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Santa Maria, Santa Maria, 97105-900, RS Brazil; [email protected] (P.A.N.); [email protected] (F.B.O.) 3 Dipartimento di Medicina Molecolare e Traslazionale, Università degli Studi di Brescia, Viale Europa 11, 25123 Brescia, Italy; [email protected] (G.R.) * Correspondence: : [email protected] (J.B.T.R), [email protected] (L.O.); † Presented at the 1st International Electronic Conference on Catalysis Sciences, 10–30 November 2020; Available online: https://eccs2020.sciforum.net/ Published: 10 November 2020 Abstract: Chalcogen-nitrogen chemistry deals with systems in which sulfur, selenium or tellurium is linked to a nitrogen nucleus. This chemical motif is a key component of different functional structures, ranging from inorganic materials and polymers to rationally designed catalysts, to bioinspired molecules and enzymes. The formation of a selenium-nitrogen bond, and its disruption, are rather common events in organic Se-catalyzed processes. In nature, along the mechanistic path of glutathione peroxidase, evidence of the formation of a Se-N bond in highly oxidizing conditions has been reported and interpreted as a strategy to protect the selenoenzyme from overoxidation.
  • Periodic Trends

    Periodic Trends

    Periodic Trends There are three main properties of atoms that we are concerned with. Ionization Energy- the amount of energy need to remove an electron from an atom. Atomic Radius- the estimate of atomic size based on covalent bonding. Electron Affinity- the amount of energy absorbed or released when an atom gains an electron. All three properties have regularly varying trends we can identify in the periodic table and all three properties can be explained using the same properties of electronic structure. Explaining Periodic Trends All of the atomic properties that we are interested in are caused by the attractive force between the positively charged nucleolus and the negatively charged electrons. We need to consider what would affect that relationship. The first thing to consider is the effective nuclear charge. We need to look at the number of protons. Secondly we will need to look at the nucleolus - electron distance and the electron shielding. Lastly we will need to consider electron - electron repulsion. Ionization Energy As we move across a period the general trend is an increase in IE. However when we jump to a new energy level the distance increases and the amount of e-- shielding increases dramatically. Reducing the effective nuclear charge. In addition to the over all trend we need to explain the discrepancies. The discrepancies can be explained by either electron shielding or by electron electron repulsion. 1 Atomic Radius The trend for atomic radius is to decrease across a period and to increase down a family. These trends can be explained with the same reasons as IE.
  • Periodic Trends Remember from the "Periodic Table" Notes

    Periodic Trends Remember from the "Periodic Table" Notes

    November 07, 2014 Periodic Trends Remember from the "Periodic Table" Notes... • The periodic table is a tabular display of the chemical elements, organized by their atomic number, electron configuration, and recurring properties. • Periodic law: There is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number November 07, 2014 Atomic Radius Graph • What are some initial observations about the atomic radius data/graph? • What is atomic radius? November 07, 2014 Go finish the rest of the worksheet with your group! You have 20 minutes. November 07, 2014 Atomic Radius Trend Discussion • What happens to atomic radius as you go across the period? Why? • What happens to atomic radius as you go down the group? Why? November 07, 2014 Periodic Trends Notes Get your handout out! November 07, 2014 Why is it called a periodic table? • The properties of the elements in the table repeat in a "periodic" way (specific pattern). • Periodic law: There is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number • The modern periodic table is arranged by > atomic number = # of protons > properties > electron configuration November 07, 2014 Periodic Law • Now lets look at some properties of elements > We looked at some of these in "Meet My Family"! Alkali Metals Halogens November 07, 2014 Periodic Trends • Chemical properties of elements are determined by their electron configuration. • Properties are periodic because the number of valence electrons is periodic. November 07, 2014 Electron Configuration and the Periodic Table • Remember electrons are found in atomic orbitals > Principle energy level (n, shells) tells us the relative size and energy of atomic orbitals.