The Periodic Table - Abhinandan Chowdhury

The Periodic Table - Abhinandan Chowdhury

The Periodic Table The Periodic Table The most popular version of the periodic table shows the elements arranged in order of increasing atomic number and grouped into periods and groups. Each group contains elements with similar chemical properties. In most cases, the elements in a column also have similar electronic configuration. The two most important exceptions are hydrogen and helium. 2 The Periodic Table Provides a basis for predicting general trends in a

number of physical properties, including the relative size of atoms and the ions they form, and the relative ease with which atoms either gain or lose electrons. These properties, such as: the size of the atoms or the ions, ionization energies, electron affinity, electronegativities etc. profoundly influence the chemical behavior of elements. 3 Classification of the Elements 4 Metals

Readily lose electrons Usually solid at room temperature (mercury is an exception) High luster (shiny) metallic appearance Good conductors of heat and electricity Malleable (can be bent and pounded into thin sheets) Ductile (can be drawn into wire) Corrode or oxidize in air and sea water Usually dense (exceptions include lithium, potassium,

and sodium) May have very high melting point Metalloids Metalloids have some of the properties of metals and some nonmetallic characteristic. Dull or shiny Usually conduct heat and electricity, though not as well as metals Often make good semiconductors Often ductile &

malleable May gain or lose electrons in reactions Non metals Nonmetals exhibit very different properties from metals. Dull appearance usually brittle Poor conductors of heat and electricity Usually less dense, compared to metals Usually low melting point of solids,

compared with metals Tend to gain electrons in chemical reactions Trends in Metallic Character Tro's Introductory Chemistry, Chapter 9 7 Metals Tend to Lose Electrons Prentice-Hall 2002 General Chemistry: Chapter 10

Slide 8 of 35 Nonmetals Tend to Gain Electrons Prentice-Hall 2002 General Chemistry: Chapter 10 Slide 9 of 35 Electron Configurations of Cations and Anions of Representative Elements Na [Ne]3s1 Na+ [Ne]

Ca [Ar]4s2 Ca2+ [Ar] Al [Ne]3s23p1 Atoms lose electrons so that cation has a noble-gas outer electron configuration. Al3+ [Ne] H 1s1 Atoms gain electrons so that anion has a noble-gas outer electron configuration. H- 1s2 or [He]

F 1s22s22p5 F- 1s22s22p6 or [Ne] O 1s22s22p4 O2- 1s22s22p6 or [Ne] N 1s22s22p3 N3- 1s22s22p6 or [Ne] 10 -1 -2

-3 +3 +2 +1 Cations and Anions of Representative Elements 11 Effective Nuclear Charge (Zeff) Effective nuclear charge (Zeff) is the positive charge felt by an electron. Zeff = Z - s

0 < s < Z (s = shielding constant) Zeff Z number of inner or core electrons Z Core Zeff Radius (pm) Na 11 10

1 186 Mg 12 10 2 160 Al

13 10 3 143 Si 14 10 4 132

12 Effective Nuclear Charge (Zeff) Zeff = Zactual No. of Core Electrons or Electron shielding Chapter 5/13 Effective Nuclear Charge (Zeff) decreasing Zeff increasing Zeff 14 15

Atomic Radii Increases Down the Group 2e- Group IIA Be 2eBe (4p+ & 4e-) Mg 4 p+ Ca 2e-

Sr Ba Mg (12p+ & 12e-) 8e2e12 p+ Ra 2e8e8eCa (20p & 20e ) + - 2e20 p+ 16

Atomic Radii Decreases Across the Period Period 2 Li Be B 1e- Li (3p+ & 3e-) 4e2e6 p+ C (6p+ & 6e-) N

O 2e- 2e3 p+ C 2e- 3e2e- 4 p+ 5 p+

Be (4p+ & 4e-) B (5p+ & 5e-) 6e2e8 p+ O (8p+ & 8e-) Tro's Introductory Chemistry, Chapter 9 8e2e10 p+ Ne (10p+ & 10e-) 17 Atomic Radii & Ionic Radii Cation is always smaller than atom from which

it is formed. Anion is always larger than atom from which it is formed. 18 Isoelectronic: have the same number of electrons, and hence the same ground-state electron configuration Na+: [Ne] O2-: 1s22s22p6 or [Ne] Al3+: [Ne] F-: 1s22s22p6 or [Ne] N3-: 1s22s22p6 or [Ne] Na+, Al3+, F-, O2-, and N3- are all isoelectronic with Ne

What neutral atom is isoelectronic with H- ? H-: 1s2 same electron configuration as He 19 Radii for Isoelectronic atoms or ions Atom or Ion Radius (nm) Electron config. C4-

0.260 1s22s22p6 N3- 0.171 1s22s22p6 O-2 0.140 1s22s22p6

F- 0.136 1s22s22p6 Ne 0.112 1s22s22p6 Na+ 0.095 1s22s22p6

Mg2+ 0.065 1s22s22p6 Al3+ 0.050 1s22s22p6 20 Ionization Energy Ionization energy is the minimum energy (kJ/mol)

required to remove an electron from a gaseous atom in its ground state. I1 + X (g) X+(g) + e- I2 + X+(g) X2+(g) + e- I3 + X2+(g) I1 first ionization energy I2 second ionization energy I3 third ionization energy X3+(g) + e-

I1 < I2 < I3 21 22 General Trends in First Ionization Energies Increasing First Ionization Energy Increasing First Ionization Energy 23 Electron Affinity Electron affinity is defined as 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. In other words, the neutral atom's likelihood of gaining an electron. X (g) + e- X-(g) F (g) + e- F-(g) DH = 328 kJ/mol EA = +328 kJ/mol O (g) + e-

O-(g) DH = 141 kJ/mol EA = +141 kJ/mol DH = +780 kJ/mol EA = 780 kJ/mol O- (g) + e- O2-(g) ? EA of O is highly ve; i.e. O2 formation is unfavorable,

electron-electron repulsion (g) > stability from noble gas configuration; O2 ion stabilized by neighboring cation, e.g. Li2O, Mg2O 24 25 Periodic Properties of the Elements Prentice-Hall 2002 General Chemistry: Chapter 10 Slide 26 of 35 Variation in Chemical Properties of the Representative Elements Ionization energy (IE) and electron affinity (EA) help us

to understand: the types of reactions an element undergo the nature of the elements compounds formed IE measures the attraction of an atom for its own electrons EA expresses the attraction of an atom for additional electrons IE and EA together gives the insight into the general attraction of an atom for electron With these concepts we can survey the chemical behavior of the elements systematically. 27 Variation in Chemical Properties of the Representative Elements

The metallic character of the elements decreases from left to right across a period, and increases from top to bottom within a group Metals usually have low ionization energies, and Nonmetals usually have high electron affinity On the basis of these trends we can predict the outcome of a reaction involving some of these elements 28 Hydrogen (1s1) No suitable position for hydrogen in the periodic table, it really could be a class by itself Like alkali metals, has a single s electron and forms H+ ion, which is hydrated in solution (H3O+)

Also forms hydride ion H in ionic compounds, NaH, CaH2 Hydrides reacts with water: 2NaH(s) + 2H2O(l) 2NaOH(aq) + H2(g) CaH2(s) + 2H2O(l) Ca(OH)2(s) + 2H2(g) Most important compound of hydrogen is water, 2H2(g) + O2(g) 2H2O(l) 29 Summary Periodic law: When the elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically. Elements having similar physical and chemical properties fall within a column.

The elements are arranged from left to right in increasing ATOMIC NUMBER (number of protons an element has). Rows in the periodic table are referred to as PERIODS. Columns within the periodic table are sometimes referred to as families. Families because the elements within the column have similar physical and chemical properties

The elements, their names, and symbols are given on the PERIODIC TABLE. Group Names Group 0 is known as noble gases Group 1 is called alkali metal Group 2 metals are known as alkaline earth metals Group 7 is called Halogens Group I; Properties

Soft silvery metals Very reactive Form ions with single positive charge Down the group melting point decreases and reactivity increases All their compounds are soluble in water Nearly all compounds are stable when heated Group II; Properties Soft but not as much as Group I and slivery Reactive but less than G I Form ions with double positive charge Reactivity increases down the group Many group 2 compounds are insoluble

in water as well as unstable when heated Transition elements Has high melting and boiling point Elements and their compounds often work as catalyst They form colored compounds They can react with another element to form more than one compound Group VII; Properties Reactive but reactivity decreases down the group Colored non-metals and exist as diatomic molecule Melting point and boiling point increase down the group

React to form anions with single negative charge Group VIII; Properties Colorless gases and found in small amounts in the air Very uncreative Down the group, b.p increases and elements get more dense

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