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Periodic Relationships Among the Elements Chapter 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Development of the Periodic Table Dimitri Mendeleev Arranged the elements by increasing ATOMIC MASS, he saw a periodic repetition of properties Produced the first PERIODIC TABLE – 1871 The table placed elements with similar properties in the same column Kept “holes” for undiscovered elements, and predicted the properties in advance Development of the Periodic Table Properties of elements predicted by Mendeleev Development of the Periodic Table H. G. Moseley in 1914 Rearranged the elements by ATOMIC NUMBER This has become the MODERN PERIODIC TABLE Valence Electrons valence electrons: electrons available to be lost, gained, or shared in the formation of chemical compounds ◦ electrons in the outermost energy level ◦ electrons that are responsible for reactions Elements in a group have similar properties because they have the same valence electron configuration Inner Core Electrons • All electrons under the highest energy level Valence Electron Configuration Group 1 2 13 14 15 16 17 18 e- configuration ns1 ns2 ns2np1 ns2np2 ns2np3 ns2np4 ns2np5 ns2np6 Valence electrons -1 -2 -3 +3 +2 +1 Charges Of Representative Elements 8.2 What ions are isoelectronic with Ne? an ion that has the same electron configuration Na+: [Ne] Al3+: [Ne] O2-: 1s22s22p6 or [Ne] F-: 1s22s22p6 or [Ne] N3-: 1s22s22p6 or [Ne] Electron Configurations of Transition Metals When a cation is formed from an atom of a transition metal, electrons are always removed first from the ns orbital and then from the (n – 1)d orbitals. Fe: [Ar]4s23d6 Fe2+: [Ar]4s03d6 or [Ar]3d6 Fe3+: [Ar]4s03d5 or [Ar]3d5 Mn: [Ar]4s23d5 Mn2+: [Ar]4s03d5 or [Ar]3d5 Periodic Table Groups Properties of Metals • shiny • conductors of heat and electricity • tend to lose electrons • ductile – can be stretched out into a wire • malleable –can be hammered or rolled into sheets Properties of Nonmetals PERIODIC LAW When elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic (repeating) pattern. patterns on the periodic table are called periodic trends Atomic Radius half the distance from center-center of 2 like atoms Atomic Radii DOWN a Group As you go down a group another energy level is added, the atom size gets larger ↓ The number of occupied orbitals between the nucleus and the outermost energy level increases ↓ Shielding Effect: reduction of attraction between positive nucleus and outer electrons, outer electrons are not held tight and can move away Atomic Radius: down group P X Na X P P P P P P P P P P P X X X X X X X X X X Atomic Radius: down group P X K X P P P P P P P P P P P X X X X X X X X X X X X X X X X X X Atomic Radii DOWN a Group ↓ DOWN THE GROUP ATOMIC RADIUS INCREASES more energy levels, the larger the size of the atom Atomic Radii ACROSS a Period Each atom gains one proton and one electron in the same energy level →Each added electron is the same distance from the nucleus →As the positive charge increases and exerts a greater force on the electrons thereby pulling it closer to the nucleus → Atomic Radii ACROSS a Period Effective nuclear charge (Zeff) : “positive charge” felt by an electron. Within a period, every time a proton is added, the effective nuclear charge (Zeff) increases… radius decreases REMEMBER! PROTONS are bigger and stronger! + e + P -electrons are smaller and weaker! Atomic Radius: across period P X X X X P P P P P P P P P P X X X X X X X Atomic Radii ACROSS a Period →ACROSS THE PERIOD ATOMIC RADIUS DECREASES greater effective nuclear charge (Zeff), greater pull on the electrons, smaller radius Ionic Radii half the distance from center-center of 2 like ions Ionic Radius DOWN a Group ↓ As you go down a group another energy level is added, increasing the size of the atom. (just like the atomic radius) Ionic Radius DOWN the Group ↓ DOWN THE GROUP IONIC RADIUS INCREASES more energy levels, increase in atom size Ionic Radius ACROSS the Period Cation: positive ion formed from losing an electron → A cation is always smaller than the original atom →The more electrons lost the more protons available to attract a smaller number of electrons. Ionic Radius P X Na + P P P P P P P P P P P X X X X X X X X X X X Ionic Radius ACROSS the Period →ACROSS THE PERIOD IONIC RADIUS DECREASES greater pull on electrons, the shorter the radius Ionic Radius ACROSS the Period Anion: negative ion formed from gaining an electron → A anion is always larger than the original atom →The more electrons gained, the less protons available to attract a larger number of electrons. Ionic Radius P X -F P P P P P P P P P P P X X X X X X X X X X Ionic Radius ACROSS the Period →ACROSS THE PERIOD IONIC RADIUS DECREASES As electrons are added the atom gets Larger from right to left, General trend from left to right is decreasing 8.3 Ionization Energy amount of energy needed to remove an electron from an atom Multiple Ionization Energies I1 + X (g) X+(g) + e- I1 first ionization energy I2 + X (g) X2+(g) + e- I2 second ionization energy I3 + X (g) X3+(g) + e- I3 third ionization energy I1 < I2 < I3 Ionization Energy DOWN a Group ↓ As you go down a group atoms become larger, electrons are farther from the nucleus and more easily removed ↓ The more electrons in an atom between the nucleus and valence shell, the greater the shielding effect Ionization Energy DOWN a Group ↓ DOWN THE GROUP IONIZATION ENERGY DECREASES greater distance from the nucleus, greater shielding effect (less energy needed to remove) Ionization Energy ACROSS a Period →As atomic radius decreases there is a greater attraction between protons and electrons. (effective nuclear charge) →The stronger the attraction, the more energy needed to remove an electron. →The more electrons present, the more energy required to remove them all to become STABLE Ionization Energy ACROSS a Period →ACROSS THE PERIOD IONIZATION ENERGY INCREASES more electrons on an energy level, more energy required to remove them Electronegativity tendency for an atom to attract electrons It is a “tug of war” between the two . atoms of a bond : . H . F : : Which is the more electronegative element? Electronegativity DOWN the Group ↓ The farther away from the nucleus, the greater the shielding effect ↓ The larger the atom, the less likely it is to accept more electrons. Electronegativity DOWN the Group ↓ DOWN THE GROUP ELECTRONEGATIVITY DECREASES farther the distance from the nucleus, lower ability to attract electrons Electronegativity ACROSS the Period →As you go across a period atomic radius decreases because there is a greater attraction between protons and electrons →Metals do not attract electrons. →Non-metals do attract electrons. Electronegativity ACROSS the Period →ACROSS THE PERIOD ELECTRONEGATIVITY INCREASES greater effective nuclear charge, greater ability to add electrons Electron Affinity the negative of the energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion. Increases with ability to attract and hold an electron Electron Affinity A large positive value means the anion is very stable X (g) + e- X-(g) F (g) + e- X-(g) DH = -328 kJ/mol EA = +328 kJ/mol O (g) + e- O-(g) DH = -141 kJ/mol EA = +141 kJ/mol Electron Affinity DOWN the Group Down a group, the energy released becomes less negative so electron affinity is smaller ↓ The larger the atom the less effective nuclear charge and the more difficult to accept electrons ↓ ↓ Metals want to lose electrons. Electron Affinity DOWN the Group ↓ DOWN THE GROUP ELECTRON AFFINITY DECREASES farther the distance from the nucleus, forms poor anions Electron Affinity ACROSS the Period →Across the period the energy released becomes more negative, making electron affinity more positive →As effective nuclear charge gets stronger, it is easier to attract an electron. →Non-metals want to attract electrons to become stable Electron Affinity ACROSS the Period →ACROSS THE PERIOD ELECTRON AFFINITY INCREASES greater effective nuclear charge, easily forms anions Other Trends Reactivity of Metals Video 1 Reactivity of Metals Video 2 Increasing reactivity METAL REACTIVITY Increasing reactivity NONMETAL REACTIVITY