Periodic Law

History of the Periodic Table 1750 only 17 elements had been discovered 1789: Antoine Lavoisier (about 30) Grouped known elements into four categories Metals, earths, nonmetals, gases 1860 More than 60 elements

Mendeleev and the Periodic Table If elements are arranged in atomic mass order, similarities in chemical properties appeared at regular intervals (were periodic) He left empty spaces for undiscovered elements, which were later found

What does periodic mean?

1869: Dmitri Mendeleev Published first periodic table Discrepancies existed Lothar Meyer published similar table in 1870. Arranged by atomic volume.

1911: Henry Moseley Confirmed Mendeleev’s work with one important change Ordered elements by properties and atomic number Periodic Law: the physical and chemical properties of the elements are periodic functions of their atomic numbers Used spectral analysis. Found that elements fit into the patterns better if arranged by nuclear charge.

Periodic Table An arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column.

Modern Periodic Table Presently, 118 elements listed, although not all of them have been confirmed

Sections to know: Metals, nonmetals, metalloids

Periods on the Periodic Table Horizontal rows Called periods or series Numbered 1, 2, 3, …. Include representative elements and transition elements

Periods on the Periodic Table 1 2 3 4 5 6 7

Groups or Families Vertical columns Similar chemical properties

Representative Groups on the Periodic Table 1 2 13 14 15 16 17 18

Representative Groups Group 1: Alkali Metals Not hydrogen Silvery appearance, very soft, very reactive Group 2: Alkaline Earth Metals Harder and stronger Very reactive Groups 1 & 2 never found in nature as free elements

Group 17: Halogens Group 18: Noble Gases Most reactive nonmetals Colorless, odorless gases Very nonreactive

Location of Some Groups 1 2 13 14 15 16 17 18 A l m k e a t l a i l s A l k a i n e H a l o g e n s I G n a e s r e t s

Learning Check E3 A. Element in Group 17, Period 4 1) Br 2) Cl 3) Mn B. Element in Group 2, Period 3 1) beryllium 2) magnesium 3) boron

Solution E3 A. Element in Group 17, period 4 1) Br B. Element in Group 2, Period 3 2) magnesium

Learning Check E5 Specify metal (1) or nonmetal (2) for each: A. sulfur ____ B. chlorine ____ C. sodium ____ D. iron ____ E. Carbon ____ F. silver ____

Solution E5 Specify metal (1) or nonmetal (2) for each: A. sulfur __2__ B. chlorine __2__ C. Sodium __1__ D. iron __1__ E. Carbon __2__ F. silver __1__

Learning Check E6 Select the correct elements: A. Metals in Group 14 1) Ge, Sn, Pb 2) C, Si 3) C, Si, Ge, Sn B. Nonmetals in Group 15 1) As, Sb, Bi 2) N, P, As 3) N, P, As, Sb

Solution E6 A. Metals in Group 14 1) Ge, Sn, Pb B. Nonmetals in Group 15 2) N, P, As

Other classifications Transition metals B Group Lanthanides Actinides

Actual arrangement Lanthanides Transition Actinides

Periodicity The arrangement of the elements on the periodic table so that their chemical properties repeat at various intervals according to the periodic law Accounts for the shape of the table and the s, p, d, and f blocks

Using the Periodic Table for Electron Configurations Blocks contain elements with the same highest-energy sublevel.

The Periodic Table and Order of Fill

Periodic Trends Valence electrons participate in chemical reactions same group =same number of valence electrons very similar reactivities  can make generalizations Figure 7.25

Factors Affecting Change in Properties Some terms Valence: highest energy level electrons Kernel: Everything else in the atom Nucleus Inner level electrons

Factors Affecting Change in Properties As you move left right: Atomic number increases Greater positive charge in the nucleus

Factors Affecting Change in Properties Moving across a series of elements Lithium Boron Nitrogen [He] 2s1 [He] 2s2 2p1 [He] 2s2 2p3 kernel: 3p+ + 2e- 5p+ + 2e- 7p+ + 2e- net charge: +1 +3 +5

Factor #1 A greater net positive charge results in an increased attraction of electrons to the nucleus

Factors Affecting Change in Properties As you move down a column: Lithium Sodium Potassium [He] 2s1 [He]2s2p63s1 [He]2s22p6 3s23p64s1 Valence electrons are further from the nucleus.

Factor #2 More energy levels result in the outer electrons feeling less attraction to the nucleus (further away)

Factor #3 Shielding occurs: More inner shell electrons cause outer shell to be repulsed

Factor #4 There is a greater stability associated with half-filled and filled sublevels Electrons move closer together

Atomic Size Atomic size is often described in terms of atomic radius. Atomic radius is the distance from the center of the nucleus to the outer edge of the atom. Remember the four factors: Across a period, what happens? Down a group, what happens? Across: A greater net positive charge results in an increased attraction of electrons to the nucleus. Down: More energy levels result in the outer electrons being further away.

Trends in Atomic Size The general trend for atomic size (or radius) is for atomic size to increase from top to bottom and decrease from left to right.

Trends in Atomic Size

Ions An atom or group of bonded atoms that has a positive or negative charge A positive ion is called a cation A negative ion is called an anion

Electron configuration of ions Element Atom Ion Sodium Na 1s2 2s2 2p6 3s1 Na+ 1s2 2s2 2p6 Magnesium Mg 1s2 2s2 2p6 3s2 Mg+2 1s2 2s2 2p6 Fluorine F: 1s2 2s2 2p5 F- 1s2 2s2 2p6 Oxygen O: 1s2 2s2 2p4 O-2 1s2 2s2 2p6

Ionization Energy The energy required to remove one electron from a neutral atom of an element (How easy or hard it is to take a valence electron from a gaseous atom to form a gaseous ion) Results in an ion with a +1 charge Energy is required A + energy A+ + e-

Trends in Ionization Energy

Removing electrons from positive ions The energies for removing additional electrons from an atom are called: Second ionization energy Third ionization energy Fourth ionization energy IE’s become increasingly large as more electrons are removed

Greatest jump in energy occurs when an ion reaches a noble gas configuration Li+1 : 1s2 Be +2 : 1s2 B+3 : 1s+2

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Electron Affinity The energy change that occurs when an electron is acquired by a neutral atom Results in the formation of an ion with a -1 charge Energy is usually released A + e- A- + energy

Ionic Radii Forming a cation decreases the atomic radius Loss of highest energy level electrons Greater pull of the nucleus on fewer electrons Forming an anion increases the atomic radius No increase in nuclear charge Greater repulsion between electrons

Electronegativity The measure of the ability of an atom in a compound to attract bonding electrons to itself Scale developed by Linus Pauling Fluorine is the most electronegative atom, with a value of 4.0

Periodic Trend — Electronegativity

Periodic Trend — Ionization Energy Stability of ½ filled and filled sublevels

Periodic Trend — Electron Affinity Stability of ½ filled and filled sublevels