Chapter 6 The Periodic Table

History of the Periodic Table In the early 1700s, only 13 elements were known (gold, silver, copper, other common metals) By 1829, significantly more elements had been found 1829 – Johann Doberiner used triads to sort similar elements

History of the Periodic Table 1869 - Dimitri Mendeleev “Father of the Periodic Table” -Made the first accepted Periodic Table -Noticed trends and left empty spaces for “missing” elements -Sorted elements by atomic mass

Mendeleev’s Periodic Table Arranging the elements this way created gaps in his periodic table How did Mendeleev arrange the elements in his periodic table?

Try predicting the names and masses of the unknown elements Sc 45.0 Ga 69.7 Ge 72.6 Tc 97.9 Hf 178.5 Re 186.2 Po 209 At 210

Henry Moseley 1913 – Found a method to determine atomic number (# of protons). --Rearranged the PT so elements were arranged by increasing atomic number

Modern Periodic Table The Modern Periodic Table is arranged by atomic numbers so elements with similar properties fall in the same columns Periodic Law- Properties of elements are based on atomic number and valence electrons

Periods – 1-7, run across the periodic table Organization of the Periodic Table Periods – 1-7, run across the periodic table

Groups – 1-18, run vertically (up and down) in the periodic table Organization of the Periodic Table Groups – 1-18, run vertically (up and down) in the periodic table

Classes of Elements 3 Classes Metals – located on left of PT Nonmetals – Located on right of PT Metalloids – Located along the “staircase”

Metals

Properties of Metals Good conductors Luster (shiny) Solid at room temperature Ductile (can be drawn into wires) Malleable (can be hammered into sheets) Magnetic Form alloys High density Lose electrons (form cations)

Nonmetals Brittle Non­conductors dull

Properties of Nonmetals Poor conductors (nonconductors) Dull (not shiny) Most are Liquid or gas at room temperature Brittle Low density Gain electrons (form anions)

Metalloids Properties of both metals and nonmetals

Properties of Metalloids Semi conductors Dull (not shiny) Solids at room temperature Used in computers Have a mixture of metallic and nonmetallic properties

Some elements that are as gases at room temperature cannot exist as a single atom, but must exist as a diatomic molecule. N2, H2, O2, Cl2, F2 Copy these diatomic elements

A Look at the Bohr Model for electron configurations 1913- Niels Bohr - Young Danish physicist who developed a new atomic model - Changed Rutherford’s model to include energy levels for electrons - Proposed that an electron is found only in specific circular paths (or orbits) around the nucleus - Known as the “planetary model”

A Look at the Bohr Model for electron configurations Valence Electrons – Electrons in the outer “shell” 8e- 8e- 2e- Octet Rule – an atom is most stable when it has 8 electrons in its outer (valence) shell. It will gain or lose electrons to reach an octet. “2 will do but 8 is great”

Let’s draw some examples:

Energy Levels (rings) and the PT Energy levels correspond to periods or rows on the periodic table

Families of the Periodic Table (Groups) Group 1: Alkali metals Group 2: Alkali Earth Metals Groups 3-12: Transition Metals Group 17: Halogens Group 18: Noble Gases Inner Transition Metals – “cut out” below periodic table

Families on the Periodic Table -Group 1 = Alkali Metals Soft Extremely reactive (but…Hydrogen is NOT a metal) 1 valence electron Form an ion with +1 charge Video

Families on the Periodic Table Group 2 = Alkali-Earth Metals Not as soft as Group 1, but still somewhat soft Reactive, but less than Group 1 2 valence electrons Form ion with +2 charge Video

Families on the Periodic Table -Groups 13-18 = Properties vary greatly (due to “steps”) Valence Electrons= Group # - 10 May form cation or anion (depending on group) Example: Group 18 – 10 = 8 valence electrons

Families on the Periodic Table -Group 17 = Halogens Very reactive 7 valence electrons Form ion with -1 charge

Families on the Periodic Table -Group 18 = Noble Gases Very unreactive Many used in creating signs When gas is heated it glows 8 valence electrons They have a stable (full) valence octet

Blocks on the Periodic Table Groups 3-12 = Transition Metals Luster, conductive, Malleable, Ductile Hg is the ONLY liquid metal examples:

Blocks on the Periodic Table Lanthanides Actinides INNER Transition metals Formerly called Rare Earth Metals, then changed to Lanthanides and Actinides. Now called Inner Transition Metals “Cut Out” located below the Periodic Table