Chapter 5: The Periodic Table PEPS Rainier Jr/Sr High School Mr. Taylor
Section 1: Organizing the Elements Russian chemist Dmitri Mendeleev in the 1860’s knew about 60 elements and their atomic masses. When he placed these elements in order by atomic mass he saw that chemical properties repeated at regular intervals (periodic repetition).
Section 1: Organizing the Elements Mendeleev’s table had gaps in it but he predicted the properties of these “gap” elements Predictions were close when these elements were discovered.
Section 1: Organizing the Elements A few elements did not fit the pattern Henry Moseley (English chemist) rearranged the elements by atomic number; problem solved. The Periodic Law : when arranged by increasing atomic number, elements have similar chemical properties that repeat at regular intervals (periods).
Section 1: Organizing the Elements Chemical symbol Chemical name
Section 1: Organizing the Elements The rows are called periods Elements become less metallic from left to right The columns are called groups. Each column (group) has similar chemical properties
Section 2: Exploring the Periodic Table The periodic repetition of chemical properties is the result of the arrangement of electrons in the outer energy level (valence electrons). Variations in physical properties are due to different atomic numbers (protons).
Section 2: Exploring the Periodic Table Elements are place in; Rows by the number of electron energy levels Columns by the number of electrons in the outer energy level (valence electrons).
Section 2: Exploring the Periodic Table Ion Formation Atoms may gain or lose electrons to form ions Ions are charged particles because they do not have the same number of protons and electrons (unbalanced charges).
Section 2: Exploring the Periodic Table Ion Formation Atoms gain or lose electrons to achieve a full outer energy level. Group 1; loses an electron easily, has a positive charge (cation). Group 17; gain an electron easily, has a negative charge (anion)
Section 2: Exploring the Periodic Table Metals vs non-metals Metals are Shiny solids (mostly) Malleable (able to be hammered into shapes) Ductile (can be stretched into wires) Conductors of electricity and heat
Section 2: Exploring the Periodic Table Metals vs non-metals Non-metals are Solids, liquids, or gases at room temp. Often dull and brittle Poor conductors of heat and electricity (insulators)
Section 2: Exploring the Periodic Table Metals vs non-metals Semiconductors Have some properties of metals and non-metals Are used in computer chips
Section 3: Families of Elements Elements of a family have the same number of valence electrons Metals: left side of table Non-metals: right side of table
Section 3: Families of Elements Alkali metals: Group 1 One valence electron Form an ion with a 1+ charge HIGHLY reactive Never found in Nature except combined with another element in a compound
Section 3: Families of Elements Alkaline Earth metals: Group 2 2 valence electrons Form a 2+ ion Very reactive, but less than Group 1
Section 3: Families of Elements Transition Metals Number of valence electrons varies Some are reactive (iron), some are not (Gold) Many metals we use everyday are in this group (Iron, gold, aluminum, copper).
Section 3: Families of Elements Noble gases: Group 18 Full outer valence electron energy level Non-reactive gases do not usually form compounds or molecules.
Section 3: Families of Elements Halogens: Group 17 7 electrons in outer energy level (almost full). Gain 1 electron easily to fill the level; 1- charge VERY reactive; combine easily with metals to form a salt (NaCl, KCl, SnF 2 ).
Section 3: Families of Elements Other non-metals Oxygen and Nitrogen are the most abundant gases in the atmosphere. Carbon compounds form the basis of most of the molecules in living organisms.
Section 3: Families of Elements Semiconductors Also called metalloids Silicon makes up 28% of the matter in the Earth’s crust Sand is mostly silicon dioxide.