Unit 9 Chemistry Langley THE PERIODIC TABLE Unit 9 Chemistry Langley *Corresponds to Chapter 6 in the Prentice Hall Chemistry Book

HISTORY PROBLEM By 1860, 60 elements had been discovered The element symbols, properties, and atomic numbers were published in a book Scientists wanted an easier system to organize the elements Since different chemists used different isotopes, all chemists had different masses recorded for the same element First International Congress of Chemists met in 1860 to set the atomic mass for all 60 elements and to set the properties of each element

DIMITRI MENDELEEV Russian chemist In the process of writing a book in 1860 Decided to include a way to organize the elements in his book Began by placing all of the element names on note cards and listing their properties underneath the name Started moving note cards around and organizing the elements by different properties When note cards were organized in increasing atomic MASS, noticed that other properties started appearing at regular intervals (Ex: every 8th element was unreactive, every 9th element reacted with water) Named his table periodic Periodic – repeating pattern

IODINE/TELLURIUM Find Iodine and Tellurium on the periodic table What do you notice about their mass? When I and Te are put in the correct order of mass, then their properties don’t fit with their columns Mendeleev decided that the mass must have been recorded wrong, so he put I and Te where they fit based on their properties instead of mass

BLANK SPACES Mendeleev left empty spaces in his table Empty spaces were for elements that he thought had not yet been discovered Based on where the empty spaces were, Mendeleev predicted what the mass of the elements and the properties of the undiscovered elements would be Correctly predicted these masses and properties for Sc, Ga, and Ge

HENRY MOSELEY British chemist Decided to fix the problems with Mendeleev’s table Rearranged elements according to atomic NUMBER Solved the Iodine/Tellurium problem Created periodic law Periodic law – the physical and chemical properties of the elements are a function of their atomic numbers (in simple terms: when elements are put in order of atomic number, then they fit into a certain column that has certain characteristics like reacts with water, etc)

FAMILIES OF ELEMENTS Groups/Families: Rows/Periods: Valence Electrons: Vertical columns on the periodic table, number from left to right Rows/Periods: Left to right on the periodic table, number from top to bottom The period number is also the energy level (ring) number Example: Na is on period 2, Na has 2 energy levels/rings Valence Electrons: Electrons on the outer energy level Every element is trying to get to either 0 or 8 valence electrons

GROUP 1-ALKALI METALS All have one valence electrons Only hydrogen is not classified as an alkali metal Characteristics of Alkali metals: React vigorously with non metals Most reactive of all METALS (because they only have 1 valence electron to get rid of and reach the magic number of 0) Too reactive to be found free in nature React violently with water Have a silvery appearance Soft enough to cut with a knife

GROUP 2-ALKALINE EARTH METALS All have 2 valence electrons Harder and denser than group 1 but not as reactive (they have 2 valence electrons to lose and get to 0) Still too reactive to be found free in nature Characteristics of Alkaline Earth: Many compounds in the Earth’s crust contain calcium Compounds in seawater contain magnesium

GROUPS 3-12-TRANSITION METALS Not as reactive as groups 1 and 2 Most have 2 valence electrons Characteristics of Transition Metals: Many are found free in nature (Au, Cu, Ag, Pd) Copper is used in wire because it is a good conductor of electricity Tungsten has the highest melting point of all metals that is why it is used as the filaments for light bulbs

P-BLOCK ELEMENTS Has 8 metals to the left of the zigzag line (Al, Ga, In, T, Sn, Pb, Bi, Po) Harder and denser than group 2 but less so than transition metals Most found in nature 8 metalloids on the zigzag line (B, Si, Ge, As, Sb, Te, Po, At) Properties of both metals and nonmetals Semi-conductors Brittle solids The rest are non-metals to the right of the zigzag line

GROUP 17-HALOGENS 7 valence electrons Most reactive of the NON-METALS (only need one electron to reach the magic number of 8) Fluorine is the most reactive of all elements When nonmetal combines with a metal, it produces a salt (Na + Cl  NaCl)

GROUP 18-NOBLE GASES 8 valence electrons Helium is the exception it only has 2 valence electrons and its magic numbers are 0 and 2 Least reactive of all elements (already have the magic number of 8 valence electrons) Full outer energy level so no need to form compounds

RARE EARTH METALS LANTHANOIDS ACTINOIDS Elements 58-71 2 valence electrons Shiny metals Not actually rare, most are readily available ACTINOIDS Elements 90-103, 2 valence electrons Elements 90-92 are naturally occurring Elements 93 – 103 are man-made (synthetic) Most are radioactive

VALENCE ELECTRONS Could always write out the noble gas configuration and find the valence electrons OR use this trick: Group 1 has 1 valence electron Group 2 has 2 Groups 3-12 have 2 Group 13 has 3 Group 14 has 4 Group 15 has 5 Group 16 has 6 Group 17 has 7 Group 18 has 8 Caution: this trick only tells you valence electrons, not TOTAL electrons

PERIODIC TRENDS Atomic Number: # of protons in the nucleus Increases across a period Increases down a group Atomic Radius: Size of an atom Decreases across a period

PERIODIC TRENDS Ionization Energy: Energy required to remove an electron from an atom Trends: Increases across a period Decreases down a group Electron Affinity: How badly an atom wants electrons

PERIODIC TRENDS Electronegativity: Ability of an atom to attract electrons Trends: Increases across a period Decreases down a group

PERIODIC TRENDS Using trends with groups of elements: Rank the following elements from smallest (1) to largest (4) in terms of atomic size: Be, He, Ca, Au. Step One: Find all 4 elements on the periodic table and place your finger on each one. Step Two: Move from left to right across the periodic table using the trend for atomic size (decreases across). You only have to use the trend for up and down if you get to a point where you have 2 elements that are in the same column. Step Three: Rank the elements from 1 to 4 as you move across the table.

PERIODIC TRENDS Example 2: Rank N, O, S, and C from smallest (1) to largest (4) in terms of electron affinity.