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

2. 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

3. 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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)

13. 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

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

15. 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

16. 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

17. 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

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

19. 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.

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