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
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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:
 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 3-12TRANSITION 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
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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:
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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
 Trends:
 Increases across a period
 Increases down a group
 Atomic Radius: Size of an atom
 Trends:
 Decreases across a period
 Increases down a group
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
 Trends:
 Increases across a period
 Decreases down a group
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.