The Periodic Table

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The Periodic Table
Section 1 - Organizing the Elements
Section 2 - Exploring the Periodic Table
Section 3 - Families of Elements
State Standards
• CLE 3202.1.3 Characterize and classify
elements based on their atomic structure
• CLE 3202.Inq.1 Recognize that science is a
progressive endeavor that reevaluates and
extends what is already accepted
• CLE 3202.Inq.6 Communicate and defend
scientific findings
1 - Organizing The Elements
• KEY QUESTIONS :
• How did Mendeleev arrange the elements in his
periodic table?
• How are elements arranged in the modern
periodic table?
Mendeleev - Recognizing Patterns
• By 1860, 60+ elements were known
• Dmitri Mendeleev, Russian Chemist, studied
properties of the elements
• 1869 : he published first Periodic Table of Elements
• Arranged by rows of increasing mass number
• If chemical properties repeated, new row started
– EXAMPLE : Lithium and Sodium are very reactive
– Gold and Silver have similar properties, same column
Predicting New Elements
• Gaps existed in his table -
?
• Predicted the properties of Germanium
– Description close to what was later found to be Ge
• He was the first to use table to predict
• Work in Progress – Some predictions did not fit
– Te and I fit better in a an inconsistent way
– i.e, where the mass number decreased from left - right
Changing the Arrangement
• Mendeleev’s Periodic Table has been improved
– Henry Moseley, ~ 1910
– Elements arranged by atomic number
• Resolved problems such as at Tellurium – Iodine
– Te has larger average mass, I has 1 more proton
– They fit in rows/columns BETTER THAT WAY
Mendeleev’s Competition
• John Newlands, 1865, Law of Octaves
– Every 8th element will mimic each other in The Table
• Ordered by Atomic Weights (YET ANOTHER ‘MASS’)
• Ridiculed and DISS’ED ( dismissed by peers )
Periodic Law
• Metallic properties decrease across PERIODS
– Other properties such as reactivity and conductivity
• GROUPS have similar properties
• Groups – Columns
• Periods - Rows
• Elements with similar properties appear at
regular intervals – The Periodic Law
Let’s Describe Some Elements!!
• The chemical symbol, C, stands for carbon, which
has an atomic number of 6 and an atomic mass
[ OR, MASS NUMBER ] of 12.01
– Which value is an average ( average of what? )
– Which value also represents molar mass?
• Your turn!!
Let’s Describe Some Elements!!
• The chemical symbol, C, stands for carbon, which
has an atomic number of 6 and an atomic mass
[ OR, MASS NUMBER ] of 12.01
• KEY QUESTIONS :
• How did Mendeleev arrange the elements in his
periodic table?
• How are elements arranged in the MODERN
periodic table?
2 –Exploring the Periodic Table
• KEY QUESTIONS :
• Why do elements within a group of the Periodic
Table have similar chemical properties?
• What happens to an atom that gains or loses
electrons?
• What are the three main categories of elements?
Role of Electrons
• How many electrons in a neutral atom?
• Trends in PT are result of electron arrangement
• Valence electrons account for similar properties
– Example: Lithium and Sodium
• Element’s location related to electron arrangement
Ion Formation
• What is an “ion”?
• Once an atom gains/loses electrons, it no longer
has a balance between protons/electrons
– Charges don’t cancel  atom has net electric charge
• What is easier – GAIN or LOSE electrons?
– Group 1 elements form positive ions ( CATIONS )
– Group 17 elements form negative ions ( ANIONS )
Classifying Elements
• Elements in each category have similar properties
• Metals
• Nonmetals
• Semiconductors
2 –Exploring the Periodic Table
• KEY QUESTIONS :
• Why do elements within a group of the Periodic
Table have similar chemical properties?
• What happens to an atom that gains or loses
electrons?
• What are the three main categories of elements?
3 –Families of Elements
• KEY QUESTIONS :
• What does each element family have in common?
• What are the families of metals?
• What are some non-metal families?
• What are semiconductors
Let’s Classify Elements Further
• Relate GROUPS of elements to “family”
• Elements in family have same # valence electrons
• ONLY elements ( not compounds ) are in a family
Group Number
Number Valence Electrons
Name of Family
Group 1
1
Alkali Metals
Group 2
2
Alkaline-Earth Metals
Group 3-12
Varies
Transition Metals
Group 17
7
Halogens
Group 18
8 ( except He – has 2 )
Noble Gases
Metals
• INCLUDE: Alkali, Alkaline-Earth, and Transition
• Alkali metals are very reactive ( Li and Na )
• Alkaline-Earth metals also fairly reactive
– Form compounds found in human body/limestone
– More solid than Group 1
– Means: harder, denser, higher melting temperature
• Transition metals – less reactive than Group 1-2
– Typically more solid than Group 1-2
Transition Metals
• Very good catalysts
– Catalyst : speeds a reaction up / is not reacted
• H2 and O2 explode in presence of Pt catalyst
• Some synthetic elements
• Technetium and Promethium
• Radioactive (nuclei decays into smaller atoms)
• Atomic Number > 92 : elements are SYNTHETIC
Nonmetals
• Families include Noble Gases and Halogens
• NOBLE GASES: Group 18 ( Ne, Ar, He )
• HALOGENS: Group 17 ( Cl, F, Br )
– Combine easily with metals to form SALTS
• Nonmetals/compounds plentiful on Earth
• Carbon – backbone of life ( organic compounds )
– C forms many other compounds
Semiconductors
• Also called metalloids
– B, Si, Ge, As, Sb, Te
• Able to CONDUCT heat and electricity
– BUT only under certain conditions
– Silicon ( Si ) is found everywhere!!
– Boron ( B ) used in steel and glass
Hydrogen
• Hydrogen is in a class by itself
• 1 proton and 1 electron
– Reacts with many other elements
• Most abundant element in universe
– 3 out of every 4 atoms in universe are H
3 –Families of Elements
• KEY QUESTIONS :
• What does each element family have in common?
• What are the families of metals?
• What are some non-metal families?
• What are semiconductors

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