Transcript The Periodic Table
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 8 th 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 Group 1 Group 2 Group 3-12 Group 17 Group 18 Number Valence Electrons 1 2 Varies 7 8 ( except He – has 2 ) Name of Family Alkali Metals Alkaline-Earth Metals Transition Metals Halogens 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