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Organizing the Elements
THE PERIODIC TABLE
Organizing the Elements
 Copper, Silver, and Gold
 1700, 13 elements have been identified
 Rate of discovery increased..why?
 1765-1775
 Including hydrogen, nitrogen, and oxygen
Organizing the Elements
 Chemists used the properties of elements to
sort them into groups.
 Dobereiner (1780-1849)
 Elements were grouped into triads.
 Chlorine, Bromine, Iodine
Dobereiner’s Triads
 Chlorine, Bromine, Iodine
 Physically completely different.
 Chemically react similar: react easily with
metals.
Organizing the Elements
 1869-Mendeleev published his table of the
elements.
 More than 60 elements
 Mendeleev arranged the elements in his
periodic table in order of increasing atomic
mass.
Mendeleev’s Periodic Table
Organizing the Elements
 Based on chemical properties, arranging
elements according to atomic mass only
produced problems.
 Elements that should have been grouped
together weren’t, etc.
 Mendeleev organized his table before the
discover of protons and the assignment of
atomic numbers to all of the elements.
Organizing the Elements
 1913, Henry Moseley determined an atomic
number for each known element.
 In the modern periodic table, elements are
arranged in order of increasing atomic
number.
Modern Periodic Table
 7 periods
 Periods correspond to energy levels. Increase
as the period number increases.
 18 groups
 Elements within each group share similar
properties.
 Pattern changes from left to right.
Modern Periodic Table
 Periodic Law
 When elements are arranged in order of
increasing atomic number, there is a periodic
repetition of their physical and chemical
properties.
 Classes of elements: metals, nonmetals, and
metalloids.
Metals 80 %
 Sodium, iron, copper, any elements

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

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appearing in yellow.
Properties of metals:
Conductors of heat and electricity
High luster
Solid at room temp
Ductile
malleable
Metals
Nonmetals
Brittle
 Identified in blue (red)
 Neon, carbon, nitrogen, oxygen
 Greater variation in properties:
 Gases at room temperatures, few are solids
like sulfur and phosphorus, and one liquidbromine.
Metalloids
 Heavy stair step line separating metals and
nonmetals. Identified as green (blue).
 Metalloids have properties similar to metals
and nonmetals.
 Alter properties of metalloids by changing
the conditions of the metalloids.
 silicon
Classifying the Elements
Neon
Classifying by Group
 Group IA - Alkali Metals
 Group 2A – Alkaline Earth Metals
 Group 7A- Halogens (Nonmetals)
Classifying by Electron
Configurations
 Electrons play a key role in determining the
properties of elements.
 Place elements in groups by the number of
elements in the last orbital, or the number of
valence electrons.
 Noble Gases, Representative Elements,
transition metals, and inner transmission
elements.
Electron Configuration
1A
8A
2A
3A 4A
5A 6A 7A
Noble Gases
Group 8A
 Inert Gases
 8 electrons in last orbit
 Helium, neon, argon, etc
Representative Elements
 1A-7A
 Wide range of physical and chemical
properties
 Last orbital of electron cloud is not filled
Transition Elements
 Group B
 Transition Metals- presence of electrons in d orbitals
 Displayed in the main body of the periodic table:
copper, silver, gold, and iron
 Inner transition metals- presence of electrons in f
orbitals
 AKA: rare earth elements
Electron Orbitals
Electron Sub-orbitals
Energy Levels
Classify by Energy Level
 Noble Gases- Orbitals end in p, this will
always be filled. Helium (He) will end in s2
 Representative Element- orbitals end in s or
p, these orbitals will NOT be filled.
 Transition Elements-orbitals end with a
combination of unfilled d orbitals and s
orbitals.
Periodic Trends
 Trends in Size
 Atomic Radius-one half of distance between
the nuclei of two atoms of the same element
when the atoms are joined.
 Atomic size increases from top to bottom
within a group and decreases from left to
right across a period.
Atomic Size
Atomic Radius
Ions
 Atom or a group of atoms that have a positive
or negative charge
 Formed when electrons are transferred
between atoms
 Positive = cation, written as 1+
 Negative = anion, written as 1-
Sodium Ion
Trends in Ionization Energy
 Energy required to remove an electron from
an atom
 Decreases from top to bottom within a
group, and increases from left to right across
a period.
Trends in Ionization Energy
Trends in Ionic Size