Chemistry Chapter 5 The Periodic Law Mendeleevs Periodic Table Dmitri Mendeleev.
Chapter 5 The Periodic Law
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Transcript of Chapter 5 The Periodic Law
Chapter 5The Periodic Law
Patterns of the Periodic Table
Section 1
History of the Periodic Table
History
Atomic masses standardized in 1860
Mendeleev organized all known elements according to atomic mass and chemical and physical properties
History
Medeleev noticed a trend in physical/chemical properties
Trends were “periodic” which means there is a repeating pattern
History
Mendeleev left several empty spaces
Predicted that some elements were not discovered yet.
Scandium, Gallium, and Germanium
History
Mendeleev arranged elements by atomic mass
In 1911, Henry Moseley arranged elements by nuclear charge (proton or atomic number)
History
Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.
patterns repeat according to atomic number
Modern Periodic Table
About 40 more elements have been discovered or created since Mendeleev’s time
Noble Gases
Discovered in 1894 by Lord Rayleigh and Sir William Ramsay (Argon)
Very difficult to discover since they are not reactive (inert)
Helium was discovered to exist on the Sun in 1865, but thought not to exist on Earth. (discovered in 1895)
Noble Gases
Ramsay made a new group for Helium and Argon
1898 Ramsay discovered Krypton and Xenon
Radon discovered two years later by Dorn
S block elements Group 1 and 2
Highly reactive elements Usually found bonded to other
elements in nature (compounds)
Group 1 elements
Known as the alkali metals All have an ns1 outer electron
configuration Hydrogen, Lithium, Sodium,
Potassium, Rubidium, Cesium, Francium
Group 2 elements
Known as the alkaline earth metals ns2 valence electron configuration Less reactive than Group 1
elements Beryllium, Magnesium, Calcium,
Strontium, Barium, and Radium
Hydrogen and Helium
Exceptions Hydrogen’s properties do not
resemble the alkali metals (behaves like a metal under extremely high pressures)
Helium’s E.C. is 1s2, but it doesn’t act like a Group 2 (acts like noble gas)
The d-Block ElementsGroups 3-12
Known as transition metals Less reactive than alkali
metals/alkaline earth metals Some exist as free elements in
nature Palladium platinum and gold
P-Block ElementsGroups 13-18
Properties vary greatly Includes metals, metalloids, and
nonmetals Valence electrons are equal to
group number minus 10
Halogens
Group 17 elements Fluorine, Chlorine, Bromine, Iodine,
and Astatine valence configuration is ns2 np5
Most reactive non metals React vigorously with metals
F-block ElementsLanthanides and Actinides
Shiny metals Most are radioactive Elements above atomic number 92
(Uranium) are man made
Periodic Trends
Periodic Law
When elements are arranged in order of increasing atomic #, elements with similar properties appear at regular intervals.
Chemical Reactivity
Families Similar valence e- within a group
result in similar chemical properties
Chemical Reactivity Alkali Metals Alkaline Earth
Metals Transition Metals Halogens Noble Gases
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Atomic Radius Atomic Radius
Li
ArNe
KNa
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Atomic Radius Increases to the LEFT and DOWN
D. Atomic Radius
Why larger going down? Higher energy levels have larger orbitals Shielding - core e- block the attraction
between the nucleus and the valence e-
Why smaller to the right? Increased nuclear charge without additional
shielding pulls e- in tighter
D. Atomic Radius
First Ionization EnergyE. Ionization Energy
KNaLi
Ar
NeHe
First Ionization Energy Increases UP and to the RIGHT
E. Ionization Energy
Why opposite of atomic radius? In small atoms, e- are close to the nucleus where
the attraction is stronger
E. Ionization Energy
Successive Ionization Energies
Mg 1st I.E. 736 kJ
2nd I.E. 1,445 kJCore e- 3rd I.E. 7,730 kJ
Large jump in I.E. occurs when a CORE e- is removed.
E. Ionization Energy
Al 1st I.E. 577 kJ
2nd I.E. 1,815 kJ
3rd I.E. 2,740 kJCore e- 4th I.E.11,600 kJ
Successive Ionization Energies Large jump in I.E. occurs when a
CORE e- is removed.
E. Ionization Energy
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Which atom has the larger radius?
Be or Ba
Ca or Br
Ba
Ca
Examples
Which atom has the higher 1st I.E.?
N or Bi
Ba or Ne
N
Ne
Examples
Which particle has the larger radius?S or S2-
Al or Al3+
S2-
Al
Examples
Electron Affinity
Neutral atoms can also acquire electrons.
The energy change that occurs when an electron is acquired by a neutral atom is call the atoms electron affinity.
Electron affinity
Trend EA increases left to right EA decreases going down
Electronegativity
Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound.
Electronegativity
Tend to increase across each period (left to right)
Tend to decrease going down