Periodic Law
Chemistry I
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Group IA
alkali metals
Group IIA
alkaline earth
Metals
Group IIIB-IIB
transition metals
Inner Transition
Metals
Lanthanide Series - also called the rare earth elements.
Actinide Series
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Group VIIIA
noble gases
or inert gases
Group VIIA halogens
Bright Green nonmetals
Purple metalloids or
semiconductors
Light Blue - other
metals
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The Periodic Law states that “The physical and
chemical properties of the elements are
periodic functions of their atomic numbers.
1. the properties of the elements go through a
pattern of change
2. elements of similar properties occur at certain
intervals, provided the elements are arranged
in a periodic table in order of increasing
atomic number.
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Periodic Chart in Block Form
http://www.gordonengland.co.uk/elements/blo
cks.htm
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Periodic Trends
Atomic Radius – ½ the distance between 2
adjacent nucleii in the crystalline forms of
elements and/or in the molecules of gaseous
elements.
Pattern of radius increase is as follows:
Top to Bottom
Right to left
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Periodic Trends of Ionic Radii
• Ionic radii are formed by the loss of electrons forming
positive ions (cations) or by the gain of electrons
forming negative ions (anions). Metals usually form
cations which, due to the loss of electrons are smaller
than the atomic radius from which they were derived.
Nonmetals usually form anions which, due to the gain
of electrons, are larger than the atomic radius from
which they were derived.
• Radii increase from top to bottom
• Radii increase from right to left
• See chart on next frame.
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Source: http://picsicio.us/image/5e6a3797/
Ionization Energy
• The amount of energy needed to remove an
electron from an atom. Low ionization energy is
characteristic of metals and high ionization
energy is characteristic of nonmetals. For any
given atom, the ionization potential increases as
successive electrons are removed.
• Within groups, 1st ionization potential increases
with decreasing atomic number – Bottom to Top.
• Within periods, 1st ionization potential decreases
with increasing atomic number – Left to Right
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http://www.grandinetti.org/Teaching/Chem121/Lectures/IonizationEnergy/index.html
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Electron Affinity
• The energy change that is required for a
neutral atom to acquire an electron.
• Negative electron affinities indicate that
energy is emitted when an electron is
accepted indicating an exothermic reaction.
• Positive electron affinities indicate that energy
is absorbed when an electronic is accepted
indicating an endothermic reaction.
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Electron Affinity Patterns
• Within a family of light, active elements,
electron affinity tends to increase with
decreasing atomic number – BOTTOM TO TOP.
• Within a family of transition or rare earth
metals, electron affinity tends to increase with
increasing atomic number – TOP TO BOTTOM.
• Within a given period of elements, electron
affinity tends to increase with increasing
atomic number – LEFT TO RIGHT.
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Source: http://www.grandinetti.org/Teaching/Chem121/Lectures/ElectronAffinity/index.html
High
Affinity
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Electronegativity
• Electronegativity is a measure of the tendency
of an atom to attract a bonding pair of
electrons.
Fluorine has the highest electronegativity (4
on the Pauling scale).
Cesium and Francium are only 0.7.
We will discuss electronegativity later when
we discuss bonding types.
Source:
http://www.chemguide.co.uk/atoms/bonding/electroneg.html
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Periodic Trends of Valence Electrons
• Valence Electrons – found in the outermost
energy level of an atoms that can be transferred
or shared with other atoms.
• Within a given group, the number of valence
electrons tend not to vary from one element to
the next. (Same # of valence e’s in a group.)
• Within a given period, the number of valence e’s
increase with increasing at. number – LEFT TO
RIGHT. Note “d” & “f” block elements have only 2
valence electrons.
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Source: http://www.chemprofessor.com/periodicqm_files/image005.gif
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Chemical Activity is dependent on:
1. Size of atom or ion 2. Ionization potential
3. Electron affinity
4. # of valence electrons
• Most active metal: Francium (lower left) which
has a large atom/ionic radius, low ionization
potential, low electron affinity, & has the least
number of valence electrons.
• Most active nonmetal: Fluorine (upper right)
which has a small atomic/ionic radius, high
ionization potential, high electron affinity; &
greatest number of valence electrons without
achieving the stable octet of the noble gases.
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Ions – charged particles
• Ions form when a neutral atom loses or gains
electrons. Atoms become more stable (full
outer shell) when they form ions.
• Losing yields a positive ion called a cation.
• Gaining yields a negative ion called an anion.
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A Sodium ion has
11 protons
+11 charge
12 neutrons
0 charge
10 electrons
-10 charge
Total charge
+1
A cation!!
A Chlorine ion has
17 protons
+17 charge
18 neutrons
0 charge
18 electrons
-18 charge
Total charge
-1
An anion!!
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Source: http://www.grandinetti.org/Teaching/Chem121/Lectures/ElectronAffinity/index.html
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Source: http://www.grandinetti.org/Teaching/Chem121/Lectures/ElectronAffinity/index.html
Affinity
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