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The Periodic Law
The Periodic Law states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements.
What is a periodic trend?
Periodic trend… properties of the elements change in a
predictable way as you move through the periodic table
Atomic Radius
The textbook definition is:
Atomic radius is the distance from the center of an atom’s nucleus to its outermost electron.
I will show you a visual of the property.
Atomic Radius
Do you have an atomic radius graph?If you turned yours in, does someone near you have a graph that you can look at?
Atomic Radius
What is the trend for the atomic radius going down a group?
Do the data points generally show an increasing pattern or a decreasing pattern?
Atomic Radius
When you look at the atomic radius graphs, what is the trend for atomic radius across a period?
Do the data points generally show an increasing pattern or a decreasing pattern?
Atomic radius
• Atoms get smaller moving from the left to the right across each period
• Why?
• Going from the left to the right across a period, the atom’s outer electrons are increasingly attracted to the nucleus because they stay within the same principal energy level.
Trend for atomic radius
• Atoms get larger going down a group
• Why?
• As you move down a group, the principal quantum number of the outermost electrons increases
Atomic Radius – Think of a Snowman
http://www.shodor.org/chemviz/ionization/students/background.html
Ionization Energy (IE) Ionization energy this is the energy needed to remove one
of the atom’s outermost electrons.
Chemical Equation:
Li (g) ---> Li+ (g) + e–
IE = 8.64 X 10-19 J/atom
I will show you a visual of the property.
Ionization Energy
When you look at the ionization energy graph, what is the trend for ionization energy across a period?
Do the data points generally show an increasing pattern or a decreasing pattern?
Trend for IE
IE’s increase as you move from the left to the right across a period.• Why?
• The valence shell fills moving across a period, so the number of electrons gets closer to a full valence shell of 8 electrons. It becomes harder and harder to remove an electron as the valence shell fills.
Ionization Energy
What is the trend for ionization energy as you move down a group?
Do the data points generally show an increasing pattern or a decreasing pattern?
Trend for IE
IE’s decrease as you move down a group• Why?
• The principal energy level increases moving down a group, so the outermost electrons are farther away from the pull of the nucleus.
Successive IE’s
The energy required to remove a second electron from an atom is called its second IE, and so on…
Ionization Energy
Do you think that it takes more or less energy to remove a second or third electron?
Take a look at the Ionization Energy graph with both first and second ionization energies plotted to answer this question.
Electronegativity
An atom’s electronegativity reflects its ability to attract electrons in a chemical bond.• It is NOT an amount of energy
• It is NOT a property of an atom that can be directly measured
Electronegativity
The highest electronegativity values are located in the upper-right hand corner of the periodic table• Fluorine has the highest electronegativity
value of 4.0
The lowest electronegativity values are located in the lower-left hand corner of the periodic table
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