1. Section 3: Periodic Trends
Trends among elements in the periodic table include their sizes and their abilities to lose or attract electrons. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions
What are the period and group trends of different properties?
How are period and group trends in atomic radii related to electron configuration?
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Periodic Trends

3. Vocabulary Review New principal energy level ion ionization energy
octet rule
electronegativity
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Periodic Trends

4. Atomic Radius
Atomic size is a periodic trend influenced by electron configuration.
For metals, atomic radius is half the distance between adjacent nuclei in a crystal of the element.
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Periodic Trends

5. Atomic Radius
For elements that occur as molecules, the atomic radius is half the distance between nuclei of identical atoms that are chemically bonded together.
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Periodic Trends

6. Atomic Radius
Atomic radius generally decreases from left to right, caused by increasing positive charge in the nucleus.
Valence electrons are not shielded from the increasing nuclear charge because no additional electrons come between the nucleus and the valence electrons.
Atomic radius generally increases as you move down a group.
The outermost orbital size increases down a group, making the atom larger.
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Periodic Trends

7. Atomic Radius
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Periodic Trends

8. Atomic Radius Animation Periodic Trends
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9. Interpret Trends in Atomic Radii
Use with Example Problem 2.
Problem
Which has the largest atomic radius: carbon (C), fluorine (F), beryllium (Be), or lithium (Li)? Answer without referring to Figure 11 (slide 7). Explain your answer in terms of trends in atomic radii.
SOLVE FOR THE UNKNOWN
Determine the periods.
From the periodic table, all the elements are found to be in period 2.
Apply the trend of decreasing radii across a period.
Ordering the elements from left-to-right across the period yields: Li, Be, C, and F.
The first element in period 2, lithium, has the largest radius.
Response
ANALYZE THE PROBLEM
You are given four elements. First, determine the groups and periods the elements occupy. Then apply the general trends in atomic radii to determine which has the largest atomic radius.
EVALUATE THE ANSWER
The period trend in atomic radii has been correctly applied. Checking radii values in Figure 11 (slide 7) verifies the answer.
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Periodic Trends

10. Ionic Radius
An ion is an atom or bonded group of atoms with a positive or negative charge.
When atoms lose electrons and form positively charged ions, they always become smaller for two reasons:
The loss of a valence electron can leave an empty outer orbital, resulting in a smaller radius.
Electrostatic repulsion decreases allowing the electrons to be pulled closer to the nucleus.
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Periodic Trends

11. Ionic Radius
When atoms gain electrons, they can become larger, because the addition of an electron increases electrostatic repulsion.
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Periodic Trends

12. Ionic Radius
The ionic radii of positive ions generally decrease from left to right.
The ionic radii of negative ions generally decrease from left to right, beginning with group 15 or 16.
Both positive and negative ions increase in size moving down a group.
Periodic Trends
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13. Ionic Radius
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Periodic Trends

14. Ionization Energy
Ionization energy is defined as the energy required to remove an electron from a gaseous atom.
The energy required to remove the first electron is called the first ionization energy.
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Periodic Trends

15. Ionization Energy
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Periodic Trends

16. Ionization Energy
Removing the second electron requires more energy, and is called the second ionization energy.
Each successive ionization requires more energy, but it is not a steady increase.
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Periodic Trends

17. Ionization Energy
First ionization energy increases from left to right across a period.
First ionization energy decreases down a group because atomic size increases and less energy is required to remove an electron farther from the nucleus.
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Periodic Trends

18. Ionization Energy
The ionization at which the large increase in energy occurs is related to the number of valence electrons.
The octet rule states that atoms tend to gain, lose or share electrons in order to acquire a full set of eight valence electrons.
The octet rule is useful for predicting what types of ions an element is likely to form.
Periodic Trends
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19. Electronegativity
The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond.
Electronegativity decreases down a group and increases left to right across a period.
Periodic Trends
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20. Trends in Electronegativity
Animation
Periodic Trends
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21. Review Essential Questions Vocabulary
What are the period and group trends of different properties?
How are period and group trends in atomic radii related to electron configuration?
Vocabulary
ion
ionization energy
octet rule
electronegativity
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Periodic Trends