1. 6.3
6.3 - Periodic Trends
Trends in Atomic Size
What are the trends among the elements for atomic size?

2. 6.3
Trends in Atomic Size
The atomic radius is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined.
This diagram lists the atomic radii of seven nonmetals. An atomic radius is half the distance between the nuclei of two atoms of the same element when the atoms are joined.

3. Group and Periodic Trends in Atomic Size
6.3
Trends in Atomic Size
Group and Periodic Trends in Atomic Size
In general, atomic size increases from top to bottom within a group and decreases from left to right across a period.

4. 6.3
Trends in Atomic Size
This graph plots atomic radius versus atomic number for 55 elements. INTERPRETING GRAPHS a. Analyzing Data Which alkali metal has an atomic radius of 238 pm? b. Drawing Conclusions Based on the data for alkali metals and noble gases, how does atomic size change within a group? c. Predicting Is an atom of barium, atomic number 56, smaller or larger than an atom of cesium (Cs)?

5. 6.3
Trends in Atomic Size
The size of atoms tends to decrease from left to right across a period and increase from top to bottom within a group. Predicting If a halogen and an alkali metal are in the same period, which one will have the larger radius?

6. 6.3
Ions
Ions
How do ions form?

7. Ions
Positive and negative ions form when electrons are transferred between atoms.
When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes?
Na becomes a positive ion, Na+

8. Ions
Positive and negative ions form when electrons are transferred between atoms.
When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes?
Chlorine becomes a negative Chloride ion, Clˉ

9. A cation is an ion with a positive charge (+).
6.3
Ions
An ion is an atom or group of atoms that has a positive or negative charge due to an uneven number of protons and electrons.
A cation is an ion with a positive charge (+).
An anion is an ion with a negative charge (ˉ).

10. Anions are Negative

11. Trends in Ionization Energy
6.3
Trends in Ionization Energy
Trends in Ionization Energy
What are the trends among the elements for first ionization energy, ionic size, and electronegativity?

12. 6.3
The energy required to remove an electron from an atom is called ionization energy.
The energy required to remove the first electron from an atom is called the first ionization energy.
The energy required to remove an electron from an ion with a 1+ charge is called the second ionization energy.

13. 6.3
First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.

14. Trends in Ionization Energy
6.3
Trends in Ionization Energy

15. Trends in Ionization Energy
6.3
Trends in Ionization Energy

16. Trends in Ionization Energy
First ionization energy tends to increase from left to right across a period and decrease from top to bottom within a group. Predicting Which element would have the larger first ionization energy—an alkali metal in period 2 or an alkali metal in period 4?

17. 6.3
During reactions between metals and nonmetals, metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons. The transfer has a predictable effect on the size of the ions that form.

18. 6.3
Trends in Ionic Size
Cations are always smaller than the atoms from which they form. Anions are always larger than the atoms from which they form.

19. Relative Sizes of Some Atoms and Ions
6.3
Trends in Ionic Size
Relative Sizes of Some Atoms and Ions
This diagram compares the relative sizes of atoms and ions for selected alkali metals and halogens. The data are given in picometers. Comparing and Contrasting What happens to the radius when an atom forms a cation? When an atom forms an anion?

20. Trends in Ionic Size
The ionic radii for cations and anions decrease from left to right across periods and increase from top to bottom within groups.

21. Trends in Electronegativity
6.3
Trends in Electronegativity
Trends in Electronegativity
Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound.
In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.

22. The term electronegativity is defined as the attractive force on electrons caused by the nucleus. Electrons are negatively charged, and the nucleus is positively charged; therefore, opposites attract.

23. Electronegativity is the atomic tug o’ war – whichever element has a higher electron affinity and ionization energy will also have a higher electronegativity

24. Trends in Electronegativity
6.3
Trends in Electronegativity
Representative Elements in Groups 1A through 7A

25. Summary of Trends What is the underlying cause of periodic trends? 6.3

26. 6.3
The trends that exist among these properties can be explained by variations in atomic structure, such as effective nuclear charge and electron shielding.

27. 1. Which of the following sequences is correct for atomic size?
6.3 Section Quiz
1. Which of the following sequences is correct for atomic size?
Mg > Al > S
Li > Na > K
F > N > B
F > Cl > Br

28. gain electrons to form cations. gain electrons to form anions.
6.3 Section Quiz
2. Metals tend to
gain electrons to form cations.
gain electrons to form anions.
lose electrons to form anions.
lose electrons to form cations.

29. 3. Which of the following is the most electronegative?
6.3 Section Quiz
3. Which of the following is the most electronegative? Cl Se Na I

30. END OF SHOW