1. Periodic Trends 6.3

2. 6.3
Periodic Trends
Sodium chloride (table salt) produced the geometric pattern in the photograph. Such a pattern can be used to calculate the position of nuclei in a solid. You will learn how properties such as atomic size are related to the location of elements in the periodic table.

3. 6.3
Trends in Atomic Size
Trends in Atomic Size
What are the trends among the elements for atomic size?

4. 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.

5. Atomic radius is measured in pico meters. 10 12 pm = 1 m

6. 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.
Why? Nucleus charge increases, the number of occupied energy levels increases.
# protons = # of electrons

7. Group Trends
Increase nucleus charge draws the electrons closer to the nucleus. Occupied energy levels tend to shield the electrons in the outer energy level so the atomic size increases.

8. Rank the order of the following atoms in order of decreasing radii.
Al , Ga, In
Ans: In, Ga, Al
b. As, Ge, Ga
Ans: Ga, Ge, As

9. 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)?

10. Atomic size
Each element has one more proton and one electron. Electrons are added to the same energy level. Shielding is constant. Higher charge of nucleus pulls the electrons in the highest energy level. Atomic sizes decreases.

11. 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?

12. Question
Arrange these elements in order of decreasing atomic size. sulfur, chlorine, aluminum, and sodium Is the arrangement a periodic or group trend? Ans: Na, Al, S, Cl periodic I

13. 6.3
Ions
Ions
How do ions form?

14. 6.3
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?

15. Na e- + Na +

16. 6.3
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?

17. Cl + 1 e Cl-

18. Some compounds are composed of particles called ions.
6.3
Ions
Some compounds are composed of particles called ions.
An ion is an atom or group of atoms that has a positive or negative charge.
A cation is an ion with a positive charge.
An anion is an ion with a negative charge.

19. 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?

20. Trends in Ionization Energy
6.3
Trends in Ionization Energy
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. Mg +716kJ/mole e- + Mg+1
The energy required to remove an electron from an ion with a 1+ charge is called the second ionization energy.
Mg KJ/mole Mg e-

21. Trends in Ionization Energy
6.3
Trends in Ionization Energy
Group and Periodic Trends in Ionization Energy
First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.

22. Trends in Ionization Energy
6.3
Trends in Ionization Energy

23. Why is the first ionization energy of a non metal much higher than that of an alkali metal? Ans: The nuclear charge increases from left to right across the period and the shielding effect stays the same, it is more difficult to remove the electrons.

24. Trends in Ionization Energy
6.3
Trends in Ionization Energy

25. Trends in Ionization Energy
6.3
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?

26. Review
Remember that ionization energy is a measure of the difficulty in removing an electrons from the highest occupied energy level.

27. Question
Which element in each pair has the larger first ionization energy? a. sodium, potassium ans: sodium b. magnesium, phosphorus ans: phosphorus

28. 6.3
Trends in Ionic Size
Trends in Ionic Size
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.

29. 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.

30. 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?

31. When the atom loses the electrons, the attraction between the remaining electron and the nucleus is increased so the ion formed is smaller. When an atom gains electron, the attraction between the nucleus and the electrons are reduced. Ion formed is larger.

32. Trends in Ionic Size 6.3 Size generally increases 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.

33. 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.

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

35. Question?
Why aren’t the noble gases included in the discussion of electronegativity? Ans: they form very few compounds.

36. Electronegativity values are based on the ionization energy and electron affinity . Electron affinity is a measure of an atom’s ability to gain electrons.

37. Rank the following atom in order of decreasing electronegativity.
Na, Li, K
Ans: Li, Na, K
b. As, Sn, S
Ans: S, As, Sn

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

39. Nuclear Charge Electronegativity Size of anions Ionic size Shielding
6.3
Summary of Trends
Nuclear Charge
Electronegativity
Size of anions
Ionic size
Shielding
Ionization energy
Size of cations
Atomic Size
Decreases
Constant
Increases
Decreases
Increases
Properties that vary within groups and across periods include atomic size, ionic size, ionization energy, electronegativity, nuclear charge, and shielding effect. Interpreting Diagrams Which properties tend to decrease across a period?

40. 6.3
Summary of Trends
The trends that exist among these properties can be explained by variations in atomic structure.

41. 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

42. 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.

43. 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

44. END OF SHOW