6.3
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.

Chapter 6 The Periodic Table
6.3 Periodic Trends

Today we are learning to:-
1. Describe trends in the periodic table for atomic size
2. Explain how ions form
3. Describe periodic trends for 1 st ionization energy , ionic size and electronegativity

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.

Trends in Atomic Size
The are 3 main factors that will have an effect on the size on an atom.
1. Nuclear charge (the charge on the nucleus). A larger positive charge on a nucleus will pull electrons closer to it.
2. The number of the outermost energy level containing electrons. n = 3 is further from the nucleus than n = 2.
3. The number of inner electrons shielding the outer electrons from the nucleus
Periodic Trends Atomic Radius

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.
Radius (pm)
250
K
200
1st transition series
2nd period
Li
3rd period
Na
150
Kr
100
Ar
Ne
50
0
0
He
5 10 30 35 40 15 20
Atomic Number
25

6.3
Trends in Atomic Size
Size goes UP on going down a group.
Because electrons are added farther from the nucleus, there is less attraction.
Size goes DOWN on going across a period.
Because of greater nuclear attraction

6.3

Trends in Ionic Size
Positive and negative ions form when electrons are transferred between atoms.

6.3
Trends in Ionic Size
Positive and negative ions form when electrons are transferred between atoms.

6.3
Trends in Ionic Size
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.
•
Metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons when they react together. The transfer of electrons effects the size of the ions formed
•
Cations are always smaller than the atoms from which they form.
•
Anions are always larger than the atoms from which they form.

Trends in Ionic Size
Li,152 pm
3e and 3p
+
Li +, 60 pm

Trends in Ionic Size
Li,152 pm
3e and 3p
+
Li +, 78 pm
2e and 3 p
Forming a cation.

Does the size go up or down when gaining an electron to form an anion?

Trends in Ionic Size
-
F, 71 pm
9e and 9p
F- , 133 pm
10 e and 9 p
Forming an anion.
ANIONS are LARGER than the atoms from which they come.
The electron/electron repulsion in the
2p orbital increases because of the extra electron and so size INCREASES .
Trends in ion sizes are the same as atom sizes.

6.3
Trends in Ionic Size
Relative Sizes of Some Atoms and Ions

Trends in Ionic Size

6.3
Trends in Ionic Size
Trends in Ionic Size
Trends in Ionic Size

6.3

6.3
Trends in Ionization Energy
The energy required to remove an electron from an atom in its gaseous state is called ionization energy . Unit of measurement is KJ/mol (kilojoules per mole)
•
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 .
•
First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.

6.3
Trends in Ionization Energy

6.3
Trends in Ionization Energy

6.3
Trends in Ionization Energy

6.3
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.

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

6.3
Summary of Trends
Decreases

Summary of Trends
The succession of elements within a group demonstrates characteristic trends in properties. As you progress down a group:
1.
2.
atomic radius increases .
electronegativity decreases .
3.
4.
first ionization energy decreases .
Ionic size increases .

Section Assessment
Summary of Trends
The succession of elements within a period demonstrates characteristic trends in properties. As you progress across a group from left to right:
1.
2.
atomic radius decreases .
electronegativity increases .
3.
4.
first ionization energy increases .
Ionic size decreases .

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

6.3 Section Quiz
2. Metals tend to a. gain electrons to form cations.
b. gain electrons to form anions.
c. lose electrons to form anions.
d. lose electrons to form cations.

6.3 Section Quiz
3. Which of the following is the most electronegative?
a. Cl b. Se c. Na d. I

6.3 Section Quiz
4. How does the size of a barium ion compare with the size of a barium atom?
a. The ion is smaller because it has fewer electrons b. The ion is smaller because it has more electrons c.
The ion is larger because it has fewer electrons d. The ion is larger because it has more electrons

6.3 Section Quiz
5. Which ion has the largest radius?
a. Na + b. Mg 2+ c. K + d. Ca 2+

6.3 Section Quiz
6. Which of the following is the most electronegative?
a. Cl b. Se c. Na d. I

6.3 Section Quiz
7. Which element has the highest first ionization energy?
a. sodium b. aluminum c. calcium d. phosphorus

6.3 Section Quiz
9. Properties of metals include a. Low ionization energy and high electronegativity b. Low ionization energy and low electronegativity c. High ionization energy and high electronegativity d. High ionization energy and low electronegativity

6.3 Section Quiz
10. An element has a 1 st ionization energy of
1314KJ/mol and an electronegativity of 3.5.
It is classified as a a. metal b. nonmetal c. metaloid d. halogen

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

6.3 Section Quiz
2. Metals tend to a. gain electrons to form cations.
b. gain electrons to form anions.
c. lose electrons to form anions.
d. lose electrons to form cations.

6.3 Section Quiz
3. Which of the following is the most electronegative?
a. Cl b. Se c. Na d. I

6.3 Section Quiz
4. How does the size of a barium ion compare with the size of a barium atom?
a. The ion is smaller because it has fewer electrons b. The ion is smaller because it has more electrons c.
The ion is larger because it has fewer electrons d. The ion is larger because it has more electrons

6.3 Section Quiz
5. Which ion has the largest radius?
a. Na + b. Mg 2+ c. K + d. Ca 2+

6.3 Section Quiz
6. Which of the following is the most electronegative?
a. Cl b. Se c. Na d. I

6.3 Section Quiz
7. Which element has the highest first ionization energy?
a. sodium b. aluminum c. calcium d. phosphorus

6.3 Section Quiz
9. Properties of metals include a. Low ionization energy and high electronegativity b. Low ionization energy and low electronegativity c. High ionization energy and high electronegativity d. High ionization energy and low electronegativity

6.3 Section Quiz
10. An element has a 1 st ionization energy of
1314KJ/mol and an electronegativity of 3.5.
It is classified as a a. metal b. nonmetal c. metaloid d. halogen