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.

6.3

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 1st ionization energy, ionic size and

electronegativity

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.

6.3

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

Trends in Atomic Size

Periodic Trends Atomic Radius

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.

Trends in Atomic Size

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40

Li

Na

K

Kr

He

NeAr

2nd period

3rd period 1st transitionseries

Radius (pm)

Atomic Number

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40

Li

Na

K

Kr

He

NeAr

2nd period

3rd period 1st transitionseries

Radius (pm)

Atomic Number

6.3Trends 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

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

Atomic RadiiAtomic Radii

6.3

Positive and negative ions form when electrons are transferred between atoms.

Trends in Ionic Size

Positive and negative ions form when electrons are transferred between atoms.

6.3Trends 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.

6.3Trends in Ionic Size

Li,152 pm3e and 3p

Li+, 60 pm2e and 3 p

+Does the size goup or down when losing an electron to form a cation?

Does the size goup or down when losing an electron to form a cation?

Trends in Ionic Size

CATIONS are SMALLER than the atoms from which they come.

There is no longer an electron in the 2s orbital and so size DECREASES.

Li,152 pm3e and 3p

Li +, 78 pm2e and 3 p

+Forming a cation.

Forming a cation.

Trends in Ionic Size

F,64 pm9e and 9p

F- , 136 pm10 e and 9 p

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

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

Forming an anion.

Forming an anion.F, 71 pm

9e and 9pF-, 133 pm10 e and 9 p

-

Trends in Ionic Size

Relative Sizes of Some Atoms and Ions

6.3Trends in Ionic Size

Trends in Ionic Size

Trends in Ionic Size

Trends in Ionic Size

6.3S

ize

ge

ner

ally

incr

ease

sTrends in Ionic Size

6.3

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.

6.3Trends in Ionization Energy

6.3Trends in Ionization Energy

6.3Trends in Ionization Energy

6.3Trends in Ionization Energy

6.3Trends 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.

Representative Elements in Groups 1A through 7A

6.3Trends in Electronegativity

6.3

Atomic Size Increases

Incr

ease

s

Decreases

Dec

reas

es

Size of cationsShieldingNuclear ChargeElectronegativityIonization energySize of anionsIonic size Constant

Summary of Trends

Summary of Trends

The succession of elements within a group demonstrates characteristic trends in properties. As you progress down a group:

1. atomic radius increases.

2. electronegativity decreases.

3. first ionization energy decreases.

4. Ionic size increases.

Section Assessment

The succession of elements within a period demonstrates characteristic trends in properties. As you progress across a group from left to right:

1. atomic radius decreases.

2. electronegativity increases.

3. first ionization energy increases.

4. Ionic size decreases.

Summary of Trends

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

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 1st ionization energy of 1314KJ/mol and an electronegativity of 3.5. It is classified as a

a. metal

b. nonmetal

c. metaloid

d. halogen

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

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 1st ionization energy of 1314KJ/mol and an electronegativity of 3.5. It is classified as a

a. metal

b. nonmetal

c. metaloid

d. halogen

END OF SHOW