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# Chapter 10 PowerPoint PPT Presentation

Chapter 10. Periodic Trends Density Atomic and Ionic Radii. Density. Density. Iridium (Z = 77) has the highest density. Why not Meitnerium (Z = 109?) We can predict that an element is more dense if it is closer to Iridium. Density. Effective Nuclear Charge (Z eff ).

Chapter 10

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## Chapter 10

Periodic Trends

Density

### Density

• Iridium (Z = 77) has the highest density.

• Why not Meitnerium (Z = 109?)

• We can predict that an element is more dense if it is closer to Iridium.

### Effective Nuclear Charge (Zeff)

• The effective nuclear charge (Zeff) of an atom is basically how well it is able to hold on to its most loosely held electron.

• Theatomic radius is essentially the size of an atom.

• The largest atom is Francium (Z = 87).

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Na, K, O, N

O < N < Na < K

### Atomic Radius and Effective Nuclear Charge

• The atomic radius decreases as effective nuclear charge increases.

### Effective Nuclear Charge (Zeff)

• The effective nuclear charge of an atom is primarily determined by:

• The nuclear charge

• The shielding effect

### The Nuclear Charge (Z)

• Based on the number of protons in the nucleus.

• Example: Carbon vs. Nitrogen

Carbon

Nitrogen

### The Nuclear Charge (Z)

• The greater the number of protons in the nucleus the greater the effective nuclear charge.

Nitrogen

Carbon

### Conclusion: Nitrogen is a smaller atom than carbon because nitrogen has 7 protons to pull in its electrons whereas carbon only has 6.

Nitrogen

Carbon

Nuclear charge explains why atoms get smaller across a period

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### Shielding Effect.

• The shielding effect is when electrons between the nucleus and the outermost electrons in an atom shield or lessen the hold of the nucleus on the outermost electrons.

### Shielding Effect.

He

Ne

Conclusion: Neon is larger than helium because it has an increased shielding effect from having two energy levels whereas helium only has one energy level.

He

Ne

Shielding Effect explains why atoms get larger down a group

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### Chemical Reactivity

• Metals tend to lose electrons when reacting.

• Large metal atoms are more reactive.

• Nonmetals tend to gain electrons when reacting.

• Small nonmetal atoms are more reactive.

### Chemical Reactivity

• Metals increase in reactivity left and down.

• Nonmetals become more reactive up and to the right.

• Most reactive metal is?

• Most reactive nonmetal is?

Fr

F

• Ionic Radius is the size of an ion.

### Size Change in Ion Formation

• Anions (negative ions) are “always” larger than cations (positive ions).

• Ionic Radius goes by the same rules as atomic radius (ions get larger as we move down and to the left).

• However it is necessary to treat anions and cations separately. (Anions are bigger).

### Rank the ions from smallest to largest

K+, N3-, Na+, O2-

Na+ < K+ < O2- < N3-

### Homework

• Worksheet: Density, Atomic and Ionic Radii