Chapter 10 Periodic Trends Density Atomic and Ionic

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 (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.

Atomic radius (radii) • The atomic radius is essentially the size of an atom. • The largest atom is Francium (Z = 87).

Atomic Radius Xylophone monkey

Rank the atoms from smallest to largest K, S, Rb, Cl Cl < S < K < Rb How does effective nuclear charge relate to the sizes of these atoms?

Atomic Radius and Effective Nuclear Charge • The atomic radius increases as the effective nuclear charge decreases.

Effective Nuclear Charge (Zeff) • The effective nuclear charge of an atom is primarily determined by: 1. The nuclear charge – The number of protons.

Rank the atoms from smallest to largest Cl < S < K < Rb Why is Cl smaller than S? Both atoms are in the 3 rd row (period) of the periodic table. What does this tell us?

The Nuclear Charge (Z) • The size of atoms in the same period (row) is determined by the nuclear charge (number of protons in the nucleus).

Nuclear charge explains why atoms get smaller across a period Atomic Radius Xylophone monkey

Rank the atoms from smallest to largest Cl < S < K < Rb Why is K smaller than Rb? Does the number of protons in each of these atoms explain their size?

Effective Nuclear Charge (Zeff) • The effective nuclear charge of an atom is primarily determined by: 1. The nuclear charge – The number of protons 2. The shielding effect.

The Shielding Effect College Lecture Class

Effective Nuclear Charge (Zeff) • The effective nuclear charge of an atom is primarily determined by: 1. The nuclear charge – The number of protons 2. The shielding effect. – The number of energy levels.

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

K vs. Rb

Shielding Effect explains why atoms get larger down a group Atomic Radius Xylophone monkey

The Nuclear Charge (Z) • Example: Carbon vs. Nitrogen • Which atom would you predict to be smaller?

The Nuclear Charge (Z) Carbon Nitrogen

Conclusion: Nitrogen has a greater effective nuclear charge than carbon because nitrogen has 7 protons to pull in its two energy levels whereas carbon only has 6 protons holding it’s two energy levels. Therefore nitrogen atoms are smaller than carbon atoms. Nitrogen Carbon

Shielding Effect. Why is He smaller than Ne? He Ne

Conclusion: Helium has a greater effective nuclear charge than neon because helium has a lower shielding effect from having only one energy level whereas neon has two. He Ne

Chemical Reactivity

Chemical Reactivity

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? Fr • Most reactive nonmetal is? F

Francium • Francium is the least stable naturally occurring element with a half-life of only 22 minutes. • It has been calculated that there is at most 30 g of francium in the Earth's crust at any time.

Ionic Radius • Ionic Radius is the size of an ion.

Size Change in Ion Formation

Rules for Ionic Radius • 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+, N 3 -, Na+, O 2 - + Na <K < + 2 O < 3 N

Homework • Worksheet: Density, Atomic and Ionic Radii (due tomorrow). • Lab Summary: Reactivity and the Periodic Table (due Monday). • Study Guide Chapter 10 (due Tuesday).