Periodic Properties

Periodic Properties

Periodic Trends

Don’t Confuse a trend with the explanation for that trend!!!!!

• Example- • Why is Br atom larger than a Kr atom?????• Why is a cation smaller than its parent atom?• Why is an anion larger than its parent atom??

Ionization energy

• Endothermic –requires energy to remove outermost electron

• Decreases down a group- large atomic radium and sheilding effect means that less energy needed to remove electrons

• Increases across a period , the effextive nuclear charge increases, which causes an increased attraction between valence elctron and proton

Ionization Energy- Why drop Be to B and N to O

Ionization Energy Exceptions

What happens to the IE as increasing number of electrons are removed from an

atom? Where do the “jumps” occur?

• I1 < I2 < I3

Electron Affinity

• Energy released when an atom attracts an addition electron

• Negative- exothermic process• More negative, the greater the affinity• Elements in Group 2, 15 and 18 have lower

than expected EA because of full (s) or ½ full (diamagnetic)(p) sublevels-electron=electron repulsion

Sample MC• Questions 1-3refer to the following elementsa. Ob. Lac. Rbd. Mge. N

1. What is the most electronegative element of the above?2. Which element exhibits the greatest number of different oxidation

states?3. Which of the elements above has the smallest ionic radius for its

most commonly found ion?

Sample MC

4. The effective nuclear charge experienced by the outermost electron of Na is different than the effective nuclear charge experienced by the outermost electron of Ne. This difference best accounts for which of the following?a. Na has a greater density at standard conditions than Ne.b. Na has a lower first ionization energy than Ne.c. Na has a higher melting point than Ne.d. Na has a higher neutron-to-proton ration than Ne.e. Na has fewer naturally occurring isotopes than Ne.

MC Sample 5

Chemical Bonding

• Types: ionic- cation and anion• covalent- nonmetal+ nonmetal• Metallic- metal + metal- cations

surrounded by a sea of electrons, valence electrons are delocalized

Ionic

• Lattice energy- amount of energy needed to separtate 1 mole of an ionic compound into its gaseous ions

• Lattice energy increases with: smaller, more highly charged atoms—Coloumb’s law

• E= k Q1 Q2/d Q1 and Q2 are charges on ions, d is distance between

ions

Covalent

• Electronegativity difference determines polarity- 0-0.3; 0.3-1.7, 1.7 and greater

• Dipole- molecule having one end with a slight + charge and the otherend with a slight negative charge

Lewis Structures

• 1. Count number of valence electrons• 2. Find central atom• 3. place outer atoms around central atom with

single bond, place valence lectrons to give them an octet

• 4. Determine if there are enough electrons to give central atom octet. If not, multiple bonds! Try Sulfur trioxide!

Formal Charge

• Determines best lewis structure.• Equal to # VE-# nonbonding electrons-1/2

number of bonding electrons• Formal charges of 0 means more likely Lewis

structure• Example CO2

Exceptions to Octet Rule

• Central atom is Be (4 VE) BeI2 B(6 VE) BF3

• Species has an odd # electrons, one atom will have only 7 electrons (NO)

• Expanded octet: Larger nonmetal central atom (period 3 and beyond) have d orbitals available for bonding. Also, the larger the atom, the more atoms that can fit around it:

• SF6, PCl5, XeF4

Sigma and pi bonds

• Single bond—sigma• Double bond—one sigma and one pi bond• Triple bond- one sigma, and 2 pi bonds

MC practice(A) CaO(B) CH2CH2 (C2H4)(C) SeO3

(D) CH2Cl2

(E) NBr3 1. The molecule with only one pi bond 2. The molecule whose molecular geometry is different from its electron

geometry 3. The molecule that has trigonal pyramidal geometry

MC practice

• 4.Which of the following molecules has the shortest bond length?

• A) N2• B) O2• C) Cl2• D) Br2• E) I2

MC practice

• 5. For which of the following molecules is the concept of resonance most likely to describe the bonding satisfactorily?

A) BeF2B) NO2

-

C) CO2

D) CN-

E) PCl5•

MC Practice

6. CCl4, CO2, PCl3, PCl5, SF6Which of the following does not describe any of

the molecules above?A) Square planarB) TetrahedralC) Trigonal pyramidalD) LinearE) Octahedral

MC Practice

7. All of these molecular shapes can be explained by sp3d hybridization of electrons on the central atom except

A) linearB) a square pyramidC) see-sawD) a trigonal bipyramidE) an octahedron

MC Practice

8. The melting point of MgO is higher than that of NaF. Explanations for this observation include which of the following? I. Mg2+ is more positively charged than Na+

II. O2– is more negatively charged than F–

III. The O2– ion is smaller than the F– ionA) II onlyB) I and II onlyC) I and III onlyD) II and III onlyE) I, II, and III

Electrons and wave properties

Electrons and wave properties

Calcuating among wavelength frequency and energy

Balmer series Hydrogen BLS

A line having a wavelength of 656 nm exists in the atomic emission spectrum of hydrogen

• For the line, calcuate the:• A. frequency• B. energy of the photon• C. energy of a mole of photons• D. discuss th origin of the line in terms of the

Bohr model of the atom

Electron Configuration Rules

Periodic table electron configuration

MC Practice• Questions 1-4 refer to the following electron configurations.•

I. 1s2 2s2 2p5 3s2 3p5

II. 1s2 2s2 2p6 3s2 3p6

III. 1s2 2s2 2p6 2d10 3s2 3p6

IV. 1s2 2s2 2p6 3s2 3p6 3d5

V. 1s2 2s2 2p6 3s2 3p6 3d3 4s2

• 1. The ground-state configuration for the atoms of a transition element.2. The ground-state configuration of a negative ion of a halogen.3. The ground-state configuration of a common ion of an alkaline earth

element.4. An impossible electronic configuration.

MC Practice

a) 1s ____ 2s b) 1s 2s c) 1s 2s 2p d) 1s 2s 2p e) [Ar] 4s 3d

5. Represents an atom that has four valence electrons.6. Represents an atom that is chemically unreactive.7. Represents an atom in an excited state

MC Practice

8. For which of the following electron transitions for a hydrogen atom does the light emitted have the longest wavelength?a. n=5 to n=4b. n=5 to n=2c. n=3 to n=2d. n=5 to n=3e. n=4 to n=3

MC Practice

9. Sr, Cr, Co, Hg, P• Gaseous atoms of which of the elements

above are paramagnetic?a. Sr and P onlyb. Hg and P onlyc. Mg, Cr, and Co onlyd. Cr, Co, and P onlye. Cr, Co, and Hg only