ATOMIC STRUCTURE AND PERIODICITY PART 2

PERIODIC TRENDS

Atomic Radii

Ionic Radii

Electronegativity

Ionization Energy

Electron Affinity

ATOMIC RADIUS

Definition: Half of the distance between nuclei in covalently bonded diatomic molecule.

Radius decreases across a period

• Increased effective nuclear charge due to decreased shielding

Radius increases down a group

• Each row on the periodic table adds a “shell” or energy level to the atom

2r

IONIZATION ENERGYDefinition: the energy required to remove an electron from an atom

**Increases for successive electrons taken from the same atom. (First Ionization Energy is lower than the second…and that lower than the third…etc)

Tends to increase across a period (general pattern-valence e-)

• Electrons in the same quantum level do not shield as effectively as electrons in inner levels.

• Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove

Tends to decrease down a group

• Outer electrons are farther from the nucleus and easier to remove

IONIZATION ENERGY AND ORBITAL NOTATION

Phosphorus vs. Sulfur

Potassium 1st Ionization vs. 2nd

ELECTRON AFFINITY

Definition: the energy change associated with the addition of an electron

Affinity tends to increase across a period

Affinity tends to increase up in a group

• Electrons farther from the nucleus experience less nuclear attraction

• Some irregularities due to repulsive forces in the relatively small “p” orbitals

ELECTRONEGATIVITY

Definition: A measure of the ability of an atom in a chemical compound to attract electrons from another atom.

Electronegativity tends to increase across a period

• As the radius decreases, electrons get closer to the bonding atom’s nucleus

Electronegativity tends to increase up a group or remain the same.

• As radius increases, electrons are farther from the bonding atom’s nucleus

IONIC RADIICations

• Positively charged ions formed when an atom loses one or more electrons

• SMALLER that the corresponding atom

Anions

• Negatively charged ions formed when an atom gains one or more electrons

• LARGER than the corresponding atom

ANALYZING PERIODIC TABLE TRENDS WITH PEERS

Explain why atomic radius increases going down a group and right to left in a period.

Rank the following from largest to smallest.

Explain why electronegativity, ionization energy, and electron affinity increase from left to right and from bottom to top.

Rank the following from largest to smallest.

SPECTROSCOPY

Photoelectron Spectroscopy (PES)

• Provides data for ionization energy trends and applications

Mass Spectrometry

• Provides atomic/molar mass data as it ionizes

PHOTOELECTRON SPECTROSCOPY (PES)

Atom

e-

Ephoton = hv

KE = mv2

2IEelectron = Ephoton - KE

MonochromaticBeam of X-Rays

PHOTOELECTRON SPECTRUM

20 MJ/mol 10 MJ/mol 0 MJ/mol

Relative Intensity = 1

Relative Intensity = 2

Each peak is relative to the others. This indicates the relative number of electrons. If the peak is twice as big, there are twice as many electrons.

PHOTOELECTRON SPECTRUM

20 MJ/mol 10 MJ/mol 0 MJ/mol

19.3 MJ/mol 1.36 MJ/mol

0.80 MJ/mol

Valence

RI = 2 RI = 2

RI = 1

Gap is due to increased energy of the orbital (decreased amount of energy to remove the electron)

PHOTOELECTRON SPECTRUM

20 MJ/mol 10 MJ/mol 0 MJ/mol

19.3 MJ/mol 1.36 MJ/mol

0.80 MJ/mol

RI = 2 RI = 2

RI = 1

Analysis:1) Valence has 2 values: 2) RI is 2 to 1 in valence:

3) Closest core has RI 2 not 6:

4) s2s2p1 must be 1s22s22p1

Boron (Z=5)

1s2 2s2 2p1

Inner orbitals require the most energy

Valence orbitals require the least energy

PHOTOELECTRON SPECTRUM

Depending on the size of the table, 1s may be intentionally cut out of view because it’s too far away and makes the graph too long

Remember IE is about REMOVING electrons, which means they are removed from the OUTSIDE to the INSIDE, and NOT in reverse order of energy! For example, 4s is removed BEFORE 3d.

PHOTOELECTRON SPECTRUM

104 MJ/mol 6.84 MJ/mol

0.50 MJ/mol

8 MJ/mol 4 MJ/mol 0 MJ/mol

Sodium (Z=11)2p6

2s2

3s1

{ }

3.67 MJ/mol

1s2

http://www.chem.arizona.edu/chemt/Flash/photoelectron.html

https://www.youtube.com/watch?v=NRIqXeY1R_I

https://www.youtube.com/watch?v=vANbxozsRSA

Online PES Resources

From the AP Sample Questions…

From the AP Sample Questions…

Which peaks in the photoelectron spectrum are representative of the binding energy of p orbital electrons?a. C only c. C and Eb. D only d. B, C and D

Mass Spectrometry

• Mass spectrometry gives the mass to charge ratio

• Like PES, the relative size of the peaks indicates the relative number of particles

• Separates isotopes according to mass• Used to find relative abundance and

atomic/molar mass of unknown samples

Mass Spectrometry

From the AP Sample Questions…

The elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer, resulting in the data above. All of the following statements are true. Which one would be the best basis for concluding that the sample was pure Te?

From the AP Sample Questions…

a. Te forms ions with a -2 charge, whereas I forms ions with a -1 charge.

b. Te is more abundant that I in the universe.c. I consists of only one naturally occurring isotope with 74 neutrons,

whereas Te has more than one isotope.d. I has a higher first ionization energy than Te does.

Based on the mass spectrum of atom Y, which of the following statements is false? a. peak A and peak D come from atoms that have the same number of electrons b. there are seven isotopes of atom Yc. peak C comes from the most abundant isotope of atom Yd. peak D comes from an atom with 4 more protons than the atom that gave peak B

PREPARATION OF A STANDARD SOLUTION

A chemist whishes to prepare 1.00L of a 0.200 M sodium hydroxide solution. Describe the steps, with calculations, necessary to complete this task starting with solid sodium hydroxide and distilled water.

DILUTION OF SOLUTIONS- M1V1 = M2V2

You’ve been asked to prepare 150 ml of a 0.035M solution of sodium hydroxide from the 0.200M stock sodium hydroxide solution prepared earlier. Detail the steps necessary to complete this task.

(a) A Measuring Pipet

(b) A Volumetric (transfer) Pipet

BEER- LAMBERT LAW

Relates the amount of light being absorbed to the concentration of the substance absorbing the light

A=abc

A = measured absorbance

a = molar absorptivity constant (a characteristic of the substance being monitored).

b = path length through which the light must pass.

c = Molar concentration of the absorbing substance.

BEER’S LAW SAMPLE PROBLEMS1. A solution with a concentration of 0.14M is measured to have an absorbance of 0.43. Another solution of the same chemical is measured under the same conditions and has an absorbance of 0.37. What is its concentration?

2. The following data were obtained for 1.00 cm samples of a particular chemical. What is the concentration of a 1.00 cm sample that has an absorbance of 0.60?

Conc. (M)

Abs.

0.50 0.69

0.40 0.55

0.30 0.41

0.20 0.27

3. The absorptivity of a particular chemical is 1.5/M·cm. What is the concentration of a solution made from this chemical if a 2.0 cm sample has an absorbance of 1.20?

BEER’S LAW SAMPLE PROBLEMS

4. Using the data from the graphing example in question #2, what are the concentrations of solutions with absorbances of 0.20, 0.33, and 0.47? 

5. A solution is prepared to be 0.200M. A sample of this solution 1.00 cm thick has an absorbance of 0.125 measured at 470nm and an absorbance of 0.070 measured at 550nm. Calculate the concentrations of the following solutions:

Sample Absorbance Wavelength Path length

1 0.055 470nm 1.00cm

2 0.155 470nm 1.00cm

3 0.120 550nm 1.00cm

4 0.048 550nm 5.00cm

GATORADE LAB/INVESTIGATION

What is the relationship between the concentration of a solution and the amount of transmitted light through the solution?

Video Spectrophotometer

See Pre-lab and Report Sheet for support.

**Dilution calculations MUST be done prior to data collection!!** (Due Monday!) –complete first 3 columns in data table prior to entering lab.

LAB PARTNERS AND DILUTION ASSIGNMENTS 2ND BLOCK

Dilution Assignments (mL of stock/ mL of water)

Group 1: Jackson and Kenny

• 10mL/0mL; 6mL/4mL

• 9mL/1mL; 3mL/7mL

Group 2: Garrett and Nelson

• 5mL/5mL; 0mL/10mL

• 8mL/2mL; 1mL/9mL

Group 3: Ashley and Taylor

• 2mL/8mL; 4mL/6mL,

• 0mL/10mL, 7mL/3mL

Will share class data for plots.

UNIT 3 REVIEW

Now available on the blog!! (Practice Tab)

Begin working through.

BRING QUESTIONS TOMORROW!!!!