Atomic Spectra &The Periodic Properties Of Elements

Objectives 1. Determine the emission spectrum of Hydrogen and other elements.

2. Calculate the expected wavelengths of H using the Rydberg equation.

3. Discover the relationship between the chemical reactivity of various elements and their positions on the periodic table.

Animation of the dispersion of white light as it travels through a triangular prism.

Ibn Alhazen is considered the “Father of Optics” He wrote the “Book of Optics”, which correctly explained and proved the modern theory of vision. His experiments on optics greatly influenced later scientists. His experiments included ones on lenses, mirrors, refraction, reflection, and the dispersion of light into its constituent colors. He studied the electromagnetic aspects of light, and argued that rays of light are streams of energy particles traveling in straight lines.

History of Optics & Light Studies

Ibn Alhazen(965 – 1039)

Arab Muslim Scientist“Father of Optics”

In 1608, Galileo Galilei is credited as the first to turn his telescope to the heavens.

He soon discovered craters on our Moon, sun spots, the moons of Jupiter, and that Venus has phases like our Moon.

Galileo claimed that his observations only made sense if all the planets revolved around the Sun (as proposed by Aristarchus and Copernicus) rather than the Earth. Galileo Galilei

1564 - 1642

Historical Background of Spectroscopy

The Inquisition eventually forced Galileo to publicly recant this conclusion.

Sir Isaac Newton1643 - 1727

Sir Isaac Newton was one of the first people to study light scientifically.

In 1672, Newton directed a beam of white light through a triangular bar of glass, called a “prism”. He discovered that the light coming out of the prism was separated into bands of colors.

The arrangement of colors produced by a prism is called a “spectrum”.

Prior to this it was believed that “white light” was equal to purity.

A Quantitative Study of Light

.

When a narrow band of light from a “white” light source is sent through a prism, a continuous spectrum containing all wavelengths of visible light is formed.

Original Studies Of Light Used Only One Prism

Newton’s Contribution to Spectroscopy

In fact, his main contribution was to show that after the sunlight had been broken down into its components by one prism, if a narrow ray of the light from the first prism was passed through another prism no further breakdown of light occurred.

Newton contributed more to spectroscopy than scientifically proving that sunlight traveling through a prism was always broken down into the components of the rainbow.

                                                              

       

Classification of Electromagnetic Radiation

The color components of light are separated along the visible range of light. The visible range of light (400-700 nm) is merely a small portion of the entire electromagnetic spectrum.

Joseph von Fraunhofer discovered the dark absorption lines in the Sun's spectrum (known as Fraunhofer lines) and designed achromatic telescope objectives.

At age 11, he was orphaned and forced to apprentice for no pay with a harsh glassmaker named Philipp Anton Weichelsberger. In 1801, the glass shop collapsed and Fraunhofer was buried alive.

When Fraunhofer survived the collapse, the court-councilor von Utzschneider, gave him books on mathematics and optics. King Max Joseph gave him a present of eighteen ducats. With this money Joseph acquired his own glass grinding machine and bought his release from Weichelsberger.

Joseph von Fraunhofer (March 6, 1787 – June 7, 1826)

German Optician

Advancements in the Study of Light

Joseph von Fraunhofer’s initial desire was to create a glass lens that did not produce an image that was fringed with a rainbow of colors. He realized the problem was that the glass lens bent some colors more than others. He began searching for a source of light of a single color.

In 1814, he developed a spectroscope to study the spectrum of the light given off by the sun. He was amazed to discover that in the midst of the rainbow of colors was a series of black lines.

These dark lines were later determined to be the result of the absorption of selected frequencies of the electromagnetic radiation by an atom or a molecule.

Development of the Spectroscope

Joseph von Fraunhofer (March 6, 1787 – June 7, 1826)

Fraunhofer lines observable in the Solar Spectrum390 nm

700 nm

Fraunhofer also completed an important theoretical work on diffraction and established the laws of diffraction. One important innovation that Fraunhofer made was to place a diffraction slit in front of the objective of a measuring telescope in order to study the solar spectrum. He later made and used diffraction gratings with up to 10,000 parallel lines per inch. By means of these gratings he was able to measure the minute wavelengths of the different colors of light. (Diffraction gratings will be discussed more later.)

Development of Diffraction Gratings

Gustav Robert Kirchhoff(March 12, 1824 – October 17, 1887)

German Physicist

Robert Wilhelm Eberhard Bunsen (March 31, 1811 – August 16,1899)

German Chemist

Bunsen and Kirchhoff further developed the spectroscope by incorporating the Bunsen burner as a source to heat the elements. In 1861, experiments by Kirchhoff and Bunsen demonstrated that each element, when heated to incandescence, gave off a characteristic color of light. When the light was separated into its constituent wavelengths by a prism, each element displayed a unique pattern or emission spectrum.

1855-1860 - Gustav Kirchhoff and Robert Bunsen

The emission spectrum seemed to be the complement to the mysterious dark lines (Fraunhofer lines) in the sun's spectrum. This meant that it was now possible to identify the chemical composition of distant objects like the sun and other stars. They concluded that the Fraunhofer lines in the solar spectrum were due to the absorption of light by the atoms of various elements in the sun's atmosphere.

Emission Spectra Complement Absorption Spectra

Johann Jakob Balmer(May 1, 1825 – March 12, 1898)

Swiss Mathematician & Honorary Physicist

In 1885, Johann Jakob Balmer analyzed the hydrogen spectrum and found that hydrogen emitted four bands of light within the visible spectrum. His empirical formula for the visible spectral lines of the hydrogen atom was later found to be a special case of the Rydberg formula, devised by Johannes Rydberg.

Wavelength (nm) Color

656.2 red

486.1 blue

434.0 blue-violet

410.1 violet

Hydrogen Spectrum – The Balmer Series

Max Karl Ernst Ludwig Planck(April 23, 1858 – October 4, 1947)

German Physicist

The Nobel Prize in Physics 1918 forThe discovery of energy quanta.

The profile of radiation emitted from a black body

In 1900, Planck hypothesized that energy was quantized (i.e. energy can be gained or lost only in whole-number multiples of the quantity h.) This hypothesis was later extended by Albert Einstein to include light. Einstein envisioned light as small discrete particles of energy which he called photons.

E = nh

E – the change in Energy

n= 1, 2, 3, …

h – (Planck’s constant)

h = 6.62610-34 Js

= frequency

Quantum Properties of Light

The permitted energy levels of a hydrogen atom.

)11

(22

21 nn

R

Where v = frequencyn = the quantum numberR = (Rydberg constant) R = 3.29 1015 Hz1 Hz = 1 s-1

Calculating the Balmer & Lyman Series

The four bands of light calculated by Balmer can be simply calculated using the Rydberg equation:

*This equation will be used on page 159.

*

Wavelength (): Distance between two consecutive peaks [unit: nm]

Frequency (): Number of waves per second that pass a given point in space [unit: s-1 (Hertz)]

= cWhere C is the speed of light

&C = 2.9979108 m/s

Recall that Frequency and Wavelength are related where frequency times wavelength equals the speed of light.

Since the speed of light is a constant, as wavelength decreases, then frequency must increase.

The Nobel Prize in Physics 1922for the investigation of the structure

of atoms and of the radiation emanating from them.

Niels Henrik David BohrOct. 7, 1885 – Nov. 18, 1962

Danish Physicist

In 1913, Bohr developed a quantum model for the hydrogen atom.

Proposed the Solar System model of the atomwhere the electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits.

These orbits then correspond to the energy levels seen in the Balmer series. (p 167)https://www.youtube.com/watch?v=-YYBCNQnYNM

Atomic Spectra Experiment

PART A: Hydrogen emission spectrum.

PART B: Emission spectrum of other elements.

PART C: Tests on elements: Mg, Al, Si, Ca & Zn.

The hydrogen line spectrum contains only a few discrete wavelengths.In the visible region, there are only four wavelengths.

PART A: Record Hydrogen line spectrum with a Scanning Spectrophotometer.

Scanning Spectrophotometer (top view)

A hydrogen light source will be viewed using a scanning spectrophotometer. The wavelengths will be calculated for the Balmer and Lyman series and then compared to those generated by the computer attached to the scanning spectrophotometer.

Computer Output from a Scanning Spectrophotometer

The peaks on the spectrograph correspond to the energy changes of the electrons for the Hydrogen atom.

3. Measure the line spectrum of the gas tubes set up near chalkboards.Note: The fastest/easiest way to do this is have one partner view the lines

and the other write down the observations.

4. Compare your results with NIST literature values. For the fluorescent light compare it to the element mercury.

PART B: Emission spectrum of other compounds using The STAR Spectrophotometer.

1. View the line spectrum through the STAR Spectrophotometer- point slit towards the light and view to the right.

2. In the hallway, verify that the scale is lined-up accurately by looking at the fluorescent light. In addition to other lines, you should see a green doublet for mercury at ~570 nm (the scale on the bottom).

Argon

Neon

Helium

Atomic Spectra of Noble Gases

The Atomic Spectra will be determined for the Noble Gases by looking at the gas discharge tubes.

Krypton

Xenon

Room 201 & 212

Room 201 & 212

Room 201 only.

212 StudentsRoad Trip!

Room 201 only.

212 StudentsRoad Trip!

Room 212 only.

201 StudentsRoad Trip!

A period is a horizontal row of elements in the periodic table.

Atomic numbers increase from left to right across the table.

There are 7 periods.

A group (also called a family) is a vertical column in the periodic table. Elements in a given group have similar electronic configurations for their valence shell electrons, and so they have similar chemical properties.

Atomic numbers increase from top to bottom.

There are 18 groups.

The Periodic Table

Periodic PropertiesBy looking at the relationship between the chemical reactivity of magnesium, aluminum, silicon calcium & zinc and their positions on the periodic table, we hope to discover periodic trends within the 3rd & 4th period & the alkaline earth metal group (family).

** * *

Some well known periodic trends.

Magnesium, 12

Calcium, 20

Silicon, 14Aluminum, 13

Zinc, 30

*

Magnesium, Mg (Z=12)

Properties: an alkaline earth metal, silvery white, fairly tough, oxidizes slowly in air, burns rapidly in air with a brilliant white flame. Normally magnesium is coated with a layer of oxide, MgO, that protects magnesium from air and water.

Available in several forms including chips, granules, powder, rod, foil, sheet, rod, turnings, and ribbon.

Properties: a bright white metal that oxidizes slowly in air, burns rapidly in air with a brilliant white flame,

2 Mg(s) + O2(g) → 2 MgO(s)

reacts with water at room temperature,

Mg(s) + H2O(l) → Mg(OH)2 (aq)

and reacts with dilute acids with the liberation of hydrogen gas

Mg (s) + HCl(aq) → MgCl2 (aq) + H2(g)

does not appear to react with dilute aqueous alkaline solutions.

Magnesium, Mg (Z=12)

Magnesium burns with a

bright white flame.* *Do NOT look directly at the magnesium flame.

Occurrence: Widely distributed and it is third in abundance on earth after oxygen and silicon.

Aluminum, Al (Z=13)

Properties: a silvery-white metal that can be highly polished. It is light, nontoxic (as the metal), a good conductor of heat and electricity, nonmagnetic and nonsparking.

Aluminum is ductile and malleable and can be drawn into wire and rolled into sheets. Pure aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties.

Aluminum, Al (Z=13)Reactions: Aluminum reacts rapidly with the oxygen in air to form aluminum oxide,

4 Al (s) + 3 O2 (l)→ 2 Al2O3(s)

Because the surface of aluminium metal is covered with this thin layer of oxide, it is actually protected from further attack by oxygen. So, aluminum metal does not normally react with air or water.

If the oxide layer is damaged, the aluminium metal is exposed to attack, even by water. Aluminium metal dissolves in dilute hydrochloric acid

2Al(s) + 6HCl(aq) → 2Al3+(aq) + 6Cl-

(aq) + 3H2 (g)

Aluminium dissolves in sodium hydroxide with the evolution of hydrogen gas, H2, and the formation of aluminates [Al(OH)4]-

2Al(s) + 2NaOH(aq) + 6H2O(l) → 2Na+(aq) + 2[Al(OH)4]-

(aq) + 3H2(g)

Occurrence: Silicon is present in the sun and stars and is a principal component of a class of meteorites known as aerolites.

Silicon makes up 25.7% of the earth's crust by weight, and is the second most abundant element, exceeded only by oxygen.

Silicon, Si (Z=14)

Properties: a semi-metallic element, dark grey with a bluish tinge; amorphous silicon is a dark brown powder.

Elemental silicon transmits more than 95% of all wavelengths of infrared and and has been used in lasers to produce coherent light at 456 nm.

Silicon, Si (Z=14)Reactions: The surface of lumps of silicon is protected by a very thin layer of silicon dioxide, SiO2. This renders silicon insoluble in water and most acids.

Silicon does dissolve in hydrofluoric acid forming fluorosilicic acid,

Si(s) + 6 HF (aq) → 2 H2 (g) + H2SiF6 (aq)

Silicon dissolves in sodium hydroxide forming sodium silicate,

Si (s) + 2 NaOH (aq) + H2O (l) → 2 H2 (g) + Na2SiO3 (aq)

and highly complex species containing the anion [SiO4]4-

Si (s) + 4NaOH (aq) → [SiO4]4- (aq) + 4Na+

(aq) + 2H2 (g)

Occurrence: Widely found as its carbonate in rocks, chalk, limestone, and marble, and as mixed carbonates in dolomite, gypsum, CaSO4

.2H2O, fluorite, CaF2, apatite, Ca5(PO4)3, diopside, CaMg(SiO3)2, and lime feldspar, CaAl2Si2O8.

The soluble calcium salts are responsible for the hardness of natural spring water.

Calcium, Ca (Z=20)Properties: an alkaline earth metal, silver-white, which tarnishes slowly in air and is approximately as hard as tin.

Calcium, Ca (Z=20)Reactions: highly reactive chemically, oxidizes slowly in air, burns rapidly when heated in air to form calcium oxide,

2 Ca (s) + O2(g) → 2 CaO(s)

reacts with water to form calcium hydroxide and hydrogen gas,

Ca(s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)

and reacts with dilute acids with the liberation of hydrogen gas,

Ca(s) + HCl(aq) → CaCl2(aq) + H2(g)

Calcium burns with a light red glow.

Zinc, Zn (Z=30)

Occurrence: available in many forms including dust, foil, granules, powder, pieces, shot, and a mossy form.

Properties: a transition metal: bluish-white & lustrous. Brittle at ambient temperatures, but malleable at 100-150 oC.

Flame Test: burns with a light green glow.

Reactions: When exposed to the atmosphere, zinc reacts with oxygen to form zinc oxide, which reacts with water molecules in the air to form zinc hydroxide. Finally zinc hydroxide reacts with carbon dioxide in the atmosphere to yield a thin, impermeable, tenacious and quite insoluble dull gray layer of zinc carbonate which adheres extremely well to the underlying zinc.

2 Zn(s) + O2(g) → ZnO(s) + H2O(g) → Zn(OH)2 (s) + CO2(g) → 2 ZnCO3(s)

when the zinc carbonate surface is scratched, the underlying zinc reacts with water with the liberation of hydrogen gas:

Zn (s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)

and reacts with dilute acids with the liberation of hydrogen gas:

Zn(s) +2 HCl(aq) → ZnCl2(aq) + H2(g)

and in weak basic solutions, it reacts to form zinc hydroxide, a white precipitate:

Zn(s) +2 NH4OH (aq) → Zn(OH)2(s) + H2(g)

but in stronger basic solutions, this hydroxide is dissolved to form soluble zincates.

Zn(OH)2(s) + 2 OH- (aq) → Zn(OH)42-

(aq)

Zinc, Zn (Z=30)

Checkout – (All items checked out should be returned) STAR Spectroscope 5 vials with metals: Mg, Al, Si, Ca & Zn

Set of Crayons ROYGBV 1 piece of sandpaper1 bottle of phenolphthalein 6M HCl in a squeeze bottle1 flint striker 6M NaOH in a squeeze bottle

In Lab Computerized scanning spectrophotometer – 1 setup in 212Gas discharge tubes (for viewing by STAR spectroscope)

He & Ne on in both rooms. Ar & Kr in 201. Xe in 212.

All students View Scanning Spectrophotometer for Part A in Room 212.

TAs will let you know when to go to see the demonstration.View Gas Discharge tubes for Part B, located near the chalkboards.Do tests on metals for Part C at your lab bench.

Hazards: 6M HCl – strong acid, corrosive (use solid NaHCO3 on spills) 6M NaOH - strong base, corrosive

Phenolphthalein – laxative effect if swallowed Bunsen Burner – open flames

Waste: Liquid waste - all waste, metals, acid & rinses.

For November 17-21

Read: Radiochemistry (pp 119-136) in Lab packet.

Due: Atomic Spectra & Periodic Properties Handout (Note: Page 159 counts as your calculations page.

That is, if calculations are shown on p159, then you do not have to do an additional calculations page.

Reactor Trip in Class November 17-21 will take the full 3 hours.Reminder: You must have your student id to go to the reactor.Also: NO backpacks, NO cell phones & NO electronic devices are allowed in the reactor! Still

needs to be verifie

d.

We might be skyping the reactor.