LECTURE: ATOMIC MASS/MASS

NUMBERISOTOPESRADIOACTIVE ISOTOPESMASS SPECTROMETERHYDROGEN SPECTRUM

ATOMIC MASS, MASS NUMBERThe atomic mass number is the

AVERAGE of all the isotopes of an element (will be a decimal number)

The mass number is the number of protons and neutrons in a single atom (will be a whole number)

CALCULATING ATOMIC MASS NUMBER

Chlorine has 2 naturally occurring isotopes: 35Cl and 37Cl. They are abundant at 75% and 25%, respectively. Calculate the atomic mass of Cl.

CALCULATING % ABUNDANCE FROM ATOMIC MASS OF KNOWN ISOTOPESIridium is composed of almost entirely 191Ir

and 193Ir. Its molar mass is 192.2 g mol-1. What are the naturally occurring percentages of the two isotopes?

RADIOACTIVE ISOTOPESRadioactive isotopes of all elements can

be produced by exposing the natural element to a flux of slow-moving neutrons in a nuclear reactor; the nucleus captures neutrons

USES OF “RADIOISOTOPES”CARBON-14 DATING

C-14 is found in all living things due to the exchange occurring in the carbon cycle

When an organism dies, the C-14 proportion stops and begins to decay

Half-Life = 5,700 years

USES OF “RADIOISOTOPES”TRACERS

Radioisotopes can be used biologicallyEx. Iodine radioisotopes can be ingested

(drank) to measure the activity of the thyroid gland (which absorbs iodine)

The increase in radioactivity of the gland is then measured

USES OF “RADIOISOTOPES”INTENSE RADIATION

Some radioisotopes produce intense radioactivity (gamma rays)

EX. Co-60; which is used in radiation treatment or industrially to monitor the thickness of a steel plate from a rolling mill

MASS SPECTROMETERA mass spectrometer is an instrument

which separates particles according to their masses.

VAPORIZEDIONIZEDACCELERATEDDEFLECTEDDETECTED

ELECTROMAGNETIC SPECTRUM The study of the emission of light by atoms and

ions is the most effective technique for deducing the electronic structure of atoms.

The best evidence that electrons in an atoms surround the nucleus in certain allowed energy levels, or orbitals, comes from a study of the emission spectra of elements.

ELECTROMAGNETIC SPECTRUMRemember the flame test????Excited electrons will absorb energy and

jump to higher energy levels.To return to ground state, they will emit

light energy of a characteristic color.Ex.

Lithium – REDSodium - YELLOW

ELECTROMAGNETIC SPECTRUM Energy levels are

not evenly spaced, so as the wavelength gets shorter (and frequency gets higher) the lines in the spectrum will converge

BALMER SERIES - HYDROGEN

APPLICATION PROBLEMSWhich of the following are usually

found in the nucleus of an atom?A. Electrons and neutrons only.B. Neutrons only.C. Protons, neutrons, and electrons.D. Protons and neutrons only.

APPLICATION PROBLEMSThe number of neutrons in an atom

of 135Ba isA. 56B. 82C. 138D. 194

APPLICATION PROBLEMSHow many electrons would have

about the same mass as a proton or a neutron?

A. 200B. 500C. 2000D. 5000

APPLICATION PROBLEMSWhich one of the following is not a

common use of a radioactive isotope?

A. As a fuel in fuel cellsB. Irradiating tumors in patients with

cancerC. Measuring the rate of uptake of a

drug that has been swallowedD. Finding the age of rocks

APPLICATION PROBLEMSRadioisotopes of normally stable elements

areA. Chemically extracted from the natural

elementB. Mined from scarce underground depositsC. Formed from the stable element in nuclear

reactorsD. Produced through chemical reactions of the

stable element

APPLICATION PROBLEMSIdentify the following subatomic particles

A. The particle that has a much lower mass than the others ______________________

B. The particle that has no electrical charge ______

C. The particle that is not found in the nucleus ____________

D. The number of these in the nucleus is equal to the atomic number ___________

E. The particle that is gained or lost when ions form __________________