LECTURE: A TOMIC M ASS /M ASS N UMBER I SOTOPES R ADIOACTIVE I SOTOPES M ASS S PECTROMETER H YDROGEN S PECTRUM

A TOMIC M ASS, M ASS N UMBER The 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)

C ALCULATING A TOMIC M ASS N UMBER Chlorine has 2 naturally occurring isotopes: 35 Cl and 37 Cl. They are abundant at 75% and 25%, respectively. Calculate the atomic mass of Cl.

C ALCULATING % A BUNDANCE FROM A TOMIC M ASS OF K NOWN I SOTOPES Iridium is composed of almost entirely 191 Ir and 193 Ir. Its molar mass is g mol -1. What are the naturally occurring percentages of the two isotopes?

R ADIOACTIVE I SOTOPES Radioactive 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 biologically Ex. 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

M ASS S PECTROMETER A mass spectrometer is an instrument which separates particles according to their masses. VAPORIZED IONIZED ACCELERATED DEFLECTED DETECTED

E LECTROMAGNETIC S PECTRUM 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.

E LECTROMAGNETIC S PECTRUM Remember 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 – RED Sodium - YELLOW

E LECTROMAGNETIC S PECTRUM 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 - H YDROGEN

APPLICATION PROBLEMS Which 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 PROBLEMS The number of neutrons in an atom of 135 Ba is A. 56 B. 82 C. 138 D. 194

APPLICATION PROBLEMS How many electrons would have about the same mass as a proton or a neutron? A. 200 B. 500 C D. 5000

APPLICATION PROBLEMS Which one of the following is not a common use of a radioactive isotope? A. As a fuel in fuel cells B. Irradiating tumors in patients with cancer C. Measuring the rate of uptake of a drug that has been swallowed D. Finding the age of rocks

APPLICATION PROBLEMS Radioisotopes of normally stable elements are A. Chemically extracted from the natural element B. Mined from scarce underground deposits C. Formed from the stable element in nuclear reactors D. Produced through chemical reactions of the stable element

APPLICATION PROBLEMS Identify 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 __________________