Atomic Structure 1. Atomic and Mass Number The number of protons in an atom = atomic number (symbol “Z”) The mass = protons + neutrons (symbol “A”) Mass.

Atomic Structure

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Atomic and Mass Number

The number of protons in an atom = atomic number (symbol “Z”)

The mass = protons + neutrons (symbol “A”) Mass is measured in atomic mass units (µ)

Number of neutrons = mass number – atomic number

Standard Atomic Notation: “Biggie over small”

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Practice

For each example find the For each example find the number of protonsnumber of protons number of neutronsnumber of neutrons number of electronsnumber of electrons atomic numberatomic number mass numbermass number

F19

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A)

B)

C) An element that has 91 An element that has 91 protons and 140 protons and 140 neutronsneutrons

Isotopes and Radioisotopes

Isotopes are different forms of an element having the SAME atomic number but DIFFER in the amount of neutrons (and mass).

Radioisotopes: Atoms with an unstable nucleus and decay (or break apart) to produce radioactive particles Three types: alpha (α), beta (β), and gamma (γ)

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Cl35

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37Cl

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Medical Uses of Isotopes

Used to detect thyroid diseases

Iodine–131 Body uses it the same

as naturally-occurring iodine (Iodine-127)

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Other uses of isotopes…

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Carbon Dating(carbon-14)

Smoke Detectors(americium-241)

Agricultural Research

(carbon-14, Phosphorous-32)

Isotopic Abundance and Atomic Mass

Different elements have different numbers of isotopes that exist in different relative abundances Ex: An average sample of magnesium contains:

78.7% Mg-24,10.1% Mg-25 and 11.2 % Mg-26

Atomic mass is the weighted average of the masses of all isotopes of that element

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Calculate the relative atomic mass of chlorine if the relative abundance of Cl-35 is 75.43% and Cl-37 is 24.47%.

mCl = (percent abundance of Cl-35 x atomic mass Cl-35) +

(percent abundance of Cl-37 X atomic mass Cl-37)

mCl = (0.7543 X 35 u) + (0.2447 X 37 u)

= 26.40 + 9.05 u

= 35.45 u

Calculating Relative Atomic Mass

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Radiation

Three main types: Alpha (), Beta (), Gamma () Alpha radiation = 2p+, 2n0 same as He nucleus

Beta radiation = high energy electrons or positrons

Gamma radiation = high energy electromagnetic waves (have no mass and travel at the speed of light)

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Different types of radiation have different penetrating power

Radioisotope HALF-LIFE

HALF-LIFE refers to the time for ½ of the original number of radioactive atoms to decay

Example: The half-life of cesium-137 is 30a. What mass of cesium-137 would remain from a 12 gram sample after 30a? After 60a?

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Radioisotope HALF-LIFE

Cesium-137

12 g

2 half-lives

60 a

1 half-life

30 a

6 g 3g

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Homework

Worksheet + text questions

Old Book

Pg. 29 # 7, 8

Pg. 32 # 9

New Book

Pg. 29 # 2, 6, 8

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