Atomic Structure and Nuclear Chemistry. Chapter 4 and 18. Elements a.k.a atoms. Robert Boyle first defined an element as a substance which could no longer be broken down into other substances Each element has unique properties
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Chapter 4 and 18
Democritus (460-370 B.C.) understood that if you cut a stone in two pieces, each piece contained the same material as the original stone. He also believed that you could do this an infinite number of times. He called these infinitesimally small pieces of matter atomos, meaning "indivisible.“
Rutherford’s gold foil experiment leads to atomic nucleus and in 1919 the introduction of the proton
1808 - Dalton first proposed a theory on atoms
Discovery of the electron by J.J. Thompson in the late 1890’s
1910 -Lord Kelvin’s “plum pudding theory
1912 –Bohr model of the hydrogen atom
Mid-1920’s – wave mechanical model
1932 – Rutherford and his coworker Chadwick identified the neutron
Lord Kelvin believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model (easier to think of as “chocolate chips" in chocolate chip cookie dough.)
(a) The results that the metal foil experiment would have yielded if the plum pudding model had been correct. (b) Actual results known as Rutherford’s model.
Over 98% of the particles went straight through
About 2% of the particles went through but were deflected by large angles
About 0.01% of the particles bounced off the gold foil
Most of the volume of the atom is empty space
The atom contains a tiny dense center called the nucleus
The nucleus is essentially the entire mass of the atom (extremely dense)
The nucleus is positively charged
The electrons move around in the empty space of the atom surrounding the nucleus
A nuclear atom viewed in cross section.
Going beyond the electron, proton, and neutron
How many protons, neutron, and electrons does an atom have?
The number of protons in an atom of a given element is the same as its atomic number (Z).
(p+ + no)
Charge (if any)
Cl-1 –38 Fluorine-18
(number of p+)
Element symbol with charge
atoms of an element with the same number of protons but different numbers of neutrons
Copper – 63 Copper – 65
Balancing Nuclear Equations
A material has t1/2 = 15 minutes. How much material is left after 75 minutes if you begin with 100 g?
What is the half-life of a material that decays from 16 g to 2 g over 20 minutes?
32He + 11H 42He + 01e
20984Po 12552Te + 8432Ge