CHEM100: Introduction to College Chemistry Atoms Dr. Aleksey Kocherzhenko Fall 2018
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CHEM100: Introduction to College Chemistry
Atoms
Dr. Aleksey KocherzhenkoFall 2018
Down the rabbit hole…
Ø Atoms – smallest constituent units of
ordinary matter that have the properties
of a chemical element)(what kind?)
(what’s that?)
species of atoms having the same number
of protons in their atomic nuclei(not all atoms are the same?)
(what are these?) (what are these?)
small, dense region consisting of protons and neutrons
at the center of an atom(hey, that word came up again, might be important!)
(what are these?)(how small and dense?)
What it really means
Richard Feynman in The Pleasure of Finding Things Out, directed by Christopher Sykes
Atomic hypothesis
Leucippus Democritus
Thales of Miletus“…water!”
Anaximenes of Miletus“…air!”
“Everything is composed of…”
Anaximander (of Miletus)“…apeiron!”
“Everything is composed of atoms : tiny particles that cannot be divided further.”
Not yet a scientific statement:no evidence to support it
Looking at atomsChemists were convinced that atoms existed and identified many types of atoms long before we could look at them directly Iron atoms
Copper surface
“Atom”
Today, scanning tunneling microscopes (STMs) allow looking at and manipulating individual atoms
More writing and drawing with atoms
1989
What we know about atoms today
Atoms are fundamental building blocks of ordinary matter
We know 118 types of atoms (chemical elements)
94 occur naturally on Earth 24 are synthetic
Atoms are made of yet smaller particles
Composition defines type of atom and how it can connect to other atoms
Terminology
ü Ordinary matter
ü Atom
ü Chemical element
ü Atomic hypothesis
CHEM100: Introduction to College Chemistry
Electrons
Dr. Aleksey KocherzhenkoFall 2018
Cathode raysØ Atoms – smallest particle of an element, initially assumed to be indivisible
J.J. Thomson
Cathode ray tube (CRT) TV and a cathode ray tube
Particles that make up cathode rays are more than a 1000 times lighter than the lightest atom – hydrogen, and have negative electric charge
Electric charge
Ø All objects have mass(describes gravitational interaction)
Ø Some objects have electric charge (describes electromagnetic interaction)
(always attract)
Particles that J.J. Thomson discovered have negative electric charge
These particles are called electrons
Terminology
ü Electric charge (positive, negative)
ü Electron
CHEM100: Introduction to College Chemistry
Atomic structure
Dr. Aleksey KocherzhenkoFall 2018
The plum pudding model
Where is positive and negative charge in neutral atoms?
Ø If amounts of positive and negative charges in an object are the same, then this object is overall electrically neutral
“Plum pudding” model
J.J. Thomson’s initial guess:small negative electronsin a “pudding” of positive charge
Wrong!
Nuclear model of atom
Ernest RutherfordMost particles passthrough foil (or are deflected a little)
Some particles bounce back!
Nucleus
Protons and neutrons
Neutron
Proton
Electron
Number of protons = atomic number,determines chemical identity of element
IsotopesIsotopes are atoms of the same chemical atoms that have different numbers of neutrons in their atomic nuclei
Protium Deuterium Tritium
Isotopes of hydrogen
Terminology
ü Electrically neutral
ü Nucleus
ü Proton
ü Neutron
ü Atomic number
ü Isotope
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