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Structure of an Atom. A brief review of the structure of atoms. History of Atomic Theory. See the Powerpoint on Atomic Theory Scientists for more information and pictures/models. Review/Summary: - PowerPoint PPT Presentation
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STRUCTURE OF AN ATOM
A brief review of the structure of atoms
HISTORY OF ATOMIC THEORY See the Powerpoint on Atomic Theory Scientists for more
information and pictures/models. Review/Summary:
Democritus, 460 BC – proposes particles so small they can not be destroyed or divided, and describes them as “atomos” (uncuttable)
John Dalton, early 1800’s - first to use “atom”; proposes that atoms of the same element are identical, and atoms of different elements have different weights/masses; Solid Sphere Model
JJ Thomson, ~1897 – discovers the first subatomic particle, electrons; Plum Pudding Model
Ernest Rutherford, ~1912 – discovers the proton, and nucleus; Nuclear Model
Niels Bohr, ~1915 – discovers energy levels for the electrons; Planetary Model
Erwin Schrodinger, ~1926 – developed the Electron Cloud Model James Chadwick, ~1932 – discovers the neutron in the nucleus
Most Modern Model – The electron cloud model with all three subatomic particles
DEVELOPMENT OF ATOMIC THEORY
A more extensive review of Atomic Theory Development: http://
www.abcte.org/files/previews/chemistry/s1_p1.html
Use the “next” button at the bottom of the webpage above to cycle through the different scientists and their theories/models.
WHAT IS AN ATOM? Smallest particle of an element (pure substance)
that still has the properties of that element. Most of the atom is made of EMPTY SPACE
Example: an atom of gold is the smallest particle of gold (an element or pure substance) that still has the properties of gold.
Video: http://www.youtube.com/watch?v=o-3I1JGW-Ck
Brainpop (username: sclee password: cougars): Atom:
http://www.brainpop.com/science/matterandchemistry/atoms/
Atomic Model: http://www.brainpop.com/science/matterandchemistry/atomicmodel/
TWO MAIN REGIONS OF THE ATOM
Nucleus Positive charge Almost all of the mass of an atom Tiny, dense center of the atom Can be broken apart in chain reactions to produce
HUGE amounts of energy for use in electricity, medicine, weapons, etc (nuclear energy)
Electron cloud Negative charge Almost 0 mass Energy levels/shells
Max # electrons – 2,8,8* Valence level – outermost energy level
THE NUCLEUS OF AN ATOM Tiny and dense Center of the atom Contains protons and neutrons Positive charge (positive protons plus neutral neutrons) Very little of the volume (space) in an atom, but almost all
of the mass Mass = protons + neutrons Units for mass are amu (atomic mass unit)
Held together by a strong nuclear force Can be split apart in controlled chain reactions to release
nuclear energy: http://www.youtube.com/watch?v=ufEAg9h9wU8 http://www.youtube.com/watch?v=mBdVK4cqiFs Fermi is the first scientist to conduct controlled chain
reactions Nuclear energy in weapons:
http://www.brainpop.com/science/energy/radioactivity/
Video tutorial: http://www.youtube.com/watch?v=FSyAehMdpyI
ELECTRON CLOUD
Most of the volume in the atom, but almost 0 mass
Contains only electrons Negative charge Energy levels
Closest to the nucleus is the lowest level Outermost level is the valence level
SUBATOMIC PARTICLES
Protons Neutrons Electrons
Video tutorial: http://www.youtube.com/watch?v=FSyAehMdpyI
ISOTOPES Atoms of the same element can have different
numbers of neutrons. This means their mass is also different (mass =
protons + neutrons)
Naming isotopes: use the name of the element, followed by the mass number of that atom Ex: Carbon-12, Carbon-13
Video Brainpop: Isotopes: http
://www.brainpop.com/science/matterandchemistry/isotopes/
Radioactivity: http://www.brainpop.com/science/matterandchemistry/periodictableofelements/
IONS In a neutral atom, the number of protons equals the
number of electrons. Neutral atoms are often unstable, because they do not have a
full valence level. Unstable atoms will gain or lose electrons to become
stable.
Atoms which have gained electrons (gained negative particles) are negative ions. They will have more electrons than protons.
Atoms which have lost electrons (lost negative particles) are positive ions. They will have fewer electrons than protons.
To see if it is an ion, compare protons and electrons.
Video Tutorial Brainpop: Ions:
http://www.brainpop.com/science/matterandchemistry/ions/
PERIODIC TABLE ARRANGEMENT
Dimitri Mendeleev developed the first (near) modern Periodic Table of Elements Page 71 in your book Based on physical properties, especially atomic
mass (later rearranged by atomic number)
Periods are rows, and tell how many energy levels the neutral atom has; elements increase left to right across the periods and are very different in properties/reactivity;
Groups or families are columns; atoms in the same group have the same number of valence electrons, and similar chemical reactivity.
CHEMICAL REACTIVITY ON THE PERIODIC TABLE
Metals on the left (2/3 of the table), metalloids on the break, metals on the right (except hydrogen). Most reactive metals – group 1, with 1 valence electron; Most reactive nonmetals – group 17, with 7 valence electrons; Nonreactive (inert) elements – group 18, with full valence level
METALS, NONMETALS, METALLOIDS ON THE PERIODIC TABLE
Property Metals Metalloids Nonmetals
Luster (shine) Yes No No
Malleable Yes No (brittle) No (brittle)
Ductile (wires) Yes No No
Conductivity Yes Semi- No
State at rom temp.
Solid (except mercury)
Solid Solid, liquid, or gas
PERIODIC TABLE TRENDS
Atomic number increases
Ato
mic n
um
ber in
crease
s
Atomic Mass Increases
Ato
mic M
ass In
crease
s
Metallic Properties Increase