Download Elements, Atomic Structure, and Atomic Models

Elements, Atomic Structure,
and Atomic Models
Physical Science
Mrs. Baker
Chemical Symbols
•  Capitals matter!
•  Element symbols contain ONE capital
letter followed by lowercase letter(s) if
necessary.
Metal that
forms bright
blue solid
compounds.
Co vs. CO
Poisonous
gas.
History of Atomic Theory
(or how do we study atoms?)
•  How can we study atoms? They are so
SMALL!!!
•  Over time, scientists have invented several
experiments to help increase our
understanding of atoms.
•  A scientific model is a representation of an
object or event that makes it easier to
understand things that are difficult to observe
directly.
–  Example: Solar system mobile
–  Example: Atomic theories
The Structure of an Atom
•  Nucleus—small, dense, positively
charged central portion of the atom
–  Protons
–  neutrons
•  Area outside of the nucleus
–  Electrons
Subatomic Particles
•  Protons
–  Positively charged (assigned charge of +1)
–  Mass of 1
–  Found in nucleus
•  Electrons
–  Negatively charged (assigned charge of -1)
–  RELATIVELY no mass
–  Found outside of nucleus
•  Neutrons
–  Existence proven by James Chadwick in 1932
–  Mass of 1
–  Neutral particle (0 charge)
–  Found in nucleus
+
-
Secton 4.2 – The Structure of an Atom
Comparing Subatomic
Particles
•  Protons, electrons and neutrons are
distinguished by
–  Mass
–  Charge
–  Location inProperties
an atom
of Subatomic Particles
Particle
Symbol
Electron
Proton
Neutron
e
+
p
n
-
Relative
Charge
1
+
1
0
Relative Mass
(Proton = 1)
1/1836
1
1
Actual
Mass (g)
9.11E-28
1.67E-24
1.68E-24
Secton 4.2 – The Structure of an Atom
Atomic Number and Mass
Number
•  Atomic number
–  Atoms of any given element always have same number of
protons
–  Atoms of different elements always have different number of
protons
–  Atomic number of an element = # of protons in one atom of
that element
–  Atoms are neutral, so each proton in an atom (with its
positive charge) is balanced by one electron (with a negative
charge); thus, atomic number also equals number of
electrons
•  Mass number
–  Mass number of an atom = # of protons + # of neutrons in
nucleus of that atom
–  Number of neutrons = Mass number – Atomic number
Mass Number
•  Sum of the protons and
neutrons in the nucleus
of an atom.
♦ Always a whole
number.
© Addison-Wesley Publishing Company, Inc.
♦ # of neutrons = mass # - atomic #
Secton 4.2 – The Structure of an Atom
Isotopes
•  All atoms of an element have the same number of
protons
•  NOT ALL atoms of an element have the same
number of neutrons
•  Isotopes of an element: atoms of the same element
that have different numbers of neutrons, and thus
different mass numbers
•  Isotopes are referred to by their name and mass
number when needed (example: hydrogen-1 and
hydrogen-2)
•  Example: heavy water is made up of two hydrogen-2
atoms bound to oxygen
Isotopes
© Addison-Wesley Publishing Company, Inc.
Subatomic Particles
ATOM
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
POSITIVE
POSITIVE
CHARGE
NEUTRAL
NEUTRAL
CHARGE
Most of the atom’s mass.
NEGATIVE
CHARGE
NEGATIVE CHARGE
in a neutral atom
Atomic Number
equals the # of...
Subatomic Particles
•  Quarks
–  6 types
•  3 quarks = 1
proton or 1
neutron
He
Atomic Structure Timeline
A basic history of our understanding of the
atom.
Democritus (400 B.C.)
•  Proposed that matter was
composed of tiny indivisible
particles
•  Not based on experimental
data
•  Greek: atomos
Alchemy (next 2000 years)
•  Mixture of science and mysticism.
•  Lab procedures were developed, but alchemists did not
perform controlled experiments like true scientists.
John Dalton (1807)
•  British Schoolteacher
–  based his theory on others’
experimental data
•  Billiard Ball Model
–  atom is a
uniform,
solid sphere
Secton 4.1 – Studying Atoms
Dalton’s Atomic Theory
• 
5 Parts of Dalton’s Theory:
1)  All elements are composed of atoms
2)  All atoms of the same element have the same
mass, and atoms of different elements have
different masses
3)  Compounds contain atoms of more than one
element
4)  In a particular compound, atoms of different
elements always combine the same way
5)  Atoms cannot be divided.
Henri Becquerel (1896)
•  Discovered radioactivity
–  spontaneous emission of
radiation from the nucleus
•  Three types:
–  alpha (α) - positive
–  beta (β) - negative
–  gamma (γ) - neutral
J. J. Thomson (1903)
•  Cathode Ray Tube
Experiments
–  beam of negative particles
•  Discovered Electrons
–  negative particles within
the atom
•  Plum-pudding Model
J. J. Thomson (1903)
Plum-pudding Model
–  positive sphere
(pudding) with
negative electrons
(plums) dispersed
throughout
Ernest Rutherford (1911)
•  Gold Foil Experiment
•  Discovered the nucleus
–  dense, positive charge in
the center of the atom
•  Nuclear Model
Ernest Rutherford (1911)
•  Nuclear Model
–  dense, positive nucleus surrounded
by negative electrons
Niels Bohr (1913)
•  Bright-Line Spectrum
–  tried to explain presence
of specific colors in
hydrogen’s spectrum
•  Energy Levels
–  electrons can only exist in
specific energy states
•  Planetary Model
Bohr’s Model of the Atom
•  Focused on electrons
–  Electrons move with constant speed in fixed orbits
around the nucleus
–  Each electron has a specific amount of energy
–  Energy levels: the possible energies that
electrons can have
–  No two elements have the same set of energy
levels
•  An electron in an atom can move from one
energy level to another when an atom gains
or loses energy
•  Evidence for energy levels: Light given off in
fireworks
Niels Bohr (1913)
Bright-line spectrum
•  Planetary Model
–  electrons move in circular
orbits within specific
energy levels
Erwin Schrödinger (1926)
•  Quantum mechanics
–  electrons can only exist in
specified energy states
•  Electron cloud model
–  orbital: region around the
nucleus where e- are likely
to be found
Erwin Schrödinger (1926)
Electron Cloud Model (orbital)
•  dots represent probability of finding an enot actual electrons
James Chadwick (1932)
•  Discovered neutrons
–  neutral particles in the
nucleus of an atom
•  Joliot-Curie
Experiments
–  based his theory on their
experimental evidence
James Chadwick (1932)
Neutron Model
•  revision of Rutherford’s Nuclear Model