Chapter 4 - H
Atoms
4.1 Journal – Using Analogies
The network of blood vessels in your body is like the network of
streets and highways in a large city. How are the two
networks similar? Both networks are used to transport
objects from one location to another. The comparison is an
example of an analogy. An analogy uses a similarity to
compare two objects or systems. A familiar object is often
used to help explain a less familiar object.
1.
Atoms in compounds are like bricks in a wall. Explain
this analogy.
2.
Think of and explain another analogy for atoms in
compounds.
3.
WORK ON THE “ATOMIC MATH” WORKSHEET.
4.1 Studying Atoms
ANCIENT GREEKSDEMOCRITUS:
 “atomos” = indivisible, uncut
 Different types of atoms with specific properties
ARISTOTLE:


Only 4 elements
No limit to divisions
4.1 Studying Atoms
DALTON’S ATOMIC THEORY: all matter is made of
particles that cannot be divided
Evidence:

Compounds have fixed compositions
H2O
2g H always combines with 8g O
4g H always combines with 16g O
4.1 Studying Atoms
DALTON’S ATOMIC THEORY: all matter is made of
particles that cannot be divided
MAIN POINTS:
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different
kinds of atoms.
H2O, CO2, CH4, H2SO4
4) A chemical reaction is a rearrangement of atoms.
4.1 Studying Atoms
DALTON’S ATOMIC THEORY:
4.1 Studying Atoms
THOMSON’S ATOMIC THEORY: matter is made of
particles that CAN be divided
EVIDENCE:

Conducted a current thru a tube
4.1 Studying Atoms
THOMSON’S ATOMIC THEORY: all matter is made
of particles that CAN be divided
EVIDENCE:


No matter what metal was used, the particles had a mass
1/2000 of a Hydrogen atom.
The beam was always attracted to the positive side
Hypothesis- these particles came from the atoms.
4.1 Studying Atoms - Thomson’s “plum
pudding” Model
The 'Plum Pudding' Model of an Atom
4.1 Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms
positive charge is concentrated in the nucleus
4.1 Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms
positive charge is concentrated in the nucleus
Discovered:

Uranium emits fast moving positive particles
Hypothesis:

If you shoot positive particles at gold foil (other atoms), what
would happen to the particle?
 Their path will not change (according to Thomson’s plum
pudding)
4.1 Studying Atoms – Gold Foil Experiment
4.1 The Gold Foil Experiment
RUTHERFORD’S ATOMIC THEORY
all atoms positive charge is concentrated in the nucleus
4.1 Studying Atoms – Modern Atomic Theory
Bohr Atom: focused on the electrons
Electrons
are in energy levels
They move when the atom gains or loses energy
4.2/4.3 The Structure of the Atom & Modern Atomic Theory
JOURNAL:
1.
Work on the “Bohr Model” Worksheet from the back
table. Use the Periodic Table to help you.
FILL IN THE Parts of an ATOM:
Subatomic particles – distinguished by mass,
charge and location
Subatomic particle PROPERTIES
 Protons (p+):
In the nucleus
 Charge of 1+
 Mass of 1
 DEFINES THE ELEMENT
(equals the ATOMIC NUMBER)

Protons (p+):

Atoms of DIFFERENT elements have
DIFFERENT numbers of protons
Subatomic particle PROPERTIES
 Neutrons (n°):




In the nucleus
NO charge
Mass of 1
Protons + neutrons =
the ATOMIC MASS
Neutrons (n°):

Atoms of the same element with
DIFFERENT numbers of neutrons are called
ISOTOPES

Neutrons (n°):

ISOTOPES of Hydrogen. Same Atomic #,
different Mass #
Electrons (e-):





In ENERGY LEVELS around the nucleus
Charge of 1Mass of 1/1836 of a p+
Equal to the number of protons
The outermost shell of electrons is called the
VALENCE SHELL which holds the VALENCE
ELECTRONS.
Take out Bohr Diagram Sheet.
Electrons (e-):

Change ENERGY LEVELS when the atom GAINS or
LOSES energy
The most stable
electron arrangement
Electrons (e-):

Current Theory – “Electron Cloud Model” (p116-17)


Shows POSSIBLE locations of electrons around nucleus
It’s a good approximation of how electrons behave
Electrons (e-):

ORBITALS: the most likely location of the
electrons in the cloud.
Electrons (e-):

Atoms of the same element with different
number of ELECTRONS are called IONS
IONS: form to make the outermost shell stable