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Inside the Atom
Chapter 1
Models of the Atom
• What is a scientific model?
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a representation of an object or system
can be used to make a prediction
can be tested
must be able to explain as many characteristics of
the observations as possible
▫ must be as simple as possible
▫ all models have limitations
Models of the Atom
A. Greek philosophers devised a theory of atoms,
or tiny particles.
B. John Dalton combined the idea of elements
with the Greek theory of the atom.
1.
2.
3.
4.
5.
Matter is made up of atoms.
Atoms cannot be divided into smaller pieces
All atoms of an element are exactly alike.
Different elements are made of different atoms.
Dalton’s theory was tested by William Crookes
and his cathode-ray tube experiment.
• The negatively charged electrons are attracted to
the positive plate and repelled by the negative
plate
C. J.J. Thompson discovered negatively charged
particles, electrons, which are a part of every
atom.
1. Thompson revised Dalton’s model to include a
sphere with positive charge and negatively
charged electrons spread evenly within the
positive charge.
2. The negatively charged electrons and the
positive charge in the sphere neutralize each
other.
D. Earnest Rutherford tested Thompson’s
model, which was found to be an inaccurate
model of the atom.
 Golf foil experiment
 Only a large positive charge would cause the
particles to bounce back!
D. An atomic model with a nucleus was developed.
1. The positively charged proton is located in a very
small space at the center of an atom
2. Most of an atom is empty space occupied by nearly
massless electrons.
3. Electrically neutral particles, neutrons, are also
located in the nucleus.
4. The number of electrons equals the number of
protons in an atom.
E. The electron cloud model explains the
unpredictable wave behavior of electrons, which
could be anywhere in the area surrounding the
nucleus.
• We are going to model our own atom according
to the electron cloud model.
• Half will be protons and half will be electrons.
• The entire room is our atom.
The Simplest Matter
A. Elements – matter made up of one kind of
atom.
1. There are 112 known elements
2. 90 naturally occurring elements, 25 synthetic
elements – made by scientists
B. Periodic Table – Chart that organizes and
displays information about the elements.
1. Atomic number – the top number in the
element’s periodic table block
a. Tells the number of protons in the nucleus of each
atom of that element
b. The number of protons remains constant in every
atom of an element.
2. Isotopes – atoms of the same element that have
different numbers of neutrons
3. Mass number – number of protons plus number
of neutrons
4. Atomic mass – the number found below the
element symbol
a. The average mass of an atom of an element
b. The unit used for atomic mass is the atomic mass
unit, which is given the symbol u.
C. Elements fall into three general groups
characterized by similar properties.
1. Metals – most of the elements
a.
b.
c.
d.
e.
Shiny luster
Good conductors of heat and electricity
Most are solids at room temperature
Malleable , or can be shaped
Ductile, or can be drawn into wires without
breaking
2. Nonmetals – found on the right side of the
periodic table
a.
b.
c.
d.
e.
Dull in appearance
Poor conductors of heat and electricity
Many are gases at room temperature
Brittle, cannot change shape without breaking
96 percent of the human body is made up of
nonmetals.
3. Metalloids – found between the metals and
nonmetals on the periodic table
a. Have characteristics of both metals and nonmetals
b. Do not conduct heat and electricity as well as
metals
c. All are solids at room temperature
Compounds and Mixtures
A. Substance – matter that has the same composition
and properties throughout
B. Compound – substance whose smallest unit is
made up of atoms of more than one element
1. Formula – tells which elements make up a
compound as well as how many atoms of each
element are present
a.
b.
The subscript number tells how many atoms of the
preceding element are in the compound
No subscript is used when only one atom of the element
is present
2. A given compound is always made of the same
elements in the same proportion.
Questions:
• H2O
– How many elements are there?
• C6H12O6
– How many oxygen atoms are there?
• KOH
– How many atoms are there?
• C2Cl3F3
– How many elements are there?
– How many Carbon atoms are there?
• NaCl
– How many elements are there?
Bonus question:
• C10H7N3S
– How many atoms are there?
• Mixture – two or more substances mixed
together which don’t make a new substance
▫ Unlike compounds, the proportions of the
substances can be changed without changing the
identity of the mixture
▫ Examples: air, blood…
▫ Can separate mixtures easily
▫ Homogeneous mixtures – the same throughout
▫ Heterogeneous mixtures – you can see the
different parts