Download Atomic Structure - Mr. Fischer.com

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Matter can be broadly classified into 3 types
◦ Mixtures
◦ Compounds
◦ Elements
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Nearly all matter (molecules) we encounter in
life is a mixture of substances.
Mixture = blend of 2 or more substances
◦ Air = mixture of gases
◦ Tap water = minerals and gases
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When components of mixture are separated,
they are separated into pure substances.
Pure substance =constant properties and
constant composition
◦ Example: Salt water = salt + water
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Pure substances can be divided into 2
categories: compound or element
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Element = simplest type of matter with
unique physical and chemical properties.
◦ Element consists of only one kind of atom
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Compound =type of matter composed of two
or more different elements that are
chemically bound together.
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An atom is the smallest particle of an element
that retains its identity in a chemical reaction.
1. All elements are composed of tiny particles called
atoms.
2. Atoms of the same element are identical.
3. Atoms of different elements can physically mix in
simple whole number ratios to form compounds.
4. Chemical reactions occur when atoms are
separated, joined, or rearranged.
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We draw circle pictures!!!
Dalton drew circle pictures to represent each
kind of atom.
Element A
Element B Mixture
of A & B
Compound Another
of A & B
Compound
of A & B
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What’s in the box?
◦ Individual atoms, or
molecules?
◦ Substance (pure) or mixture?
◦ Compound, element, or both?
10

What’s in the box?
◦ Individual atoms, or
molecules?
◦ Substance (pure) or mixture?
◦ Compound, element, or both?
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What’s in the box?
◦ Individual atoms, or
molecules?
◦ Substance (pure) or mixture?
◦ Compound, element?
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Rutherford proposed:
◦ The atom’s mass is concentrated
in a tiny positive nucleus
◦ Lightweight negative electrons
circle the nucleus as planets orbit
the sun
◦ Most of the atom is empty space
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Atoms are made up of subatomic particles:
Particle
Charge
Location
Mass
Electron (e-)
Negative (-)
Outside
nucleus
9.109 x 10–28 g
Proton (p+)
Positive (+)
Inside nucleus
1.673 x 10–24 g
Neutron (n0)
No charge
Inside nucleus
1.675 x 10–24 g
1. Most of the volume in an atom is occupied by
electrons.
2. The nucleus is the central core of an atom and it is
composed of protons and neutrons.
• The number of protons present in an atom determines
which atom you have.
 Protons = atomic number.
• The mass # of an atom is determined by the number of
protons and neutrons.
 Mass # = protons + neutrons
 Neutrons = mass – protons
• Not all elements are the same.
 Isotopes =same element with a different # of neutrons
 This is called the weighted mass average.
• This system of mass based on the mass of Carbon-12.
mass number, A
protons + neutrons 
atomic number, Z 
protons
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23 1+
Na
11
 ion charge
protons – electrons
Atomic number is found on the periodic table
Mass number is NOT found on the periodic
table
An atom may gain/lose electrons to form an
ion
If no charge is shown, the charge is zero (a
neutral atom)
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Symbol
12
Protons
Neutrons
Electrons
Atomic #
C
21
Mass #
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Atoms with the same number of protons but
different numbers of neutrons are isotopes of
the same element
6Li and 7Li are isotopes of lithium

Both are the element lithium

6Li
has 3 protons, 3 neutrons

7Li
has 3 protons, 4 neutrons
Their chemical behaviors are identical
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Oxygen has three naturally-occurring
isotopes, with 8, 9, and 10 neutrons. Write
the symbols for each of the isotopes.