Download Introduction to Atoms

Introduction to Atoms
Chemistry Standard 1 a:
Essential Question:
How is an element’s position on
the periodic table related to its
atomic number and atomic mass?
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I. Atoms
A. Tiny particles that make up all
matter.
B. Contain three smaller subatomic
particles: protons, neutrons, &
electrons.
C. Have two parts:
1. Nucleus
2. Electron cloud.
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II. Atomic mass
1. Atoms have a VERY SMALL mass.
2. An atom’s mass is measured in
atomic mass units (amu)
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3. 1 amu = 1.66 x 10
kg
4. The mass of an atom is found on
the periodic table.
1. What is Carbon’s mass?
a. 12.01 amu
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III. Protons and neutrons
1. The nucleus is the center of the
atom.
2. Protons and neutrons are found
in the nucleus.
3. Protons have a positive charge.
4. Protons are very large
(compared to electrons)
a) A proton’s mass is about 1.00
amu (1840 times greater than
the mass of an electron!)
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5)Neutrons have no charge
6)Neutrons have an mass of 1.00
amu.
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IV. Electrons
1. Electrons are found outside the
nucleus, in the electron cloud.
2. Electrons have a negative
charge.
3. Electrons are VERY small
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V. Atomic number
1. Protons are positively charged
and electrons are negatively
charged.
2. Atoms are neutral (they have no
charge).
a) Each atom must have the same
number of protons and
electrons so their charges
cancel each other.
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3. The atomic number is the
number of protons.
A.If an atom is neutral, the
number of electrons is the
same as the atomic number.
B. Atoms of the same element
have the same atomic number.
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C. The atomic number is found
on the periodic table.
D. To Symbolize the atomic
number …
atomic number
element’s symbol
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VI. Mass number
1. (Or the atomic mass) is the
number of protons + the number
of neutrons.
+
0
a) atomic mass = #P + #N
2. You can find the #of neutrons
by subtracting # of protons
from atomic mass
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3. The mass number (atomic mass)
is found on the periodic table.
4. The mass number can be
written with the element’s
symbol…
A. C-12
mass number
B. .
atomic number
element’s symbol
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5. Atoms of the same element:
A. Can have different mass numbers
(called isotopes): C-12, C-14
B. Must have the same number
of protons BUT they can have
a different number of
neutrons.
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6. Atoms with the same number of
protons and electrons but
different numbers of neutrons
are called isotopes.
7. The atomic mass of an element is
an average mass of the atoms in
a naturally occurring sample of
the element.
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