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Notes – Chapter 4;
Unit 2 Section A
Atomic Structure
Atoms
• Atoms - The building
blocks of matter.
• Aristotle “Matter is
continuous and can be
subdivided endlessly
into smaller and smaller
parts”
• Democritus
“Subdivision of matter
will eventually end”
• “Atomos” – its name means
“uncut”. It is the smallest
part of an element which
has the properties of that
element.
Atom
Sub-atomic Particles (3)
Building blocks of atoms
1) Protons (+)
p+
2) Electrons (-)
e-
3) Neutrons (no charge) no
Nitrogen
• Atoms - The building
blocks of matter. The
smallest part of an
element with the
properties of that element
p+
e-
no
Nucleus – The central
core of an atom
made up of protons
and neutrons.
Contains almost all
of an atom’s mass
p+
no
• AMU – Atomic Mass Unit
Used for comparing the mass of
atoms and particles (Also
called daltons Da)
Protons – Positively charged
particles in the nucleus.
eAMU = 1
Neutrons – Neutrally charged
(no charge) particles in the
nucleus. AMU = 1
Electrons – Negatively charged
particles. Orbit the nucleus in
shells or clouds 1/1836 AMU
Nitrogen
p+
no
1 AMU = 1/12 the
mass of a neutral
Carbon atom
•
Atoms are mainly empty space
with 99.9% of their mass in the
nucleus
The nucleus is (+)
positively charged
because of its protons.
• In a neutral atom the
proton # = electron #
• B = Boron = __p+, __e• Cl = Chlorine
= ____p+, ____e-
e-
p+
•
Atoms are mainly empty space
with 99.9% of their mass in the
nucleus
The nucleus is (+)
positively charged
because of its protons.
• In a neutral atom the
proton # = electron #
• B = Boron = __p+, __e• Cl = Chlorine
= ____p+, ____e-
p+
e-
Atomic Number
• Atomic Number –
The number of
protons in an atom’s
nucleus. It is used to
determine and
#1=H–
describe each
#2 = He –
element
#3 = Li –
Dalton’s Atomic Theory
• 1) All elements are
composed of indivisible
particles called atoms
• 2) Atoms of different
elements can physically
mix together or
chemically combine in
whole number ratios to
form compounds
• 3) Atoms of the same
element are identical. The
atoms of any one element
are different from those of
any other element.
• 4) Chemical reactions occur
when atoms are separated,
joined, or rearranged.
Atoms are never changed
into atoms of another
element as a result of
chemical reactions.
Atomic Mass (Weight)
• Atomic Weight (Mass)=
Number of protons and
neutrons in an atom’s
nucleus.
Subtracting the atomic
mass and atomic
number tells the
number of neutrons
Neutrons give the atom
mass but no charge
Helium = He = Atomic # 2
Atomic mass = 4.0026
2 p+, 2 no
Atomic mass –
Atomic # = # no
In neutral atoms
# of p+ = # of e-
15
Atomic number
Chemical symbol –
one or two letters for
each element
p+ =
e-=
no =
30.974
Atomic mass
Atomic Particles
• Lithium =
Atomic Mass =
• Chlorine =
Atomic Mass =
Mass
#
(rounded)
=
mass =
-#
Mass
#
(rounded)
p+ =
e- =
no =
=
mass =
-#
p+ =
e- =
no =
Isotopes – Atoms of the same pair of
elements with different #’s of neutrons
14
C
6
__________
8 neutrons
13
C
6
_______
7 neutrons
12
Mass number
C
6
Atomic number
______
6 neutrons
Same elements, same # protons and electrons, different # neutrons
Isotopes – Atoms of the same pair of
elements with different #’s of neutrons
14
13
C
C
6
__________
8 neutrons
6
_______
7 neutrons
12
Mass number
C
6
Atomic number
______
6 neutrons
Same elements, same # protons an electrons, different # neutrons
C 12 =
C 13 =
C 14 =
98.89 % x 12 =
1.1 % x 13 =
.0000000001% x 14 = .
11.668
.1443
.0000000000014
= 12.0111 = 12.011
Isotopes
• Chemical symbol
shorthand:
Shows symbol with
atomic number and
mass number
Isotope name is from
mass number
17 = Atomic #
Cl
35 = Mass #
Chlorine-35
Isotopes – Atoms of the same pair of
elements with different #’s of neutrons
14
C
6
__________
8 neutrons
13
C
6
_______
7 neutrons
12
Mass number
C
6
Atomic number
______
6 neutrons
Same elements, same # protons and electrons, different # neutrons
Carbon-14
Carbon-13
Carbon-12
Ions – Charged atoms or groups of atoms
•
Most atoms are not in the neutral state.
Atoms will lose, gain, or share electrons to
become stable
Sodium atoms have a tendency to lose electrons.
Na
11p+
11e-
11p+
10e- =
+1 Na
+ 1 = Cation (positive)
Chlorine atoms have a tendency to gain electrons.
Cl
17p+
17e-
17p+
18e- =
-1 Cl
- 1 = Anion (negative)
Na +1 + Cl-1 = NaCl o
Sodium Chloride is an Ionic Compound
Ionic Bond – Positive (+) and negative (-) ions attract –
formed by the transfer of valence electrons.
Dalton’s Atomic Theory
• 1) All elements are
composed of indivisible
particles called atoms
• 2) Atoms of different
elements can physically
mix together or
chemically combine in
whole number ratios to
form compounds
• 3) Atoms of the same
element are identical. The
atoms of any one element
are different from those of
any other element.
• 4) Chemical reactions occur
when atoms are separated,
joined, or rearranged.
Atoms are never changed
into atoms of another
element as a result of
chemical reactions.
Discovering the Atom’s Sub-Atomic
particles
• 1897 Thompson
discovered the electron
• Cathode ray – Particles
• 1/1840 mass of H atom
Discovering the Atom
Electrons
• 1897 Thompson
discovered the electron
• Cathode ray – Particles
• 1/1840 mass of H atom
• Deflected negative
source, attracted
toward positive source
Discovering the Atom
Electrons
• 1897 Thompson
discovered the electron
• Cathode ray – Particles
• 1/1840 mass of H atom
• Deflected negative
source, attracted
toward positive source
• Devised “plum
pudding” model
Discovering the Atom
Atomic nucleus
• 1911 Rutherford used
Alpha particles ( Helium
atoms that have lost their
two electrons and have
double positive charges)
to bombard a sheet of
gold foil.
• A small fraction bounced
off the gold at very large
angles
Discovering the Atom
Atomic nucleus
• Proposed that the atom
is mainly empty space
• Positive charge and
mass are concentrated
in a small central core
called the nucleus.
Discovering the Atom
Atomic nucleus
• Proposed that the atom
is mainly empty space
• Positive charge and
mass are concentrated
in a small central core
called the nucleus.
Properties of Atoms
• Atoms are distinguished
from each other by
their number of protons
• This determines the
different types of
elements.
• Atoms are mainly
empty space with a
concentrated core in
the center
Properties of Atoms
• If an atom were the size
of a football field the
nucleus would be the
size of a marble
Properties of Atoms
• If an atom were the size
of a football field the
nucleus would be the
size of a marble
.
Periodic Table
• The Periodic Table is an
arrangement of
elements into groups
based on a set of
repeating properties
• It is based on the
number of protons and
the electron
configuration
Periodic Table
• The Periodic Table is an
arrangement of
elements into groups
based on a set of
repeating properties
• It is based on the
number of protons and
the electron
configuration
Valence electron
Periodic Table
• The Periodic Table is an
arrangement of
elements into groups
based on a set of
repeating properties
• It is based on the
number of protons and
the electron
configuration
Periodic Table
Period
• Each horizontal row of
the periodic table is
called a period.
• It is based on the
number of electrons
shells
Periodic Table
Group (family)
• Each vertical column of
the periodic table is
called a group of family.
• Elements within a group
have similar chemical
and physical properties
• They are grouped by
their number of outside
electrons
Periodic Table
Group (family)
• Each vertical column of
the periodic table is
called a group of family.
• Elements within a group
have similar chemical
and physical properties
• They are grouped by
their number of outside
electrons