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The Structure of Matter
Atomic Models
Subatomic Particles
Forces Within the Atom
Atomic Structure
I. Structure of the Atom
 Chemical Symbols
 Subatomic Particles
A. Chemical Symbols
Capitals matter!
 Element symbols contain ONE capital
letter followed by lowercase letter(s) if
necessary.

Metal that
forms bright
blue solid
compounds.
Co vs. CO
Poisonous
gas.
B. Subatomic Particles
ATOM
ATOM
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
POSITIVE
CHARGE
NEUTRAL
CHARGE
Most of the atom’s mass.
NEGATIVE
CHARGE
NEGATIVE CHARGE
in a neutral atom
Atomic Number
equals the # of...
B. Subatomic Particles

Quarks
6
types
3
quarks = 1
proton or 1
neutron
He
A. Atomic Mass
 atomic mass unit (u)
 1 u = 1/12 the mass of a
 1 proton = 1 u
12C
atom
1
neutron = 1 u
 1 u = 1.67  10-24 g
© Addison-Wesley Publishing Company, Inc.
B. Mass Number
 Sum of the protons and
neutrons in the nucleus of
an atom.
 Always a whole number.
© Addison-Wesley Publishing Company, Inc.
 # of neutrons = mass # - atomic #
C. Isotopes
 Atoms of the same element with different
numbers of neutrons.
 Isotope symbol:
Mass #
Atomic #
“Carbon-12”
12
6
C
C. Isotopes
© Addison-Wesley Publishing Company, Inc.
Identity of the Atom:
Understand that the number of protons determines the
identity of an atom (an element).
Understand that an atom of a given element may lose or
gain electrons yet it still remains the same element.
Mass of the Atom:
Understand that only the total number of protons and
neutrons determines mass.
Reactivity of the Atom:
Electrons determines properties.
Chemical reactions occur in the electron cloud.
The number of electrons in the outer energy level of the
atom and the relative distance from the nucleus of these
outer-energy level electrons determine how the atom will
react chemically.
Volume of the Atom:
The volume of the electron cloud determines the volume of
the atom.
Atomic Number = Number of Protons
- Elements are in order by atomic #
- Identifies an element
Mass Number = Protons and Neutrons added
together
Charge
Mass
Location
Protons
+
1 AMU
Nucleus
Neutrons
0
1 Amu
Nucleus
Electrons
__
0 AMU
Electron
Cloud
Atomic
Number
Mass
Number
Protons Electrons
K
5
Be
8
36
Neutrons
Identify the element:
•1.This element has 6 protons _____________________.
•2.This element has 9 electrons ___________________.
•3.This element has a mass of 11 amu and 4 electrons.
_______________.
•4.This element has a mass of 23 amu and 10 electrons.
______________.
•5.This element has a mass of 20 amu and 9 electrons.
_______________.
•6This element has a mass of 19 amu and 8 electrons.
_______________.
•7.This element has 1 electron ___________________
C. Isotopes
 Average Atomic Mass


reported on Periodic Table
weighted average of all isotopes
Avg.
(mass # )(# of atoms)  (mass # )(# of atoms)
Atomic 
total # of atoms
Mass
C. Isotopes
 EX: About 8 out of 10 chlorine atoms are chlorine-35.
Two out of 10 are chlorine-37.
Avg.
(35 u)(8 atoms)  (37 u)(2 atoms)
 35.4 u
Atomic 
10 atoms
Mass
Isotopes
Name
C-12
C-14
Cl-35
Cl-37
U-235
U-238
Atomic Mass # P
#
E
N
Three main subatomic particles



Proton
Neutron
Electron
Protons





Positively charged
Found in nucleus
Has a mass of 1 amu
The number of protons determines the
identity of the atom
The atomic number tells the number of
protons
Elements are made of atoms
Hydrogen-1proton
Helium-2 protons
Lithium-3 protons
The number of protons determines the identity
of the element!! (atomic number)
What is that other particle found in the
nucleus?


It’s a neutron!
Neutrons have no charge
–


(they’re neutral)
Neutrons have a mass of 1 amu
Proton + neutron = mass number
Electrons




Electrons hang out in “orbitals” outside the
nucleus of the atom
Electrons have almost no mass
The electron cloud is the majority of the
volume of the atom
ELECTRONS ARE NEGATIVELY
CHARGED!
More electron info!


In a neutral atom, the number of electrons is
equal to the number of protons
When an atom gains or loses electrons, it is
called an ion.
The ionization process
Now I’m a happy ion!
I’m POSITIVE! And my
outer shell is full, without that
troublesome extra electron.
This chloride ion has
added an electron. It is
a NEGATIVE ion!
(note: the inner 2
electrons are not
shown)
Now I’m a happy ion!!!
Sodium chloride-everybody’s
happy!
One lost……
(positive ion)
One gained.
(negative ion)
Quick Review:
• The three subatomic particles
are proton, neutron and electron
• Protons are positively charged,
electrons are negative,
neutrons are neutral
• When an electron is lost or
gained, the atom becomes an
ion.
Isotopes
► Atoms
with the same number of protons but
different numbers of neutrons are called
isotopes.
► Isotopes are designated by the symbol and
the mass number:
 H-1: 1 proton, no neutrons
 H-2: 1 proton, one neutron
 H-3: 1 proton, two neutrons
It’s the Isotopes!
What symbols represent ions?
 Elements
on the left side of the
periodic table will lose electrons to
become positive ions
– Examples: Ca2+, Na+,Fe3+,Fe2+,Al3+
 Elements
on the right side of the
periodic table will gain electrons to
become negative ions
– Examples: F-, O2-, P3-, Cl-
How big is the nucleus?

If an atom was as
big as a football
field, the electrons
would move over
the entire field,
while the nucleus
would be the size
of a lima bean in
the middle of the
field.
If an atom was an elephant, the
nucleus would be as big as a flea
on the elephant
How massive is the nucleus?
 Even
though the nucleus is VERY
small, it is VERY massive. Even
though it’s the size of the flea, it
would weigh as much as the
elephant. And though the electrons
take up as much space as the
elephant, they would only weigh as
much as the flea.