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Atom Structure
Chapter 3
I. Defintion
Atoms
are the
fundamental unit
of which elements
are composed.
II. Structure
What
makes up
an atom?
–3 Subatomic
particles
Subatomic Found
Particle
Charge
Mass
(amu)
III. Atomic Mass
Where
is the mass
of the atom found?
–Nucleus
p + n = amu
IV. Periodic table
V. Practice
Li
Ne
Cl

How many protons,
neutrons, and
electrons?
VI. Atomic Notation
Lets try!
VII. Isotopes

Why is the AMU not a whole number?
– ATOMIC MASS IS AN AVERAGE MASS OF
ALL ATOMS OF AN ELEMENT

ISOTOPE – Different numbers of
neutrons in nucleus.
Isotopes



Protons job- giving the element it’s
identity
Neutron’s job - give the element more
mass
Isotopes- same element (same # of
protons), but different masses (so the
# of neutrons can change!)
Isotopic Notation



This would be Carbon-14
(the name of the element (dash) the
mass of the element)
This is Carbon-12
ISOTOPES CONT….


Example: Chlorine has a mass on the
periodic table of 35.453 amu.
There are 2 isotopes of chlorine.
75% chlorine-35
25% chlorine-37.
Sample Problem

Chlorine-35 has an atomic mass of
34.969 amu and has an abundance of
75.770%. Chlorine-37 has an atomic
mass of 36.966 amu and has an
abundance of 24.230%. Calculate the
average atomic mass of chlorine.
Step 1: Multiply the mass of each isotope by its percent
abundance
Step 2: Sum the results
You Try

Calculate the average atomic mass for
element X. Can you figure out what X
is? It is Used to treat mental disorders.
ISOTOPE
MASS
(AMU)
Abundance
%
6X
6.015
7.5%
7X
7.016
92.5%
VIII. IONS



A neutral atoms
have same # of
protons and
electrons.
Atoms can gain or
lose electron(s)
becoming a charged
ion
Example: Na has 11
protons and 11
electrons
IONS
• Na can lose 1
electron making
it have a charge
of +1
Na1+ or Na+
IONS

Some elements
can become
negative ions
by GAINING
electrons.
IONS
Will gain 1 electron
therefore an overall
(1-) charge.
9++ 10-= 1 F-
Ions Charges & The
Periodic Table
Label these on your periodic tables
Atoms want to be like the noble gases (group 8)
because noble gases are very stable
(unreactive/inert)… Other atoms will lose/gain
electrons to become like one.
IX. Bohr Diagrams
Sec 11-2 (p. 366)
Wave Mechanical Model
A. Electron Energy Levels
•Energy levels begin closest to nucleus
& move further out
1st energy level = max. of 2 e2nd energy level = max. of 8 e3rd energy level = max. of 8 e-
•An energy level must be full
before electrons move to the
next level.
•An element is more stable
when energy levels are full
Practice- Lets draw them!
1.Lithium
2. Magnesium