Download Atoms and the PT

Warm-Up?
Q). What information do you think you can get
about elements reading the periodic table?.
Elements
• Elements are a
substance that can not
be separated or broken
down into simpler
substances by chemical
means.
• Each element contains
only one set of
particles.
• These particles are
called atoms.
Example: the element copper is
made of only copper atoms
Atoms
Atom: the smallest unit of
matter that retains the identity
of the substance
Atomic Structure
• Atoms are composed of 2 regions:
–Nucleus: the center of the
atom that contains the mass of
the atom
–Electron cloud: region that
surrounds the nucleus that
contains most of the space in
the atom
What’s in the Nucleus?
• The nucleus contains 2 of the 3
subatomic particles and most of the
mass of an atom:
– Protons: positively charged
subatomic particles
– Neutrons: neutrally charged (no
charge) subatomic particles
Electrons
• The 3rd subatomic particle resides
outside of the nucleus in the electron
cloud
– Electron: the subatomic particle with
a negative charge and relatively no
mass
How do these particles interact?
• Protons and neutrons live
compacted in the tiny positively
charged nucleus accounting for
most of the mass of the atom
• The negatively charged electrons
are small and have a relatively small
mass but occupy a large volume of
space outside the nucleus
Using the Periodic Table of Elements to find Out the
Number of Protons, Neutrons, and Electrons are in Each
Atom
The atomic number is
the number located on
top and the atomic
mass/weight is the
decimal number located
on the bottom.
- As in this example for
krypton:
Finding the Number of Protons
The atomic number is
the number of protons
in an atom of an
element. In our
example, krypton's
atomic number is 36.
This tells us that an
atom of krypton has 36
protons in its nucleus.
Protons
The interesting thing here is that every
atom of krypton contains 36 protons. If an atom
doesn't have 36 protons, it can't be an atom of
krypton. Adding or removing protons from the
nucleus of an atom creates a different element.
For example, removing one proton from an
atom of krypton creates an atom of bromine.
The Number of Electrons is...
• By definition, atoms have no overall electrical
charge. That means that there must be a
balance between the positively charged
protons and the negatively charged electrons.
Atoms must have equal numbers of protons
and electrons.
# Protons = # of Electrons
Losing Electrons
• An atom can gain
or lose electrons,
becoming what is
known as an ion.
• Don’t worry, we
will get to that
later!
The Number of Neutrons is...
• The atomic mass is basically a measurement of
the total number of particles in an atom's nucleus.
Nucleus/Atomic mass= (Number of Protons) + (Number of
Neutrons)
The Number of Neutrons is...
So then….to find the number of neutrons,
all you need to do is …
1. Round the atomic mass to the nearest
whole number
2. Subtract the number of protons
(Atomic Number) from the atomic
mass.
1. Round the atomic mass to the
nearest whole number
In our example,
krypton's atomic
mass is 84 .
* 83.80, rounds
up to 84.
The Number of Neutrons is...
• Then all we have to
do is plug in the
numbers…
• 84 = 36 + (Number
of Neutrons)
• 84-36 = 48
• Krypton has 48
neutrons
In Summary...
For any element:
• Atomic Number = Number of Protons
• Number of Protons = Number of Electrons
• Number of Neutrons = Atomic Mass (rounded)
- Atomic Number