Transcript What is the atomic number?

The Atom
The Periodic Table
Comparing Atoms
The Atom


Atoms are the smallest part of all
matter.
All atoms contain three smaller particles
called subatomic particles:




Protons: positive particle
Neutrons: neutral particle
Protons and neutrons have the same mass
Electrons: negative particle with very little
mass
Atoms


Atoms are neutral; they have the same
number of electrons as protons.
Example: An atom of 42He has an atomic
number of 2 and a mass of 4.
Therefore, it has 2 protons and
2 neutrons in its nucleus.
Since it has 2 positive protons
(neutrons are neutral) it must
have 2 negative electrons to make
the total charge neutral.
How does one kind of
atom differ from
another?
 Number of protons
determines an element.
 Even if atoms bond or
break apart, number of
protons will always be
the same.



Protons and neutrons
cluster together in the
atom’s center called the
nucleus.
Electrons orbit the
nucleus.
An atom is only about
0.0000000001 meters big.
It would take 10 BILLIONS
atoms lying side by side to
equal 1 meter!
What is the atomic number?
Atomic number is
number of protons an
atom contains.
 Atomic numbers start at
one, with hydrogen, and
go up by ones until
element 111, unununium.

MASS NUMBER

The mass
number is
equal to the
total number
of protons
plus
neutrons.
AVERAGE ATOMIC MASS

Atomic mass
is the average
of all the
known
isotopes of
an element.
Atomic Mass/Mass Number

The mass number can be
written as a superscript
above the symbol and the
atomic number as a
subscript below the symbol.
Isotopes



Atoms of the same element can have
different numbers of neutrons.
These different forms of the same
element are called isotopes.
The atomic mass is the average mass of
all the known isotopes of the element.
How are electrons arranged?




Electrons are located in different energy
levels.
The farther away from the nucleus the
electron is found, the higher the energy.
As electrons move from a lower level to
a higher level energy is absorbed.
As electrons move from a higher level
to a lower level energy is release in the
form of light.
Group
Periodic Table
Period



The elements are listed in order of increasing atomic
number.
By looking at the row (period) number you can
determined how many energy levels are filled.
By looking at the column (group) number you can
determine how many electrons are in the outermost
level.







Group 1 (blue) – Alkali metal; note Hydrogen is a gas, not a
metal
Group 2 (red) – Alkali Earth Metals
Group 7 (pink)– Halogens
Group 8 (brown) – Nobel Gases – do not react with anything
Metalloids – (purple, staircase) acts like both metal and
nonmetal
Metal – (yellow, red, blue) – left of metalloids
Nonmetal – (green, pink, brown) – right of metalloids