4.2 A guided tour of
the Periodic Table
I CAN:
-RECOGNIZE THAT ATOMS CAN BECOME CATIONS AND ANIONS
BECAUSE THEY GAIN OR LOSE ELECTRONS.
-RECOGNIZE THE ATOMIC NUMBER WILL STAY THE SAME AND DUE TO
ISOTOPES THE MASS NUMBER CHANGES.
-CALCULATE THE ATOMIC NUMBER, MASS NUMBER, CHARGE, AND
IDENTITY OF THE ELEMENT BASED ON THE PROTONS, NEUTRONS, AND
ELECTRONS
What is the purpose of the periodic
table?

To organize elements so you can find what you need to know
quickly.
Organization of the periodic table.

Properties can be predicted based on where the element is
located.

Based on # of protons.


hydrogen=1, helium-2, etc.
Periodic Law: repeating chemical and physical properties of
elements change periodically with the atomic number of elements.

This meaning will become much clearer soon!
The periodic table helps determine
electron arrangement

Horizontal rows=periods

Based on number of protons.

Can also determine electrons.

Electron configurations.

Energy level, orbital, number of electrons.

Carbon

1s2

2s2

2p2
Elements in the same group have
similar properties

Groups: vertical column of elements

Valance electrons determine chemical properties

Elements in same group have some number of valance electrons
therefore…
Some Atoms for Ions

Why are Group 1 elements reactive?

Atoms that do not have filled outer layers undergo ionization.


Gain or lose electron.
Will no longer have the same number of electrons as protons
(charged)

Ion: has lost or gained electron, has positive or negative charge.

Positive ions (lost electron)= cations


Lithium
Negative ions (gained electron)=anions

Fluorine
How do Structures of Atoms Differ?

Atomic number (Z): Number of protons

Mass Number (A): the sum of the number of protons and neutrons in
the nucleus.

Fluorine has 9 protons and 10 neutrons=?

Oxygen has 8 protons and 8 neutrons=?

Why aren’t electrons included in mass?

Atoms of each element will always have same atomic number, but
may have different mass numbers.
Isotopes

An atom that has the same number of protons as other atoms of the
same element do but that has different number of neutrons.

3 times the mass.
Calculating the number of neutrons
in an atom

Uranium:

Atomic number=92

Mass Number=235

Number of neutrons: 143
The mass of an atom

Fluorine atom has a mass less than
one trillionth of a billionth of a
gram.

Atomic mass unit (amu): a unit of
mass that describes the mass of an
atom or molecule; it is exactly one
twelfth of the mass of a carbon
atom with a mass number of 12.

Average atomic mass: the
weighted average of the masses
of all naturally occurring isotopes
of an element.