Chapter 9: Electrons in Atoms and the Periodic Table
Date:____________
Section 5: Periodic Trends - Notes
Objectives:
 Identify and understand periodic trends such as atomic size, ionization energy, and metallic
character.
Chemical Properties:

The chemical properties of elements are largely determined by the number of ______________
___________________ they contain.
o
Their properties vary in a ______________________________ because the number of
valence electrons is periodic.

The noble gases are chemically stable because they have _______________________________.
o
Elements with electron configurations close to the noble gases are the ______________
________________________ because they can attain noble gas configurations by losing
or gaining a small number of electrons.
Atomic Size:

As you move right across a period, atomic size _________________________.
o
The atomic size of an atom is determined by the ___________________________
between the outermost electrons and the _______________________.
o
With each step across a period, the number of protons in the nucleus
_________________________. This results in a _______________________________
on the electrons from the nucleus.

As you move down a column, atomic size _________________________.
o
Since the ______________ of an orbital increases with each energy level, the electrons
that occupy the outermost orbitals are farther from the nucleus as you move down a
column.
Ion Size:

When an atom ____________________________________, it forms a cation.
o
Cations are ____________________ than their respective atoms.
o
When an electron is lost, the electron-electron repulsion is _____________________
and protons are better able to pull the electrons in.

When an atom ____________________________________, it forms an anion.
o
Anions are much ____________________ than their respective atoms.
o
When an electron is gained, the electron-electron repulsion is _____________________
and pushes the electrons further apart.
Ionization Energy:

Ionization energy is the amount of energy needed to _________________________________
_______________________ from an atom.

Ionization energy _____________________________ as you move to the right across a period
and _____________________________ as you move down a column in the periodic table.
Metallic Character:

Metals tend to ________________________________ in their chemical reactions.

As you move across a period, electrons are __________________________ to be lost in
chemical reactions.

Metallic character ______________________________ as you move right, and
___________________________ as you move down a column.
Electronegativity:

Electronegativity is a measure of the ability of an atom in a chemical compound
__________________________________________ from another atom in the same compound.

Electronegativity tends to ________________________________ as you move right across a
period and ____________________________ as you move down a column.