Download Pretest time!

Pretest time!
Clear desk except for pen or pencil
Done? Turn it in, pick up a pink packet and read the
periodic table lab
Periodicity
The similarities and differences
among elements based on their
location on the periodic table
Dmitri Mendeleev
In 1869 he published a table of the elements organized by
increasing atomic mass.
The “Father of the
Modern Periodic
Table”
1834 - 1907
Elements by Discovery Year
Periodic Table Lab
On a separate sheet of paper, create the following:
Title:
Purpose:
Using your group, identify the purpose for this lab
Data Table (observations):
Observations list
No numbers are necessary
Periodic Table Lab
Safety
Cover immediately (Group 1A, step 3)
Razor Blade
Alkali Metals and Skin
Phenolphthalein
**Done? Work with your group on the lab questions
(they are your homework)
Friday 3/23
General Periodic Trends
• Atomic and ionic size
• Ionization energy
• Electronegativity
With a neighbor, write down everything you know about Sodium.
Then, do the same for Potassium
Atomic
Size
• Size goes UP going down a group
• Size goes DOWN going across a period
(left to right)
Atomic Size
Size decreases across a period
Large
Small
Which is Bigger?
• Na or K ?
• Na or Mg ?
• Al or I ?
Ion Sizes
Li,152 pm
3e and 3p
Does+the size go
up+or down when
Li , 60 pm
losing
2e and an
3 p electron
to form a cation?
Ion Sizes
+
Li,152 pm
3e and 3p
Forming a cation.
Li + , 78 pm
2e and 3 p
• CATIONS are SMALLER than the atoms from
which they come.
• The electron to proton ratio has changed.
• The size DECREASES.
Ion Sizes
Does the size go up or down
when gaining an electron
to form an anion?
Ion Sizes
F, 71 pm
9e and 9p
F- , 133 pm
10 e and 9 p
Forming an
anion.
• ANIONS are LARGER than the atoms from
which they come.
• The electron to proton ratio has changed.
• The size INCREASES.
Trends in Ion Sizes
Similar to Figure 11.36 in book (pg 350)
Which is Bigger?
• Cl or
?
+
• K or K ?
• Ca or Ca+2 ?
• I - or Br - ?
Cl
Ionization Energy
IE = energy required to remove an electron from an atom
Mg (g) + 738 kJ ---> Mg+ (g)
+ eThis is called the FIRST ionization
energy because we removed
only the OUTERMOST electron
Mg+ (g) + 1451 kJ ---> Mg2+ (g) + eThis is the SECOND IE.
Successive ionization energy
Explaining the trends in ionization energy
Trends in Ionization Energy
IE increases across a period.
Why?
• Distance from the nucleus
• Becoming ‘more full’
IE decreases down a group. Why?
• Because size increases (Shielding Effect)
Which has a higher 1st ionization
energy?
• Mg or Ca ?
• Al or S ?
• Cs or Ba ?
Electronegativity
A measure of the ability of an atom or a
molecule to attract electrons to itself.
Concept proposed by
Linus Pauling
1901-1994
Periodic Trends:
Electronegativity
• In a group: Atoms with fewer energy
levels can attract electrons better (less
shielding). So, electronegativity
increases UP a group of elements.
• In a period: More protons, while the
energy levels are the same, means
atoms can better attract electrons. So,
electronegativity increases RIGHT in a
period of elements.
Electronegativity
Which is more electronegative?
• F or Cl ?
• Na or K ?
• Sn or I ?
How is electronegativity used?
• To predict the nature of the bond between
two atoms
• Is the bond polar or nonpolar?
• The larger the difference, the more likely that
the bond is ionic
• NOTE: A large difference in electronegativity
does not equate with a strong bond!!!