Transcript Activity 17: Modeling Molecules

Major Concepts
Activity 16/Periodic Table Activity
• There are more than 115 elements that
combine in a multiple of ways to produce
compounds
• Compounds do not have the same
properties as the elements that made
them
• Elements in the same family (group) have
similar properties
Major Concepts
• Scientists communicate their findings and
build on each other’s work
• Atoms are the smallest building block of
matter
• The periodic table is organized by atomic
number which is the number of protons in
the atom (# protons = # electrons because
the atom has no electrical charge)
• The number of protons defines the atom
Activity 17
Title: Modeling Molecules
Read B-31
Problem: How do atoms combine to form
molecules?
Hypothesis/Initial Thoughts:
Molecular Models
• What is an atom?
– The smallest building block of matter
• What is an element?
– A molecule composed of only one type of
atom
• What is a compound?
– A molecule composed of two or more
different types of atoms
Prior Knowledge
Structure of the Atom
Subatomic
Particle
Proton
Neutron
Electron
Positive
No Charge
+
0
Negative
-
Location
Nucleus
Nucleus
Electron
Cloud
Mass
1
1
0
Charge
Structure of the Atom
Molecular Model Sets
• A complete set contains:
– 4 elements, 64 atoms
•
•
•
•
Black: Carbon (18)
White: Hydrogen (32)
Blue: Nitrogen (4)
Red: Oxygen (14)
– 54 white bonds
• Colors do not correspond to actual
physical properties of the atoms
Molecular Model Sets
• The spherical center of each model
represents the center of the atom
– Nucleus
• The protruding “sticks” represent the
bonding sites
– Electrons
• NOT TO SCALE!!!!!
Procedure: Follow procedure on pgs. B-32 to B-33
• Steps 1-3 Together
– Elements are written using the capitalized
chemical symbols shown on the periodic table.
– The number of atoms in one molecule is noted
by writing the number as subscript after the
atomic symbol.
– When there is one atom in a molecule, such as
the one oxygen molecule in H2O, the one is not
written, it is implied.
• Steps 5-10 Guided
• Steps 11-15 In Your Group
E
Data/Observation:
Part A
Procedure step 2 and 3
H
H
O
Water, H2O
Procedure step 5
H
H
H
H
C
H
N
H
Methane, CH4
H
Ammonia, NH3
Procedure step 6
O
O
Oxygen, O2
Procedure step 7
H
H
Hydrogen, H2
N
N
Nitrogen, N2
Part B
Procedure step 11
• Follow the rules in the book to construct
4 different molecules
• Go on to procedure steps 12-15
Read the Procedure!
Discussion
• What information do the models show about
atoms, elements, and molecules?
– Each model atom shows the number of bonds
that a particular atom can make.
• Nitrogen - 3 bonds
• Hydrogen - 1 bond
• NH3
– From this information you can predict the
molecules the atom can form and the formulas
of compounds that will result.
Discussion
• Given that nitrogen forms three bonds
with hydrogen to make NH3, how many
hydrogen atoms do you think will bond
with an atom of phosphorus?
– Phosphorus will bond with 3 hydrogen atoms
to form PH3
– Phosphorus is in the same family (column)
as nitrogen
Discussion
• How many bonds with hydrogen would sulfur
form?
– With 2 hydrogen atoms like oxygen
• How many different elements were you
working with?
• What was the role of the “sticks” on each
atom model?
Demo: Sodium in Water
Chemical Formula
2Na(s) + 2H2O(l) ------ 2NaOH(aq) + H2(g)
Sodium and hydrogen are both in group 1 and are
very reactive. When the sodium reacts with the
water it takes the place of one of the hydrogen
atoms. This happens because sodium is more
reactive than the hydrogen it is replacing.
Reactivity is largely due to the atomic radius of an
element and the valence. Larger metals lose their
outer electrons more easily. If the sodium was less
reactive than the hydrogen then there probably
would be no chemical reaction in this case.