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

• 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

Major Concepts

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 KnowledgeStructure of the Atom

Subatomic Particle

Proton Neutron Electron

Charge

Location

Mass

Positive

+

No Charge

0

Negative-

Nucleus Nucleus Electron Cloud

1 1 0

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

H H

O

Data/Observation:

Part AProcedure step 2 and 3

Water, H2O

E

Procedure step 5

CH

H

H

H

Methane, CH4

N

H

H

H

Ammonia, NH3

Procedure step 6

O O

Oxygen, O2

Procedure step 7

H H N N

Hydrogen, H2 Nitrogen, N2

Part BProcedure 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 WaterChemical Formula2Na(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.