Elements

1
Elements Compounds

• Section 3.4

2
Elements

• Substances that cannot be broken down or
  decomposed into simpler substances by any means.
• Definite properties.
• Homogeneous
• Formulas have 1 uppercase letter.

3
(No Transcript)
4
Atom

• The smallest particle of an element that
• retains the properties of the element.
• can undergo a chemical reaction.

5
Diatomic Triatomic Elements

• Some elements occur as molecules, not atoms.
  Describe the following
• He N2 O3 S8 Ar Cl2 P4

6
Plastic Sulfur
Volume 2, CCA
Plasulf1.mov
Plasulf2.mov
Plasulf3.mov
Plasulf4.mov
Plasulf5.mov
7
Compounds

• 2 or more elements chemically combined in a
  definite ratio.
• Properties of compounds are different from those
  of the elements from which they are formed.

8
source
Source
2Na Cl2 ? 2NaCl
Unique Properties
source
9
Compounds

• Homogeneous.
• Broken into elements by a chemical decomposition
  reaction.
• Formulas have 2 or more uppercase letters.

10
Particle Diagrams

• Each kind of circle represents a different
  element.
• Circles that are touching are chemically combined.

11
Particle Diagrams
Atoms of a monatomic element.
?
?
?
?
?
?
?
?
Molecules of a diatomic element.
?
?
?
?
?
?
?
?
12
Particle Diagrams
Pure substance units the same. molecules of a
triatomic compound.
?
?
?
?
?
?
?
?
?
Mixture units differ. monatomic element,
diatomic element, triatomic compound.
?
?
?
?
?
?
?
?
?
?
?
?
?
13
Mixture vs. Pure SubstanceThe Scheme of Things!
14
(No Transcript)
15
Phys. M.
Chem.
Mixtures ? Separated by physical
methods. Compounds ? Separated by chemical
methods.
16
(No Transcript)
17
Law of Definite Proportions

• A given compound always has the same elements in
  the same proportions by mass.
• A definite recipe!

18
Percent by Mass

• ? Part X 100

Whole
Part mass of each element Whole mass of
compound
19
Chemical Analysis

• Given a 5.0 gram sample of NaCl.
• Analysis yields 1.96 grams of Na and 3.04 grams
  of Cl2. What is the percent composition?

20
(No Transcript)
21
Law of Multiple Proportions

• Same elements can make more than 1 compound
  different recipes!
• H2O 2 parts H to 1 part O
• H2O2 2 parts H to 2 parts O
• So H2O2 has twice as much O as H2O.
• The different masses of O that can combine with a
  fixed mass of H are related by small whole
  numbers.