Lecture 2.3- Elements vs. Compounds

Section 2.3 Lecture for Honors & Prep Chemistry

1. Bellwork- Classify Matter
Identify 5 items that fit each of the following
categories.
a) Substance
b) Homogeneous mixture
c) Heterogeneous mixture
d) Solution
Select one thing from category b and one
from category c and outline a method for
separating the components.

2. Lecture 2.3- Elements vs. Compounds
Elements and compounds are
both pure substances.
How are they different?
2.3
3

3. An element is the simplest form of
matter.
A compound is a substance that
contains two or more elements
chemically combined in a fixed
proportion.
2.3

4. Compounds can be broken down into
simpler substances by chemical
means, but elements cannot.
2.3

5. Breaking Down Compounds
A chemical change
produces matter with a
different composition
than the original matter.
When table sugar is heated,
it goes through a series of
chemical changes.
2.3

6. The final products of these chemical
changes are solid carbon and water vapor.
The following diagram summarizes the
process.
2.3
Because sugar can be chemically broken into
more than one element, it is a compound.

7. Liquid H
2
O ® H
2
O vapor

8. Liquid H
2
O ® H
2
O vapor
Physical change because it is still H
2
O!

9. Liquid H
2
O ® H
2
O vapor
Physical change because it is still H
2
O!
Glass cup ® pile of broken glass

10. Liquid H
2
O ® H
2
O vapor
Physical change because it is still H
2
O!
Glass cup ® pile of broken glass
Physical change because it is still glass!

11. Liquid H
2
O ® H
2
O vapor
Physical change because it is still H
2
O!
Glass cup ® pile of broken glass
Physical change because it is still glass!
H
2
+ O
2
® H
2
O

12. Liquid H
2
O ® H
2
O vapor
Physical change because it is still H
2
O!
Glass cup ® pile of broken glass
Physical change because it is still glass!
H
2
+ O
2
® H
2
O
Chemical change because H
2
and O
2
become
something different.

13. Properties of Compounds
The properties of compounds are
very different from those of their
component elements.
When the elements sodium and
chlorine combine chemically to form
sodium chloride, there is a change in
composition and a change in
properties.
2.3

14. Chlorine is
used to kill
harmful
organisms in
swimming
pools.
2.3

15. Sodium is
stored under oil
to keep it from
reacting with
oxygen or water
vapor in the air.
Sodium vapor
produces the
light in some
street lamps.
2.3

16. Sodium Chloride
(commonly known
as table salt) is
used to season or
preserve food.
2.3

17. Sodium Chloride
(commonly known
as table salt) is
used to season or
preserve food.
2.3
Cl + Na  NaCl

18. Sodium Chloride
(commonly known
as table salt) is
used to season or
preserve food.
2.3
Cl + Na  NaCl
Poison explosive food!

19. Sodium Chloride
(commonly known
as table salt) is
used to season or
preserve food.
2.3
Cl + Na  NaCl
Poison explosive food!
element element compound

20. This flowchart
summarizes the
process for
classifying
matter.
Figure 2.11 on
page 50
2.3

24. for Conceptual Problem 2.2

25. Chemists use chemical
symbols to represent elements,
and chemical formulas to
represent compounds.
These chemical symbols were used in
earlier centuries.
2.3

26. Each element is represented by a
one or two-letter chemical symbol.
The first letter is always capitalized.
The 2nd letter (if applicable) is always
lowercase

27. 1.Passing an electric current through a
certain substance produces oxygen and
sulfur. This substance cannot be a(n)
a.compound.
b.mixture.
c.element.
d.solution.
2.3 Section Quiz

28. 2.Which of the following is a mixture?
a.sodium chloride
b.carbon dioxide
c.sucrose
d.air
2.3 Section Quiz

29. 3.The symbol for the element
potassium is
a.K.
b.Po.
c.P.
d.Pt.
2.3 Section Quiz.