Topic 1 - Matter and Energy - Revsworld

Topic 1 - Matter . and Energy
8. Chemical Symbols of matter: Recognizing chemical symbols of matter
Chemical symbols are used to show the compositions of elements, compounds and mixtures.
Examples:
Au(s) is the chemical symbol for gold, an element.
H 2 O (l) is the chemical symbol for water, a compound.
C 6 H 12 O 6 (aq) is the chemical symbol for sugar water, a mixture.
Concept Task: Be able to determine which chemical symbol
represents an element, a compound,
and a mixture.
Pure substances
To determine formula or name of a pure substance:
To determine a formula that has fixed or definite composition
LOOK for a name or a symbol of an element or a compound
Elements
To determine formula or name of an element:
To determine which substance CANNOT be decomposed:
To determine which substance is composed of atoms
with the same atomic number.
LOOK for a name or symbol that can be found on the
Periodic Table
LOOK for a symbol written with one capital letter only
Compounds
To determine formula or name of a compound……………………………………………………………… Which set of substances ………… can only be
To determine which substance CAN BE decomposed by
decomposed by chemical methods?
chemical method:
LOOK for name or symbol containing two or more
different elements (or with two or more capital letters)
Binary compounds
To determine formula or name of a binary compound
LOOK for a name or a symbol containing JUST TWO different
elements.
Formulas of binary compounds contains TWO capital letters
NOTE: (s), (l), or (g) may be written next to a chemical
symbol of show the phase (solid, liquid, or gas)
of the pure substance (compound and element).
Mixtures
To determine symbol of a homogeneous mixture
To determine symbol of matter whose composition can vary
LOOK for symbol containing (aq)
Example 1
Which set of formulas contains only
of pure substances?
1) Ca(s) and CaCl 2 (aq)
2) NH 3 (g) and NH 3 (aq)
3) Cl 2 (g) and NaCl(s)
4) NaOH(aq) and H 2 O (l)
Answer: Choice 3 because Cl 2 (g) is
an element and NaCl(s) is a
compound.
Example 2:
Which substance cannot be
decomposed into simpler substances?
1) Water 3) Lithium
2) Carbon monoxide 4) Ethanol
Answer: Choice 3 Because Lithium
an element (See Periodic Table), and
elements cannot be decomposed.
Example 3:
1) H 2 O 2 (l) and KClO 3 (s)
2) Na(s) and NaCl(aq)
3) N 2 (g) and NO 3 (g)
4) CH 4 (g) and CO 2 (aq)
Answer: Choice 1 because both
H 2 O 2 and KClO 3 are composed of
two or more elements, and
therefore are compounds.
Compounds CAN BE decomposed
by chemical methods.
NOTE: H 2 O 2 is a binary compound?
Example 4:
Which of the followings represents a
homogeneous mixture?
1) NH 3 (aq) 3) Br 2 (l)
2) MgSO 4 (s) 4) Ar (g)
Answer: Choice 1 because (aq)
always indicates a mixture
Wrong: Choice 2, MgSO4(s) is a
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