ECM: elements, compounds & mixtures

Question 1

define a compound and answer if compounds can exist as atoms

Answer 1

a compound is a substance containing two or more elements chemically combined together. it cannot exist as atoms.

Question 2

define an element

Answer 2

an element is a substance made up of the same type of atoms

OR

an element is a substance that cannot be broken down into two or more simpler substances using chemical methods

Question 3

what are the types of particles that elements can exist as?

Answer 3

• monatomic (exists as individual atoms)
• diatomic molecules (two atoms chemically combined together)
• polyatomic molecules (three or more atoms chemically combined together)

Question 4

list the chemical formulas of hydrogen, oxygen, nitrogen, halogens, ozone, phosphorus and sulfur, and group them into diatomic and polyatomic molecules

Answer 4

DIATOMIC MOLECULES
hydrogen: H₂
oxygen: O₂
nitrogen: N₂
fluorine: F₂
bromine: Br₂
iodine: I₂
chlorine: Cl₂

POLYATOMIC MOLECULES
ozone: O₃
phosphorus: P₄
sulfur: S₈
*how to remember: the number to call for special OPS is 348

Question 5

properties of compounds

Answer 5

1. physical and chemical properties of a compound are different from those of its constituent elements
2. the elements that make up a compound are always chemically combined in a fixed proportion by mass
3. a compound cannot be broken down by physical methods (see ST)

Question 6

define a mixture

Answer 6

a mixture is a substance made up of two or more different substances (elements and/or compounds) that are mixed but not chemically combined

Question 7

properties of mixtures

Answer 7

1) a mixture has the physical and chemical properties of the substances it is made up of
2) the components in a mixture are not fixed and can be present in any ratio
3) when a mixture is formed, no chemical reaction occurs. hence, mixtures can be easily separated by chemical methods.

Question 8

test to prove that an unknown liquid is pure or impure.

Answer 8

heat the liquid.

• if it boils at a fixed temperature, it is pure.
• if it boils over a range of temperatures, it is impure.

Question 9

test to prove that an unknown solid is pure or impure

Answer 9

heat the solid

-if it melts at a fixed temperature, it is pure.

-if it melts over a range of temperatures, it is impure.

Question 10

pure vs. impure substances

Answer 10

pure substances are made up of only one element or compound, while impure substances are made up of two or more substances that are mixed but not chemically combined.