elements, compounds and mixtures

Question 1

what is a molecule

Answer 1

-diatomic (molecules consists of 2 atoms chemically combined together)
-polyatomic (molecules consists of 3 or more atoms chemically combined together)
-triatomic (molecules consists of exactly 3 atoms chemically combined together)

Question 2

element

Answer 2

made up of same type of atoms
cannot be broken down into 2 or more simpler substances by chemical methods

Question 3

how are they classified

Answer 3

metals & non-metals are differentiated by their physical properties:

appearance
physical state at r.t.p
melting point and boiling point
thermal conductivity
electrical conductivity
ductility and malleability

Question 4

periodic table contents

Answer 4

group (vertical columns)
period (horizontal columns)
group 1: alkali metals
group 2: alkaline earth metals
group 3-12: transition metals
group 13-16: no name
group 17: halogens
group 18: noble gases

Question 5

compound

Answer 5

substance containing 2 or more elements chemically combined together

Question 6

properties of compund

Answer 6

1. a compund has different physical and chemical properties as it constituent elements
2. the elements that make up a compound are always combined in a fixed propeortion by mass.
3. a coumound CANNOT be broken down by PHYSICAL METHODS

Question 7

mixtures

Answer 7

-a misture consists of 2 or more different substances that are mixed, but not chemically combined
-the components of a mixture are not fixed. they can be present in any ratio

Question 8

properties of mixtures

Answer 8

1. a mixture has the properties of the substance it is made up of
2. the components of mixtures are not mixed in any ficed proportion
3. when a misture is formed, no chemical reactions occurs. Hence, a mixture can be easily separated by ohysical methods.

Question 9

test for pure substance (element or compound)

Answer 9

for solid: fixed melting point/ MELTS at a fixed temperature
for liquid: BOILS at a fixed temperature

Question 10

impure substances (mixtures)

Answer 10

for solid: MELTS over a RANGE of temperatures
for liquids: BOILS over a RANGE of tmeperatures.