MID-TERM REVISION
Unit 2 : Materials and their structure
HOW ARE THE PARTICLES
ARRANGED IN A SOLID,
LIQUID, AND GAS?
•In a solid, particles are tightly packed
and do not move much. In a liquid,
particles are close but can move around
each other. In a gas, particles are far
apart and move freely.
WHY DO GASES SPREAD
OUT TO FILL THE ENTIRE
SPACE IN A CONTAINER?
The particles in a gas move quickly in all
directions, so they spread out to fill the
space.
WHAT IS THE DIFFERENCE
BETWEEN BOILING AND
EVAPORATION?
•Boiling happens throughout the liquid
at a specific temperature, while
evaporation only happens at the surface
of the liquid and at any temperature.
WHAT IS SUBLIMATION?
CAN YOU GIVE AN
EXAMPLE?
•Sublimation is when a solid changes
directly into a gas without becoming a
liquid first. An example is dry ice
turning into carbon dioxide gas.
YOU HAVE A BALLOON FILLED WITH AIR.
IF YOU PUT IT IN THE FREEZER, WHAT
WILL HAPPEN TO THE BALLOON? WHY?
•The balloon will shrink because the cold
temperature causes the gas molecules to move
more slowly and come closer together, taking up
less space.
HOW DOES THE WATER
CYCLE AFFECT THE AMOUNT
OF FRESH WATER AVAILABLE
TO US?
•The water cycle continually moves water
through evaporation, condensation, and
precipitation, making fresh water available to
lakes, rivers, and groundwater that we can use
for drinking and farming.
•\
IF A GOLD RING IS CUT INTO
TINY PIECES, WILL THE
PIECES STILL BE GOLD? WHY
OR WHY NOT?
•Yes, the pieces will still be gold
because gold is an element. Each piece,
no matter how small, is made up of gold
atoms, which retain the properties of the
element.
HOW CAN WE EXPLAIN WHY WATER
(H₂O) IS DIFFERENT FROM THE
ELEMENTS HYDROGEN (H) AND OXYGEN
(O) THAT MAKE IT UP?
•Water is a compound formed when hydrogen and oxygen atoms
chemically bond. Although water is made from hydrogen and oxygen,
its properties (like being a liquid at room temperature) are very
different from the gases hydrogen and oxygen because when atoms
combine, they form new substances with different properties.
IF YOU MIX TWO ELEMENTS
TOGETHER, WILL THEY
ALWAYS FORM A COMPOUND?
•No, just mixing two elements together doesn’t guarantee a
compound will form. For a compound to form, the elements
must chemically bond. For example, mixing iron filings and
sulfur will not create iron sulfide unless you heat them so
they chemically react.
WHY DO WE NEED TO KNOW
THE CHEMICAL FORMULA OF
COMPOUNDS?
The chemical formula tells us which elements are in a compound
and in what proportions. For example, the formula H₂O shows that
water is made up of two hydrogen atoms and one oxygen atom.
This helps us understand the composition of substances.
WHY IS CARBON DIOXIDE
(CO₂) CALLED A
"DIOXIDE"?
•The "di-" prefix means "two," and since carbon dioxide
is made of one carbon atom and two oxygen atoms, it’s
named carbon dioxide to reflect its composition.
WHAT WOULD YOU NAME A
COMPOUND MADE OF SODIUM (NA)
AND SULFUR (S)?
The compound would be named sodium sulfide because it
follows the naming rule for ionic compounds: the name of
the metal (sodium) comes first, followed by the non-metal
(sulfur), with the "-ide" suffix added.
WHY IS THE PERIODIC
TABLE ORGANIZED IN
ROWS AND COLUMNS?
•The rows (called periods) represent increasing atomic numbers, while the
columns (called groups) contain elements with similar chemical properties.
This organization helps scientists easily predict how elements will behave in
reactions based on their position.
WHY ARE ELEMENTS LIKE HELIUM (HE)
AND NEON (NE) PLACED IN THE SAME
GROUP ON THE PERIODIC TABLE?
•Helium and neon are both noble gases, meaning they are
very stable and don’t usually react with other elements.
Elements in the same group share similar chemical
properties, which is why they are placed together.
WHICH OF THE FOLLOWING IS A
CHARACTERISTIC OF A MIXTURE?
A) FIXED COMPOSITION
B) CHEMICAL BONDS BETWEEN COMPONENTS
C) COMPONENTS RETAIN THEIR INDIVIDUAL
PROPERTIES
D) UNIFORM COMPOSITION THROUGHOUT
C)Components retain their individual
properties
WHICH OF THE FOLLOWING IS AN EXAMPLE OF
A COMPOUND?
A) AIR
B) SALTWATER
C) SODIUM CHLORIDE (TABLE SALT)
D) SAND
C) Sodium chloride (table salt)
WHICH OF THE FOLLOWING IS AN EXAMPLE OF
A COMPOUND?
A) AIR
B) SALTWATER
C) SODIUM CHLORIDE (TABLE SALT)
D) SAND
C) Sodium chloride (table salt)
WHICH OF THE FOLLOWING BEST DESCRIBES A
COMPOUND?
A) A SUBSTANCE THAT CAN BE PHYSICALLY SEPARATED
INTO ITS COMPONENTS
B) A SUBSTANCE WITH A FIXED RATIO OF ELEMENTS
C) A MIXTURE WHERE COMPONENTS ARE IN DIFFERENT
PHASES
B) A substance with a fixed ratio of
elements