Density
What is density?
Density is mass divided by volume (mass/volume)
Why do scientists use models of particles in substances?
To visualize particles too small to see and explain properties based on particle structure.
What are plastics made of?
Long chains of hydrocarbons called polymers, usually derived from petroleum.
What happens to the temperature of ice during melting?
The temperature stays the same until all the ice melts.
What is heat in scientific terms?
Heat is the transfer of thermal energy from a warmer object to a cooler one.
Will a wooden cube with a density of 1.13 g/cm³ float or sink in water?
It will sink because its density (1.13 g/cm³) is greater than water's density (1.0 g/cm³).
What does a particle model of carbon in diamonds show about its structure?
It shows an extended structure, which explains why diamonds are hard solids.
Why have plastics become important in modern society?
Because they can be designed with many properties for use in packaging, equipment, and medical devices.
What state change occurs at the boiling point?
The substance changes from liquid to gas.
What is a monomer?
A small molecule that can join with others to form a polymer.
If you cut a wooden cube with density 1.13 g/cm³ in half, will each half float or sink? Why?
Each half will sink because cutting it in half halves both mass and volume, keeping the density the same (1.13 g/cm³).
Name three crosscutting concepts illustrated by particle models.
Scale, proportion, and quantity; structure and function; patterns.
What is a polymer?
A large molecule made by linking many smaller molecules called monomers.
What happens to particles at point B on a heating graph where boiling occurs?
Particles separate farther apart as the liquid becomes gas.
How is heat different from temperature?
Heat is energy transfer; temperature is a measure of particle kinetic energy.
Calculate the density of a cube with mass 9 grams and volume 8 cm³.
Density = 9/8=1.1389=1.13 g/cm³.
How do particle models help explain the properties of materials?
By showing arrangement, bonding, and interactions between particles at the atomic scale.
What is a major environmental concern about plastics?
They do not break down easily and last a long time, causing pollution.
How does thermal energy affect particles at point A on the graph?
It increases particle kinetic energy and temperature.
What does cross-linking do to the flexibility of a polymer?
It decreases flexibility, making the polymer stronger and more solid.
Why does an object with density higher than water sink?
Because it is denser than water, so gravity pulls it down more strongly than buoyant force can keep it afloat.
Draw and describe a simple particle model that explains a property of a substance you choose.
carbon in diamond has a strong lattice making it hard
How does cross-linking affect polymers?
It makes them stronger and more solid.
What is the effect of thermal energy on particles at point C (after boiling)?
Thermal energy increases particle kinetic energy and temperature of the gas.
What is a trade-off when using plastics?
They are useful but can cause environmental problems due to their persistence.