Properties of Matter

Density• Density is a measure of how closely packed

the atoms are in a substance• Density will change as temperature changes– As a substance is heated, particles tend to spread,

making it less dense (ice is an exception)– Solids tend to be more dense than liquids; liquids

tend to be more dense than gasses.

Calculating Density• Density equals mass divided by volume• d = m/v– Mass usually measured in grams (g)– Volume either found by displacement or calculated

using a formula (mL, cm3, or cc)• Units: g/mL or g/cm3 or g/cc

Sinking and Floating• Density determines whether an object will sink

or float.• Substances/Objects that are

more dense will sink in substances that are less dense.

• Substances/Objects that are less dense will float in substances that are more dense.– The diet coke is less dense than

water. The regular coke is more dense than water. • Coke = 1.042 g/mL Diet Coke = 0.997g/mL• Water = 1.000 g/mL

Conductivity• Electrical Conductivity – the ability of a substance to

allow electrical energy to flow through it• Thermal Conductivity – the ability of a substance to allow

thermal energy to flow through it– Both are related to density• CONDUCTORS: more dense materials tend to be better

conductors (allow energy to flow through them easily)• INSULATORS: less dense materials tend to be poor conductors

(resist the flow of energy through them)

Special Properties of Water• Unlike most substances, the freezing point and

boiling point of water allow it to exist as a solid, liquid, and gas at natural Earth temperatures

Special Properties of Water• Water heats up & cools down very slowly

compared to other substances– Due to a property called “specific heat”– This maintains a moderate environment on Earth that

is suitable for life

Special Properties of Water• Water forms “polar molecules”, creating “hydrogen

bonds” between molecules. This results in…– Cohesion – water molecules attracted to each other

– Adhesion – water molecules attracted to other substances

Special Properties of Water• Water is called the “universal solvent”– Many other substances dissolve in water• The water we encounter is rarely pure because so many

minerals can easily dissolve in it.