• Characteristics of a substance

• characteristics that can be observed without changing the chemical identity of the substance
– Not dependent on amount of sample
Appearance
Odor
Melting Point
Boiling Point
Density
Hardness
Texture
Ductility/Malleability
Solubility
Electrical/Thermal
Conductivity
Magnetism

• Characteristics that describe the ways a substance can react to form new materials
– Cannot be observed without changing the chemical composition of the substance
• Examples
Flammability
Reaction with Oxygen
Reaction with Water
Decomposition by light
Decomposition by heat
Tendency to Corrode

• Changes that do not result in the formation of a new substance
– Chemical bonds have not been broken or formed; the molecules are still connected in the same way
• Change of state
• Change in appearance

• Changes in the chemical bonds of a substance
– Always produce a new substance
– Chemical bonds are broken and/or formed
– Signs:
• Visible flame
• Color change
• Bubbling/Fizzing
• Smoke
• Heat/Light given off
• Formation of a substance in a different state

• Elements
– cannot be broken down into any other substance
– All matter is composed of elements.
– Each element is made of a specific type of ATOM
• Ex: Oxygen
• Ex: Hydrogen

• Compounds
– two or more elements chemically combined in a specific ratio

• Mixtures
– two substances that are together in the same place but are NOT chemically combined

• Matter is made of tiny particles that are in constant, random motion
– can be classified as a solid, liquid, gas, or plasma depending on the motion and arrangement of the particles

• Particles do not move freely, but vibrate in place
– Packed tightly together, usually arranged in a specific & fixed pattern
• Definite volume
• Definite shape

• Particles move freely
– Fairly close together, but not in a fixed pattern
• Definite volume
• Indefinite shape (take shape of container)
– Viscosity: resistance to flow
• High viscosity – slow flow (honey)
• Low viscosity – easy flow (water)

• Particles move very energetically in all directions
– Very fast and far apart
• Indefinite volume (take up all available space)
• Indefinite shape (take shape of container)

• Particles have extremely high energy
– Highly energetic charged particles that move independently
– Extremely fast and far apart
• Most of the matter in the universe!

• Solids – particles tend to move slowly (vibrate) and keep their shape
• Liquids – particles move freely and take the shape of their container
• Gasses – particles move excitedly and fill all available space
• Plasmas – charged particles move extremely excitedly and fill all available space
What misconceptions could be created by the model shown here of particles in a solid, liquid, gas, and plasma?

• Transfer of heat energy is required to change the state
(or phase) of a substance
– Freezing/Melting Point
– Boiling/Condensation Point
Argon Ice melting and sublimating at the same moment

• 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.

• 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, cm 3 , or cc)
• Units: g/mL or g/cm 3 or g/cc

• 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

• 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)

• 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

• 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

• 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

• 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.