Chapter 2. 2.1 Pure Substances Elements Compounds Mixtures Solutions, Suspensions and Colloids.
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Transcript of Chapter 2. 2.1 Pure Substances Elements Compounds Mixtures Solutions, Suspensions and Colloids.
Properties of MatterChapter 2
Classifying Matter2.1
Types of Matter
Pure Substances Elements Compounds Mixtures Solutions, Suspensions and Colloids
Pure Substances
Matter that always has exactly the same composition
Every sample of a substance has the same properties because a it has a fixed composition.
Ex: salt, sugar, flour 2 Types
1. Elements2. Compounds
Elements
Cannot be broken done into simpler substances
fixed composition because contains only one type of atom
No two elements contain the same type of atom
Atom = smallest particle of an element
Element Example
Gold
Aluminum
Carbon
Sodium
Compounds
Made from two or more simpler substances
Contains two or more elements in a fixed proportion
Can be broken down into its simpler substances (either elements or other compounds)
Properties of a compound differ from those substances from which it is made
Compound Examples
Sodium Chloride
Sodium: soft, highly reactive metal Chlorine: greenish colored gas, can
be toxic
Compound Examples
Liquid Petroleum Gas (mixture of propane and butane gas)
Made-up of carbon and hydrogen. Both gases More reactive than diesel, thus spark
ignition
Compound Examples
Petrol Diesel (mixture of hydrocarbons) Made up of carbon and hydrogen Both Gases Does not burn as easily as gasoline thus
air is compressed in cylinder and creates higher temperatures
Summary
Pure Substances: same properties, uniform composition
Elements:Fixed composition, contains one type of atom
Compounds: two or more elements in a fixed proportion
Mixtures
Properties of mixtures can vary because the composition is not fixed
2 Types: Heterogeneous and Homogeneous
Heterogeneous Mixture
Parts of mixture are different from one another Ex: salsa, salad, sand
Hom0geneous Mixture
Substances are so evenly distributed it can hard to distinguish them Ex: stainless steel, made of iron, chromium and
nickel Swimming pool, water at the shallow end is the
same as the water at the deep end
Solutions, Suspensions , Colloids
Size of particles in a mixture effect the properties
Based on the size of the largest particle a mixture can be classified as a solution, suspension or a colloid
Solutions
When substances dissolve and form a homogeneous mixture Ex: tap water, lemonade
Can see light through these solutions Particles are small so light passes
through without being scattered in all directions
Particles will not settle out but can be filtered out
Solutions
Suspensions
Heterogeneous mixture that separates into layers over time
Suspensions are cloudy because larger particles can scatter light Ex: Muddy water, sawdust in air
Suspensions
Colloids
Contains some particles that are intermediate (between solution and suspension)
Do not separate into layers Cannot filter out particles Scatters light
Ex: Fog, milk
Colloids
Physical Properties2.2
Physical Properties2.2
Physical Properties
Characteristic that can be observed or measured without changing the composition (make-up) of a substance
Viscosity, conductivity, malleability, hardness, melting point, boiling point and density
Viscosity
Resistance to flowing Greater the viscosity the slower the
liquid Thin liquids have a low viscosity
Ex: Honey vs. soda Heating up a liquid lowers its
viscosity Ex: oil
Conductivity
Ability to let heat flow Materials with high conductivity are
called conductors Ex: Metals
Hardness
Resistance to scratching The hard the material the less likely
it can be scratched and the more likely it will scratch something else Ex: Diamond Drill Tips
Melting and Boiling Points
Melting Point: temperature a substance goes from a solid to a liquid
Boiling point: temperature at which a substance boils
Density
Amount of matter in an object Ratio of the mass to volume Different substances have different
densities
D = M/V
Using Physical Properties
Used to identify materials Choose materials for a specific
purpose Separate materials in a mixture
Filtration and Distillation
Filtration
Separates materials based on size of particles
Distillation
Separates substances based on their boiling points
Physical Changes
Occurs when some properties of the material change but not the composition
Some are reversible, some are not
Chemical Properties2.3
Chemical Changes
Chemical Property: ability to produce a change in the composition of matter
Observed only when substances are changing into different substances Ex: Flammability and Reactivity
Flammability
Materials ability to burn in presence of oxygen
Reactivity
How easily a substance combines chemically with another Ex: Rust (oxygen and iron) Ex: Water and baking soda
Chemical Changes
Chemical Change: when a substance changes from one form to another
Evidence of Chemical changes:1. Change in color2. Production of gas3. Formation of a precipitate (a solid that
forms)