Science 9 – Chemistry 2Science 9 – Chemistry 2Sci 924 – Sci 926Sci 924 – Sci 926

Quick ReviewQuick Review

Law of Conservation of Mass reviewLaw of Conservation of Mass review– In a chemical change, the total mass of the new In a chemical change, the total mass of the new

substance is always the same as the total mass of the substance is always the same as the total mass of the original substance.original substance.

Law of Definite CompositionLaw of Definite Composition– Compounds are pure substances that contain two or Compounds are pure substances that contain two or

more elements mixed together in fixed or definite more elements mixed together in fixed or definite proportions.proportions.

Therefore, we know that the mass of reactants Therefore, we know that the mass of reactants must equal the mass of the products in every must equal the mass of the products in every chemical reaction.chemical reaction.

Dalton’s Atomic TheoryDalton’s Atomic Theory

Dalton found that the particle theory could Dalton found that the particle theory could not explain why the properties of a not explain why the properties of a compound are different then the properties compound are different then the properties of the element that make it up.of the element that make it up.

The particle theory could not explain how The particle theory could not explain how particles of different substances could particles of different substances could combine or decompose to form new ones.combine or decompose to form new ones.

Then came Dalton’s theory:Then came Dalton’s theory:– All matter is made up of sm.particles clld atoms.All matter is made up of sm.particles clld atoms.– Atoms can’t be created or destroyed or splitAtoms can’t be created or destroyed or split– All atoms of the same element are the same All atoms of the same element are the same

size and weightsize and weight– Atoms of different elements differ in size and Atoms of different elements differ in size and

weightweight– Compounds are created when atoms of Compounds are created when atoms of

different elements link together in definite different elements link together in definite proportionsproportionsEg. Water and peroxide both contain H and O2 but in Eg. Water and peroxide both contain H and O2 but in

different proportion. Water is 11%H and 89% Odifferent proportion. Water is 11%H and 89% O22 whereas peroxide is 6% H and 94% Owhereas peroxide is 6% H and 94% O22

The Scientific ProcessThe Scientific Process

Observations

HypothesisExperiments

Theory

Revised Hypothesis

Laws, Theories, Models and Laws, Theories, Models and ObservationsObservations

Law- describes and summarizes Law- describes and summarizes what what always always happens.happens.

Theory – a creative way to describe Theory – a creative way to describe why why something happens.something happens.

Observation- Scientists observe how matter Observation- Scientists observe how matter behaves and reacts during experiments.behaves and reacts during experiments.– Many observations and experiments are needed before Many observations and experiments are needed before

a hypothesis can become an accepted theory.a hypothesis can become an accepted theory. Model – helps to picture structures or processes Model – helps to picture structures or processes

that cannot be directly seen.that cannot be directly seen.

Classifying ElementsClassifying Elements As elements were discovered, they were given names. As elements were discovered, they were given names.

The scientist who first discovered an element had the right The scientist who first discovered an element had the right to name it.to name it.

Over time there were many elements with very long namesOver time there were many elements with very long names So, a system of element symbols was developed.So, a system of element symbols was developed. The symbol system is universal which means the same The symbol system is universal which means the same

chemical symbols are used by scientists throughout the chemical symbols are used by scientists throughout the worldworld

As more and more elements were discovered, Scientists As more and more elements were discovered, Scientists needed a way to classify the elements and organize their needed a way to classify the elements and organize their observations.observations.

Thus the invention of the periodic table by Dmitri Thus the invention of the periodic table by Dmitri Mendeleev.Mendeleev.

The periodic table invented my Mendeleev is still used The periodic table invented my Mendeleev is still used today with a few modifications.today with a few modifications.

Ways of Classifying ElementsWays of Classifying Elements

State at Room State at Room Temp.Temp.

AppearanceAppearance ConductivityConductivity Malleability Malleability and ductilityand ductility

MetalsMetals

Eg. Mercury, Eg. Mercury, Silver, Gold, Silver, Gold, CopperCopper

SolidsSolids

Except for Except for MercuryMercury

ShinyShiny Good conductors Good conductors of heat and of heat and electricityelectricity

MalleableMalleable

DuctileDuctile

Non-MetalsNon-Metals

Eg. Oxygen, Eg. Oxygen, SulpherSulpher

Some gasSome gas

Some solidSome solid

One liquid One liquid BromineBromine

Not very shinyNot very shiny Poor conductors Poor conductors of heat and of heat and electricityelectricity

BrittleBrittle

Non ductileNon ductile

MetalloidsMetalloids

Eg. SiliconeEg. Silicone

SolidsSolids Can be shiny or Can be shiny or dulldull

May conduct May conduct electricityelectricity

Poor heat Poor heat conductorsconductors

BrittleBrittle

Non ductileNon ductile

Groups of ElementsGroups of Elements Alkali MetalsAlkali Metals

– Highly reactive (Boom!)Highly reactive (Boom!)– Has one unpaired electronHas one unpaired electron– GivesGives up the unpaired electronup the unpaired electron

Alkaline Metals (Earth metals)Alkaline Metals (Earth metals)– Can react vigorously but not as reactive as the Alkali metalsCan react vigorously but not as reactive as the Alkali metals

Noble GasesNoble Gases– Unreactive or inert gasesUnreactive or inert gases– All the electrons here have “dates”All the electrons here have “dates”

HalogensHalogens– Highly reactiveHighly reactive– Have unpaired electronsHave unpaired electrons– TakesTakes an electron an electron– CorrosiveCorrosive

There are other groups and families but were are only covering these.There are other groups and families but were are only covering these.

A couple things:A couple things:– Sci 926 will be changing. Check to make sure Sci 926 will be changing. Check to make sure

my name is in the assignment before you my name is in the assignment before you complete it.complete it.

There will be a quiz at the end of Sci 926 on There will be a quiz at the end of Sci 926 on the periodic table and symbols! the periodic table and symbols!