Unit 2 Lesson 1: Classification of Matter

Unit 2 Lesson 1: Classification of Matter

by Ryan McCluskey

​Classification

• ​Classification is the art of separating items into groups.

• ​In order to separate items we must look for differences.

• ​Sometimes these are observations we can make visually but other times we have to dig deeper to separate items into groups.

• Separation by classification occurs with a layered approach. We continue to separate further until we can identify an individual item.

Open Ended

List 3 groups you could sort all of these animals into for characterization.

​Classification

• ​Here is an example of a dichotomous key used in biology for the separation of animals for classification.

• This is something most of us ar​e familiar with at the higher levels of classification but how many levels of separation are used for biological organisms?

​Classification

We continue separation down for 8 levels until we can identify individual organisms. ​

​With chemistry, our goal is to determine levels of classification to separate all matter.

​Matter

• Don't forget matter is defined as anything that has mass and takes up space.

• ​So as we look to separate matter into groups we are talking about a very massive and diverse amount of items.

• ​We must make sure our groups encompass all substances.

​Matter

• The first separation we make with matter is into 2 groups.

• ​Pure Substances and Mixtures are different on how they can be separated or broken down.

​Matter

• Pure substances can only be separated by chemical means.

• ​Mixtures can be separated by physical means.

• ​This is not always an easy straightforward process

​Separation Techniques

• Filtration - Separating Mixtures with differences in particle size.

• ​Distillation - Separating Mixtures with differences in boiling point.

• ​Sedimentation - Separating Mixtures with differences in solubility/density.

Pure Substances

As we separate further we break down Pure Substances into two groups: Elements and Compounds.

​

Pure Substances

Elements are a pure substance made of only 1 type of atoms.

​We usually identify these as they are found on the periodic table of elements.

Pure Substances

Elements are a pure substance made of only 1 type of atoms.

​We usually identify these as they are found on the periodic table of elements.

Pure Substances

​Compounds are a pure substance made of 2 or more types of atoms.

​

​

​Different from mixtures in the fact that they are chemically bound.

Pure Substances

We can easily identify compounds from the chemical formula.
Being made up of 2 or more elements they will contain more than 1 capital letter.

Multiple Select

Which of the following is an Element?

• Iron (Fe)

• Steel

• Water (H₂O)

• Aluminum (Al)

• Carbon dioxide (CO₂)

Multiple Select

Which of the following is a Compound?

• Sodium (Na)

• Oxygen ( $$O_2$$ )

• Water ( $$H_2O$$ )

• Neon (Ne)

• Calcium carbonate (CaCO₃)

Pure Substances

​As we split mixtures into two groups we look at how uniform the mixture is.

​

The two types of mixtures are defined as heterogeneous and homogeneous.

Pure Substances

Heterogeneous means that the mixture is NOT uniform. This means that the different components of the mixture are visible or that if a sample is taken from different parts of the mixture the composition would be different.

Pure Substances

Homogenous means that the mixture IS uniform. This means that the different components of the mixture are NOT visible or that if a sample is taken from different parts of the mixture they will still have an identical composition.

Multiple Choice

Which of the following would be considered a homogenous mixture?

• Pure Water

• Air

• M&M's

• Titanium

Multiple Choice

Which of the following would be considered a heterogeneous mixture?

• Pure Water

• Air

• M&M's

• Titanium

Compounds versus Mixtures

Probably the hardest forms of matter to differentiate are compounds and mixtures.

The biggest difference between the two is how they are separated but also their composition.

Compounds are defined by two scientific laws.

The Law of Definite Proportions and the Law of Multiple Proportions.

Compounds versus Mixtures

So now we see what constant or definite composition looks like but what about mixtures that have a "varying" composition?

​The best way to describe this to me is by thinking about a glass of sweet tea.

Compounds versus Mixtures

I like to think of composition like a recipe.

In compounds the recipe is absolutely rigid and unchanging.

Where as mixtures are more like the substances we are used to. The recipe can be a little different based on who is making it .

Percent Composition

The last thing we are going to practice today is calculating the percent composition of some common compounds.

​This begins by learning to calculate molar mass.

​In order to do this we have to make sure we understand how the subscript works in a compound.

​For example with H₂O we have to understand the subscript only speaks to the element directly before it.

​We also must understand that an element with no subscript simply means 1.

​So in H₂O we have 2 hydrogen elements and 1 oxygen element.

Percent Composition

Now once we break the compound down we are going to multiply the number of each element by its mass. This is found underneath each element on our periodic table. We will round these masses to the nearest tenths place or one decimal.

​

​H₂O

​H -2 x 1.0 = 2.0

​O -1 x 16.0 = 16.0

​ = 18.0 (This is simply the mass of all pieces of the . compound added together)

Percent Composition

At this point to find the composition of an element you divide the amount it provides to the total mass by the total mass and multiply by 100.

​

​H₂O

​H -2 x 1.0 = 2.0

​O -1 x 16.0 = 16.0

​ . = 18.0

​

​Percent Oxygen by mass 16/18 x 100 = 88.9%

​Percent Hydrogen by mass 2/18 x 100 = 11.1%

Percent Composition

So what we have discovered in Chemistry is that no matter how much water or how little water you have these compositions or percentages (recipe) never change. It also does not matter where the water sample is obtained.

Water has a definite and universal composition.

​Percent Oxygen by mass 16/18 x 100 = 88.9%

​Percent Hydrogen by mass 2/18 x 100 = 11.1%

Extra Video Resource