General Chemistry Basic Concepts of Chemistry

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Today's lesson from general chemistry is on the basic concepts of chemistry.0003

Let's go ahead and take a look at the lesson overview.0009

We are going to first start off with a brief introduction and basically define what we mean by chemistry.0012

Then get on to the three traditional states of matter.0018

After we define the states of matter, we will then get on to classifying matter into a couple of categories.0021

What we call pure substances and mixtures.0027

After discussing what we mean by pure substance and mixture,0031

we will then go on to discuss what we mean by physical and chemical properties and changes.0034

We will finish up the lesson with some sample problems that you can expect0040

when taking this class for real during hot chemistry or high school.0046

These are the types of questions that you can definitely expect you will encounter on some type of quiz or exam.0051

Introduction, what is chemistry?--we typically define chemistry as the following.0058

It is the study of matter, its properties, and the changes that matter can undergo.0063

Within this definition of course we have to define each of these terms that I just underlined.0071

Let's go ahead and first define what we mean by matter.0076

Matter is considered as any substance that has mass; that has some type of weight to it.0079

The conventional forms of matter of course are therefore what we call solids, liquids, and gases.0089

What we are going to do in the next slide is to look at each of these three physical states individually.0096

Solids generally have the following characteristics; they are relatively dense.0105

What that means is that a small volume can weigh a lot, is relatively heavy.0110

They are going to have a definite shape and volume.0125

You can think of any type of solid and yes it has a concrete shape to it and a definite size to it.0127

Number three, another characteristic that is typical for solids is that they have very strong attractive forces.0135

We are going to talk about attractive forces later.0143

But when you think of a solid, you think of an object that is tough.0144

So yes it makes sense that the forces that are holding it together are relatively strong.0149

We also like to look at what is called a particulate-level drawing.0154

The particulate-level drawing allows us to describe the sample on a microscale level.0157

We will say that particulate-level drawing is a microscale description.0167

The basic thing for a solid is that solids are going to be closely packed; closely packed atoms.0174

Basically we are going to represent each atom as a sphere.0187

We are going to have blue, red, blue, red, and that can repeat this alternating pattern below like so.0194

You see that these spheres which represent atoms are physically touching each other and are very very closely spaced together.0207

This is our particulate-level drawing for a solid.0216

Liquids on the other hand are going to have definite volume just like a solid but they have no shape.0221

They tend to have weaker attractive forces than solids.0228

They are less tightly held together than their solids.0231

For a particulate-level drawing, we like to think of liquids as still consisting of the same type of spheres.0235

But because of the spacing, they are now going to be farther apart.0244

This farther apart is going to be indicative of the weaker attractive forces.0249

Weaker attractive forces are farther apart.0256

Finally onto the third physical state which is what we call gases.0263

A gas is going to be the following; they are going to have no shape.0266

Really their volume is determined by the container that the gas is placed into.0273

That is because gases expand entirely.0279

If you release a gas in one corner of the room, it will eventually expand and fill the entire room.0284

Gases tend to have the weakest attractive forces and the lowest density of all three physical states.0292

Something that is unique that we did not talk about with solids and liquids0297

is that gas particles are going to be having very high movement velocities.0300

For a particulate-level drawing, we like to show a gas being enclosed in some type of container.0306

The gas particles are represented by red spheres like so; very far apart.0312

We like to draw little comet tails on the end of them.0316

Showing that they are going to have relatively high movement and that gas particles move in random directions.0320

Now onto the classification of matter; matter can be defined as the following.0329

It can either be what is called a pure substance or a mixture.0333

Pure substances can be either elements or compounds.0338

Mixtures can be either homogeneous or heterogeneous.0343

Now that we have introduced the vocabulary terms, let's discuss each one individually0347

in the next couple of slides followed by a couple of examples.0351

Pure substances are composed of only one type of material.0355

An element refers to matter that is not combined with any other different material.0360

Elements cannot be broken down any further.0366

Something like Fe which is iron; something like Ca which is calcium; something like K which is potassium.0370

When we describe just the basic unit of all which is an element, this is one example of a pure substance.0385

What happens when we have nothing but a pure substance?0394

Nothing but one type of compound which is going to be a combination of elements?0399

Something like CO₂ or something like H₂O or Cl₂ or F₂.0404

If you have different samples of each of them, say in separate containers, then each container represents a different compound.0413

Again a compound is simply the combination of more than one element.0423

Mixtures therefore are going to be combinations of more than one compound.0428

In homogeneous mixtures, the compounds are uniformly distributed.0432

The typical example is salt water.0439

In salt water we are going to have the following that is uniformly dispersed.0443

We are going to have water and inside the water we are going to have salt; just like so.0449

This is going to be uniformly distributed.0456

It is going to be looking like that visually too; visually uniformly distributed.0459

However in a heterogeneous mixture we have more than one compound and the distribution is nonuniform.0472

Usually you see physical layers.0481

The typical example of course is going to be a mixture of water and oil.0485

We are going to get water on the bottom and we are going to get a layer of oil on the top.0492

Once again this is known as a heterogeneous mixture.0496

Now onto the final part of the definition of chemistry.0501

We define chemistry as the study of matter and the changes that it undergoes.0505

Let's now discuss what we mean by changes.0509

A physical change is anything that retains chemical composition.0512

Specifically phase changes are going to be your typical examples.0516

When a solid goes to a liquid for example; for melting.0526

Melting, for example as an ice cube melts, is just H₂O solid becoming H₂O liquid.0535

But it starts off H₂O; it winds up H₂O; all it is is in a different state.0545

Another type of physical change is when you dissolve something.0550

When you dissolve salt in water, you still have H₂O and you still have salt.0555

It is just the salt is now broken up and is not a visible solid anymore.0563

Again these are physical changes that retain chemical composition.0570

Chemical changes however alter chemical composition; so any reaction.0573

Basically how do you know if a chemical change has occurred?0582

Usually you are going to see a change in color.0585

You could see a change in temperature; sometimes you see bubbles appearing.0588

Some typical examples of a chemical change will be burning.0599

Anytime you burn something, you notice that the color always changes to black.0604

You release some type of gas that you smell.0609

Basically you see a release of carbon dioxide and water.0612

So burning is an example of a chemical change.0616

Typically when you cook something, cooking involves a lot of changes at the microscopic level in your food.0619

So cooking is another example of a chemical change.0628

Rust formation, when you see rust forming, it is really iron plus oxygen going on to form rust.0633

We start off with iron and oxygen at first and we wind up with rust in the end.0643

These are examples of where the composition of the reactants literally change.0650

We have talked about physical and chemical changes.0658

There is also what we call physical and chemical properties.0660

Physical properties tend to be measurable traits of an object or relates to its description by your senses.0663

Senses, as an example, we see color; we feel or see texture.0671

Density is going to be a physical property because it is something you can measure.0679

Volume is a physical property; it is something you can measure.0684

Mass of course is going to be a physical property because it is something also measurable.0689

Once again physical properties tend to be measurable traits or relate to a description given to us by our senses.0693

Chemical properties describe an object's reactivity and the types of chemical changes that it tends to undergo.0703

For example is something flammable?--for example is something an oxidizer?--for example is something a radical?0709

We always hear that a lot; how they are very very very reactive; especially inside the body.0720

Once again chemical properties describe something as a chemical change.0725

These may be measurable actually; may be measurable also.0732

Now that we have gone over our brief introduction into the study of chemistry, let's now hit up some sample problems.0744

For example, does step one represent a chemical or physical change and explain.0754

Remember that each of these spheres represents a different element.0759

Before step one, the white spheres are separated from the black spheres.0771

However after step one, you notice that we have a white and a black sphere pair now.0776

They are physically touching, showing the formation of a new compound.0782

This is going to be representative of a chemical change.0786

Number two, does step two represent a chemical or a physical change?0789

These pairs of white and black spheres you see that they are still here next to each other.0794

The only difference is that now they are brought closer together.0802

If they are brought closer together, remember that goes into what we said about solids, liquids, and gases.0807

With solids being very close together and gases being very far apart.0813

So step two most likely represents a phase change of sort.0817

For example, it could be a liquid going to a solid.0822

So we would call step two a physical change.0827

Sample problem number two, we are going to classify each of the following situations as an element, a compound, or a mixture.0833

In part A, we have black, white, and black.0841

That is uniformly distributed throughout the entire area.0845

We know that it is not an element because there is more than one type of colored sphere here.0851

We only see this order of black, white, black.0859

This is entirely one type of compound.0863

Part B; part B, we see nothing but one color which represents just one element.0870

Also you see a pair here; this is going to also represent a compound.0877

Finally, part C, we see a black sphere and a pair of white spheres here.0886

You see that it is not uniformly distributed at all.0893

This is going to be representative of a mixture.0896

Finally sample problem number three, classify each of the following properties as chemical or physical.0905

The hardness of diamond is something that is measurable actually.0912

This refers to also using our senses; this is going to be a physical property.0916

Part B, combustibility of gasoline; combustibility refers to how reactive gasoline can be.0928

Especially in the presence of a flame; this is going to be a chemical property.0937

Part C, elasticity of a rubber band; we see how and we feel how elastic a rubber band can be.0945

Elasticity is something that can be measurable; this is going to be physical.0952

The taste of chocolate; obviously taste is going to be using our senses; that is going to be physical.0958

Finally the darkness of coffee is described as color which we use our senses to detect.0966

Darkness of coffee is going to be an example also of a physical change.0971

That is our opening introduction into the basic concepts of chemistry.0977

I want to thank you for your attention.0982

I hope to see you next time on Educator.com.0983