The Science of Chemistry

Chemistry

The science that deals with the materials of

the universe and the changes that these

materials undergo

Macroscopic World

chemists “look inside” ordinary objects to observe how the

fundamental components (the smaller parts that make it

up) are behaving

For example: when we view a tree from a distance we see

the tree as a whole (the trunk, branches, and leaves all

blend to give us an overall view of the object)

This overall view is called the macroscopic picture

Microscopic World

As we get closer to the tree we begin to see detail: pieces

of bark, individual leaves, large, and tiny branches, etc.

If we examine a single leaf we see veins, variation in color,

surface irregularities, etc.

What lies inside the leaf? What causes it to change from a

bud in the spring to a green leaf in the summer then to a

red or golden color in the fall?

To answer these questions, we must observe the leaf

under a microscope (microscopic world)

Macroscopic / Microscopic

“motion” in the macroscopic world would

consist of the swaying of the tree and the

rustling of its leaves

“motion” in the microscopic world would refer

to the cells acting as tiny machines that

absorb energy from the sun and nutrients

from the air and soil

Chemistry

Chemists answer questions like: What are the building

blocks of the individual cells that make up the tree?

What are the components of the water that contains the

dissolved nutrients the plant needs?

The microscopic world of the chemist is a world of

molecules and atoms

Chemists connect the macroscopic world in which we live

to the microscopic world that makes it all work

macroscopic world

microscopic world

world of the chemist

Why is chemistry important?

it lies at the heart of our efforts to produce

new materials that make our lives safer and

easier

it produces new sources of energy that are

abundant and nonpolluting

it helps us understand and control many

diseases that threaten us and our food

supply

Why study chemistry?

as a society, sometimes we are shortsighted and

concentrate too much on present benefits without

considering long-range implications of our actions

Example: the production of chlorofluorocarbons (CFCs)

created for refrigeration purposes that replaced more

dangerous chemicals

Long-term studies have proven that CFCs destroy ozone

(O3)molecules that protect us from harmful solar

radiation

Why study chemistry?

we need to learn about the chemical nature of the earth so that we can be

good stewards of its resources

we need to pursue a clean and safe approach to the production and use of

chemicals

Scientific Method

1. State the problem and collect data (make

observations)

a qualitative observation does not involve a

number

a quantitative observation is called a

measurement and does involve a number

and a unit of measure

Scientific Method

2. Formulate a hypothesis

a hypothesis is a possible explanation for the

observation

Scientific Method

3. Perform experimentsan experiment is something we do to test the hypothesis,

we gather new information that allows us to decide

whether the hypothesis is supported by our results or

not

experiments always produce new observations and these

observations bring us back to the beginning of the

process

Scientific Method

steps 1-3 are repeated many times in order to

gather knowledge necessary to understand

and explain the behavior of a given part of

nature

A theory (model) is a set of tested hypotheses

that gives an overall explanation of some

part of nature

Observation vs Theory

an observation is something that is witnessed

and can be recorded

a theory is an interpretation - a possible

explanation of why nature behaves in that

particular way

Theories

change as more information becomes

available

we continue doing experiments to refine our

theories

theories are human inventions that represent

our attempts to explain observed natural

behavior in terms of our human experiences

Theories vs Natural Laws

a law is a summary of observed (measurable)

behavior

a theory is an explanation of behavior

a law tells what happens while a theory is our

attempt to explain why it happens

theories DO NOT become laws

Scientific Method

scientists are human: they have prejudices, they

misinterpret data, they can become emotionally

attached to their theories and thus lose objectivity, and

they may play politics

science is affected by profit motives, budgets, fads, wars,

etc.

the scientific method is only as effective as the humans

using it, it does not automatically lead to progress

Matter

the “stuff” of which the universe is composed

has mass

occupies space

composed of tiny particles called atoms

(about 100 different kinds)

we call these 100 kinds of atoms the elements

of the universe

Elements

elements are substances that contain only

one type of atom

atoms of an element can bond together to

form a molecule

● example: two atoms

of oxygen can

combine to form a

molecule of oxygen

Compounds

substances made by bonding different kinds

of atoms together

example: water (a compound) is made up of

many molecules of H₂O (two hydrogen and one oxygen atom bonded together)

● the properties of a compound

are typically very different

from those of the elements it

contains

States of Matter

all substances exist in the three states of

matter: solid, liquid, and gas

a solid is rigid and has a fixed shape and

volume

a liquid has a definite volume but takes the

shape of its container

a gas has no fixed volume or shape and

uniformly fills any container

Physical Changes

do not affect the composition of a substance

example: ice changing to liquid water and

liquid water changing to steam

Chemical Changes

involve a change in the components of a

substance

a given substance changes into a different

substance or substances

chemical changes are called reactions

examples: a fire burning wood or silver

tarnishing when exposed to air

Mixtures

something that has variable composition

examples: wood, soda, coffee, air

the composition of mixtures varies but the

composition of compounds is always the

same

example: people can put different amounts of

cream and sugar in their coffee but pure

water is only ever composed of H₂O

Mixtures

a mixture is a collection of compounds and/or

elements that are present in varying

amounts

the composition of a mixture depends on how

much of each component is used when the

mixture is formed

mixtures of metals are called alloys

example: gold alloys

Gold Alloys

24 karat gold is made up of 100% gold atoms

18 karat gold is made up of 56% gold atoms,

20% silver atoms, and 24% copper atoms

14 karat gold is made up of 36% gold atoms,

25% silver atoms, and 37% copper atoms

these gold alloys (mixtures) differ in their

composition

Pure Substances

always have the same composition

can be elements or compounds

pure water is a pure substance because it is

made up of only H₂O moleculeswater found in nature is a mixture because it

contains dissolved substances in it

Homogeneous vs. Heterogeneous Mixtures

a homogeneous mixture is the same throughout, it is also

called a solution

example: salt dissolved in water...all regions of this

mixture have the same properties

a heterogeneous mixture contains regions that have

different properties from those of other regions

example: a sand and water mixture...one region contains

mostly sand while another contains mostly water

Heterogeneous Mixture

Homogeneous Mixture

Separation of Mixtures

two methods: distillation and filtration

distillation separates mixtures by boiling away a solvent

(the liquid) leaving the solutes behind (solid particles)

example: boiling the water out of ocean water and leaving

behind the dissolved salts

filtration separates a mixture by separating a solid from a

liquid by using filter paper

distillation and filtration physically change a mixture but do

not chemically change a mixture because the same

substances are present before and after the process

distillation demonstration

Filtration

Demonstra

tion

https://www.youtube.com/watch?v=N0f73tbGCREhttps://www.youtube.com/watch?v=tLmh_rMQu7M

states of matter/separation of mixtures

https://www.youtube.com/watch?v=peofSydfTpo