Chem 103 Chapter 1- Introduction to Chemistry

chemistry is considered the

central science

what is chemistry

The science that
seeks to understand
the world around us
by studying
what atoms and
molecules do.

Five subfields of chemistry

Org chem, inorg chem, biochemistry, analytical chem, physical chem

The scientific method

a way of learning observation and experimentation to establish knowledge.

its core is the establish the cause and effect. explaining observed and demonstrable facts about the properties and behavior of nature.

observation in the scientific method

“I see something I want to know more about”

hypothesis in the scientific method

maybe it happens because….

must be falsfiable (can be tested and proven wrong)

Law

every time, the same thing happens

• a summary of repeated observations

Theory

“this is why it happens”

• a well tested explanation based on proven hypotheses and evidence

What three parts of the scientific method must be always tested by experimented. what happens also if the new results don’t match the old explanation

laws, hypotheses, and theories

• scienctist revise/replace it

What happens overtime with the scientific method

Weak or incorrect ideas are discarded
Strong theories, supported by evidence, survive and become accepted

science is ____________

self correcting—only explanations that match evidence first

Which scientist was considered the “father of modern chemistry”

Antoine Lavoiser (1743-1794)

Antoine Lavoiser 

First chemist to measure
weights of chemicals in
reactions
• Focused on:
• Precise measurements
• Identification of elements
• Rendered alchemy obsolete.

Lavoiser showed

reservoir of mercury (liquid)
Phosphorus (brown solid)
Oxygen gas in bell jar
Lavoisier showed what happens to a substance when it burns:
it combines with oxygen.

Lavoiser is known with what law as well

Law of conservation of mass.

Law of conservation of mass

“In a chemical reaction matter is
neither created nor destroyed.”

Lavoisier burned substances inside a closed
container.
• He weighed the container before and after
burning
• Result: No change in mass - even though the
substance looked different.
“In a chemical reaction matter is
neither created nor destroyed.”

The “father” of atomic theory

John Dalton (1766-1844)

John Dalton

His theory explained:
• Law of Conservation of Mass
• Lavoisier’s observations

Dalton’s atomic theory

Matter is made of tiny, indestructible atoms
• Atoms of the same element are identical
• Atoms combine in whole-number ratios to form compounds
• Atoms can rearrange, but aren’t destroyed in reactions

“All matter is made of tiny,
indestructible atoms!”

how to know when to classify something as a observation, law or theory?

Observation (What you notice)

• Something you see, measure, or detect directly.

• It’s a fact you record with your senses or instruments.

• Example: When magnesium burns, it gives off a bright white light.

👉 Think: “I saw it happen.”

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🔹 Law (What always happens)

• A statement or equation that summarizes a pattern in nature.

• Doesn’t explain why, just what happens consistently.

• Example: Law of Conservation of Mass → Matter is not created or destroyed in chemical reactions.

👉 Think: “This always happens.”

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🔹 Theory (Why it happens)

• A well-tested explanation for why observations and laws occur.

• Backed by lots of evidence, but can be refined if new evidence shows up.

• Example: Atomic Theory → All matter is made of atoms, which explains chemical behavior.

👉 Think: “This is the best explanation.”

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⚡ Easy way to tell:

• Observation = fact (what you saw).

• Law = rule (what always happens).

• Theory = explanation (why it happens).