Chemistry 101

What is Chemistry?

The study of MATTER and changes in MATTER

What is Matter?

The smallest, most basic unit of “stuff” in the universe.It has mass and volume.

Why does Matter matter?• Matter makes up Atoms• Atoms make up

Elements• Elements can combine to

make Molecules• Elements and Molecules

make up Chemicals

• Chemicals make up everything around us!

Sounds simple enough, right?

Let’s make things a little more complicated…

Atoms

• Are made up of matter• The matter is organized

into three types of particles

•Protons•Electrons•Neutrons

Atomic Particles

• Protons are positive• Neutrons are neutral

• Electrons are negative

Are found in the atom’s nucleus

Are found in the electron cloud around the nucleus

electron

neutron

proton

Electronic Rain?

• Electron clouds are not actually little clouds of electrons around the nucleus.

• An electron cloud is a drawing that represents the likelihood that an electron will be found in a general area around the nucleus.

• Electrons are SO fast that we can never actually tell where one is.

Well, if we can’t see them….

• How do we know where they are?

• In 1911, Dr. Ernest Rutherford performed an experiment.

• He shot a beam of high energy alpha particles at a very thin piece of gold foil.

• He detected where the particles hit with a detecting screen made with zinc sulfide.

© Murray Robertson 2001 - 2005

RSC chemsoc timeline, http://www.rsc.org/chemsoc/timeline//pages/1911.html

The Gold Foil Experiment

• Rutherford found out that most of the particles went straight through, but about 1 in 8000 bounced off.

• He determined that most of the atom was made up of 'empty space'.

• Before this, everyone figured atoms were solid mixes of all the different particles.

• This is how we know the weight of an atom is all in a small nucleus in the center.

Atomic Notation

• X is the chemical symbol

• A is the atomic number– A = # of protons

• M is the atomic mass– M = # protons +

neutrons

Isotopes

• Elements are determined by their number of protons. This number does not change.

• Elements with a different number of neutrons than protons are called isotopes.

• Some elements have many isotopes, some have none.

• Isotopes are identified by atomic mass.

Ions

• Elements are determined by their number of protons. This number does not change.

• Elements with a different number of electrons than protons are called ions.

• If an element loses an electron, it becomes more positive and is called a cation.

• If an element gains an electron, it becomes more negative and is called an anion.

Ion Notation

• Ions are notated by placing a positive or negative sign after the chemical symbol.

• If there is more than one charge, the number is placed before the charge.

Back to our first definition

• Chemistry is the study of matter AND changes in matter.

• What kind of changes are we talking about?

Physical v. Chemical Changes

• Physical changes do not actually change matter, they just reshape it.– melting– freezing– boiling– condensing– sublimating*– crushing– bending

• Chemical changes change the arrangement of matter at the molecular level.– burning– rusting– chemical reactions!

* we’ll get to this word, don’t worry

State changes• Some physical changes are called

“state changes”.• These occur when matter shifts

between a solid, liquid, or gas state.

solid gasliquid

solidgas liquid

gassolid

melting boiling

condensing freezing

sublimating

Congratulations!

You are now on your way to becoming a chemist.