Chemistry Notes

MatterMatter consists of chemical elements-anything

which occupies space and has mass.Matter is found in two ways; pure-form or

compoundsThe Greeks first proposed four elements that made

matter; earth, air, fire, and water.Scientists later discovered 92 naturally occurring

elementsThey can be man-made or naturally occurringTwo or more elements may combine to form

compoundsThey can be found naturally in three ways called

phases; solid, liquid, and gas

• All matter is made of atoms.

Antimony atoms

• Atoms have a nucleus of protons (+) and neutrons (o)

Electrons are distributed outside the nucleus in energy levels called orbitals (or shells).

The mass number = the number of protons + neutrons.

• The atomic number = the number of protons

• This also equals the number of electrons.

Atoms Movie

Element Nursery

• All materials are made from elements. All known elements are listed on the periodic table.

April 2003 ~ The Omega Nebula is a center of star formation. It is 5500 light years away, and contains vast amounts of hydrogen,

oxygen, and sulfur.Elements are formed through nuclear fusion.

An element is a substance made up of only a single type of atom.

Gold (Au) and Copper (Cu)

Diamond is made of only carbon (C) atoms.

ElementsThere are 92 known elements (naturally occurring)These elements are found on the periodic table of

the elementsSome different elements combine together to form

compoundsTable salt is a compound made up of sodium and

chlorineIt is written using the abbreviation NaClNa = Sodium and Cl = chlorine

The 92 elements are found on the periodic table of the elements

Symbols for Elements

• Symbols are letters that represent the elements on the periodic table

1. If only a single letter, it is Capitalized.

2. If two letters, the 1st is Capitalized and

the 2nd is lower case.

Example: Ca not CA

Periodic Table of the Elements

• Check out the initials for Aluminum in this example off of the Periodic Table:

Periodic Table of the Elements

• The number of protons in an atom is listed above each abbreviation. It is called the Atomic Number.

Periodic Table of the Elements

• The number listed underneath the abbreviation is the Atomic Weight.

The atom is the smallest unit to have properties of an element

About one million fit onto a period at the end of a sentence

They are comprised of neutrons, protons, and electrons

Neutrons and protons are neatly packed in the nucleus

Neutrons and Protons have almost exactly the same mass Each one has the mass of ~1.7 x 10-24 grams Electrons are 1/2000 the size of + and N

The number of protons unique to an element is the atomic number

Atomic Particles

Matter• Anything that takes up space and

has mass.• Matter can have physical and

chemical properties• Physical properties: density,

melting points, boiling points, freezing points, colors or smells.

• Chemical properties: the way an element combines with others.

States of matter

• Four main states of matter– Solid– Liquid– Gas– Plasma

• Matter may change “phases” when physical forces are present– Example: temperature causes matter

to move to a more excited state

If energy is added or taken away, matter changes

phases

Solids

Solids can be composed of many different thingsFor example: mixtures, different

elements, or compounds.Solids hold their own shapeAtoms inside a solid are not

allowed to move around a lot- they are trapped inside their spaces

                                  

When does a liquid become a solid?

• Freezing point is the point at which a liquid becomes a solid.

• Many factors affect freezing points:– Temperature– Pressure- easier to freeze at higher

temps.

Liquid Basics

• Liquids are an in-between phase (between solid and gas)

• Liquids fill the shape of a container

• Liquids are hard to compress (atoms are already so close together)

Becoming a liquid

• When a solid reaches it’s melting point, it becomes a liquid. It just needs energy (heat)

Becoming a liquid

• For a gas to become liquid, it needs to lose energy. How?

• Easy- lowering the temperature allows atoms to move slower, thus settling down allowing it to reach it’s condensation point.

• Gas becomes a liquid at it’s condensation point.

Evaporation

• Liquid may undergo evaporation and become a gas.

• All liquids can evaporate at room temperature and pressure.

• What is evaporation?– Evaporation is when

atoms escape the liquid and become a gas.

Gas• Gases are random groups of atoms.

• Gases contain a lot of energy; atoms are in constant motion

• Atoms in gases are really spread out

• Gases can fill a container of any size or shape- atoms and molecules spread out evenly

Becoming a gas…

• Becoming a gas needs energy (temperature increase)

• When energy is added, the atoms become excited

Plasma

• Plasma is like a gas, but the atoms are made up of free electrons and ions.

• Plasmas are not common on Earth, however you may have seen plasma.– Northern lights or lightning

Becoming plasma

• When electrons are stripped from atoms, what is left is negative and positively charged particles (ions)

• When ions are in equal concentrations, the charge is neutral.

• Lots of energy is needed to change a gas into plasma.

Becoming plasma

• Adding large amounts of energy causes the neutral atoms to break apart into positive and negative charged ions and free electrons

• Leaving electrons and ions is a gaseous ball!

Isotopes

• Atoms of the same element that have different numbers of neutrons are called isotopes.

• In the drawing there are 2 different Helium isotopes; one with 3 neutrons and one with 4 neutrons

Ions

• When an atom gains an extra electron or looses an electron the atom is called an ion.

There can be (+) ions or (-) ions

Mixtures• Substances held together by

physical forces. • Mixtures are all around us- oceans,

rocks, tap water… everywhere!

Just H2O molecules

Tap waterhas other substances dissolved in it

If you boiled the tap water, you would have the dissolved substances left over (salt for example). Salt would maintain it’s own properties.If you wanted to boil away salt you would need higher temps.

Mixtures

• Substances in mixtures can always be separated by physical means.

– Example: mixture of sand, salt and water – How would you separate the substances?

Solutions

• Solutions are groups of molecules that are mixed up in a completely even distribution.– Homogenous (homo = same)

Example: Sugar dissolved in water is evenly distributed as in kool-aid.

Solutes, Solvents, Concentration

• A solution is two substances combined• Solute is what is being dissolved• Solvent is what is doing the dissolving

• Solubility is the ability of the solvent to dissolve the solute.

• What is the universal solvent?

http://www.chem.vt.edu/RVGS/ACT/graphics/property.jpg

Chemical reactions

Only electrons are involved in chemical reactions.

The transfer of electrons results in ionic bonds.

Covalent bonding involves the sharing of valence

electrons

A chemical change is a process in which reactants are changed into one or more different products. During this reaction, there is a rearrangement of atoms that makes or breaks chemical bonds. This change is usually not reversible, unlike physical changes, which typically are reversible. In short, chemical change is a change of one substance into another substance (i.e. a new substance is formed). By contrast, no new substance is formed in a physical change (for example, the melting of ice is a physical change because when ice changes into water, no new substance is formed.)

The pH scale uses numbers (0-14) to indicate acids and bases