Basics of Chemistry

Biology

• Atoms are the basic unit of matter.

• Atoms are made of small subatomic particles: protons, neutrons, electrons

History of the Atom

• Democritus a fifth century B.C. Greek philosopher proposed that all matter was composed of indivisible particles called atoms (Greek for uncuttable).

Models of the Atom• Billiard Ball Model  (1803)• Plumb Pudding Model (1897)• Solar System Model• In 1913 Neils Bohr proposed that electrons

traveled in circular orbits and that only certain orbits were allowed.  This model of the atom helped explain the emission spectrum of the hydrogen atom.  He received the Nobel Prize in physics in 1922 for his theory.

Bohr Model

1st energy level 2 electrons

2nd energy level 8 electrons

3rd energy level 18 electrons

4th energy level 32 electrons

• Electron Cloud Model (1920's)- an atom consists of a dense nucleus composed of protons and neutrons surrounded by electrons that exist in different clouds at the various energy levels. 

Atoms…

• Electrons have a negative charge, Protons have a positive charge and neutrons have no charge.

• Protons and neutrons make up the nucleus

• Electrons surround the nucleus

Particle Type ChargeLocation in the

atomMass

Proton (+) positive Nucleus 1  a.m.u.

Neutron (0) neutral Nucleus 1  a.m.u.

Electron (-) negative Electron Cloud 0  a.m.u.

Matter

• Matter can be divided or classified into three classes called elements, mixtures, and compounds.

• Elements:  Pure substances made up of only one type of atom.  All matter is made of atoms.  The types of atoms or matter are listed on the periodic table of elements. 

• Elements are represented by chemical symbols. Some examples are Cu for copper and H for hydrogen. 

Compounds

• Compounds:  Pure substances made up of two ore more elements combined chemically.  Compounds are represented by chemical formulas such as H2O for water and CO2 for carbon dioxide. 

• Compounds that contain carbon are called organic compounds and compounds that do not contain carbon are called inorganic compounds. 

Mixtures

• Mixtures: Mixtures are not pure.  They are made up of two or more substances combined physically, but are not chemically.  Mixtures can easily be separated while pure substances can not.

• Mixtures may or may not have the same composition throughout.  Mixtures may be more than one color or a solid color.   Any substance that is multicolored is a mixture.

Types of Mixtures

• Homogeneous mixture:  has the same composition through out     Ex: fresh milk, mayonnaise

• Heterogeneous mixture:  does not have the same composition through out     Ex: Unstirred chocolate milk, unshaken italian dressing

  Law of Conservation of Mass and Energy

• Law of Conservation of Mass and Energy:  A set amount of matter  and energy exists in the universe.  New matter and energy can not be created.  Matter and energy can not be destroyed.

• Matter and energy are interchangeable.  Matter can be turned into energy and energy can be turned into matter.

• All matter may be classified into four physical states or phases: • Solid:  has a definite shape and volume, the molecules are

very close together and vibrate very slowly in place.• Liquid:  has a definite volume, but no definite shape.  Liquids

take the shape of their container.  Molecules are further apart and move slowly.

• Gas:  has no definite volume and no definite shape.  Molecules will move as far apart from each other as possible and move very fast.

• Plasma: an electrically charged gas.  Molecules move faster than a gas.  The sun is made of plasma.  Plasma can not usually be contained on earth with our current technology.

Kinetic Theory of Matter

• When you add heat energy, molecules move faster and further apart.  When you remove heat energy, molecules move slower and closer together.  This is what causes matter to change from one state to another.  For example,  when you add heat energy to ice, the molecules move faster and further apart turning it into a liquid.

Transitions of matter

• Evaporation:  When a substance changes from a liquid to a gas.

• Condensation:  When a substance changes from a gas to a liquid.

• Sublimation:  When a substance changes from a solid to a gas, skipping the liquid phase (dry ice).

• Boiling Point:  The temperature at which a substance turns from a liquid to a gas.

• Freezing Point:  The temperature at which a substance turns from a liquid to a solid.

• Melting Point:  The temperature at which a substance turns from a solid to a liquid.

Bonds

• An attraction between two or more atoms.

• There are three types of bond: covalent (sharing), ionic (transfer) and van der Waals forces (attraction between molecules)

Covalent Bond

• Atoms will share electrons in order to have their outer most energy level filled.  When atoms are connected together because they are sharing electrons, this is called a covalent bond.

Molecule

• Two or more atoms held together by a covalent bond.

Ionic Bonds

• Atoms lose or gain electrons.  One atom will lose its electron(s) and another atom will gain its electron(s).  When an atom loses an electron, it becomes a positively charged ion.  When an atom gains an electron, it becomes a negatively charge ion.  Oppositely charged ions attract to each other forming an ionic bond.