Outline 2-1 Nature of Matter

I. Matter is made of Atoms A. Atoms are the smallest units of matter that cannot be broken down by chemical means. 1. Named by the Greek philosopher Democritus B. Atoms consist of three kinds of particles: 1. protons 2. neutrons 3. electrons

The subatomic particles in a helium atom.

C. Arrangement of parts of atom: 1. Nucleus contains: a. protons = (+) charge; mass = 1 b. neutrons = no charge; mass =1 2. Electron cloud a. Region where electrons are found constantly moving b. Electrons have (-) charge; almost no mass (1/1840 mass of proton) 3. No overall charge on atoms since atoms have equal numbers of protons & electrons

D. Elements 1. An element is a substance made of only one kind of atom (pure substance) 2. Each element is represented by a symbol 3. Elements differ in # of protons 4. More than 100 elements are known but only about 2 dozen are found in living organisms

E. Electron Arrangement 1. Electrons are grouped into different levels a. Inner levels have less energy than outer levels  Innermost level holds 2 electrons  Other levels can hold up to 8 electrons

F. Isotopes 1. Atoms of the same element that differ in the number of neutrons they contain a. Example: Carbon-12 has 6 P and 6 N Carbon-13 has 6 P and 7 N Carbon-14 has 6 P and 8 N 2. All isotopes of an element have the same chemical properties

G. Radioactive Isotopes 1. Some atoms have unstable nuclei that break down at a constant rate over time. 2. Uses of radioactive isotopes: a. Used to determine ages of rocks and fossils b. Treat cancer c. Kill bacteria in food d. Used as “tracers” to follow movements of molecules

II. Periodic Table - one box 15 Phosphorus P Symbol Atomic number = # protons Mass # = # protons + number neutrons Round to whole #

III. Atom Drawings A. Hydrogen B. Helium C. Oxygen Copy from overhead Do on own. Use Periodic Table to get information D. Carbon E. Nitrogen F. Sodium G. Phosphorus H. Chlorine

I. Boron J. Fluorine K. Silicon L. Argon Do for HW

IV. Atoms can bond together A. A compound is a substance made by chemical combination of two or more different elements in definite proportions 1. Examples: a. Na joined with Cl forms NaCl (table salt) b. 2 H joined to O forms water (H 2 O) NaCl and H 2 O are chemical formulas

2. Properties of compounds a. Physical and chemical properties of a compound are usually very different from the elements from which it is formed. b. Examples: 2 gases (H & O) combine to form liquid water Na is an explosive metal while Cl is a poisonous gas. These combine to form NaCl which is a white solid that is not poisonous or explosive

B. Chemical Bonds 1. The force that joins atoms together is called a chemical bond 2. Bond formation involves the electrons that surround each nucleus. 3. The electrons that are available to form bonds are called valence electrons.

4. Reasons for bonding a. An atom becomes stable when its outer electron level is full. b. If the outer electron level is not full, an atom will react readily with other atoms that can provide electrons to fill its outer level

C. Ionic Bonds 1. Formed when electrons are transferred from one atom to another 2. An atom that has gained or lost an electron is called an ion a. This is because they now contain an unequal # of protons & electrons b. Atom loses an electron = (+) c. Atom gaining electron = (-)

3. Ions of opposite charges may exchange electrons to form an ionic bond a. Sodium (Na) gives up its only outer electron to become Na +. b. Chlorine (Cl) has 7 outer electrons and will take the electron from Na and become Cl - c. The (-) Cl is attracted to (+) Na and they form an ionic bond

Protons +17 Electrons - 18 Charge -1 Protons +11 Electrons - 11 Charge 0 Protons +11 Electrons - 10 Charge +1 Protons +17 Electrons - 17 Charge 0 Chloride ion (Cl - ) Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+)

D. Covalent Bonds 1. Covalent bonds form when two or more atoms share electrons to form a molecule. 2.Sharing means the electrons actually travel in the orbitals of both atoms. a. Single bond shares a pair of electrons b. Double bond shares 2 pairs c. Triple bond shares 3 pairs 3. Examples = water, carbon dioxide

Each hydrogen atom forms a single covalent bond with the oxygen atom. Each oval shows the electrons that are being shared

E. Van der Waals Forces 1. The slight attraction found between the oppositely charged regions of nearby molecules. 2. Not as strong as ionic or covalent bonds but they can hold molecules together, especially large ones. 3. Example: Hold gecko feet to walls

Gecko climbing on glass wall

Go to Section 2-1 Quiz