Chapter 3 ATOMS AND THE PERIODIC TABLE Atom

Chapter 3 ATOMS AND THE PERIODIC TABLE

Atom Review (Dalton’s Atomic Theory) Atom: the smallest particle that still has the properties of an element Elements are made of atoms and atoms of the same element are alike Atoms combine in order to make molecules (either elements or compounds)

Structure of the Atom Inside the nucleus A. Protons (positive charge) Neutrons (no charge) Outside the Nucleus B. Electrons (negative charge) Electrons are orbiting the nucleus so fast that we can’t determine their exact position C. Neutral atoms have no overall charge They have equal numbers of protons and electrons

Calculating Protons, Neutrons, and Electrons # of protons: Always the same as the atomic # on the periodic table #of electrons: usually the same as the atomic number. (different in atoms that have a charge) # of neutrons: Atomic mass – atomic # Ex. Chlorine has 18 neutrons

Drawing Electrons in their orbitals (shells) The first orbital can hold 2 e The second orbital can hold 8 e The third energy level can hold 8 e Valence Electrons: the electrons in an atom’s outermost shell Example:

Changing Atoms A. Ions- Atoms that carry a charge Atoms gain/lose electrons from their valence shell in order to be more stable. This causes the # of protons to no longer equal the # of electrons. B. Two types of Ions Anions- Negatively charged atom (gained e- , Has more e- than p+) Cations- positively charged atom (lost e-, has less e- than p+)

Changing atoms (cont. ) Isotopes- Atoms that have the same number of protons, but different numbers of neutrons A. Changes the atomic mass of the atom B. The atomic mass written on the periodic table is the weighted average atomic mass of ALL the isotopes. Changing the # of protons = New Element

Developed by a Russian chemist named Dmitri Mendeleev (duh-MEE-tree mehn-duh-LAY-uhf) Mendeleev used the following categories to organize his table: � chemical properties � physical properties � atomic mass � density � color � melting point � Valence electrons �

Design of the Periodic Table organizes information in a logical, usable, and meaningful way allows prediction of physical and chemical properties of an element by position can predict how elements will react with other elements arranged in columns and rows because of similar characteristics

Columns in the Periodic Table vertical classification or groupings often referred to as families or groups elements within the same family have similar properties

Rows in the Periodic Table horizontal classification or groupings each row is called a period elements in a period are not alike in properties, properties change greatly across a given row the first element in a period is a very reactive metal the last element in most periods is a noble gas only seven periods

Physical and Chemical Properties of Metals � � � � Physical Properties luster (shininess) conductivity of heat and electricity high density high melting point ductility (they are ductile) malleability (they are malleable) Chemical Properties Tend to lose their electrons in a reaction Metals will have either 1, 2, 3, or 4 electrons in their outermost energy level (depending on the family)

Alkali Metals Group 1 Very reactive because they only have one valence electron Forms a 1+ ion (ex. Na+) Found in nature as a compound http: //www. youtube. com/wat ch? v=m 55 kgy. Ap. Yr. Y You. Tube - Alkali Metals: Explosive reactions

Alkaline Earth Metals Group 2 2 valence electrons Form 2+ Ions (ex. Ca 2+) Reactive, but less reactive than alkali metals

Transition Metals Groups 3 -12 Typically have 3 valence electrons Less reactive than first 2 families Most metals we think of are from this family Very good conductors of heat and electricity

Nonmetals (right side of PT) Physical Properties No luster Don’t conduct heat or electricity well Not malleable or ductile Can be solids, liquids, or gases Chemical Properties Typically gain electrons to fill valence shell Form Negative Ions (ex. O 2 -) React mainly with metals

Halogens Group 17 Have 7 valence electrons Very reactive nonmetals because they need one electron for full valence shell Are found as solids, liquids and gases at room temp

Noble Gases Group 18 Have 8 valence electrons (He only has 2) Full valence shell makes them unreactive Also called “inert”

Metalloids (Semiconductors) Only 7 elements (B, Si, Ge, As, Sb, Te, Po) Classified as nonmetals but have some properties of metals Can conduct heat and electricity but not as well as metals.