Chapter 4 Chemical Foundations: Atomic Theory, Chemical symbols and formulas, Periodic table, ions, and isotopes

Chemical Symbols Names come from many sources Often from a Greek, Latin, or German word that describes the element Ex/ Gold was called “aurum”, latin for shining dawn. Gold = Au Ex/ Lead was called “plumbum”, meaning heavy. Lead = Pb!!!! Abbreviations are easier to use (CT v. Connecticut) In chemistry, these are called element symbols, one or two letters used to represent a specific element

Dalton’s Atomic Theory At Dalton’s time, these were known concepts: Materials are mixtures of pure substances Pure substances are elements or compounds(combo of elements) Law of constant composition- a given compound always has the same composition Aware of these observations, Dalton offered an explanation that became known as Dalton’s Atomic Theory.

Dalton’s Atomic Theory Elements are made of tiny particles called atoms All Atom’s of a given element are identical

Dalton’s Atomic Theory Continued 3. The atoms of one element are different from those of another element 4. Atoms of one element can combine with atoms of another element to form compounds

Dalton’s atomic theory continued 5. Atom’s are not created or destroyed in chemical reactions. A chemical reaction changes the way the atoms are grouped together.

4.4 Formulas of Compounds A compound is a distinct substance composed of the atoms of 2 or more elements and always contains exactly the same number of atoms of those elements. Ex/ water is H2O, Glucose is C6H12O6 Chemical Formula- Represent the types of atoms and the number of each type in one molecule of the compound Rules for Chem. Formula: 1. Chemicals indicated by their symbol 2. # of atoms shown as a subscript following the symbol. 3. When one atom of a element is present, the subscript 1 is not written

4.7 Isotopes Isotope- atoms with the same number of protons but different number of neutrons. Or: Name – mass number ex/ Oxygen-17

Review up to this point….. Dalton’s atomic theory Structure of the atom Isotope Ways to represent an isotope Periodic table Trends: metallic v nonmetallic, size, Ionization energy, electronegativity, ionic charges

4.8 Periodic table Arranged by atomic number Mostly metals (~80%) Nonmetals, besides Hydrogen, found on the right Atomic size trend Ionization energy trend Electro negativity trend Ionic charges- ? Group names

4.9 Natural State of the Elements It is rare to find elements in their pure form--- uncombined with other elements. Some bond to themselves in pair- like O2, N2, H2, These are called Diatomic Molecules. Or molecules made up of two atoms of the same element. Some examples of diatomic molecules to remember: O2, N2, H2

4.10 Ions Neutral (protons = electrons)atoms can gain or lose electrons, creating a charged atom (pros<>e-). Ions- a charged atom that has gained or lost an electron If an electron is lost, the atom is left with a +1 charge or a positive charge. These are called Cations. Cations form when one or more electrons is lost from a neutral atom

Ions continued When an electron is GAINED by a neutral atom, a negative charge is formed. This is called an anion Representing Ions: The Atomic symbol will be followed by a superscript showing the value and the charge (+ or -) Ex/ Mg2+ Ex/ could also be an isotope: 47108Ag2+

Naming Anions To know if an element has a charge, we change the ending of its name. 1. Use the root of the element’s name 2. drop the ending and add –ide Ex/ Fluorine adds an electron and becomes Fluoride Chlorine – to – Chloride Oxygen –to- Oxide Cations- keep the name of the parent atom ex/ sodium loses its valence electron and is just called a sodium ion

Ion charges and the Periodic Table For groups 1-3 the ionic charges is identical to the group number. (group 1 has an ionic charge of +1, group 2 is +2, Group 3 is +3) For transition metals- no easy way to predict the charges of the cation that will be formed. Depends on the other element it is bonding to. Metals always form positive ions (cations). Remember a fundamental property of metals is to lose electrons

4.11 Compounds that contain Ions A cation and an anion will combine to form a neutral compound Charges MUST be balanced Called Ionic Compounds- a bond between a metal and a non metal Must have a net(total) charge of zero There must be both positive (cation) and negative (anions) ions present The number of cations and anions must be such that the net charge is zero. Ex/ N from group 5, so its charge is -3 And K from group 1, so its charge is +1 Together they produce K3N This shows we needed 3 of the K’s to balance the 3+ charge of N

Practice & HW(p. 106 #20a-f, 25, 29-34, 37-40 What are the 5 points to Dalton’s Atomic theory? Write the formula for: a molecule containing 3 carbon atoms and 8 hydrogen atoms A compound containing two nitrogen atoms for every oxygen atom A compound containing half as many barium atoms as iodine atoms A compound containing aluminum atoms and also three times as many chlorine atoms as there are aluminum atoms A compound that contains twice as many potassium atoms as carbon atoms, and three times as many oxygen atoms as carbon atoms

Chapter 4 Review