Chapter 2 cont’ Reacting Atoms when elements undergo chemical reactions, the reacting elements do not turn into other elements Dalton’s Atomic Theory since the number of protons determines the kind of element, the number of protons in the atom does not change in a chemical reaction however, many reactions involve transferring electrons from one atom to another

Mixtures and Chemical Compounds

Molecules and Covalent Bonds compounds are made of atoms held together by chemical bonds covalent bonds result when two atoms share some of their electrons Nonmetal + Nonmetal Molecule: The unit of matter that results when two or more atoms are joined by covalent bonds.

Molecules and Covalent Bonds

Naming Chemical Compounds Binary Molecular Compounds Because nonmetals often combine with one another in different proportions to form different compounds, numerical prefixes are usually included in the names of binary molecular compounds.

Naming Covalent Compounds Chapter 2: Atoms, Molecules, and Ions 2/17/2019 Naming Covalent Compounds N2F4 The first element listed is more cationlike and takes the name of the element. The second element listed is more anionlike and takes the name of the element with an “ide” modification to the ending. The prefix is added to the front of each to indicate the number of each atom. dinitrogen tetrafluoride Copyright © 2008 Pearson Prentice Hall, Inc.

Naming Covalent Molecules Chapter 2: Atoms, Molecules, and Ions 2/17/2019 Naming Covalent Molecules Binary Molecular Compounds Whenever the prefix ends in “a” or “o” and the element name begins with a vowel, drop the “a” or “o” in the prefix. N2O4 dinitrogen tetroxide Whenever the prefix for the first element is “mono,” drop it. CO2 carbon dioxide CO carbon monoxide Copyright © 2008 Pearson Prentice Hall, Inc.

Name the following NO2 PCl5 I2F7

Example – Binary Molecular dinitrogen pentoxide Identify the symbols of the elements nitrogen = N oxide = oxygen = O Write the formula using prefix number for subscript di = 2, penta = 5 N2O5

Write formulas for the following dinitrogen tetroxide sulfur hexafluoride diarsenic trisulfide

Ions and Ionic Bonds Ionic Bond: A transfer of one or more electrons from one atom to another. A strong electrical attraction between charged particles. Typically a metal bonded to a nonmetal. Ion: A charged particle Cation: A positively charged particle. Metals tend to form cations. Anion: A negatively charged particle. Nonmetals tend to form anions.

Charged Atoms when atoms gain or lose electrons, they acquire a charge charged particles are called ions when atoms gain electrons, they become negatively charged ions, called anions (Cl-) when atoms lose electrons, they become positively charged ions, called cations (Na+) ions behave much differently than the neutral atom e.g., The metal sodium, made of neutral Na atoms, is highly reactive and quite unstable. However, the sodium cations, Na+, found in table salt are very nonreactive and stable

Ions and Ionic Bonds 2 1 Na + Cl2 Na+ + Cl– In the formation of sodium chloride, one electron is transferred from the sodium atom to the chlorine atom. 2 1 Na + Cl2 Na+ + Cl– Sodium is very reactive in water! Chlorine gas can kill someone (Fritz Haber, WWI). Sodium chloride: preservative, common food additive

Atomic Structures of Ions Nonmetals form anions For each negative charge, the ion has 1 more electron than the neutral atom F = 9 p+ and 9 e-, F ─ = 9 p+ and 10 e- Metals form cations For each positive charge, the ion has 1 less electron than the neutral atom Na atom = 11 p+ and 11 e-, Na+ ion = 11 p+ and 10 e-

Naming Chemical Compounds Cation Charges for Typical Main-Group Ions 1+ 2+ 3+ Metals tend to form cations. Note some in 3A and 4A with multiple charges.

Naming Chemical Compounds Cation Charges for Typical Main-Group Ions 3– 2– 1– Nonmetals tend to form anions. Noble gases do not naturally form ions in this sense.

Examples Predict the charge and identify the number of proton and electron from that ion Mg  Al  O  P 

Naming Chemical Compounds Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges. Binary Ionic Compounds Sodium chloride: Na+ Cl– NaCl Magnesium oxide: Mg2+ O2– MgO Aluminum sulfide:

Naming Chemical Compounds Some transition metals form more than one cation.

Naming Chemical Compounds Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation. Binary Ionic Compounds Iron(III) oxide: Fe3+ O2– Fe2O3 __________: Sn2+ Cl– SnCl2 The common system (stannous, stannic, etc.) is still used, but its use is becoming less frequent. Mn2+ N3– ___________:

Polyatomic ions Memorize these ions Polyatomic ions are covalently bonded atoms with a net charge.

Naming Chemical Compounds Polyatomic Ionic Compounds Sodium hydroxide: Na+ OH– NaOH Magnesium carbonate: Mg2+ CO32– MgCO3 Sodium nitrite: _____ ____ ____ Chromium(II)bromate: _____ _____ _____