Chemistry Unit 7 Study Guide

I.  Chemical Bonds

• chemical bonds: forces of attraction that hold 2 atoms together, formed  by the attraction between the positive nucleus of 1 atom and the negative electrons of another atom; it has a significant effect on chemical and physical properties and involves the atom’s valence electrons (electrons on outermost energy level) - 

1. ionic bond: electrostatic attraction (attraction forces) between positive and negative ions

2. covalent bond: sharing of electrons

3. metallic bond: metal atoms bonded to several other atoms

• octet rule: states that atoms will combine to form compounds in order to reach 8 electrons in their outer energy level; atoms with less than 4 valence e^- tend to lose electrons (metals, becoming cations), and atoms with more than 4 valence e^- tend to gain electrons (nonmetals, becoming anions)

• cations: positive ions, left side of periodic table (metals); have lost electrons, becoming +

• anions: negative ions, right side of periodic table (nonmetals); have gained electrons, becoming - 

• group ion charges - 

1. group 1 - 1+ (most reactive, only need to lose 1 electrons to have 8)

2. group 2 - 2+

3. group 13 - 3+

4. group 15 - 3-

5. group 16 - 2-

6. group 17 - 1- (most reactive, only need to gain 1 electron to have 8)

7. group 18 - 0 (stable, full set out 8 valence electrons)

• electron-dot/lewis structure of ionic compounds: consists of an element’s symbol, representing the atomic nucleus and inner-level electrons, that is surrounded by dots, representing the atom;s valence electrons 

II.  Ionic Bonds and Compounds 

• positive and negative ions exist in a ratio determined by the number of electrons transferred from the metal atom to the non-metal atom (ie sodium chloride has a 1:1 ratio of sodium cation and chlorine anions, as 1 electron is lost in each sodium ion and 1 electron is gained in each chlorine ion)

• ionic crystal: the repeating pattern of particle packing in an ionic compound

• crystal lattice: the three-dimensional geometric arrangement of particles, and is responsible for the structure of many minerals; is a result of the attraction forces between the positive and negative ions in an ionic compound

• lattice energy: the energy required to separate 1 mol of ions in an ionic compound

• lattice energy trends - 

1. increases with the charge of the ions - the more negative (gained electrons) the lattice energy is, the greater the attraction forces between the positive and negative ions in an ionic compound

2. increases with the decreasing size of ions - lattice energy is directly related to the size of the ions that are bonded, because smaller ions form compounds with more closely spaced ionic charges, and require more lattice energy to separate; the smaller the ion, the greater the attraction forces 

• ionic bonds: attraction formed by transferring electrons between metals and nonmetals

• ionic compounds: 

1. strong attractions from a 3 dimensional crystal lattice

2. zero net charge (cations and anions balance each other)

3. hard, crystalline solid

4. brittle

5. good conductor (when melted or dissolved, solids are poor conductors)

• melting point, boiling point, and hardness are dependent on the strength of attraction between the cations and anions in the ionic bond that forms the ionic compound

• solid ions in ionic compounds: are locked into position and electrons cannot flow freely; are poor conductors of electricity; have strong attraction forces than molecules, very hard but brittle; high boiling and melting points; are conductors once dissolved or melted, because their ions are broken up - non-conductive in their solid state; do not vaporize at room temperature

• liquid ions in ionic compounds: have electrons that are free to move, so they conduct electricity easily

• electrolyte: an ion in an aqueous solution that conducts electricity  

• in chemical reactions, energy is involved either - 

1. to break some (or all) bonds between atoms in the reactants so the atoms can form new bonds 

2. when the atoms or products form new bonds to make new products

• exothermic reaction: chemical reaction in which forming new bonds releases more energy than it took to break the old bonds; makes new bonds, releasing energy (ie reaction of hydrogen with oxygen); energy releases > energy used; the formation of a stable ionic compound from ions is always exothermic, making new bonds

• endothermic reaction: if forming new bonds releases less energy than it took to break the old bonds; breaking old bonds, requiring energy (ie photosynthesis); energy used > energy released

• dissolution reaction: occurs when an ionic compound (like ammonium nitrate) dissolved in water to make an ionic solution

• binary compound: 1 metal + 1 nonmetal, contains only 2 different elements; name of cation (metal) + base name of anion (nonmetal) + ide (ie Ba²⁺ S^2- -> barium sulfite)

potassium oxide -> K⁺ O^2- -> K₂ O

Al₂ O₃ -> aluminum oxide 

• roman numerals: transition metals (groups 3-12) + nonmetals; the roman numeral represents the charge of the transition metal, or how many electrons the ion has lost

Cu (II) Bromide -> C²⁺ Br^1- -> Cu Br₂ 

Fe Cl₃ -> Fe³⁺ Cl^1- -> Fe (III) Chloride

• polyatomic: metals and multiple atoms of oxygen (ie SO^-₄² sulfate)

Fe (III) Carbonate -> Fe³⁺ CO₃^2- -> Fe₂ (CO₃)₃ (do not touch number in () )

IV.  Metallic Bonds

• metallic bond: the attraction of a metallic cation for delocalized electrons; metal + metal; bonding is based on the attraction of particles with unlike charges, like with ionic bonds; involves lattice structures, like with ionic compounds; involves delocalized electrons

• metals: consist of closely packed cations floating in a sea of electrons (delocalized electrons); all of the metal’s atoms are able to share the delocalized electrons, because they are not bound to specific or individual atoms

• delocalized electrons: electrons present in the outer energy levels of the bonding metallic atoms that are not held by any specific atom and can move easily from 1 atom to the next; present in the sea of electrons and serve as the negative force of attraction to the positive cations of metals, forming the metallic bond and holding the metallic compound together

• properties of metals - 

1. greatly vary in melting points

2. malleable

3. ductile

4. good conductors (when solid)

5. form alloys

• alloy: a mixture of elements that has metallic properties; properties differ from the elements it contains -

1. substitutional alloy: forms when some atoms in the original metallic solids are replaced by other metals of similar atomic structure (same group); some metal atoms replaced by other of similar size

2. interstitial alloy: forms when small holes in a metallic crystal are filled with smaller atoms 

• metallic bonds are named for the metals in the mixture or are given a special name -

1. solder: mixture of tin and lead

2. silver sterling: mixture of silver and copper

3. brass: mixture of zinc and copper