Law of Definite Proportions ● 2 or more elements combine chemically in definite proportions by mass ● Explained by Dalton’s Atomic Theory
● The size of the sample does not change the mass ratio (also known as percent composition)
Atoms and Ions Atoms: ● Electrically neutral ● Can gain, lose, or share electrons when forming compounds
Ions: ● When number of protons does not equal number of electrons ● Ions have positive or negative charge
The Octet Rule ● 1916: Gilbert Lewis
● Atoms tend to achieve noble gas configuration when forming compounds (8 electrons in valence shell) ● Ex: Sodium form a sodium ion with a 1+ charge which has the same econfiguration as neon.
Ions Metals: ● Form positive ions (cations) o lose 1 or more electrons ● Charge for Group A metals can be determined by the group number o Group 1A metals have a 1+ charge o Group 2A metals have a 2+ charge, etc. ● Group B metals form multiple cations o Charge of 3+ or more is unlikely -- must consult a table for their charges o Group B metals achieve pseudo-noble gas config (18 e-s)
Ions Non-metals: ● Form negative ions (anions) o gain 1 or more electrons ● Charge for Group A non-metals is determined by the group number minus 8 o Group 5A non-metals gain 3 electrons o Group 6A non-metals have a 2- charge o Group 7A non-metals have a 1- charge (called hallide ions), etc.
Exceptions to Octet Rule ● Silver would have to lose 11 electrons or gain 7 to acquire the configuration of xenon ● Ions with charge greater than 3 are uncommon ● Instead silver loses 1 electron to attain pseudo-noble gas configuration (18 electrons) ● Other exceptions: Ag+, Au+, Cd2+, Zn2+
Example 1 Write electron configurations for the following ions: a) Calcium ion
b) Fluoride ion
Lesson 2 Ionic Bonds and Ionic Compounds
Ionic Compounds ● Made of positive and negative ions (metals + non-metals) ● Cations and anions are attracted by electrostatic force ● Arranged in orderly 3D pattern o Each + ion is between 2 or more - ions ● Electrically neutral
Ex: Sodium gives a valence electron to chlorine and both ions achieve a stable octet
Ionic Compounds ● Crystalline solids at room temperature ● High melting points ● Can conduct an electric current when melted or dissolved in water o Ions are free to move
Coordination Number Coordination Number: ● The number of ions of opposite charge that surround an ion in a crystal ● Example: o Each Na-ion is surrounded by 6 Cl-ions therefore Na’s coordination # is 6 o Each Cl-ion is surrounded by 6 Na-ions therefore it’s coordination # is also 6
Example 2 In TiO2, each Ti-ion is surrounded by 6 O-ions. What is its coordination #? Each O-ion is surrounded by 3 Ti-ions. What is its coordination #?
Lesson 3 Bonding in Metals
Metallic Bonds & Properties ● Metals are made up of closely packed cations rather than neutral atoms ● Valence electrons modeled as sea of electrons o Drift freely
Metallic Bonds & Properties ● Metallic bonds: o Attraction of free floating valence e-s for + metal ions Force of attraction that hold metals together
Metallic Bonds & Properties ● Sea of electrons explains many physical properties of metals o Good conductors Electrons flow freely in them As electrons enter one end of metal, an equal number leaves the other end o Ductile and Malleable Sea of valence electrons insulates cations from one another When under pressure, cations slide past one another
Crystalline Structure of Metals ● Metals that contain one type of atom are among the simplest forms of all crystalline solids ● Metal atoms are arranged in very compact and orderly patterns o BCC o FCC o HCP
Alloys ● Mixtures of 2 or more elements o At least 1 is a metal! ● Properties often superior to component elements
Alloys Substitutional alloy: ● If atoms of components are similar in size, they replace each other in the crystal Interstitial alloy: ● If sizes are very different, smaller atoms fit into interstices (spaces) between larger atoms Amalgam: ● An alloy containing mercury