Molecules and Ions LecturePLUS Timberlake

The Periodic Table Horizontal rows are referred to as periods Vertical columns are referred to as groups or families Special names on periodic table Group 1: alkali metals Group 2: alkaline earth metals Group 17: halogens Group 18: noble gases LecturePLUS Timberlake

Molecule Molecule – an aggregate of at least two atoms in a definite arrangement held together by chemical bonds In a fixed ratio! May include the same element or different Compounds only have different elements LecturePLUS Timberlake

Diatomic Molecules Remember the lucky seven? These seven ALWAYS are diatomic in nature Memorize these H2, N2, O2, F2, Cl2, Br2, I2 LecturePLUS Timberlake

Ions Ion – has either GAINED or LOST electrons Anion – negatively charge (gained electrons), ex: Cl- Cation – positively charged (lost electrons), ex: Na+ Anion usually on the right, cations on the left Must memorize these! LecturePLUS Timberlake

Empirical vs. Molecular Formula Empirical - Tells us which elements are present in the lowest-whole number ratio, NOT necessary how many atoms are present Molecular – shows the EXACT composition of elements Ex: hydrogen peroxide, used to kill bacteria, has the molecular formula of H2O2, there are 2 H and 2 O, however, the empirical formula is HO Empirical – simplest, molecular - true

Empirical Formula When analyzing an unknown compound, first step is to find the empirical formula LecturePLUS Timberlake

Ex: Write empirical formulas for the following molecules (a) C2H2 CH (b) C6H12O6 CH2O (c) N2O Empirical formula is the same as the molecular formula LecturePLUS Timberlake