Chemical Formulas, Isomers, and Periodic Table Basics for Chemistry

Molecular formula

A representation of a molecule or compound which consists of : chemical symbols (Ab) and subscripts (#) to indicate the number of each type of atom in the molecule.

Structural formula

Shows the same information as a molecular formula but also shows how the atoms are connected.

Diatomic molecules

Molecules that consist of two atoms, examples include H2, N2, O2, F2, Cl2, Br2, I2.

Elemental sulfur (-)

The most common form exists as S8.

Empirical formula

Indicates the simplest whole-number ratio of the number of atoms (or ions) in the compound.

Example of benzene

Molecular formula = C6H6; Empirical formula = CH.

Example of acetic acid

Molecular formula = C2H4O2; Empirical formula = CH2O.

Example of acetic acid dihydrate

Molecular formula = C2H8O4; Empirical formula = CH04O2.

Example of phosphoric acid

Molecular formula = H3PO4; Empirical formula = H3PO4.

Isomers

Compounds with the same chemical formula but different molecular structures.

Example of isomers

Acetic acid and methyl formate both are C2H4O2, but are different

Periodic Table

Recognized by Dimitri Mendeleev and Lothar Meyer, showing a periodic relationship among the properties of the elements.

Father of the Periodic Table

Dimitri Mendeleev

Group 1 Elements

shiny, conduct heat and electricity well, and have similar chemical properties.

Group 2 Elements

less reactive than group 1

First Periodic Table

Mendeleev used his table to predict the existence

of elements that would have the properties similar

to aluminum and silicon, but were not yet known

Modern Periodic Table

Arranges the elements in increasing order of their atomic numbers and groups atoms with similar properties in the same vertical column.

Periodic Law

The properties of the elements are periodic functions of their atomic numbers.

Periods or series

Horizontal rows (→ ←) in the periodic table. (1-7)

Groups

Vertical columns (↑ ↓) in the periodic table, numbered 1-18.

Metals

Shiny, malleable, good conductors of heat and electricity.

Nonmetals

Appear dull, poor conductors of heat and electricity.

Metalloids

Conduct heat and electricity moderately well, possessing some properties of metals and nonmetals.

Main group elements

Groups 1, 2, 13-18.

Transition metals

Groups 3-13.

Inner transition metals

Two rows at the bottom of the periodic table.

Lanthanides

Top row of the periodic table.

Actinides

Bottom row of the periodic table.

Alkali metals

Group 1 elements (except hydrogen). 1+ Charge

Alkaline earth metals

Group 2 elements. 2+ Charge

Transition Metals

Groups 3-12 elements (Require Roman Numerals)

Group 13

3+ Charge

Group 14

4+/- Charge

Pnictogens

Group 15 elements. 3- Charge

Chalcogens

Group 16 elements. 2- Charge

Halogens

Group 17 elements. 1- Charge

Noble Gases

Group 18 elements (also known as inert gases).

valence electrons

Matches group number

Ionic bond

A bond formed when electrons are transferred between atoms.

Covalent bond

A bond formed when electrons are shared between atoms.

Monatomic ions

Ions formed from only one atom.

Polyatomic ions

Electrically charged molecules formed from a group of bonded atoms.

Predicting Ion Charge

Using the periodic table to determine the ionic charge of main-group elements.

Group 2 ion charge

Lose two electrons, form a cation with a 2+ charge.

Group 17 ion charge

Gain one electron, form an anion with a 1- charge.

Ionic Compound

A compound that contains ions and is held together by ionic bonds; electrically neutral

Ionic Compounds formed by

Metal + Nonmetal/Polyatomic

Properties of Ionic Compounds

Typically solids with high melting and boiling points; nonconductive in solid form; conductive in molten form.

Example of Ionic Compound Formula

Ca2+ and PO43- forms Ca3(PO4)2.

Molecular Compounds

Molecular compounds (covalent compounds) result when atoms share electrons

Properties of Molecular Compounds

Exist as discrete, neutral molecules;

usually formed by a combination of nonmetals;

often exist as gases, low-boiling liquids, and low-melting solids.

Difference Between Ionic and Covalent Compounds

Ionic compounds transfer electrons; covalent compounds share electrons.

Chemical Nomenclature

A collection of rules for naming things; compounds are identified by both their formula and name.

Naming Ionic Compounds with Variable Charge

The charge of the metal ion is specified by a Roman numeral in parentheses after the name of the metal.

Nomenclature Prefixes

1-mono

2-di

3-tri

4-tetra

5-penta

6-hexa

7-hepta

8-octa

9-nona

10-deca

Hydrate

Compound, often ionic, that contains one or more water molecules bound within its crystals.

Naming Ionic Hydrates

1. Name the anhydrous compound (per usual rules); 2. Add the word hydrate with a Greek prefix denoting the number of water molecules.

Example of Ionic Hydrate

copper(II) sulfate pentahydrate = CuSO4·5H2O.

Example 2 of Ionic Hydrate

calcium chloride monohydrate =

CaCl2·H2O

Naming Binary Molecular Compounds

Molecular compounds are named using a different set of rules; covalent bonding allows for significant variation in the ratios of the atoms in a molecule; the names for molecular compounds must explicitly identify these ratios.

Naming Acids

Some compounds containing hydrogen are members of an important class of substances known as acids; many acids release hydrogen ions, H+, when dissolved in water.

Names of Some Simple Acids

HF(aq), hydrofluoric acid; HCl(aq), hydrochloric acid; HBr(aq), hydrobromic acid; HI(aq), hydroiodic acid; H2S(aq), hydrosulfuric acid.

Acid Symbol: HF(aq)

Acid Name: hydrofluoric acid

Acid Symbol: HCl(aq)

Acid Name: hydrochloric acid

Acid Symbol: HBr(aq)

Acid Name: hydrobromic acid

Acid Symbol: HI(aq)

Acid Name: hydroiodic acid

Acid Symbol: H2S(aq)

Acid Name: hydrosulfuric acid

Oxyacids

Compounds that contain hydrogen, oxygen, and at least one other element

Formula: HC2H3O2

Acid Name: acetic acid

Formula: HNO3

Acid Name: nitric acid

Formula: HNO2

Acid Name: nitrous acid

Formula: HClO4

Acid Name: perchloric acid

Formula: H2CO3

Acid Name: carbonic acid

Formula: H2SO4

Acid Name: sulfuric acid

Formula: H2SO3

Acid Name: sulfurous acid

Formula: H3PO4

Acid Name: phosphoric acid