Atoms, Molecules, and Ions in General Chemistry

Atoms

Atoms are the smallest particles of an element that retain the chemical identity of that element.

Comparison to the macroworld

1022 atoms in 1 penny, equivalent to 1 grain of sand in a sandbox the size of Texas.

Silicon (Si) Atoms Size

Si atoms have sizes of ~ 0.2 nm or 2 Å.

Sir John Dalton

Proposed that atoms were indivisible and all atoms of a given element were identical.

J. J. Thomson

Discovered the electron using a cathode ray tube apparatus.

Cathode Ray Tube

An apparatus used by J. J. Thomson to discover the electron.

Cathode Rays

Cathode rays move toward the anode, indicating they must be negatively charged.

Mass-to-Charge Ratio of Electron

Thomson used his CRT experiment to determine the mass-to-charge (me/e) ratio of the electron.

Robert Millikan

Conducted the oil-drop experiment to measure the charge of the electron.

Ernest Rutherford

Studied the nuclear structure of the atom and conducted the Gold-Foil Experiment.

Gold-Foil Experiment

Demonstrated that most particles passed straight through gold foil, indicating most of an atom is empty space.

Nucleus

At the center of an atom is the nucleus, which must be positively charged and contains protons and neutrons.

Average Diameter of Nucleus

Average diameter of the nucleus is 10^-15 m (1 fm), which is 10^5 times smaller than the average diameter of an atom.

Proton (p+)

A positively charged subatomic particle that has an equal but opposite charge of the electron and mass 1800 times greater than that of an electron.

Neutron (n0)

A subatomic particle that is neutral in charge (charge of 0).

Three Subatomic Particles of the Atom

Proton (p+): Positively charged, Neutron (n0): Zero charge, Electron (e-): Negatively charged.

Periodic Table of Elements

Developed in 1869 by Dmitri Mendeleev, it consists of 18 Groups (vertical columns) and 7 Periods (horizontal rows).

Groups (or Families)

Vertical columns in the Periodic Table where elements have similar properties, labeled by Arabic Numerals (1 - 18) or 1A, 2A,....8A; and 1B - 8B.

Metals, Nonmetals, and Metalloids

Elements in the Periodic Table can be classified as metals, nonmetals, and metalloids.

Atomic Number (Z)

The number of protons in the nucleus of an atom, which defines the element.

Atomic Mass (A)

The sum of the protons and neutrons in the nucleus of an atom.

Bromine (Br)

Z = 35; A = 79.90 (round up to 80).

Iron (Fe)

Z = 26; A = 55.85 (round up to 56).

Atomic Mass Calculation

Atomic Mass (A) = p+ + n0. Therefore, n0 = A - p+ = A - Z.

Ions

Ions are defined as charged particles formed when atoms lose or gain one or more electrons.

Cations

Positively charged ions that are formed when an atom loses one or more electrons.

Anions

Negatively charged ions that are formed when an atom gains one or more electrons.

Charge of an Ion

The charge of an ion is indicated in the upper right corner of an element's symbol.

# e-

# e- = Z - charge of ion

Sodium ion (Na+)

Z = 11; A = 22.99 (round up to 23)

Aluminum ion (Al3+)

Z = 13; A = 26.98 (round up to 27)

Carbide ion (C4-)

Z = 6; A = 12.01 (round down to 12)

Chloride ion (Cl-)

Z = 17; A = 35.45 (round down to 35)

Isotopes

Isotopes are atoms of the same type of element that differ in mass number, or in their number of neutrons.

Symbolic Forms of Isotopes

A second common form for representing isotopes is the chemical symbol (or name) of the element followed by a hyphen and the mass number of the isotope.

Average Atomic Mass

The average atomic mass is calculated from the isotopes present.

Chemical Formulas

Representation of a chemical compound showing the elements present in the compound (written by their atomic symbols) and the number of atoms of each element in the compound (written as a subscript integer).

Water

Chemical formula: H2O

Iron(III) Oxide

Chemical formula: Fe2O3

Carbon Dioxide

Chemical formula: CO2

Calcium Nitrate

Chemical formula: Ca(NO3)2

Hydrogen Peroxide

Chemical formula: H2O2

Glucose

Chemical formula: C6H12O6

Sodium Chloride

Chemical formula: NaCl

Caffeine

Chemical formula: C8H10N4O2

Molecular Formula

Shows the actual number of atoms of each type of element present in a compound. Also called the 'complete formula'.

Empirical Formula

Shows the simplest whole-number ratio of atoms of each type of element present in a compound. Also called the 'simplified formula'.

Structural Formula

Two-dimensional drawing of the chemical structure of a compound showing the chemical bonding of neighboring atoms in the compound represented by solid lines.

Binary

Two elements

Ionic compounds

Composed of metals that form only one type of ion (Type I) and more than one type of ion (Type II)

Binary Ionic Compounds

Composed of only one type of metal element & one type of nonmetal element.

Systematic Rule for Naming Binary Ionic Compounds

Base Name of Anion (Nonmetal) + '-ide' and Name of Metal Cation

Monatomic Anions

Base Name of Nonmetal Element + -ide + ion

Fluoride ion

F-

Oxide ion

O2-

Chloride ion

Cl-

Sulfide ion

S2-

Bromide ion

Br-

Nitride ion

N3-

Iodide ion

I-

Phosphide ion

P3-

Carbide ion

C4-

Monatomic Cations

Name of Element + ion

Sodium ion

Na+

Potassium ion

K+

Calcium ion

Ca2+

Type II Metals

Metals that form more than 1 type of ion

Roman Numeral (Stock) System

Name of metal with the charge of ion written by Roman numerals in parentheses following the metal name.

Old Latin Root System

Older Name of the metal ion, written in its Latin root stem, followed by the suffixes "-ous" or "-ic".

Criss-Cross Method

Look at the cation and anion components of the compound.

Oxoanion

Type of polyatomic anion that contains oxygen and another element.

Ammonium phosphate

NH4+ PO43-; Formula: (NH4)3PO4

Sodium hydroxide

Na+ OH-; Formula: NaOH

Potassium carbonate

K+ CO32-; Formula: K2CO3

Ferric chlorate

Fe3+ ClO3-; Formula: Fe(ClO3)3

Binary Molecular Compounds

Composed of two types of nonmetal elements.

Acid

An acid is a molecular compound that produces H+ ions when dissolved in water.

Binary Acids

Contain hydrogen and a nonmetal element.

Oxoacids

Contain hydrogen, oxygen, and another nonmetal element.

Hydrochloric acid

HCl

Hydrofluoric acid

HF

Hydrobromic acid

HBr

Hydroiodic acid

HI

Hydronitric acid

H3N

Hydrosulfuric acid

H2S (Base Name: 'sulfur')

Hydrophosphoric acid

H3P (Base Name: 'phosphor')

Chemical Equation

A representation of a chemical reaction that has the chemical formula(s) of the starting materials (REACTANTS) written on the left side and the chemical formula(s) of the end/finished materials (PRODUCTS) written on the right side.

General Setup of Chemical Equation

REACTANT(S) PRODUCT(S)

State Abbreviations

The physical state of a pure substance in a chemical equation is often specified by writing the correct abbreviation in parentheses after the chemical formula of the substance.

Balanced Chemical Equation

A balanced chemical equation is one in which the numbers of each type of atom on both sides of the equation are equal.

Integer Coefficients

Inserted in front of the formulas of the reactants and products when balancing chemical equations.

Combustion of methane

CH4(g) + O2(g) CO2(g) + H2O(g)

Balancing Order for Combustion Reactions

Balance Carbon, Balance Hydrogen, Balance Oxygen.

Example of Balancing Chemical Equations

C8H18(l) + O2(g) CO2(g) + H2O(g)

Polyatomic Unit

Treat the polyatomic unit as a single unit and balance it out as a whole.

Practice Examples

Ca + B2O3 B + CaO, NO2 + H2O HNO3 + NO, H2 + Mn2O3 Mn + H2O, C4H10 + O2 CO2 + H2O.