Atoms, Molecules and Ions

Greeks (1000BC – 400BC)• First to suggest that all matter was composed of

4 fundamental substances: Fire, Earth, Water and Air.

• Democritus and Leucippos believed that matter was composed of small indivisible particles However, the Greeks had no experiments to test

their ideas, no definitive answer could be reached. Alchemy (400BC – 1500)

• Mystics and fakes who were obsessed with the idea of turning cheap metals to gold.

• Many alchemist were serious scientists and discovered many elements.

Georg Bauer (1494-1555)• Development of systematic metallurgy (extraction of

metal from ores) Robert Boyle (1627-1691)

• First chemist to perform truly quantitative experiments.• Measured the relationship between the pressure and

volume of air.• Initial idea of compounds and elements led to the

discovery of several new elements and shot down the Greek’s idea of 4 atoms.

Georg Stahl (1660-1734)• Studies of combustion led to the idea of a substance

flowing out of a burning material and he called it Phlogiston.

Joseph Priestly (1733-1804)• Found a gas that supported combustion and called it

dephlogisticated air.

Law of conservation of mass• Discovered by Antoine Lavoisier• Quantitative experiments where he measured the

mass of reactants and products in different chemical reactions.

Law of definite proportions• Discovered by Joseph Proust• Found that a given compound always contains

exactly the same proportion of elements by mass. Law of multiple proportions

• Discovered by John Dalton• Found that two elements can form a series of

compounds with different ratios of each element.

Theory• Each element is made up of tiny particles

called atoms.• The atoms of a given element are identical.• Compounds are formed when atoms of

different elements combine.• Chemical reactions involve reorganization of

the atoms. Proposed the first table of atomic

masses (later proven incorrect)

Electron• J.J. Thomson passed electrical current through

partially evacuated tubes called cathode-ray tubes.

• Thomson found that the ray emanated from the cathode (negative electrode) and repelled the negative pole of an applied electric field.

• Proposed that all atoms must contain electrons since the cathode could be made from many different types of metals.

• Assumed that the atoms must contain some positive charge.

• Proposed what is known as the plumb pudding model of the atom.

The nuclear atom• Ernest Rutherford carried out an experiment to test

Thomson’s proposed atomic model.• This experiment is known as the “Gold Foil

Experiment.” Rutherford shot alpha particles at a thin sheet of gold

foil. If Thomson’s model is correct most of the alpha particles

would shoot directly through the foil and a few may be deflected slightly due to the positive charges spread throughout the atom.

Rutherford found that most alpha particles did in fact go directly through but occasionally an alpha particle was deflected at a large angle or directly back at the source.

From these results, Rutherford knew that Thomson’s model was incorrect and he proposed the idea of the nucleus containing the positive charges.

Nucleus• Protons

Contain a positive charge equal in magnitude to an electron Mass = 1.67x10-27 kg

• Neutrons Neutral particle having virtually the same mass as the

proton. Isotopes

• Atoms with the same number of protons but different number of neutrons.

• Represented using nuclear symbols or hyphen notation. Nuclear symbol

Contains the element’s symbol preceded by the mass number as a superscript and the atomic number as a subscript

Hyphen notation Contains the element’s name written out followed by the mass

number. Examples:

Chemical bonds• Are the forces that hold atoms together• Three types of chemical bonds exist:

Covalent Results from the sharing of electrons/typically between

two nonmetals/results in molecules Ionic

Results from the attraction of oppositely charged ions (cations/anions)/typically between a metal and nonmetal/results in compounds

Metallic Results from the mutual sharing of valence

electrons/electrons are free to move form one atom to another through the empty or partially filled d orbitals in an attempt to satisfy all of the atoms.

Types of atoms found on the periodic table• Metals• Nonmetals• metalloids

Specific groups of the table• Alkali metals• Halogens• Alkaline earth metals• Transition metals• Noble gases• Lanthanides• Actinides

Binary compounds• Compounds containing only 2 different atoms.• Two different types of binary compounds exist.

Binary ionic compounds Binary covalent compounds

• Rules for naming Ionic compounds (type-1 metal with only 1 charge) Ionic compounds (type-2 metal can have numerous

charges) Covalent compounds (type-3)

Ionic compounds with polyatomic ions• Rules

Named the same as type-1 and type-2 but polyatomic’s name is used instead of element name

You must memorize the common polyatomic ions. Acids

• Molecules that produce free H+ ions when dissolved in water.

• And acid can be viewed as one or more H+ attached to an anion.

• Rules for naming. No oxygen present

Hydro- ______ - ic acid Oxyacids

Name is based on the anion’s name with a suffix of –ic or –ous.

P4O10 Nb2O5 HClO3 Li2O Ti(NO3)4 H2SO4 Calcium oxide Dioxygen difluoride Vanadium V fluoride Phosphorous acid Gallium oxide