Chapter 2

Atoms, Molecules, and Ions

Matter

• What accounts for matters secrets?

– Atomists – Democritus – All things are made of Fire – Herclitus – Four Elements – Aristotle

• Conservation of Mass and Law of Definite Proportions

Robert Boyle (1627 –1691):

Provided evidence for the atomic nature of matter.

– Element - A substance that cannot be chemically broken down further •

Joseph Priestley (1733 – 1804):

Conservation of Mass and Law of Definite Proportions • Antoine Lavoisier (1743-1794):

Conservation of Mass •

Law of Mass Conservation:

Mass is neither created nor destroyed in chemical reactions.

Hg(NO 3 ) 2 + 2 KI → Hg I 2 + 2 K NO 3 3.25g + 3.32g → 4.55g + 2.02g

6.57g = 6.57g

Law of Definite Proportions

•

Law of Definite Proportions:

In a unique compound the elements will always be found in the exact same ratio.

Dalton’s Atomic Theory and the Law of Multiple Proportions •

John Dalton (1766 –1844):

Proposed explanations for the laws of mass conservation and definite proportions.

– Postulate 1: Elements are made of atoms – Postulate 2: Atoms of the same element have the same properties (including mass). Atoms of different atoms have different properties – Postulate 3: Compound are comprise of elements joined together in small whole ratios – Postulate 4: Chemical reactions only rearrange the way the atoms are combined

Dalton’s Atomic Theory and the Law of Multiple Proportions •

Law of Multiple Proportions:

– When two elements form two

different

compounds, the mass ratios are related by small whole numbers.

The Structure of Atoms: Electrons • Elements are composed of atoms • Compounds are composed of atoms of elements in a given ratio • What does an atom look like?

The Structure of Atoms

•

Structure of the Atom:

The Structure of Atoms

• Comparison of Subatomic particles Particle Grams amu Coulombs Electron Proton Neutron 9.109382 x 10 -28 0.0005485799 -1.602176 x 10 -19 1.672622 x 10 1.674927 x 10 -24 -24 1.007276

1.008665

1.602176 x 10 -19 0 e -1 1 0

Atomic Number

• # protons in an atom determines the element – atomic number (Z) - Atomic number is found on the periodic table • # electrons = # protons in a neutral atom

Mass Number

• mass of the atom ≈ # neutrons + # protons – Mass number = # protons + # neutrons – An element may have more than one mass # • • Hydrogen, Deuterium, Tritium

Isotopes:

Atoms with identical atomic numbers, but different mass numbers.

• Due to different # of neutrons

NOT

protons

Atomic Mass

•

Atomic Mass:

A weighted average of the isotopic masses of an element’s naturally occurring isotopes.

– Unit – atomic mass unit (amu)

Example

• Chlorine has two naturally occurring isotopes: with an abundance of 75.77% and an isotopic mass of 34.969 amu, and with an abundance of 24.23% and an isotopic mass of 36.966 amu. What is the atomic mass of chlorine?

Compounds and Mixtures

Chemical Bonds • 2-types of bonding are found in compounds – Ionic bond – Covalent bond

Ionic Bond

• Molecules, Ions and Chemical Bonds

Ionic Bonding (Ionic Solids):

Occur between metal and non-metal

Ionic Bonds

Problem

• Which of the following ions occurs commonly?

– A. N 3+ – B. S 6+ – C. O 2 – D. Ca + – E. Cl +

Ionic Bonds

Ionic Bonds •

Formula for Ionic Compounds

combine to form neutral – Ions compounds

Examples:

Na + and Cl – combine to form NaCl.

Ca 2+ and Cl – combine to form CaCl 2 .

Al 3+ and Cl – combine to form AlCl 3 .

Fe 2+ and Cl combine to form FeCl 2 .

Molecules, Ions, and Chemical Bonds

Naming Chemical Compounds

• Naming Ionic Compounds - name the cation, then name the anion.

– The positive ion (the metal or ammonium) • Single charge or ammonium – write its name • More than one possible charge – Write the elements name – Indicate the magnitude of charge as a roman numeral in parenthesis – The negative ion (non-metal or polyatomic ion) • Non-metal element - write root of element name with suffix –ide • Polyatomic – write the ions name

Problem

• Which one of the following combinations of names and formulas of ions is incorrect?

– A. O 2 – B. Al 3+ oxide aluminum – C. NO 3 – D. PO 4 3 nitrate phosphate – E. CrO 4 2 chromate

Problem

• Which one of the following combinations of names and formulas of ions is incorrect?

– A. Ba 2+ barium – B. S 2 sulfate – C. CN cyanide – D. ClO 4 – E. HCO 3 perchlorate bicarbonate

Problem

• Convert the names into formulas and the formulas into names – Sodium oxide – BaO – CoCl 2 – (NH 4 ) 2 S – Zinc Acetate – Chromium (VI) oxide

Covalent Bond

Molecules, Ions and Chemical Bonds •

Covalent Bonding (Molecules):

Between 2 non-metals or a non-metal and a metalloid.

Covalent Bonds

Naming Chemical Compounds

•

Naming Binary Molecular Compounds:

– Identify which element is more

cationlike.

Naming Chemical Compounds

• If cation-like element is H

and

anion-like element is O, S, Se, or a halogen – Name hydrogen – Name the anion-like element using root and – ide ending

Naming Chemical Compounds

• All other non-metal / metalloid combinations – Name the cation-like element – Name the anion-like element with root and –ide – Using prefixes indicate how many of each atom is present

Covalent Compounds

• Formula – Translate name of each element – Make the prefix of the element it’s subscript

Problem

• Convert formulas into names and names into formulas – PCl 3 – Diiodine pentoxide

Naming Compounds

• Acids – are a special type of covalent compound – Acids are species that dissociate to form H + cations and an anion when added to water.

• Hence you will need to be told that they are aqueous compounds (aq) – Acids are typically indicated by writing the H first in the formula • Elemental symbols are typically written in alphabetical order

Naming Compounds

• Acids cont.

– For current purposes, acids are going to be described as aqueous compounds of H combined with a group 17 element or a polyatomic ion.

– H with group 17 elements or cyanide • Named as hydro + 17 element root + ic – H with all other polyatomic ions • Root of polyatomic ions ending in -ate + ic • Root of polyatomic ions ending in –ite + ous

Problem

• What is the name of the acid formed when HBr gas is dissolved in water?

– A. bromic acid – B. bromous acid – C. hydrobromic acid – D. hydrobromous acid – E. hydrobromidic acid

Optional Homework

• Text – 2.26, 2.28, 2.29, 2.38, 2.46, 2.48, 2.50, 2.52, 2.54, 2.56, 2.58, 2.68, 2.78, 2.82, 2.84, 2.86, 2.88, 2.90, 2.96, 2.100, 2.104, 2.112

• Chapter 2 Homework – from website