chapter 2 atoms, molecules, and ions. matter what accounts for matters secrets? –atomists –...
TRANSCRIPT
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(NO3)2 + 2 KI → HgI2 + 2KNO3
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 e
Electron 9.109382 x 10-28 0.0005485799 -1.602176 x 10-19 -1
Proton 1.672622 x 10-24 1.007276 1.602176 x 10-19 1
Neutron 1.674927 x 10-24 1.008665 0 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. N3+
– B. S6+
– C. O2-
– D. Ca+
– E. Cl+
Ionic Bonds
Ionic Bonds
• Formula for Ionic Compounds – Ions combine to form neutral compounds
Examples:
Na+ and Cl– combine to form NaCl.
Ca2+ and Cl– combine to form CaCl2.
Al3+ and Cl– combine to form AlCl3.
Fe2+ and Cl- combine to form FeCl2.
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. O2- oxide
– B. Al3+ aluminum
– C. NO3- nitrate
– D. PO43- phosphate
– E. CrO42- chromate
Problem
• Which one of the following combinations of names and formulas of ions is incorrect?
– A. Ba2+ barium– B. S2- sulfate– C. CN- cyanide
– D. ClO4- perchlorate
– E. HCO3- bicarbonate
Problem
• Convert the names into formulas and the formulas into names– Sodium oxide– BaO
– CoCl2– (NH4)2S
– 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– PCl3– 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