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CHAP 2
Atoms, Molecules, and ions
History
• Greeks
• everything made up of 4 fundamental substances
(earth,air,fire,water)
• “atomos” – later became atom – small, indivisible
particles
• Dalton’s Atomic Theory –
• Each element made up of atoms
• Atoms of same element same; different element different
• Compounds form from combinations of elements in
definite proportions.
• Chemical reactions involve rearrangements of atoms.
More History
• Thomson – studied cathode-ray tubes/Plum Pudding
Model
• Negative particle (electron)
• Determined charge to mass ratio of electron
• Milikan – Oil Drop Experiment
• Determined magnitude of electron charge
• Rutherford – Gold Foil Experiment
• Found positive center of atom (nucleus)
• Positive particle – proton
• Bohr – model of Hydrogen atom
• Chadwick – discovered neutron
Key Terms
Atomic mass – average # of protons & neutrons in
an atom
Atomic weight – weighted average mass
determined by a standard
Atomic number – # of protons in an atom
Mass number – total # of protons & neutrons
Isotope – same # protons, but different # neutrons
Ion – gain or lost electrons (no longer equal to #
protons)
Neutral atom – equal # of protons and electrons
Nucleus – positively charged, dense center of the
atom
Atomic Structure
Symbol
Mass
Charge
Location
Proton
P+
1
+
nucleus
Neutron
n0
1
-
nucleus
Electron
e-
0
0
Electron
cloud
Nucleus – contains mass of atom
Electron cloud – gives volume to
atom
Periodic Table
• Types of elements
• Metals – left side; majority of elements; good
conductors; lose electrons (+ ions)
• Nonmetals – right side; poor conductors; gain electrons
(- ions)
• Metalloids – stair-step line
• Groups – columns; grouped by similar properties
• 18 – each has a name
• Periods – rows
•7
More on Periodic Table
• Group 1 – Alkali Metals
• Group 2 - Alkaline Earth metals
• Groups 3-12 – transition metals
• Groups 13-16 – named after first element and word
family (ie. Carbon family – group 14)
• Group 17 – Halogens
• Group 18 – Noble Gases
• Bottom – Lanthanide and Actinide series
Naming
Binary Compounds
• Cation (+ion) named first, anion (-ion) named
second
• First element is named as the element
• Second element, keep root & change ending to –
ide
• if has more than 1 charge possible, use Roman
numeral to indicate charge of metal (systematic)
• May use latin root of element – higher charge
ends in –ic, lower charge in –ous
• Polyation ions named as is – change nothing
• If covalent compound (2 nonmetals) – need to
use prefixes.
Formula Writing
• Compound needs to be electrically neutral – balance
out charges.
• Criss-cross the ion charges to become the subscripts
in the formula.
• Polyatomic ions belong in parentheses. Any crisscrossed subscript goes outside parentheses.
• Remember roman numeral indicates charge of that
metal.
• Prefix value goes with the element it is attached to –
no criss-crossing if have prefix.
Acids
• Always contain hydrogen first in the formula
• If it does not contain oxygen (just H and another
element), named with prefix hydro-, root, and ends in
–ic.
• If does contain oxygen, if polyatomic ion ends in –ite,
acid ends in –ous. If polyatomic ion ends in –ate,
acid ends in -ic