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Transcript
```Chapter 2
Atoms, Molecules, and Ions
LAW OF CONSERVATION OF
MASS
• Antoine Lavoisier (1743-1794)
• During a chemical change, the total mass
remains constant
LAW OF DEFINITE
PROPORTIONS
• Joseph Proust (1754-1826)
• Law of Constant Composition
• Different samples of a pure compound
always contain the same proportion of
elements by mass.
LAW OF MULTIPLE
PROPORTIONS
• John Dalton (1766-1844)
• When two or more elements form more than
one compound, the ratio of the masses of
one element in these compounds for a fixed
mass of the other element is a small whole
number.
ATOMIC THEORY OF
MATTER (1808)
• John Dalton (1766-1844)
• Elements (matter) are composed of atoms
• Each element is characterized by the mass
of its atoms.
• A compound is a chemical combination of
atoms in definite proportions.
• A chemical reaction is the rearrangement of
ATOMIC STRUCTURE
Subatomic Particles (Table 2.1)
• ELECTRON (cathode ray)
1899 JJ Thomson
– Negative charge, -1
– Mass about 1/1836 of proton or neutron mass Milliken
• PROTON 1911 Rutherford
– Positive charge, +1
• NEUTRON
– No charge, 0
Relative mass = 1 amu
Relative mass = 1 amu
•MODELS OF THE ATOM
• Thomson (Plum Pudding) Model: positive
mass with electrons embedded in it
• Rutherford Model (1911): positive charge
in small volume with (diameter = 1E-15 m)
electrons occupying mostly empty space (d
= 1E-10 m) around the nucleus
• Bohr Atom - Chapter 5
• Quantum Mechanical Atom - Chapter 5
ATOMIC STRUCTURE
• Atomic Symbol
– Shorthand notation for element
– One or two letters on Periodic Table
• Atomic Structure
– Atomic Number (Z) = #protons, uniquely
defines an atom
– Mass Number (A) = #protons + #neutrons
– If atom is neutral, Z = #electrons
NUCLIDE SYMBOL
• Atomic symbol, E; symbol in the middle of each
element box on the Periodic Table.
• Z (left subscript); number on the top of each
element box on the Periodic Table.
• A (left superscript)
• If species is an ion (has a charge), add + or charge (right superscript)
•
A
ch
E
Z
IONS
• A charged species with unequal numbers of
protons and electrons.
• If # protons > # electrons, the ion has a net
positive charge and is called a cation
• If # protons < # electrons, the ion has a net
negative charge and is called a anion
• An ion may consist of an atom or a group of
atoms
ISOTOPE
• Atoms which have the same Z but a
different A
• This means that the #protons is the same but
the #neutrons is different.
• Most elements have isotopes that occur in
nature in precise proportions (fractional
abundances, %).
• A few elements have no naturally occurring
isotopes.
ATOMIC MASS
• One C-12 atom weighs exactly 12 amu
• amu = atomic mass unit – 1.661E-24 g
• Atomic mass of an element is defined as a
weighted average over all naturally
occurring isotopes of the element.
• Number on bottom on each element box on
the Periodic Table.
PURE SUBTANCE (Fig. 2.7)
• Pure substance, not separable by physical means,
has a constant composition
– Element: smallest entity which retains all properties of
element, made up of atoms of one type (@116 with 90
occurring naturally)
• May be an atom (Na, Si) or a molecule (S6, N2)
– Compound: consists of more than one element
combined in definite proportions; separable into
constituent atoms by chemical means
• There are over 20 million compounds
CHEMICAL BONDS
• Compounds contain atoms connected by chemical bonds
which involve electron interactions. The electrons act as
the “glue” between atoms.
– If electrons are shared between two atoms, the bond is a covalent
bond. I.e., the bond between two non-metal atoms.
– If electrons are transferred to produce ions, the bond is ionic.
• Ions are charged particles which form via the gain (anion, negative
ion, formed from nonmetal elements) or loss (cation, positive ion,
formed from metal elements) of electrons.
• Oppositely charged ions attract and form an ionic bond.
• Type of bond between a metal and a non-metal atom.
• Polyatomic ions are charged groups of atoms; they can form ionic
bonds.
MIXTURE
• Mixture: two or more pure substances
present in any proportions; separable by
physical means
– Homogeneous: one uniform phase of the same
composition and properties, a solution
– Heterogeneous: > 1 phase with varying
composition and properties
CHEMICAL REACTION
• A chemical reaction involves
rearrangements of atoms; breaking initial
chemical bonds (in the reactants) and
making new chemical bonds (in the
products).
• R1 + R2  P1 + P2 + P3
CHEMICAL FORMULA
• Qualitative description of the constituent
elements : NH3, C12H22O11
• Quantitative description of the relative
numbers of atoms of each element
• Empirical - includes all atoms in molecule
in correct smallest integral ratios
• Molecular - includes all atoms in molecule
in actual numbers and correct ratios
Types of Chemical Formulas
• Chemical - shows type and number of
atoms (p. 52)
• Structural - shows chemical bonds (p. 52)
• Ball and Stick - shows spatial arrangement,
3D (Fig 2.9a)
• Space filling - shows space atoms fill, 3D
(Fig 2.9b)
ACIDS, BASES, SALTS
• Acid: Produces H+ ions and anion in water
– HCl(aq)  H+ (aq) + Cl-(aq)
– Polyprotic acids produce more than one H+ ion.
• Base: Produces OH- ions and cation in
water
– KOH(aq)  K+ (aq) + OH-(aq)
• Acid and Base react to form Salt (ionic
compound) and Water. (neutralization)
PERIODIC TABLE (Front End
Page)
• An arrangement of elements according to
increasing atomic number which shows the
periodic or regularly repeating nature of
elemental properties.
– Rows = periods
– Columns = groups or families; note similarity
of properties
– Metals
Nonmetals
Semimetals
– Main group (A)
Transition (B)
NOMENCLATURE or
NAMING COMPOUNDS
• Binary Ionic Compounds (Fig. 2.11, 2.12)
– Metal atoms tend to lose electrons and form cations.
– Nonmetal atoms tend to gain electrons and form anions.
– Use Periodic Table to determine charges and number of
each ion in the compound. Note that the ionic
compound must be neutral overall.
– Name cation first as element and anion second with
“ide” ending.
– Some transition metal elements form more than one
common ion. Designate charge with Roman numeral
NOMENCLATURE (con’t)
• Polyatomic Ions (Table 2.3)
– Memorize
– Oxoanion = nonmetal + oxygen
• Acids (Table 2.4)
– Memorize
– Oxoacids (named from oxoanions)
NOMENCLATURE (con’t)
• Binary Molecular Compounds (Table 2.2)
– Name more “cation-like” first, then the more
“anion-like) second with “ide” ending.
Hydrogen is almost always named first.
– Indicate number of each using prefix as needed.
– Note historic names
```
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