element electron
atom ion
proton cation / anion
neutron molecule
Atom – the smallest unit of matter that
displays all of the properties of the element
Nucleus - the center of the atom, with most of the mass (analogous to the solar
system)
composed of: protons positively charged particles (+) and
neutrons neutrally charged
particles (0)
Electrons - negatively charged particles that orbit the
nucleus in discrete shells (-)
An electrically stable atom has the same number of protons as electrons
the charges balance (+) = (-)
An element is defined by the number of protons in the nucleus
Examples:
1
proton hydrogen 26 protons iron
6
protons carbon 92 protons
uranium
8
protons oxygen
The Periodic Table of the Elements
Electron Shells determine chemical reactions
Figures 2.4 and
2.5
Ions – if the charges on an atom don’t balance:
cation – a positive ion,
“missing” one or
more electrons { cat ion }
most metals produce
cations
example: Na+
anion – a negative ion,
with one or more
“extra”
electrons { an ion }
example: Cl–
Elemental cations and anions
the configuration of the electron shells
determines the preferred ionic charge
Groups of elements with similar properties, also determined by
the electron shells
Isotopes of an element – same number of protons
but a different number of neutrons
Stable isotopes and radio-isotopes
Stable isotopes do NOT decay radioactively
Examples: 1H and 2H (stable)
, 3H
tritium (radioactive)
12C and 13C
(stable), 14C (radioactive)
Molecules – two or more atoms bonded together
covalent bond – example of water molecule
one oxygen atom shares electrons with two
hydrogen atoms
GAS disorder among molecules
LIQUID short-range order
SOLID long-range order
Heat results from the vibrations of atoms – this is kinetic
energy
Heat is transferred along a gradient
conductive – particle to particle
radiative – by electromagnetic radiation infra-red radiation
The
effect of heat on density of matter
Phase transitions are controlled by:
heat (energy available – outward force)
pressure (constraining force)
At 5,000 meters altitude, water boils at a:
higher or lower
temperature?
At 5,000 meters in the ocean, water boils
at a: higher
or lower temperature?
So…as temperature increases:
atoms (or molecules) vibrate faster and with greater amplitude
these vibrations “push” the atoms farther apart
which lowers the density of the material
Melting is the transition from solid to liquid
freezing is
the reverse
Evaporation (vaporization) is the transition from liquid to gas
condensation is the reverse
Because a water molecule is bipolar, it has hydrogen bonding
between the individual molecules
This is only 4% of the force of the covalent bond,
BUT it gives water unique properties
Higher melting and boiling point than other hydrogen compounds
Higher heat capacity than any substance other than ammonia
[amount of heat needed to raise the temperature of 1 gram of water
1oC]
Greater solvent power than any other substance
Highest surface tension of any other liquid
Only substance that naturally occurs as a solid, liquid, and a gas at Earth-
surface temperatures and pressures
The angle between the hydrogen atoms increases from 105o to 109.5o
The molecules form hexagons and “lock in place”
The center of the hexagons in ice are empty space, so…
ice is 8% less dense than liquid water
Energy (heat) is released
Ionic bonds are only 1/10 as strong as covalent bonds
The polar ends of water are attracted to both anions and cations,
this forms a “hydration sheath” of water molecules surrounding the ion
Ions are held in solution
Naturally occurring solid
Specific chemical composition
Crystal structure (regularly repeating units in 3 dimensions)
(1)
pattern of repeating atoms
(2)
bonding between atoms
(3)
chemical properties of Na and Cl
Structure of
halite – Mineral composed
of Na Cl Figure 2.2
Electron shells of an atom
Figure 2.3
Filling electron shells
Figure 2.4
First shell – 2 electrons equivalent to helium
2nd shell – 8 electrons equivalent to neon
Filling shells – Na and Cl
Figure 2.5
Na has only 1 electron in the outer (3rd) shell
Cl needs 1 more electron in the outer (3rd) shell
The result: two
ions Box 2.2
Each ion is much more stable
than the neutral atoms
The two ions are attracted to
each other by the electrical charge
(similar to magnets)
Ionic bonds hold together NaCl Figure 2.18
The 3-D repeating structure is a crystal, and forms the mineral halite
Ionic bonds – electrons stay on one atom, creating positive and negative ions
Covalent bonds – the electrons are shared between the atoms,
keeping the nuclei
close together
Metallic bonds – nuclei stay close together, but the electrons
are free to flow along
a group of atoms
Hydrogen bonding (between molecules)
Covalent bonds are generally strongest
Examples from the textbook:
graphite and diamond Box 2.2
Tetrahedron of silica Figure 2.7
Valence (net charge) on silica tetrahedra Figure 2.8
The Si is +4, and each O is –2 (total of –8)
Stacked tetrahedra
work together
Charge balanced by cations
Olivine crystal – Fe2+ or Mg2+ fill in between
silica tetrahedra Figure 2.10
Single tetrahedra to single chains Figure
2.9
Olivine (single) to pyroxenes (single
chain)
Charge balance in chain silicates Figure
2.11
Cation can be Fe2+ or Mg2+ or Ca2+
Single chains to double chains Figure
2.9
Amphibole group (double chains)
Double chains to sheets Figure
2.9
Mica group and clay group (sheets)
Sheet silicates (such as micas) Box
2.4
Strong bonds within layers, but weak bonds
between layers
Sheets to framework
Quartz and feldspar (framework silicates;
abundant in granite)
3-D structure of a framework silicate
-- Feldspar
alkali cations (Ca2+, Na+, K+) in a framework
of (Al, Si)O4
silica tetrahedra
connected on corners
Common silicate minerals Table 2.2
Olivine
Pyroxenes
Amphiboles
Micas
Feldspars
Quartz
*** These are in the order of Bowen’s
reaction series ***
This order of minerals will reappear and
help explain the igneous rocks
Because water is a bipolar
molecule, it easily dissolves any molecules with ionic
bonding,
such as salts
Hydration of sheet silicates (such as clays) Box 2.4
Expandable clays – water fits in between clay mineral layers