Transcript Lecture 1.1 Some preliminary chemistry knowledge, ppt file

CS882, Fall 2006
Lecture 1.1
Refresh your high school chemistry
Atoms and molecules
Atoms
Protons
Neutrons
Electrons
(much smaller)
orbiting around
the nucleus
Atom models
Electron-shell diagrams of the first 18 elements in the
periodic table
Hydrogen
1H
Atomic mass
2
He
4.00
First
shell
Atomic number
Helium
2He
Element symbol
Electron-shell
diagram
Lithium
3Li
Beryllium
4Be
Sodium
11Na
Magnesium
12Mg
Boron
3B
Carbon
6C
Nitrogen
7N
Silicon
14Si
Phosphorus
15P
Oxygen
8O
Fluorine
9F
Neon
10Ne
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Second
shell
Third
shell
Aluminum
13Al
Formation of covalent bond
Hydrogen atoms (2 H)
1
In each hydrogen
atom, the single electron
is held in its orbital by
its attraction to the
proton in the nucleus.
2 When two hydrogen
atoms approach each
other, the electron of
each atom is also
attracted to the proton
in the other nucleus.
3 The two electrons
become shared in a
covalent bond,
forming an H2
molecule.
+
+
+
+
+
+
Hydrogen
molecule (H2)
Water molecule, H2O
Electron transfer and ionic bonding
1 The lone valence electron of a sodium
2 Each resulting ion has a completed
atom is transferred to join the 7 valence
electrons of a chlorine atom.
valence shell. An ionic bond can form
between the oppositely charged ions.
Na
Na
Sodium atom
(an uncharged
atom)
Cl
Cl
Chlorine atom
(an uncharged
atom)
+
–
Na
Cl
Na+
Sodium ion
(a cation)
Cl–
Chloride ion
(an anion)
Sodium chloride (NaCl)
Sodium chloride crystal
Na+
Cl-
Hydrogen bond
–
+
H
Water
(H2O)
O
H
+
–
Ammonia
(NH3)
N
H
H
+
H
+
+
A hydrogen
bond results
from the
attraction
between the
partial positive
charge on the
hydrogen atom
of water and
the partial
negative charge
on the nitrogen
atom of
ammonia.
Hydrogen bond
Walking on water