lecture 1.1 refresh your high school chemistry cs882, fall 2006
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Lecture 1.1
Refresh your high school chemistry
CS882, Fall 2006
Atoms and molecules
Atoms
Protons
Neutrons
Electrons(much smaller)orbiting around the nucleus
Atom models
Secondshell
Helium
2He
Firstshell
Thirdshell
Hydrogen
1H
2He
4.00Atomic mass
Atomic number
Element symbol
Electron-shelldiagram
Lithium
3LiBeryllium
4BeBoron
3BCarbon
6CNitrogen
7NOxygen
8OFluorine
9FNeon
10Ne
Sodium
11NaMagnesium
12MgAluminum
13AlSilicon
14SiPhosphorus
15PSulfur
16SChlorine
17ClArgon
18Ar
Electron-shell diagrams of the first 18 elements in the periodic table
Formation of covalent bondHydrogen atoms (2 H)
Hydrogenmolecule (H2)
1 In each hydrogenatom, the single electronis held in its orbital byits attraction to theproton in the nucleus.
When two hydrogenatoms approach eachother, the electron ofeach atom is alsoattracted to the protonin the other nucleus.
2
The two electronsbecome shared in a covalent bond,forming an H2
molecule.
3
+ +
+ +
+ +
Water molecule, H2O
Electron transfer and ionic bonding
Cl–
Chloride ion(an anion)
–
The lone valence electron of a sodiumatom is transferred to join the 7 valenceelectrons of a chlorine atom.
1 Each resulting ion has a completedvalence shell. An ionic bond can formbetween the oppositely charged ions.
2
Na NaCl Cl
+
NaSodium atom(an uncharged
atom)
ClChlorine atom(an uncharged
atom)
Na+
Sodium ion(a cation)
Sodium chloride (NaCl)
Sodium chloride crystal
Na+
Cl-
Hydrogen bond
Water(H2O)
Ammonia(NH3)
– +
O
H
H
+
–
N
H
H H
A hydrogenbond results from the attraction between thepartial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia.+
+
+
Hydrogen bond
Copyright 2001 by Harcourt, Inc.
The Chemical Foundations of LifeThe Chemical Foundations of Life
So there is an So there is an attraction betweenattraction betweenthe positive andthe positive andnegative sides of negative sides of a water moleculea water molecule……this is this is hydrogenhydrogenbondingbonding..
Figure 2Figure 2--1212
Walking on water