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Lecture 2

CHEM 101 Lecture Notes - Lecture 2: Unified Atomic Mass Unit, Phosphide, Electromagnetic Radiation


Department
Chemistry
Course Code
CHEM 101
Professor
Dr.Emil F.Khisamutdinov
Lecture
2

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Elements and the structure of the atom
Atom
oThe smallest most fundamental unit of matter
Element
oA substance composed of one type of atom
Compound
oMade up of 2 or more elements
Nucleus
Tight group of protons and neutrons in the center of atom
oElectrons are outside of nucleus
Atomic mass
1 amu= 1.66
Isotope
Atoms with the same number of protons but different numbers of neutrons
Some natural some artificial
Energy levels
Called shells
on=1,2,3
oMax # of electrons in shell
2n2
Fill levels up from the inside out
Group 1A
o1 electron in outer shell
Group 2A
o2 electrons in outer most shell
Valence electrons
oElectrons occupying outer most shell
Valence electrons and periodicity
Atoms within the group have the same number of valence electrons but they are in
different numbered shells
Full valence shells are particularly stable
oTable 2-7
Highest means valence electrons
Practice problem
Give the elctron arrangement for the elements shown below from the lowest to highest:
neon, boron, nitrogen
oAnswer:
Boron, nitrogen, neon
IONS:
Are atoms that have lost or gained on or more valence electrons, giving them a net
charge
Anything with a charge is an ion
Cation:
oion with a positive charge, fewer electrons than protons
oFormed by the loss of 1 or more electrons
oIn general metals form cations by losing electrons
oNumber of electrons lost = group number (main group elements)
oAl has +3 charge
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