Diapositive 1

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Chemistry B11
Chapter 2 Atoms
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Element is a substance consists of identical
atoms. Cannot be divided by chemical physical
methods. Carbon, Hydrogen, Oxygen 116 elements
88 in nature
Compound is a pure substance made up of two or
more elements in a fixed ratio by mass. H2O
(Water) 2 Hydrogen 1 Oxygen CO2 1 Carbon
2 Oxygen 20 million compounds
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Compounds
Formula
Identifies each element
Ratios
H2O
CO
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Molecular models
CH4
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Mixtures
Mixture is a combination of two or more pure
substances.
Homogeneous uniform and throughout Air, Salt in
water
Heterogeneous nonuniform Soup, Milk, Blood
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Law of conservation of mass
C O ? CO
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Atom
Nucleus positive charge
Atoms are neutral.
Atomic mass unit (amu) 1.660510-24 g
mass of proton 1 amu mass of neutron 1
amu mass of electron 5.4810-4 amu
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Atom
Mass number Protons Neutrons
Atomic number Protons
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Isotopes
Isotopes atoms with same number of protons and
electrons but different numbers of neutrons.
different mass number
6 P 6 N
6 P 8 N
6 P 7 N
almost same properties
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Atomic Weight
Atomic weight of an element is average of the
masses (in amu) of its isotopes found on the
Earth.
Cl
37
35
Cl
Cl
36.97 amu
34.97 amu
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17
(75.77/100 34.97 amu) (24.23/100 36.97 amu)
35.45 amu
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main-group elements 1A to 8A
transition elements 1B to 8B (3 12)
inner transition elements between B3 B4
(58 to 71 and 90 to 103)
Column same properties (main group)
row or period
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Group 1A Alkali metals Li-Na-K-Rb-Cs-Fr too
reactive, unstable, solid metal
2Na 2H2O
2NaOH H2
2Na Cl2
2NaCl
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Group 7A Halogens F-Cl-Br-I-At reactive,
colored, gas, nonmetal
Group 8A Noble gases He-Ne-Ar-Kr-Xe-Rn non
reactive, stable, gas, nonmetal
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Classification of the elements
metals
nonmetals
metalloids
metals solid (except mercury), shiny, conductors
of electricity, ductile, malleable
nonmetals solid, liquid or gas, do not conduct
electricity (except graphite)
metalloids between metals and nonmetals
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Metallic properties
More metallic
More metallic
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Bohr model
E1
E2
E3
E4
E5
Principal energy levels or Shell
E1 ground state lowest energy level
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Subshell s p d f
Orbital is a region of space and can hold 2
electrons
s
px
py
pz
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Subshell s p d f
p
s
d
f
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2226
2222210
222222214
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Electrons configuration description of the
orbitals that its electrons occupy.
Orbital box diagrams
Electron configuration
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Noble gas notation
1s2 2s1
Li (3)
2s
1s
He 2s1
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Valence shell outer shell
Valence electrons outer-shell electrons
Cl (17)
1s2 2s2 2p6 3s2 3p5
7 valence electrons
1s2 2s2 2p6 3s2 3p6
Ar (18)
8 valence electrons
C (6)
1s2 2s2 2p2
4 valence electrons
8 valence electrons
1s2 2s2 2p6
Ne (10)
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Elements in same column (group) have the same
number of electrons in their valance shells.
Same chemical and physical properties.
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Lewis dot structure
Li
He
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Main groups elements
s, p
Transition elements
s, p, d
Inner transition elements
s, p, d, f
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Atomic Size
Size of atom is the size of its outermost
occupied orbital.
d
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Ionization Energy
Li energy ? Li e-
ion
Ionization energy the energy required to remove
the most loosely held electron from an atom in
the gaseous state.
Ionization energy
Ionization energy