Hydrogen has atomic number 1 and
one proton
• Is most abundant element in universe
• P.546
Fusion reaction in stars
Hydrogen-2 and Hydrogen-3 fuse to form Helium-4
Deuterium is H-2 (1 proton, 1 neutron)
Tritium is H-3 (1 proton, 2 neutron)
• Stars spend most of their active lives in a stable state fusing
hydrogen to helium. This stable state is known as the star's
main sequence.
• The sun for example is a main sequence star. It has been fusing
hydrogen to helium for about five billion years and will do so
for about another five billion years.
• Bigger stars fuse hydrogen to helium faster and live shorter
lives. Smaller stars fuse hydrogen to helium slower and live
longer lives.
• P. 546 fusion reactions described!
Fission
• Uranium- 235 split to form Krypton-92 and
Barium-141
• Large amounts of energy released
• Occurs in nuclear power plants and atomic
bombs, powers nuclear subs
• Uses radioactive fuel and produces radioactive
waste
Nuclear reactions (fission/fusion)
• Occur in nucleus of atoms
• Produces new elements
• Releases large amounts of energy
Chemical reactions
• Occurs by atoms gaining, losing or sharing
electrons
• New compounds can be formed, not new
elements
• Can be endothermic or exothermic
Section 2 Organizing the Elements
• Elements are organized by properties on the
periodic table
• The periodic table is an arrangement of the
elements showing a repeating pattern of
properties (periodic means “repeating, regular
pattern”)
Dmitri Mendeleev in 1869
• Organized elements according to their
increasing atomic mass
• Found a periodic (repeating) pattern
• Called periodic table
Similar chemical and physical
properties every 8th element
• Some elements were
missing
• Left places on table blank
for these
• Later discovered
• Two elements appeared
out of order
Henry Moseley 1914
• Improved table by arranging according to
number of protons (atomic #)
• All elements now in order
Periodic Law
• Chemical and physical properties of an
element is a periodic function of the atomic
number
Elements classified by metals,
nonmetals and metalloids
(semimetals)
• (Page 134 text)
Metals
• Most elements are metals
•
Left of the zig zag line
•
Have few electrons in the outer shell
•
Most solid at room temp (not mercury)
Nonmetals
• Most have almost full or full outer shell
•
All noble (inert)gases have full outer shell
(8)
•
Most are gas at room temp
•
Metalloids or semimetals
• Border zig-zag line
•
Have half a complete outer shell of
electrons
•
Properties of both metals and nonmetals
Chemical symbols
•
•
•
•
•
Either one or two letters
If one letter, is capitalized
If two letters, second letter is lower case
Named after scientists and places
International committee decides on names
Period
1
2
3
4
5
6
7
• Each horizontal row (7)
• Has periodic (repeating pattern) pattern
• Gradually changes chemical and physical
properties from left to right
• (metallic to nonmetallic, conductors to
nonconductors)
• Each period corresponds to an electron shell
Groups or families
• Columns (up and down)
• 18 in all
• Very similar chemical and physical
properties
Grouping the elements
• Families have similar
properties
Same number of
valence electrons
(electrons in outer
shell)
DRAW THIS CHART ON
NOTES!!!
Family
# of
valence
electrons
1
2
13
14
15
16
17
18
1
2
3
4
5
6
7
8
Reactivity
• All atoms tend to try to fill outer shell so have
complete set of electrons
• Will either share electrons, give up or take
electrons from other atoms so outer shell is
filled (forms compounds)
• Valence electrons (electrons in outer shell)
determine how an element or atom reacts
with another atom
Electron shells:
• 1st shell full at 2 electrons (holds up to 2 max)
• 2nd shell full at 8 electrons (holds up to 8
max)
• 3rd shell full can hold 18 electrons but is
considered full at 8