Transcript Review-2 - TeacherWeb

Chemical Foundations
Review-Day 2
Periodic Table
Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 74
The Modern Periodic Table
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Arranged according to their atomic number
Columns are called groups (18)
Elements in same group have similar properties
Rows are called Periods (7)
• Metals-most abundant, left side of table
mostly solid @ RT, good conductors of heat and
electricity
• Non-Metals-right side of table, mostly gas @RT, do not
conduct heat or electricity
• Metalloids-have properties of both metals & non metals
What does the Table tell us…
For each element…
• Atomic number tells us the
number of protons in the
atom
• In a balanced atom, the
atomic number is also equal
to the number of electrons
around the nucleus
• Mass Number tells us the
number of protons and
neutrons in the nucleus
(round the atomic mass),
subtract the atomic number
from the atomic mass to get
the number of neutrons.
Examples
Chemical
Name
# of protons
# of neutrons # of electrons
Hydrogen
1
0
1
Carbon
6
6
6
Oxygen
8
8
8
Argon
18
22
18
Gallium
31
39
31
Models of the Atom
Valence Electrons
(what makes an atom happy?)
• Atoms want to become stable and achieve a valence
“octet” (a full outer shell)
• Recall that valence electrons are only those in its
outermost level or “shell”
• The group number in the periodic table will predict how
many electrons in its outer shell (this only works for the
main groups)
• Atoms will bond to get that full octet by transferring
electrons (ionic bonds) or sharing electrons (covalent
bonds)
• NOTE: Protons & Neutrons do not move, only Electrons
• Atoms that lose or gain electrons, now
become charged. They are now “Ions”
• Recall that electrons are negative particles!
• Atoms which lose electrons become
Positively charged or Cations (metals)
Example: Mg → Mg2+ [loses 2 electrons]
• Atoms which gain electrons become
Negatively charged or Anions (non-metals)
Example: O → O2- [gains 2 electrons]
• Ions have a charge number on upper right
Predict the ionic charge on the
following atoms
• Na (Sodium)
• Ca (Calcium)
• Al (Aluminum)
group 1 metal
group 2 metal
group 13 metal
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group 15 non-metal
group 16 non-metal
group 17 non-metal
group 18 (huh???)
N (Nitrogen)
S (Sulfur)
Br (Bromine)
Ne (Neon)
Isotopes
Atoms that have the same atomic number but a
different atomic mass…Example Magnesium
Meaning of Chemical Formula
Count the atoms in each
chemical formula
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CH4
PbI2
Al2O3
Mg(NO3)2
Al2(SO4)3
2Al2(SO4)3