GSCI 163
Lecture 5
Review
• Electrons in an atom are distributed in shells,
orbitals and energy levels.
• When electrons absorb photons they jump to
higher orbitals
• They move back up by emitting a photon
whose energy correspond to the change in
energy level
Activity
• Finding the emission lines of different
compounds.
Chemistry
• Electrons in an atom are distributed in shells, orbitals
and energy levels.
• The way electrons are shared will determine how
elements combine with each other to form
compounds.
• The highest or last shell of an atom is the valence shell
• The valence shell determines the chemistry and
properties
The periodic table
Various groups
• Metals and non-metals
– Metals tend to lose
electrons in chemical
reactions
– Non-metals tend to gain
(or share) electrons in
chemical reactions
Semi-metals have both metallic and non-metallic properties
– Most reactive metal  Cesium
– Most reactive non-metal  Fluorine
Noble gases
• The valence shell is full. Thus they almost
never react.
– Argon gas (Ar) is used as an inert gas in light bulbs
to prevent the filament, made of tungsten (W),
from reacting under intense heat
Other families
•
Alkali metals
– Only one valence electron; very soft metals
– React so easily with Oxygen (O) and moisture that they need to be stored under oil
•
Alkaline earth metals
– Two valence electrons; harder than alkali metals
– Not so reactive.
•
Halogens
– Seven electrons in the valence shell
– Very active non-metals
•
•
•
•
Fluorine – highly corrosive,
Chlorine – purifying agent,
Bromine – desinfectant
Semi-metals (semi-conductors)
– 3,4 or 5 electrons in the valence shell
– Makes them behave both as metals and insulators
Atomic size
• Increase when:
– Add a new shell
(moving down a
group) since
electrons are farther
away from the
nucleus
– Number of protons
decrease (across a
period) since
electrons are more
loosely bound by
electrostatic force
Cs ~ 0.47 nm
He ~ 0.064 nm
Ionization energy
• Energy required to remove one electron from
the outer shell
Hardest elements to remove
one electron from
He
H
Octet rule
• Most common elements have electrons on the
s and p orbitals of their outmost shells
• We can fit 2 electrons on s and 6 on p, with a
total of 8 electrons
Octet rule: atoms will combine with other atoms
in such a way that gives a full shell of 8
electrons
Naming compounds
• We represent compounds with a chemical
formula:
Symbol of the element
H2O
Number of atoms of the element
• Names are also used to identify the
compound unambiguously
Compounds with special names
There are no rules for these. Their names are learned individually
Metal and a non-metal
• Groups 1A, 2A plus Aluminum (Al), Zinc (Zn) and
Silver (Ag). They form only one ion.
• Rule for binary compounds:
– Name of the metal + non-metal with ending –ide
Examples:
NaCl – Sodium Chloride
Al2O3 –
Ca3N2 –
Two non-metals
• Rule:
– The less metallic element (farther left and/or farther down
the periodic table) comes first. The second is named with
ending –ide .
– For more than one element use Greek prefixes: di(2),
tri(3), tetra(4), penta (5), hexa (6), hepta (7), octa (8).
Examples:
HCl – hydrogen chloride
CS2 –
PBr3 –
IF7 –
Compounds with polyatomic ions
• Metal plus a polyatomic ion:
Rule: name of the metal + the name of
of the polyatomic ion
Example:
ZnSO4 – Zinc Sulfate
NaC2H3O2 –
Mg(NO3)2 –
K3PO4 –
Next class
Calculating reactions
• To prepare for the class read:
– Handout pages 17 to 20 (day 5)
– Presentation by Rebecca Cross, Acids and Bases
• To prepare for the quiz read:
– Handout pages 16 (day 4)
– Power point for this class
– Your class notes