Transcript Ch 5 Notes

ATOMS AND
BONDING
Chapter 5
I. Atomic Structure and the Periodic
Table

The nucleus is in the center of the
atom containing protons and
neutrons. the number of protons is
the atomic number
I. Atomic Structure and the Periodic
Table (cont)

Electrons move around the nucleus in the
electron cloud. In a neutral atom the
number of electrons equals the number
of protons.
I. Atomic Structure and the Periodic
Table (cont)
Valence electrons are the electrons
in the outer shell.
The valence electrons determine which
elements combine to form compounds!

II.
Why do Elements Form Compounds?
1. Atoms combine to complete the outer
energy shell of electrons
 2. A complete outer energy shell is stable.
(atoms with filled outer energy shells won’t
combine with other atoms)
 3. 8 Electrons complete the outer shell, except
when shell #1 is the outer shell, then it is
complete with 2 electrons.

II. Why do Elements Form Compounds?
(cont)

4. A chemical bond is the force of attraction that
holds atoms together
III. What happens when a chemical
bond is formed?
1.
2.
3.
new substance is formed in a chemical
reaction
properties of the new substance are
different than the properties of the
elements that make them up
Electrons are gained, given away or
shared
Examples of Dot Diagrams
Lets try some




Lets look closely at a few common compounds we
know.
H2O
NaCl
CO2
V. Chemical Formula

Chemical Formula - A shorthand way to
write the name of the compound
 what
atoms make up the compound
 how many atoms of each element make up the
compound
 small number, written below the line that tells
how many atoms of that element are in a
compound
VIII. Formulas for ionic compounds


Shows which elements make up the compound
and the number of atoms for each element
Ex: NaCl, K2S, NaBr, LiO2
VI. Metals, Nonmetals and Semimetals


A. METALS are on the left side of the Periodic
Table. They have a low number of valence
electrons and can easily give them to other atoms.
Almost empty shells
VI. Metals, Nonmetals and Semimetals
(cont)


B. NONMETALS are on the right side of the
Periodic Table. They have a high number of
valence electrons and can easily take or share
valence electrons from other atoms
Almost full shells
VI. Metals, Nonmetals and Semimetals
(cont)


C. SEMIMETALS are found between metals and
nonmetals along the zigzag line. They can either
lose or share valence electrons with other atoms
About half full shell
Types of Chemical Bonds




Ionic Bonds: formed when a metal and nonmetal
combine to create a new substance.
One atom takes the extra electron(s) from the
other atom
Very strong bonds
Ionic compounds are hard, brittle solids with high
boiling and melting points, and conduct electricity
when dissolved in water.
X. Covalent Bonds:
Covalent Bonds form when 2 nonmetals combine to form
or create a new substance.
 the force that holds atoms together in a covalent bond
is the attraction of each atom’s nucleus for the shared
pair of electrons
 weak bonds form between these atoms; the bonds are
easily broken
 properties of molecular compounds (covalent
compounds) are low melting & boiling points, cannot
conduct electricity when dissolved in water
Covalent bonds:
XIII. Metallic Bonds


Metallic Bonds- formed when two metals combine to
create a new substance.
The loose electrons flowing over the surface of the
metal gives metals their characteristics such as ability
to conduct electricity, being malleable and ductile