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Warm up
9-30-08 What part of the
atom has a positive charge
and where is it found?
the atom
What is an atom?
The smallest particle of an element that has the
characteristics of that element
What are the parts of an atom?
protons (p+); neutrons (n); electrons (e-)
What is the structure of the
atom?
Nucleus contains protons &
neutrons, electrons circle the
nucleus in an electron cloud
eP+
n
n
P+
e-
something to think
about
• We all know that “opposites attract” and
“like charges repel” –SO:
• If electrons are negatively charged and
protons are positively charged, why don’t
the electrons fall into the nucleus?
?
something to think
about
Niels Bohr proposed a model in which
the electrons would stably occupy fixed
energy levels around the nucleus,
known as orbitals. Each orbital has a
limited capacity for electrons.
Recipe for an atom
Each element in the Periodic Table has a
different number of protons in its nucleus
 Protons have positive charge
 Change the number of protons  change elements
P+
The element also has the same number of
eelectrons
 Electrons have negative charge
 Change the number of electrons  charge the atom
Some elements also have neutrons
 Neutrons have no charge
 They are in the nuclei of atoms
n
Atomic number
Symbol
Name
Atomic weight
Protons = 8
Electrons = 8
16 – 8 = 8 neutrons
The electron orbitals
# Protons = # Electrons
# Neutrons = Atomic Weight – Atomic #
# Protons = # Electrons
# Neutrons = Atomic Weight – Atomic #
Shell structure activity
e
Carbon = C
Sulfur = S
Neon =Ne
Chlorine = Cl
e
p p
e
n n
p
n n
3 protons
3 electrons
4 neutrons
How many protons and electrons do these
elements have?
Draw the electron shell structure for each.
Navigating the Periodic
Table
The rows are the “periods”
Each period starts a new shell of electrons
The periods are numbered starting with 1 at the
top
The columns are the “groups”
Each group has similar chemical properties
The groups are numbered starting with 1 at the left
Elements with similar properties have the same
number of electrons in the outermost shell
Atoms, Elements and
Compounds
Atom: smallest unit of an element
Element: any of more than 100 fundamental
substances that consist of atoms of only one
kind (C; K; Mg; Ca)
Compound: a collection of 2 or more
different atoms, bound together.
 H2O or CO2
The mighty electron
e
e
e
17
34
e
6P
Cl
6N
e
e
e e
e
e e
ee
e
e
e
e
ee
12P
6P
12N
ee e e
e
e
e e
17P
6P
e
e e
e
17N
e
e
e
e
Carbon
magnesium
chlorine
e
10P
6P
e
10N
e
ee
e
neon
e
e
e
ionic bond: when electrons are
e
e
e
e
e
e
e
e
e
e
17N
e
e
e
e
e
e
Cl
e
e
e
17P
6P
e
17P
11P
6P
17N
11N
e
e
Ionic
bond
e
Opposites
attract
e
e
e
e
e
Na +
e
CHARGE!!!
Ion – an atom with a charge
Cation – an atom with a positive charge
less electrons than protons
Na+
Anion – an atom with a negative charge
More electrons than protons
Cl
covalent bond: When
electrons are SHARED
e
H
e
1P
1P
e
e
ee
e
17P
8P
6P
17N
8N
e
e
ee
e
O
H
MOLECULES
Molecule – a group of atoms held together
by covalent bonds
H 2O
Chemical reactions occur when bonds
between atoms are formed or broken