Download CH.3 ELEMENTS, ATOMS AND ISOTOPES

CH.3 ELEMENTS, ATOMS
AND ISOTOPES
Dalton’s Atomic Theory (1808)
I.
All matter is made of atoms
II.
Each element has its own kind of
atom. Atoms of the same element
have the same mass, atoms of
different elements have different
masses.
III. Atoms of different elements combine
in simple whole-number ratios to
produce compounds (stable groups
of atoms.)*
H2
H2O
NH3
IV. Atoms cannot be created or
destroyed.
CH4
Abundance of Elements in
Earth’s Crust
Sub Atomic Particles (smaller than atoms)
1. Protons
– Found in nucleus (center part) of atom
– Positive charge (+1)
– Mass 1 atomic mass unit (a.m.u.)
2. Neutrons
– Found in nucleus of atom
– Neutral ( 0 charge)
– Mass 1 a.m.u.
3. Electrons
– Found moving outside the nucleus
– Negative charge (-1)
– Mass approx 1/1800 a.m.u.
Atomic Structure
Atoms are electrically neutral, as the number of protons
equals the number of electrons.
Models of the atom:
There have been many models of the atom proposed
by scienctist over the years. The most recent two are:
Bohr Model
• Protons and
neutrons crammed
into the center
called the nucleus
• Electrons move in
definite orbits
around the nucleus
The electron cloud model:
- the most accepted model today
• Almost the same as
the Bohr model.
• Around the nucleus
is an electron cloud.
• Within the cloud
there are energy
levels that electrons
can jump from.
Atomic Model
The nucleus and electron
cloud are separated by
vast space, for example:
• An atom the size of
Dodgers Stadium and
parking lot would contain
a pea sized nucleus
containing 95.95% of the
atom’s mass!!!!!!
Mass
Number
A
Z
Atomic
Number
X
Symbol of
the atom
atomic number (Z) - the number of
protons in the atom
mass number (A) - sum of the number
of protons and neutrons
• Isotopes - atoms of the same element
having different masses
– contain same number of protons
– contain different numbers of neutrons
Isotopes of Hydrogen
1
1
H
Hydrogen
(Hydrogen - 1)
2
1
H
Deuterium
(Hydrogen - 2)
3
1
H
Tritium
(Hydrogen - 3)
• Isotopes of the same element have
identical chemical properties
• Some isotopes are radioactive
• Atomic Mass and mass number are close,
but not exactly the same….atomic mass
is the average of all known isotopes and
their relative abundance in nature
• Mass number and atomic mass can help
determine how many neutrons there are in
an atom (subtract mass number—atomic
number)