Download How Atoms Differ

How Atoms Differ
Learning Objective
• Explain the role of atomic number in
determining the identity of an atom.
• Define an isotope.
• Define an ion.
• Calculate the number of electrons, protons,
and neutrons in an atom, isotope, or ion given
its mass number and atomic number.
The Electron and Proton
• J.J. Thomson discovered
the electron while
conducting an
experiment with the
cathode ray tube
(vacuum tube)
• Ernest Rutherford
discovered the
positively charged
nucleus during his gold
foil experiment.
The Neutron
• James Chadwick showed
that the nucleus
contained a subatomic
neutral particle, called
the neutron.
• A neutron is a subatomic
particle that has a mass
nearly equal to that of a
proton, but carries no
electric charge.
Summary of Atomic Structure
proton
electron
neutron
Charge:
Charge:
Charge:
Location:
Location:
Location:
Mass: 1
Mass: 1
Mass:
𝟏
𝟏,𝟎𝟎𝟎
of
proton and neutron
The Atom
• The smallest particle of
an element that retains
the properties of the
element is called an
atom.
• A molecule forms when
two or more atoms form
a chemical bond.
• A compound is
a molecule that contains
at least two different
elements.
Dalton’s Atomic Theory
Write this table on page 103 of notebook
Correct
1. All matter is made up of atoms.
2. Atoms are indivisible and
indestructible.
3. All atoms of an element are identical.
4. Atoms of different elements are
different
5. Compounds form when atoms of
different elements combine
6. Chemical reactions involve
rearranging atoms, not change in the
atom.
Incorrect
Isotopes
• Dalton was incorrect
about atoms being
indivisible and in stating
that all atoms of an
element are identical.
• All atoms of an element
have the same number
of protons and
electrons, but the
number of neutrons
might differ.
Isotopes
• Atoms with the same number of protons but
different numbers of neutrons are called isotopes.
Dalton’s Atomic Theory
Correct
1. All matter is made up of atoms.
2. Atoms are indivisible and
indestructible.
3. All atoms of an element are identical.
4. Atoms of different elements are
different
5. Compounds form when atoms of
different elements combine
6. Chemical reactions involve
rearranging atoms, not change in the
atom.
Incorrect
Atomic Number
• The number of protons
in an atom identifies it
as an atom of a
particular element.
• The number of protons
in an atom is referred to
as the atomic number.
Atomic Number
• Because all atoms are
neutral, the number of
protons and electrons in
an atom must be equal.
• Atomic number
= number of protons
= number of electrons
Isotopes and Mass Number
• Each isotope of an
element is identified
with a number called
the mass number.
• The mass number is the
sum of the atomic
number (or number of
protons) and neutrons.
• Mas number = atomic
number + number of
neutrons
Isotope Notation
Identifies a specific isotope
mass number
protons + neutrons
atomic number
# of protons (= electrons)
Learning Check
• Determine how many protons, neutrons, and
electrons each of the following isotopes of
chlorine has:
–
35
17
Cl
37
– 17 Cl
Learning Check
• An atom has an atomic number of 9 and a
mass number of 19. Determine the number of
each of the following:
– Protons
– Neutrons
– Electrons
Atomic Mass
• The existence of isotopes
means that atoms of an
element can have several
different masses.
• Atomic masses are
decimal numbers on the
periodic table because
the atomic mass is the
calculated average mass
for the isotopes of an
element.
Element Notation
atomic #
# of protons (= # of electrons)
element symbol
element name
atomic mass
protons + neutrons
Calculated average mass for the isotopes of
an element
Add this to your diagram
Calculating Subatomic Particles
Ape
tomic number
A____________________
=
rotons
P____________________
=
E_____________________
electrons
Man
M____________________
ass number
- (minus)
tomic number
A____________________
=
eutrons
N_____________________
Ions
• Atoms can gain or lose one or more electrons to form
ions.
• An ion is an atom (or group of atoms) that is
electrically charged as a result of loss or gain of
electrons.
Ions
• If an atom gains one or
more electrons, it
becomes a negatively
charged ion called an
anion.
• If an atom loses one or
more electrons, it
becomes a positively
charged ion called a
cation.
Cat-ions are
pawsitive!
Learning Check
• Determine the number of protons, neutrons,
and electrons in the following ions:
– Li+
– N-3
Homework: Atomic Structure
worksheet
Attach to page 107 in notebook
Element Atomic Atomic Mass
Protons Neutrons
/Ion
Number Mass Number
H
H+
12
C
6
Electrons