Download Inside an Atom

Inside an Atom
Section 3.1
Parts of an Atom
1.
Inside Nucleus
I.
II.
2.
Protons-positive charge
Neutrons-no charge
Outside Nucleus
I.
Electrons-negative charge
Atomic Number
 Every atom of a particular
element contains the same
number of protons
 Ex. Every carbon atom has
six protons
 Atomic Number=The
number of protons of an
atom
 Every atom has a unique
atomic number
Atomic Mass
 Atoms are too small to
measure their mass with
everyday units. So instead
the atomic mass unit
(amu) is used to measure
an atom’s mass.
 Proton≈1 amu
 Neutron≈1amu
 2000 electrons ≈1amu
Atomic Mass
 The mass of an atom is determined
by its number of protons and
neutrons since electrons weigh very
little
 All atoms of an element have the
same number of protons, but can
have different number of neutrons
 Ex. Carbon has 6 protons, but can
have 5, 6, 7, or 8 neutrons
 Neutrons do not play a role in
chemical reactions so their
numbers do not effect the
properties of elements
 The atomic mass given on the
periodic table is the average mass of
an element’s atoms
Charge of an Atom
 The number of protons
always equals the number
of electrons
 Atoms have a neutral
charge because the protons
and neutrons neutralize
each other
electron
neutron
proton
The role of electrons
 Electrons move around the
nucleus so fast that it is
impossible to know exactly
when any electron is at a
particular time
 Think about the blades of a
fan, but in 3 dimensions
 Most of an atom’s mass
comes from the nucleus
(Protons, neutrons), but most
of its volume comes from the
space through which
electrons move (baseball field)
Valence Electrons
 Valence electrons are the
electrons in the outer layer
(furthest distance from nucleus)
 Valence electrons are very
important because they are
involved in the formation of
chemical bonds
 A chemical bond forms
between two atoms when
valence electrons move
between them. The valence
electrons may be
transferred (moved) from
one atom to another or
shared between atoms.
Valence Electrons
 The number of valence electrons in an
atom can range from one to eight
 Each element has a typical number of
valence electrons
 To the right is a electron dot
diagram which shows the number of
valence electrons in an element
 When a chemical bond forms one of
two things happen
1.
2.

The number of valence electrons
increases to a total of eight
All the valence electrons are
given up so there are zero
Having eight or zero valence
electrons makes an element more
stable
Electron Shells
http://en.wikipedia.org/wiki/Atomic_electron_configuration_table
Vocabulary
 Nucleus
 Proton
 Neutron
 Electron
 Atomic Number
 Atomic Mass Unit (AMU)
 Valence electron
 Electron dot diagram
Questions
 Draw an atom and label each part.
 What happens to valence electrons during the formation of a
chemical bond?
 Why is the electrical charge of an atom neutral or zero?
 Why do electrons make up much of an atom’s volume, but
not much of its mass?