Download 4.2 Structure of the Atom

4.2 Structure of the Atom
The Nucleus is:
• Positively charged
• Very Dense and at the center
portion of the atom
– Contains most of the atom’s mass,
but . . .
– Occupies only a tiny fraction of its
volume
Figure 3.9:
A nuclear atom
viewed in
cross section.
Composition of the Nucleus:
• A Proton is a
– Positively charged subatomic particle that is
found in the nucleus of an atom
– Mass of 1.673 x 10-24 grams
• Approximately 1800 times that of the
electron
• A Neutron is a neutral subatomic particle that is
found in the nucleus of an atom.
– No electrical charge (neutral)
– Mass approximately equal to the proton
Composition of the Nucleus:
• In 1932, the English physicist James
Chadwick designed an experiment to
show that neutrons exist.
• Neutron’s mass is approximately equal
to the proton.
• Electrons move around the nucleus
and are relatively far away from
the nucleus
• Most of the atom is empty space
• The nucleus contains protons &
neutrons
Protons, Neutrons, and Electrons
Symbol
Relative Mass
Charge
Electron
e-
Proton
p+
1
+1
Neutron
no
1
0
1/1800
-1
Atomic number and Mass
number
The atomic number (“Z”) of an element
equals the number of protons in an
atom of that element
– The atomic number identifies the
atom of that elements
– Atoms of different elements have
different numbers of protons
Atomic number and Mass
number
• The mass number (“A”) of an atom is the
sum of the protons and neutrons in the
nucleus of that atom.
• Mass number identifies the particular
isotope
• In an atom, electrons equal the number of
protons
• Atoms are electrically neutral
Isotopes of Atoms
• Isotopes are atoms of the same element
with different mass numbers
• Isotopes have the same atomic
number but different mass numbers
because they have different numbers of
neutrons
Two isotopes of sodium.
How to calculate the number of
neutrons in an atom?
• Number of neutrons= mass number –
atomic number
• Nuclear Symbol: See next slide
• Hyphen Notation: Bromine- 80
Nuclear Symbol
Mass Number
65
29
Cu
Atomic Number (Z)
Number of
Protons
29
Electrons
Protons + Neutrons
36 Neutrons
65
29
Cu
Protons
Remember!! Atoms are neutral!!
Practice
• Write the nuclear symbol for bromine-80
– How many protons, electrons, and neutrons
are in this atom?
Practice
• Write the hyphen notation for the
element that has 6 protons and 7
neutrons
– How many electrons does this atom
have?
– Write the nuclear symbol for this atom