Download Chapter 4 Atomic Structure Notes

Chapter 4
“Atomic Structure”
Subatomic particles of the atom
 Atoms are the building blocks of all
Matter.
 Atoms are mostly empty space with
a small dense core known as the
Nucleus.
 Atoms are made up of 3 smaller
particles (Subatomic Particles) :
Protons, Neutrons, and Electrons
Nucleus

Makes up most of the
mass of the atom.

Made up of the following
subatomic particles:



Protons: positively
charged
Neutrons: neutral particles
Has an overall + charge.
Protons






positively charged;
Located inside nucleus;
gives the atom its identity
has the mass of 1atomic mass unit (amu)
Same size as a neutron (1amu)
Protons + Neutrons = the mass of the
atom (atomic mass)
Neutrons





neutral charge;
inside nucleus;
has the mass of 1atomic mass unit (amu)
Same size as a proton (1amu)
Protons + Neutrons = the mass of the
atom (atomic mass)
Electrons


negative charged
has the mass of 1/1840
**note- electrons are extremely small compared to
Protons & Neutrons


Located in the electron cloud
Electron Cloud- Area outside the nucleus
where you are most likely able to find a
nucleus.
Subatomic Particles
Particle
Charge
Mass
Location
Electron
(e-)
-1
1/1840 amu
Electron
cloud
Proton
(p+)
+1
1 amu
Nucleus
Neutron
(no)
0
1 amu
Nucleus
Amu= atomic mass unit= a unit used to measure the particles of an atom. = 1/12th the
mass of a carbon atom
Section 4.3
Distinguishing Among Atoms
Atomic Number



Elements are different because they contain
different numbers of PROTONS.
The number of Protons gives the atom its
identity.
The “atomic number” of an element is the
number of protons in the nucleus.
Atomic Number
(# of protons)




What makes an Atom Neutral?
When an atom has the same number of protons
as electrons. (+) = (-)
 if the atom is neutral then it has not lost or
gained electrons.
Atomic charge- an atom will have a charge when
the protons and the electrons are not equal in
number. Atoms will lose or gain electrons to
become charged.
Atoms that have a charge are called ions.
Example: A sodium atom has 11 protons and 10
electrons. What is the charge?
+11 protons (+)
-10 electrons (-)
--------------------Subtract
+1 charge
What is the Charge of these atoms?
Which one is an Ion?
2 Protons (+)
6 Electons (-)
------------------------4 charge
**** Ion ****
6 Protons (+)
6 Electons (-)
-----------------------0 charge
Isotopes
Atoms of the same element can have
different numbers of neutrons.
 Thus, different mass numbers.
 These are called isotopes.
 Isotopes are atoms of the same
element having different masses,
due to varying numbers of neutrons.


Elements occur in nature as mixtures of
isotopes.
How to Name Isotopes
 Write
the name then put the
mass number after the name
of the element:
carbon-12
shorthand: C-12
carbon-14
shorthand: C-14
uranium-235
shorthand: U-235
Isotopes are atoms of the same element having
different masses, due to varying numbers of
neutrons.
The 3 Isotopes of Hydrogen
Isotope
Protons Electrons
Neutrons
Hydrogen–1
(protium)
1
1
0
Hydrogen-2
(deuterium)
1
1
1
1
1
2
Hydrogen-3
(tritium)
Nucleus
Mass number vs Atomic Mass

Atomic Mass- Atomic mass is the
average of all the naturally
occurring isotopes of that element.



the decimal you see on the periodic table
An average of all the isotopes of that element.
Mass number- the number of
protons and neutrons in the
nucleus of a specific isotope

The mass of that specific isotope.
Atomic
Mass
Mass Number
Mass number is the number of
protons and neutrons in the nucleus
of an isotope: Mass # = p+ + n0
Nuclide
Oxygen - 18
Neutrons = Mass # - p+
p+ n0 e- Mass #
8
10
8
18
Arsenic - 75
33
42
33
75
Phosphorus - 31
15
16
15
31
Complete Symbols Aka: Isotope Notation
Contain the symbol of the element,
the mass number and the atomic
number.
Mass
Superscript →
number

Subscript →
Atomic
number
X
Symbols

Find each of these:
a) number of protons
b) number of
neutrons
c) number of
electrons
d) Atomic number
e) Mass Number
80
35
Br
Symbols

If an element has an atomic
number of 34 and a mass
number of 78, what is the:
a) number of protons
b) number of neutrons
c) number of electrons
d) complete symbol
Symbols
 If an element has 91
protons and 140 neutrons
what is the
a) Atomic number
b) Mass number
c) number of electrons
d) complete symbol
Symbols
 If an element has 78
electrons and 117 neutrons
what is the
a) Atomic number
b) Mass number
c) number of protons
d) complete symbol
Complete Symbols of an ION

If the symbol has a superscript on
the right side, it has lost or gained
electrons.
Superscript →
Mass
number
Atomic
Subscript →
number
# of electrons
lost or gained
X
• Negative number = #
of electrons it has
gained
• Positive number = #
of electrons it has lost
Atomic Mass



How heavy is an atom of oxygen?
 It depends, because there are different
kinds of oxygen atoms.
We are more concerned with the average
atomic mass.
This is based on the abundance
(percentage) of each variety of that
element in nature.

We don’t use grams for this mass because
the numbers would be too small.
Measuring Atomic Mass
 Instead
of grams, the unit we use
is the Atomic Mass Unit (amu)
 It is defined as one-twelfth the
mass of a carbon-12 atom.

Carbon-12 chosen because of its isotope purity.
 Each
isotope has its own atomic
mass, thus we determine the
average from percent abundance.
To calculate the average:
 Multiply
the atomic mass of
each isotope by it’s
abundance (expressed as a
decimal), then add the
results.
 If
not told otherwise, the mass of the
isotope is expressed in atomic mass
units (amu)
Atomic Masses
Atomic mass is the average of all the
naturally occurring isotopes of that element.
Isotope
Symbol
Carbon-12
12C
Carbon-13
13C
Carbon-14
14C
Composition of
the nucleus
6 protons
6 neutrons
6 protons
7 neutrons
6 protons
8 neutrons
Carbon = 12.011
% in nature
98.89%
1.11%
<0.01%
Practice Problem:
Element X has 2 Natural occurring isotopes. Isotope 10X has the
mass of 10.012 and a relative abundance of 19.91% . The other
istotope 11X has the mass of 11.009 and the abundance of 80.09%.
Calculate the average atomic mass of this element.
Mass
X Abundance (changed to a decimal)
10X:
10.012amu X
0.1991
=
1.993 amu
11X:
11.009amu X
0.8009
=
8.817 amu
---------------------------------------------------Add-------------Average Atomic Mass = 10.810 amu
The Periodic Table:
A Preview
 A “periodic table” is an
arrangement of elements in which
the elements are separated into
groups based on a set of repeating
properties
The periodic table allows you to
easily compare the properties of
one element to another
The Periodic Table:
A Preview
 Each horizontal row (there are 7 of
them) is called a period
Each vertical column is called a
group, or family
Elements in a group have similar
chemical and physical properties
Identified with a number and
either an “A” or “B”
More presented in Chapter 6