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Chapter 4: The atom
P 93 – 101 and 109-112
What is an atom?
 Atoms:





Makes up all matter
Are incredibly small
Determines the properties of matter
91 different types of atoms
20 synthetic atoms
The atomic theory
 John
Dalton devised a theory of the atom
in 1808



Each element is composed of tiny
indestructible particles called atoms
All atoms of a given element have the same
mass and properties that distinguishes them
from other atoms/elements
Atoms combine in simple, whole number
ratios to form compounds
History of the atom

J.J Thompson (1856
– 1940)

Discovered the
electron
• Negative charge
• Smaller and lighter
• Assumed to be a
positive charge within
the atom to balance
electrons: plum
pudding model
History of the atom

Ernest Rutherford (1909)



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Gold foil experiment
Alpha particles (+ charge)
toward gold foil.
Alpha particles where
deflected….there must be
a large concentration of +
charge
Came up with nuclear
theory of the atom
History of the atom

Nuclear theory of the
atom



Most of the atoms mass
and positive charge is in
the nucleus
Most of the volume of
the atom is empty space
where tiny electrons sit
There are as many +
charges as – charges so
the atom is neutral

Conclusions:



The nucleus contains
Protons (+) and
neutrons (neutral)
The nucleus makes up
99.9% of the mass of
the atom
The electrons are
present in a cloud
surrounding the
nucleus
Atomic mass/atomic number
 What
are the 3 subatomic particles?
 Which of the subatomic particles identifies
an element?

PROTONS! Each element has a different
number of protons, thus making it unique.
 Atomic
Number: the # of protons in the
nucleus of an atom
 The # of protons is equal to the # of
electrons.

Why?
Atomic Number
Problems:
 How

13
 How

many protons are in V?
23
 How

many protons are in Al?
29
many electrons are in Copper?
Mass Number
 In
an atom, where
is most of the mass
located?
 In the nucleus
 What subatomic
particles are in the
nucleus?
 Protons &
Neutrons
 Mass
number is
the mass found in
the nucleus
 mass number: #
of protons + # of
neutrons
 You can find mass
number by looking
at the shorthand
notation.
Shorthand Notation




Used to show the mass # and atomic number of
an element.
14 is the mass #
7 is the atomic #
N is the symbol for nitrogen
14 N
7
Shorthand Notation
 Can

also be written as: element-mass #
Examples Nitrogen-14, Nitrogen-15, Nitrogen16
 How
many neutrons are in each of the
above elements?
 What is the shorthand notation for
gold-197?
Try These
 What

40
 How

is the mass number of 40Ca?
many neutrons are in germanium-73?
41
 How
many protons, electrons & neutrons
does zinc-65 have?


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Protons: 30
Electrons: 30
Neutrons: 35
Isotopes
 Think
about pizza…..
 Isotopes are similar forms of the same
element.
 More specifically, isotopes have the same
number of protons, but different number
of neutrons.
 If neutrons change, what else changes?

Mass
Atomic Mass
 We
must take in account all of the
isotopes in order to get an accurate mass.
 The mass on the PT is a weighted
average of all the naturally occurring
isotopes of an element.
 This is called atomic mass.
Carbon Isotopes
 Carbon
has several isotopes
 The two most naturally occurring isotopes
are carbon-12 and carbon-13
 This means C-12 and C-13 account for all
of the atomic mass.
 So how do we calculate atomic mass?
Carbon Isotopes

Carbon-12
 Carbon-13
 Mass: 12.000 amu
 Mass: 13.003 amu
(amu: atomic mass
 Abundance: 1.11%
unit)
 Abundance: 98.89%

How many neutrons
are in carbon-12?

How many neutrons
are in carbon-13?
Carbon Isotopes
 Atomic
mass=(mass of isotope 1 x abundance)
+ (mass of isotope 2 x abundance) + (mass of
isotope 3 x abundance)
 (12.000 x .9889) + (13.001 x .0111)=12.011
amu
 Find this value on your PT!
Hydrogen Isotopes

Hydrogen-1
 Name: protium
1e
1p
0n

Hydrogen-2
 Name: deuterium
1e
1p
1n
Hydrogen Isotopes

Hydrogen-3
 Name: tritium
1e
1p
2n