Chapter 3A
Atoms and Elements
1
CHAPTER OUTLINE







Elements and Symbols
Periodic Table of the Elements
Properties of Metals and Non-Metals
The Atomic Theory
The Modern Atom
Atomic Structure
Isotopes and Atomic Mass
2
ELEMENTS
AND SYMBOLS
 Elements
Over timeare
some
primary
elements
substances
have been
from
named
which
forall
other substances
planets,
mythological
are built.
figures,
Elements
minerals,
cannot
colors,
be
broken down
geographic
locations
into simpler
and famous
substances.
people. Some
examples are shown below:
3
ELEMENTS
AND SYMBOLS
 The symbol for most elements is the one- or twoletter abbreviation of the name of the element. Only
the first letter of an elements symbol is capitalized.
If the symbol has a second letter, it is written as
lowercase.
Co
CO
cobalt
carbon and oxygen
4
ELEMENTS
AND SYMBOLS
 Although most of the symbols use letters from
current names, some of the symbols of the elements
are based on their Greek or Latin names.
Na
sodium
(natrium)
Fe
iron
(ferrum)
5
ELEMENTS
AND SYMBOLS
 Some elements have formulas that are not single
atoms. Seven of these elements have diatomic
(2-atoms) molecules.
Fluorine (F2)
Hydrogen (H2)
Oxygen (O2)
Nitrogen (N2)
Chlorine (Cl2)
Bromine (Br2)
Iodine (I2)
6
PERIODIC TABLE
Non-metals
Metals
Metalloids
7
PROPERTIES OF
METALS & NON-METALS
Metals
Non-metals
• Mostly solid
• Can be solid, liquid or gas
• Have shiny appearance
• Have dull appearance
• Good conductors of
heat & electricity
• Poor conductors of heat
& electricity
• Malleable & ductile
• Brittle (if solid)
• Lose electrons
• Gain or share electrons
8
METALLOIDS
 Metalloids are elements
that possess some
properties of metals and
some of non-metals.
 The most important
metalloids are silicon (Si)
and germanium (Ge)
which are used extensively
in computer chips.
9
PERIODIC TABLE
Metallic
Metallic character
character decreases
increases going down
acrossaagroup
period.
Least metallic
Most metallic
element
elements
F
Cs
Fr
10
PERIODIC TABLE
 Seven elements exist as diatomic molecules.
 All others exist as monatomic (single atom).
11
PERIODS & GROUPS

 The
Elements
periodic
in the
table
same
is composed
family have
of periods
similar (rows)
properties,
and
and areorcommonly
referred to by their traditional
groups
families (columns).
names.
12
PERIODS & GROUPS
 Group
The group
Elements
Alkali
Noble
Halogens
gases
metals
2 elements
in
are
ofare
groups
metals
the
areun-reactive
most
soft
are
1-2
inmetals
called
reactive
between
and gases
13-18
alkaline-earth
that
nonmetals,
the
are
that
are
main
very
referred
aregroup
commonly
reactive.
and
metals.
to
occur
as
main-group
used
in
These
elements
nature
in
metals
light
are
only
or
bulbs.
called
are
as
representative
compounds.
less
transition
reactivewith
than
metals.
groups.
alkali
metals.
They
often
react
explosively
other
elements.
13
EARLY CONCEPTS
OF THE ATOM
 The smallest particle of matter that still retains its
properties is called an atom.
 In the fifth century B.C., the Greek
philosopher Democritus proposed
that matter is composed of a finite
number of discrete particles, named
atomos (meaning un-cuttable or
indivisible)
14
DALTON’S
ATOMIC THEORY
 In
Dalton’s
1808, John
modelDalton,
represented
built on
the
ideas of
atom
as Democritus,
a featureless and
ball of uniform
formulated a precise definition
density.
themodel
building
blocks of
 of
This
is referred
to matter.
as the
“soccer ball” model.
15
DALTON’S
ATOMIC THEORY
Dalton’s atomic theory,
 explains the difference between an element
and a compound.
 explains two scientific laws, and
 predicts a new scientific law.
16
DALTON’S
ATOMIC THEORY
Postulate
1
2
Deduction
Each element consists of
indivisible, small particles
called atoms.
All the atoms of an element
are identical to one another,
but different from others.
Gives a more precise
definition for an element.
17
DALTON’S
ATOMIC THEORY
Atoms of
oxygen are
different
from
All atoms
atomsof
ofoxygen
hydrogen
are
identical to
one another
All atoms of
hydrogen
are identical
to one
another
Atoms
of consists
each element
are identical
to one
Atoms
of indivisible,
small particles.
another, but different from others.
18
5.1
DALTON’S
ATOMIC THEORY
Postulate
3
4
Atoms combine chemically
in definite whole-number
ratios to form compounds.
Atoms can neither be
created nor destroyed in
chemical reactions.
Deduction
Supports Law of Definite
Composition; predicts Law
of Multiple Proportions.
Supports Law of
Conservation of Mass.
19
LAW OF
DEFINITE COMPOSITION
As a result
Atoms
combine
compounds
in definite
always
whole-number
contain elements
ratios in
to
form
the
same
compounds.
proportions by mass.
H
2
=
O
1
H
1
=
O
1
20
LAW OF
MULTIPLE PROPORTIONS
Two or more elements may combine in different
ratios to form more than one compound.
H
2
=
O
1
H
1
=
O
1
21
DISCOVERY OF
THE ELECTRON
 Smaller
Negatively
particles
charged
than
particles
the atom
from
also
cathode
exist and
were
are called
pulled
towards
subatomic
positively
particles.
charged plate, anode,
allowed
pass through
and beexperiments
detected on
 and
In 1897,
J.J.to
Thomson
performed
a
fluorescent
screen.
with
a cathode
ray tube.
22
DISCOVERY OF
THE ELECTRON
 In
These
absence
presence
observations
ofofaamagnetic
magnetic
indicated
field,
andthat
electric
the the
cathode
cathode
fields,
rays
the
were were
cathode
rays
notrays
deflected.
negatively
were deflected
charged.
towards the positive
 plate.
These rays were later named electrons.
23
ATOMIC
MODEL
 Based on these findings, Thomson proposed an
atomic model, composed of negatively charged
electrons embedded in a uniform positively
charged sphere.
 This model is called the
“plum pudding” model.
24
DISCOVERY OF
THE NUCLEUS
 In these
1910, experiments
Ernest Rutherford
he bombarded
carried out
a thin
a sheet
number
of experiments
to further
the
of
gold foil
with -particles
(large,probe
positively
nature of emitted
charged)
the atom.
from a radioactive source.
25
DISCOVERY OF
THE NUCLEUS
 Some
Few majority
The
ofofthe
theparticles
particles
of the particles
were
wereobserved
observed
were observed
totobebeturned
to
pass through
deflected
at large
un-deflected
slightly
back
towards
the angles.
directionor
they
camedeflected.
from.
26
NUCLEAR MODEL
OF THE ATOM
 The
Based
deflections
scatterings
on these were
observations,
caused
by glancing
head-on
Rutherford
proposed
collision
of a model of
particles
with
thethe
atom
consisting of a small,
nucleus.
massive positive
Deflection
center
(nucleus),
surrounded by
electrons in mostly
empty space.
Scattering
27
5.5
THE MODERN
ATOM
 The electrons
current model
(e-) move
of the
atom describes
rapidly
throughitthe
as aatomic
neutral spherical
volume,
held by the
entity,
composed forces
attractive
of a positively
to the
charged nucleus
nucleus.
surrounded
by negatively
 The
nucleus consists
of
charged electrons.
positively
charged protons
(p+) and neutrally charged
neutrons (n0).
28
ATOMIC
STRUCTURE
 The number
modern atom
of protons
consists
in an
of atom
3 subatomic
determines its
identity,
particles:and is called atomic number (Z).
 In a neutral atom, the number of protons (+) are
Relative
equal
to
the
number
of
electrons
(–).
Particle
Charge
Mass
 Almost all the mass of the atom rests
in the
Proton
+1
~1800
nucleus.
 Therefore
the number 0of protons and
neutrons in
Neutron
~1800
an atom is called the mass number (A).
Electron
–1
1
29
ATOMIC
STRUCTURE
 The general designation for an atom is shown
below:
Atomic number (Z) = # of protons
Mass number (A) = # of p+ + # of n0
# of n0 = A - Z
30
ISOTOPES
 Atoms
Isotopesofofthe
ansame
element
element
havethat
the same
possess
atomic
a
different(Z),
number
number
but aof
different
neutrons
mass
are number
called isotopes.
(A).
The 3 isotopes of Hydrogen
31
ISOTOPES &
ATOMIC MASS
 The mass of an atom is measured relative to the
mass of a chosen standard (carbon-12 atom),
and is expressed in atomic mass units (amu).
 The average atomic mass of an element is the
mass of that element’s natural occurring
isotopes weighted according to their abundance.
 Therefore the atomic mass of an element is
closest to the mass of its most abundant isotope.
32
Example 1:
Determine the number of protons, electrons and
neutrons in a chlorine atom .
35
17
Cl
A = 35
Z = 17
# of protons = 17 (Z)
# of electrons = 17 (= p+)
# of neutrons = 18 (35 - 17)
33
Example 2:
Which two of the following are isotopes of each
other?
410
186
X
410
185
Y
412
183
Z
412
185
R
Isotopes of an element have the same atomic
number, but a different mass number
34
Example 3:
Based on the information below, which is the most
abundant isotope of boron (atomic mass = 10.8 amu) ?
Isotope
10B
11B
Mass (amu)
10.0
11.0
Atomic mass of an element is closer to the
mass of the more abundant isotope
35
CALCULATING MASS
FROM ISOTOPIC DATA
Isotope
Mass
(amu)
Abundance
(%)
107Ag
106.91
51.84
109Ag
108.90
48.16
(106.91)
(0.5184)
55.42
amu ö æMass of öüï
ìï æAbundance
ìïï Atomic mass ü
ö æMass=of öïü
Abundance
ï
ïï ïìï æ
ïç
ï
÷
÷
÷
÷
çç
çç
x
+
x
÷
÷
÷
÷
í
ý = í çç
ý
í
ý
ç
÷ èçisotope 1ø
÷ï ï èçof isotope 2 ø
÷ èçisotope 2ø÷ï
ïîï of an elementïþ
ïîï çèof isotope(0.4816)
1ø
ï (108.90)
ï îï
ï
= 52.45
amu
þ
þ
107.87 amu
36
THE END
37