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8/9/2019 2008_Atomic Structure & Ions (Updated 27 Jan 2009)
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Atomic StructureAtomic Structure
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Unit Goals
At the end of the lesson, students should be able to:
(a) state the relative charges and approximate relativemasses of a proton, a neutron and an electron
(b) describe, with the aid of diagrams, the structure of anatom as containing protons and neutrons (nucleons) in the
nucleus and electrons arranged in shells (energy levels)
(c) define proton number (atomic number) and nucleon
number (mass number)
(d) interpret and use symbols such as 6 C
12
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Unit Goals
At the end of the lesson, students should be
able to:
(e) Describe the formation of ions by electron
loss/gain in order to obtain electronicconfiguration of an inert gas.
(f) Deduce the number of protons, electrons
and neutrons in atoms and ions, given protonand/or nucleon number
(g) define the term isotopes
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Arrangement of subatomic Particles
Inside the AtomInside the Atom
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http://www.syvum.com/cgi/online/serve.cgi/squizzes/chem/atomic1.html
Atomic ModelsAtomic Models
http://www.syvum.com/cgi/online/serve.cgi/squizzes/chem/atomic1.htmlhttp://www.syvum.com/cgi/online/serve.cgi/squizzes/chem/atomic1.html8/9/2019 2008_Atomic Structure & Ions (Updated 27 Jan 2009)
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Inside the AtomInside the Atom
Atoms are made up of3 types of sub-atomic particles:
PProtonsrotons
EElectronslectronsNNeutronseutrons
Atoms of different elements differ fromeach other because ofdifferentcombinations of these particles.
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Inside the AtomInside the Atom
Particle Charge Relativemass
Where canyou find it?
Proton +1 1 unit In the nucleus
Neutron 0 1 unit In the nucleus
Electron -1 1/18401/2000 unit
Orbitingaround the
electronshells
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Is atom electrically charged?
Atom is electrically neutral (no net charge).
An atom contains equal number of electrons and
protons.
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NUCLEUS
3-D Arrangement of sub-atomic particles
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Electron Orbital in 3D world
(optional)
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Do you recognize him?
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Mendeleev
Mendeleev, a Russian Chemist, was one of
the first to be partially sucessful in arranging
the known elements in the 1870's into a
chart that would allow the prediction ofproperties.
"The properties of the elements are a
periodic function of their atomic masses"
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Mendeleev
There were some inconsistencies in the
arrangement of the elements according to
his law, however it wasn't until the early
1900's (1914) that a Prof Moseley, aBritish Physicist, was able to determine
the atomic numbers of all the known
elements using an experimental technique.
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Do you recognize him?
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Henry Moseley
Moseley then proceeded to rearrange the
elements according to increasing atomic
numbers.
Moseley's arrangement seemed to clear upthe contradictions and inconsistencies of
Mendeleev's arrangement, but Moseley
based his arrangement on atomicnumbers and not atomic masses.
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Henry Moseley
Moseley's periodic law is now considered
the current Periodic Law. It resulted in a
slight alteration of Mendeleev's
arrangement, but the slight difference wasenough to correct the inconsistencies that
existed in Mendeleev's arrangement.
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The Periodic Table is a method of arranging elements.
In the Table, elements are arranged in order ofproton
number, which increases from left to right across the Table.
A vertical column of elements in the Table is called a Group. The Groups are numbered I, II, II, etc from left to right.
A horizontal rowof elements in the Table is called a Period. Each Period is numbered 1, 2, 3, etc.
What is a Periodic Table?
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1) A dividing line divides elements into metals and
non-metals.
In general, elements in Group I and II are metals.(elements with small number of electrons in the outer shell)
In general, elements in Group VI and VII are non-metals.(elements with large numbers of electrons in the outer shell)
Patterns in the Periodic Table
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Symbol of
element
Nucleonnumber
Proton
number
Chemical Symbol
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Symbol of
element
Nucleonnumber
Proton
number
Atomic Number
Atomic number / Proton Number is the number
of protons in an atom
In other words, Li has 3 protons.
We also know that Li has 3 electrons (why?)
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Symbol of
element
Nucleonnumber
Proton
number
Nucleon Number
Nucleon number / Mass Number is the number
of protons and neutrons in the nucleus of anatom
Can we find out the number of neutrons in an
atom?
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What information can we get
from a chemical symbol?
Since the mass number
is 7, the number of
neutrons can be
calculated by takingthe difference between
the mass number and
proton number.
Number of neutrons
= 7 3
= 4
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How to calculate no. of subatomic particles
Example 1Sodium has an Atomic Number of 11
and an Mass Number of 23 i.e.
An atom of sodium has
1) 11 Protons
2) 11 Electrons.3) Number of Neutrons = 23-11 = 12
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How to calculate no. of subatomic particles
Example 2Hydrogen has an atomic number of 1
and an mass Number of 1 i.e.
Thus, you know an atom of hydrogen
has
1 Protons 1 Electrons. Number of Neutrons = 1-1 = 0
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Arrangement of electrons
Electron arrangement determinesthe chemical propertiesof the atom.
The electrons move around thenucleus in regions known aselectron shells.
Each shell can only hold a certainnumber of electrons.
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Electronic Configuration
11 = 2.8.1
1)12 Mg24 = 2.8.2
2)17 Cl35.5 = 2.8.7
3) 7N14 = 2.5
4)20 Ca40
= 2.8.8.2
5) 6 C12 = 2.4
Based on the information above, predict what is the relationship
between electronic configuration of an element and its position in
the Periodic Table?
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Additional Information
Number of electrons
in the outermost
shell correspond to
the Group Numberofthe atom in the
Periodic Table.
Number of electron
shells in an atomcorrespond to the
Period in which it is in
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How to fill in electrons into
electron shells?
Proton no.=16
Electron no.=16
Electronic configuration= 2.8.6
16 S32
Sulphur
S
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How to fill in electrons into
electron shells?
N
Proton no.=7
Electron no.=7Electronic configuration= 2.5
7N14
Nitrogen
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How to fill in electrons into
electron shells?
Cl
Proton no.=17
Electron no.=17Electronic configuration= 2.8.7
17 Cl35.5
Chlorine
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Formation of IonsFormation of Ions
How do atoms become ions? Formation of Cations
Formation of Anions
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How do atoms form ions?How do atoms form ions?
In an atom, the number of protons is the
same as number of electrons.
The atom is electrically neutral.
However, during a chemical reaction,
electrons can either be:
added ortaken away from an atom
atom is no longer neutral
A charged particle called ION is formed.
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How do atoms form ions?How do atoms form ions?
Negative ionProtons < Electrons
Add electrons
Lose
electrons
-
Neutral atom
Protons = Electrons
+Positive ion
Protons > Electrons
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How do atoms gain chemicalHow do atoms gain chemical
stability?stability?
Atoms form ions so that they have the stable
electron configuration of a noble gas.
(See diagram below)
2,8(Octet)
2(duplet)
2,8,8(Octet)
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Formation of positive ions -Formation of positive ions -
CATIONS?CATIONS?
Cations are positive ions.
Cations are usually ions of metals, as
metals tend to lose electrons during achemical reaction.
Group No of electron(s)lost
Charge ofcation
I 1 +1
II 2 +2
III 3 +3
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12 Mg24
MagnesiumProton no.=12
Electron no.=12
Neutron no.=12
(12+) + (12-) = 0
Neutral
BUT
Chemically
Unstable
+
-
1212
+- -
-
-
- -
-
-
- -
- -
Mg atom = 2.8.2
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12 Mg24
Magnesium
12
12
+
- --
-
- -
-
-
- -
- -
Metal -Remove
2.8.2Neutral but Unstable
REMOVE 2
2.8Extra 2+ charge
BUT
STABLE
-
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12 Mg24
MagnesiumProton no.=12
Electron no.=10
Neutron no.=12
(12+) + (10-) = 2+
Charged
BUT
Chemically
stable
+
-
1212
+- -
-
-
- -
-
-
- -
Mg
2+
ion = 2.8
2+
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10 Ne20
Neon
Proton no.=10
Electron no.=10
Neutron no.=20
Neutral
AND
STABLE
+
-
Ne = 2.8 (octet)
1822
+- -
-
-
- -
-
-
- -
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Formation of negative ions -Formation of negative ions -
ANIONS?ANIONS?
Anions are negatively-charged ions.
Anions are usually ions of non-metals, as
non-metals tend to gain electrons during a
chemical reaction.
Group No of electron(s)gain
Charge ofanion
V 3 -3
VI 2 -2
VII 1 -1
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16 S32
SulphurProton no.=16
Electron no.=16
Neutron no.=16
(16+) + (16-) = 0
Neutral
BUT
Chemically
Unstable
+
-
1616
+- -
-
-
- -
-
-
- -
- -
- -
- -
S atom = 2.8.6
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16 S32
Sulphur
16
16
+
- --
-
- -
-
-
- -
- -
- -
--
NON-metal
2.8.6Neutral but Unstable
ADD 2
2.8.8Extra 2- charge
BUT
STABLE
--
-
-ADD
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16 S32
SulphurProton no.=16
Electron no.=18Neutron no.=16
(16+) + (18-) = 2-
Charged
BUT
Chemically
stable
+
-
1616
+
- --
-
- -
-
-
- -
- -
- -
- -
S
2-
ion = 2.8.8
--
2-
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18 Ar40
Argon
Proton no.=18
Electron no.=18
Neutron no.=22
(18+) + (18-) = 0
Neutral
AND
STABLE
+
-
Ar atom = 2.8.8 (octet)
1822
+
- --
-
- -
-
-
- -
- -
- -
- -
--
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How do you make
neutral but unstable atoms
STABLE???
Remove / Add resulting inthe formation of ions
(charged particle(
-
Note:
In chemical reaction, protons and neutrons are NOTNOT
removed or added!
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EXERCISE 1
Element Neutron no. Proton no. Electron no. Formula ofion
ElectronAdded /
Removed
40-20=20 20 20
2.8.8.2
Ca2+
2.8.8
Octet
Removed2 electrons
(stable)
7-3=4 3 3
2.1
Li+
2
Duplet
Removed 1electron(stable)
31-15=16 15 152.8.5
P3-
2.8.8
Octet
Added3 electrons(stable)
40
20
Ca
7
3Li
31
15P
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Element Neutron no. Proton no. Electronno.
Formula ofion
ElectronAdded /
Removed
39-19=20 19 19
2.8.8.1
K+
2.8.8
Octet
Removed
1 electron
14-7=7 7 7
2.5
N3-
2.8
Octet
Added
3 electrons
27-13=14 13 132.8.3
Al3+2.8
Octet
Removed3 electrons
EXERCISE 2
39
19 K
14
7N
27
13Al
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Isotopes Isotopes are atoms of the same element
with the same number of protons but
different number of neutrons.
Isotopes have same chemical properties
but slightlydifferent physical properties.
Chemical reactions involve only electrons not
protons or neutrons.
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Common isotopes 12 C and 14 C
Radiocarbon dating is a radiometric datingmethod that uses the naturally occurring
radioisotope carbon-14 (14C) to determine
the age of carbonaceous materials up to
about 60,000 years.[1]
Raw, i.e. uncalibrated, radiocarbon ages
are usually reported in radiocarbon years
"Before Present" (BP), "Present" being
defined as AD 1950. Such raw ages can
be calibrated to give calendar dates.
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Common isotopes1H, 2H, 3H
The most common isotope of hydrogenhas no neutrons at all
There's also a hydrogen isotope called
deuterium, with one neutron, andanother, tritium, with two neutrons.
Hydrogen Deuterium Tritium
At t M l l
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Atoms to Molecules:
Fated Attraction
When two or more atoms of the same
kind or ofdifferent kinds, chemical
combinedtogether, a molecule is
formed.
Molecules exist in both elements andcompounds.
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Molecules of
ElementsElements consist of a fixed number of one kind of atom
only!
Eg: Oxygen molecule, O2
CompoundsCompounds
consist of a fixed number of two or more kind ofdifferent atoms chemically combined together.
Eg: Water molecule, H2O
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Chemical Formula
Molecules can be represented usingchemical formula.
The chemical formula of a molecule shows thenumbernumberand types of atomstypes of atoms contained in it
The chemical formula of a substance is denoted
by chemical symbolchemical symbol and the subscriptsubscriptshowing the number of atoms present in themolecule.
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Common Examples of MoleculesCommon Examples of Molecules
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Common Examples of MoleculesCommon Examples of Molecules
Sulphur molecule, S8
Ammonia gas, NH3
1 Nitrogen atom is
bonded to 3 hydrogen
Fullerene, C60