2008_atomic structure & ions (updated 27 jan 2009)

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.html


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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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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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electron shells?

N

Proton no.=7

Electron no.=7Electronic configuration= 2.5

7N14

Nitrogen


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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

2008_atomic structure & ions (updated 27 jan 2009)

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