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AAttoommiic c SSttrruuccttuurree

ParPart 2t 2

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3

Recap

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Recap

• Atom is a particle which is electrically neutral

• No. of protons = No. of electrons

• An atom consists of 3 subatomic particles:

1) Protons2) Neutrons3) Electrons

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Recap

• Structure of an atom

• Relative charges and approximate relative masses of protons, neutrons and electrons

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ElectronsNucleus

Protons and Neutrons

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Particle Charge Relative Mass Remarks

Proton +1 1 • Mass is the same as that of a hydrogen atom• Found in the nucleus of the atom

Neutron

0 1 • Mass is the same as that of a hydrogen atom• Found in the nucleus of the atom

Electron

-1 1/1836 • One hydrogen atom weighs as much as 1836 electrons• Found around the nucleus.

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Recap

•Symbol of an atom

Chemical Symbol

Nucleon Number

Proton Number

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Recap

• Proton number (atomic number)

The number of protons in an

atom

• For an atom, no. of protons = no. electrons

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Recap

• Nucleon number (mass number)

= no. of protons + no. neutrons

• No. of Neutrons= Nucleon number – Proton

number

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Overview of topic

Atomic Structure

Structure of Atoms

Isotopes

Electronic Arrangement

Electronic Structure and the Periodic Table

Ions

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Today’s Menu•What are isotopes•Electrons arrangement in atoms

•Electronic structure•Outermost electrons •The Periodic table

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What are What are isotopes?isotopes?

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What are isotopes

Isotopes:

Atoms of the same element having the same number of protons but different number of neutrons

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What are isotopes

Isotopes:

•Same number of protons (atomic number)

•Different number of neutrons

•Different number nucleon number

•Same number of electrons

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Examples of isotopes• Three isotopes of hydrogen

1)

Hydrogen

Number of proton: 1

Number of neutrons: 0

Nucleon number: 1

Number of electron: 1

Hydrogen-1

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Examples of isotopes• Three isotopes of hydrogen

2)

Deuterium

Number of proton: 1

Number of neutrons: 1

Nucleon number: 2

Number of electron: 1

Hydrogen-2

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Examples of isotopes• Three isotopes of hydrogen

3)

Tritium

Number of proton: 1

Number of neutrons: 2

Nucleon number: 3

Number of electron: 1

Hydrogen-3

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Examples of isotopes•Two isotopes of Chlorine

Cl35

17Cl37

17Number of proton: 17Number of neutrons: 18Nucleon number: 35Number of electron: 17

Number of proton: 17Number of neutrons: 20Nucleon number: 37Number of electron: 17

Chlorine-37

Chlorine-35

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What are isotopesIsotopes Number of

Protons Neutrons

Electrons

1 0 1

1 1 1

1 2 1H3

1

H1

1

H2

1

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What are isotopesIsotopes:

• All isotopes of the same element have the same chemical properties but small differences in physical properties

• There are two types of isotopes(i) Radioactive(ii) Non-radioactive

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Why does chlorine has a nucleon

number of 35.5

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Why does chlorine has a nucleon number of 35.5

Cl5.35

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In the periodic table, chlorine is denoted as

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Why does chlorine has a nucleon number of 35.5

• 75% of all chlorine atoms have a mass of 35• 25% of all chlorine atoms have a mass of 37• Average mass of one chlorine atom=

= 35.5

%10037)(25% 35) (75%

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Practice Time

Part 3 Worksheet 2

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Electrons Electrons Arrangement In Arrangement In

AtomsAtoms

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Electrons Arrangement in Atoms

• Electrons move around the nucleus of the atom

• The electrons are held in shells since it is of opposite charge

• The attractive force between the positive charge on the nucleus and the negative charge on the electrons is called electrostatic force.

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Electronic Electronic StructureStructure

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Electronic Structure

• The way the electrons are arranged is called its electronic structure

• Electrons are arranged in shells which are numbered from the nucleus onwards

• Each shell is capable of holding up to a certain number of electrons

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Electronic Structure

• Electrons are arranged in shells which are numbered: 1, 2, 3, 4 from the nucleus onwards

Shell no. Maximum no. of electrons

Name

1 2 Duplet

2 8 Octet

3 8(for atoms with proton number 20)

Octet

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Electronic Structure

1st shell2 electrons

3rd shell8 electrons(proton number 20)

Nucleus

2nd shell

8 electrons

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Electronic StructureTo find the electronic configuration of an atom, we should

(1) Fill the electrons into the shell nearest to the nucleus first. This shell can take a maximum of 2 electrons(2) Once this shell is filled, the electrons go to the next available

shell which has a maximum capacity of 8 electrons, and so on

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Electronic Structure

Sodium, Na23

11 Electronic

Configuration

2, 8, 11st shell 2nd

shell

3rd shell

Na

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Electronic Structure

Carbon, C12

6Electronic

Configuration

2, 4 1st shell 2nd

shell

C

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Electronic Structure

Its important to know the electronic structure and electronic configuration of the first 20 elements of the Periodic Table

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SummarSummaryy

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Summary1) Isotopes are atoms of

the same element having the same number of protons but different number of neutrons

2) Electrostatic force is the force between the

positive charge on the nucleus and the negative charge on the electrons.

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Summary

• Electrons are arranged in shells which are numbered: 1, 2, 3, 4 from the nucleus onwards

Shell no. Maximum no. of electrons

Name

1 2 Duplet

2 8 Octet

3 8(for atoms with proton number 20)

Octet

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SummaryTo find the electronic configuration of an atom, we should

(1) Fill the electrons into the shell nearest to the nucleus first. This shell can take a maximum of 2 electrons(2) Once this shell is filled, the electrons go to the next available shell which has a maximum capacity of 8 electrons, and so on

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Any Any QuestionsQuestions

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Practice Time

Part 3 Worksheet 2