atomic and interatomic structure.ppt

8/11/2019 Atomic and interatomic structure.ppt

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ATOMIC STRUCTURE ANDINTERATOMIC BONDING


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ATOMIC STRUCTURE An atom consists of a

nucleus composed of

protons and neutronsand electrons whichencircle the nucleus.


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ATOMIC STRUCTURE


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Atomic number (Z) = Number protons =

number of electrons.

Atomic mass (A) = # proton + # neutron

Atomic mass unit (amu) 1 amu = 1/12 mass of Carbon 12 (12C)

ATOMIC STRUCTURE


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ATOMIC STRUCTURE Atomic weight: A

Weighted average of atomic masses of naturallyoccurring isotopes.

Atomic weight of carbon is 12.011 amu.

Atomic weight is often in mass per mole.

A mole: Amount of matter that has a mass in grams equal

to the atomic mass in amu


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ATOMIC STRUCTURE Isotopes:

Elements that have different atomic masses


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ATOMIC STRUCTURE One Mole contains Avogadros number of

atoms,

Nav= 6.023 1023.

Nav= 1 gram/1 amu.

Example:Atomic weight of iron = 55.85 amu/atom

= 55.85 g/mol


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ATOMIC STRUCTURE QUANTUM NUMBERS:

There are four quantum numbers; theirsymbols are n, l, m and s. EVERY electronin an atom has a specific, unique set ofthese four quantum numbers.


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ATOMIC STRUCTURE


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ATOMIC STRUCTUREElectron configuration

(stable)

...

...

1s22s22p 63s23p6 (stable)...

1s22s22p 63s23p 63d 10 4s24p6 (stable)

Atomic #

18...

36

Element1s11Hydrogen1s2

2Helium 1s22s13Lithium1s22s24Beryllium1s22s22p15Boron1s22s22p26Carbon

...1s22s22p6 (stable)

10Neon 1s22s22p 63s111Sodium1s22s22p 63s212Magnesium1s22s22p 63s23p113Aluminum

...Argon...

Krypton

Most elements: Electron configuration not stable.


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ELECTRONS IN ATOMS Atomic model:

Bohr atomic

- electrons revolvearound the atomic

nucleus in discrete orbital

and the energies ofelectrons are quantized.


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ELECTRONS IN ATOMS Wave mechanical

- Electron exhibits

both wavelike andparticle-like characteristics,its position is considered tobe a probability

distribution


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TYPES OF BONDING Primary Bonding:

-Also known as Chemical Bond Ionic Covalent Metallic

Secondary Bonding:


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PRIMARY BONDING IONIC:

Ionic bonding is the

complete transfer ofvalence electron(s)between atoms.

An ionic bond is formedwhen an atom loses orgains one or moreelectrons from its outershell.


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PRIMARY BONDING Between metallic and

nonmetallic

The Attractive bondingforces are coulombic

Ionic materials arecharacteristically hardand brittle and,furthermore,electrically and

thermally insulative


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PRIMARY BONDING

COVALENT:

Covalent bonding is the sharing of electronsbetween atoms.

In this type of bonding, atoms share theirvalence electrons to get a stable configuration.

This type of bonding occurs between two ofthe same element or elements close to eachother in the periodic table.


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PRIMARY BONDING

Methane (CH4): Fourhydrogen atoms share their

valenceelectrons with one carbon atomand the carbon atom in turnshares one valence electron

with each of the four hydrogenatoms. In the process both Hand C atoms get stableconfiguration and form acovalent bond.

Example:


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PRIMARY BONDING Example:

a Phosphorous moleculeis sharing its 3 unpairedelectrons with 3 Chlorineatoms. In the end product,all four of these molecules

have 8 valenceelectrons and satisfy theoctet rule.


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PRIMARY BONDING

METALLIC: Metallic bonding, the

final primary bondingtype, is found in metalsand their alloys.

Metallic bonding is theelectromagneticinteraction betweendelocalized electrons

The diagram above shows

metallic bonding.


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PRIMARY BONDING

Metallic bonding is found in theperiodic table for Group IA andIIA elements

atomic and interatomic structure.ppt

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