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Chemistry 11 Chemical Bonding. Electronegativity – the tendency of an atom to attract electrons from a neighbouring atom. . Get lost, loser!. Hey! I find your electrons attractive !. Electronegativity increases as you move from left to right. .

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chemistry 11 chemical bonding
Chemistry 11Chemical Bonding

Electronegativity – the tendency of an atom to attract electrons from a neighbouring atom.

Get lost, loser!

Hey! I find your electrons attractive!

slide2

Electronegativity increases as you move from left to right.

Electronegativity decreases as you move down each column.

slide3

Valence Electrons – electrons in the outermost occupied energy level. (s and p electrons outside the core)

Valence electrons can be represented by “dots” drawn around the atom.

slide4

Gilbert Newton Lewis

Invented “Electron-dot” formulas or “Lewis Structures”

I’m so tired of writing all those useless inner electrons, in the Bohring models!

slide5

When the electronegativities of two atoms are quite different from each other:

One atom loses an electron (or electrons)

The other atom gains an electron (or electrons)

This results in an Ionic Bond.

Chemical Bonding (Choose Ionic Bonds)crystal lattice viewer

slide6

NaCl

Crystal Lattice

slide7

Li

F

An F Atom

A Li Atom

-

+

Li

F

A Li+ Ion

An F- Ion

slide8

Be

F

F

An F Atom

An F Atom

A Be Atom

-

-

2+

F

Be

F

A Be2+ Ion

An F- Ion

An F- Ion

slide9

The melting points of some Ionic Compounds are as follows:

NaF 993 oCKCl 770 oCLiCl 605 oC

These high melting points are experimental evidence that Ionic Bonds are VERY STRONG. (Hard to break just by heating).

slide10

When Electronegativities of bonding atoms are the same (as they are in diatomic molecules) or close to the same, they SHARE electrons. Bonds formed when atoms share electrons are called Covalent Bonds.In diatomic molecules (like H2 or Cl2), the electronegativities of both atoms are exactly the same so electrons are shared equally!

Covalent Bond animation

slide12

H

H

slide13

Covalent bonds in large networks (Network Bonding) gives rise to substances with very high melting points.

slide14

diamond structure

Diamonds are “forever”!

slide15

Some melting points of Network Solids:

Diamond (Carbon) 3550 oCSilicon Carbide (SiC) 2700 oCBoron Nitride (BN) 3000 oC

Covalent bonds are very strong!

slide17

When electrons are shared unequally between two atoms, the bond is called Polar Covalent. A type of PC bond formed when “H” from one atom attracts “O” or “N” from another atom is called Hydrogen Bonding. polar covalent bonds

slide22

Bonds within molecules that hold the atoms of a molecule together are called intramolecular bonds. They are strong covalent bonds.

Covalent Bonds

slide23

I

I

I

I

I

I

I

I

I

I

I

I

The covalent intramolecular bond in I2 is very strong.

There are weaker intermolecular forces which hold covalent molecules together in a molecular solid.

slide24

A dipole is a partial separation of charge which exists when one end of a molecule has a slight positive charge and the other end has a slight negative charge. Eg. A water molecule has two dipoles.

The Greek letter “delta” means “partial”

d

slide25

Just by pure chance, there are some times when both electrons in helium are on the same side. This forms temporary dipoles

e-

e-

+2

+2

e-

e-

d -

d -

d +

d +

He

He

The weak attractive forces between the (+) side of one molecule and the (-) side of another molecule are called London Forces

slide26

I

I

I

I

I

I

I

I

I

I

I

I

The covalent intramolecular bond in I2 is very strong.

There are weaker intermolecular forces which hold covalent molecules together in a molecular solid. These are called London Forces. Since they are relatively weak, Iodine has a low melting point.

slide27

Cl

Lewis Structures (Electron-dot formulas) for Ionic Compounds.

Remember, in an ionic compound, the metal loses e-’s and the non-metal gains. There is no sharing. Here is the e-dot formula for sodium chloride (NaCl)

Na+

slide28

F

F

Here is the e-dot formula (Lewis Structure) for the ionic compound MgF2 :

Mg2+

Notice, there is no sharing. The F atoms took both valence e-’s from Mg, forming ions which do not share electrons. The + and – charges on the ions cause them to attract each other.

slide29

Electron-dot Formulas (Lewis Structures) for Covalent Compounds.

When atoms form covalent bonds, they are trying to achieve stable noble gas electron arrangements:Hydrogen will share e-’s until it feels 2 e-’s like Helium.Other elements share e-’s to achieve what is called a “Stable Octet” (8 valence e-’s)

slide30

Electron-dot formula for Methane (CH4)

H

H

C

H

H

Here is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

slide31

Electron-dot formula for Methane (CH4)

H

H

C

H

H

Here is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

slide32

Electron-dot formula for Methane (CH4)

H

H

C

H

H

Here is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

slide33

Electron-dot formula for Methane (CH4)

H

H

C

H

H

Here is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

slide36

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

H

slide37

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

H

slide38

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

H

slide39

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

H

slide40

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

H

slide41

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

Each H atom “feels” like a stable “He” atom with 2e-s

H

slide42

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

Each H atom “feels” like a stable “He” atom with 2e-s

H

slide43

Electron-dot formula for Methane (CH4)

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

H

C

H

Each H atom “feels” like a stable “He” atom with 2e-s

H

slide44

Electron-dot formula for Ammonia (NH3)

H

N

H

Here is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each)

H

slide45

Electron-dot formula for Ammonia (NH3)

H

N

H

H

Here is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each)

slide46

Electron-dot formula for Ammonia (NH3)

H

N

H

H

Here is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each)

slide47

Electron-dot formula for Ammonia (NH3)

H

N

H

H

Here is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each)

slide50

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

N

H

H

H

slide51

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

N

H

H

H

slide52

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

N

H

H

H

slide53

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

N

H

H

H

slide54

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

N

H

H

H

slide55

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

N

H

H

H

slide56

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide57

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide58

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide59

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide60

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide61

Electron-dot formula for Ammonia (NH3)

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide62

Electron-dot formula for Ammonia (NH3)

Each “H” feels like it has 2 e- like Helium.

N

H

H

H

slide75

F

F

C

F

F

Write the electron-dot formula for CF4

Because “F” is a halogen, it has 7 valence e-s, so you must show all 7 red dots around each “F” atom!

slide77

Write the electron-dot formula for H2S

S

H

H

The two H’s MUST be at right angles to each other!!

slide78

Write the electron-dot formula for H2S

These are called “lone pairs”. They must also be at right angles to each other when the central atom is in Group 16!

S

H

H

slide81

Write the Electron-Dot Formula for SeF2

Se

F

F

Because Se is in Group 16, the F atoms MUST be at right angles to each other!

slide82

Se

F

F

Write the Electron-Dot Formula for SeF2

Because “F” is in Group 17, they have 7 valence e-s, so they must have 7 red dots around them.