Chemistry 11

Unit 9 Chemical Bonding #3

Name:____________________________ Block:_________

Electronegativity

Electronegativity is defined as the ability of an atom in a molecule to .

Electronegativity is a function of two properties of isolated atoms:

· The atom’s (how strongly an atom holds onto its own electrons)

· The atom’s (how strongly the atom attracts other electrons)

For example, an element which has a large (negative) electron affinity and a high ionization (always endothermic, or positive for neutral atoms)…

…Will from other atoms and having electrons attracted awayWe say these atoms are “highly electronegative”

Electronegativity trends: across a period

Electronegativity across a period because:

1.

2.

Electronegativity trends: down a group

Electronegativity down a group because:

1.

2.

Electronegativity is dictated by:

across a period you are , but filling electrons in the same Bohr quantized . You are only filling sub-shells, so electronegativity increases from left to right

down groups, you are placing electrons into , so moving further from the attractive power of the nucleus. Outer shell becomes further away from the nucleus.

level of upon bonding electrons increases down groups, and adds to the reduction in electronegativity. Shielding is caused by for each other.

Ions & Atomic Radius

Negative Ions: As extra to a neutral atom (eg O to make O-2) the ion has the (due to protons), and an number of surrounding the nucleus.

· The electrostatic repulsion

· The occupied by the electrons

Positive Ions: As from a neutral atom (eg Mg to make Mg+2) the ion has the (due to protons), and a number of negative electrons surrounding the nucleus.

· The electrostatic repulsion

· The occupied by the electrons

Electronegativity & Ionic BondsIonic Bonding Summary:

· Formed between two atoms with in their ionization energies and electronegativity's

· An electronegativity difference of can be classified as an ionic bond

· In this case we can essentially say from one atom to another

Calculating Bonds with Values

ASSIGNMENT #3a

ASSIGNMENT #3a: complete the following questions

ASSIGNMENT #3A: complete the following questions

Why do atoms form bonds?

Bond formation begins with atoms “.”

For example as two hydrogen atoms approach each other, their as each electron cloud is to the other’s approaching .

Atoms continue moving together until the of the two and the two positive nuclei slow the atoms and convert their kinetic energy into .

As the atoms get close to each other, their enough to cause to ones.

The two electrons will move into the region of space between the atoms nuclei.

This of a pair of valence electrons between two adjacent nuclei constitutes a .

What is a covalent bond?

elements usually just need one or two electrons to fill their outer shells. So how do they form a bond?

The two non-metal atoms cannot form a bond by transferring electrons from one to another. Instead, they .

The shared electrons join the atoms together. This is called a .

How is a covalent bond drawn?

A covalent bond consists of a of electrons.

Only of electrons are involved in bonding, so the inner shells do not always have to be included in diagrams.

Two common ways to represent a covalent bond are:

Comparing covalent and ionic bonding

Covalent Bonding

Ionic Bonding

Covalent bonding in hydrogen

Many non-metal elements, such as hydrogen, exist as simple that contain covalent bonds.

How is a covalent bond formed in hydrogen?

Each hydrogen atom needs in its outer shell and so each atom shares its electron.

This shared pair of electrons forms a covalent bond and so creates a diatomic molecule of hydrogen.

What are the types of covalent bonds?

Molecule

Dot & Cross Diagram

Line Diagram

Can compounds contain covalent bonds?

Covalent bonding can also occur between atoms of to create molecules of .

These covalent bonds can be .

How is a covalent bond formed in hydrogen chloride (HCl, also represented as H–Cl)?

Hydrogen and chlorine both need one more electron to fill outer shells. By sharing one electron each, they both have a and a covalent bond is formed.

Covalent bonding in water

Compounds can contain .

Oxygen (2.6) needs more electrons, but hydrogen [1] only needsmore.

How can these three elements be joined by covalent bonding?

The oxygen atom with 1 hydrogen atom, and a with another hydrogen atom.

How is the ratio of atoms calculated?

To calculate the ratio of atoms in a stable covalent compound:

Covalent bonding in ammonia

How do nitrogen and hydrogen atoms form covalent bonds in a molecule of ?

Atomic Ratio

Line Diagram

Dot & Cross (Bohr) Diagram

Covalent bonding in methane

Atomic Ratio

Line Diagram

Dot & Cross (Bohr) Diagram

Covalent bonding in carbon dioxide

Atomic Ratio

Line Diagram

Dot & Cross (Bohr) Diagram

A is when of electrons are shared. In carbon dioxide there are two double bonds

– one between each oxygen atom and the carbon atom.

What are simple covalent structures?

Covalent molecules that contain only a few atoms are called .

Most substances that contain simple covalent molecules have and and are therefore liquids or gases at room temperature, e.g. water, oxygen, carbon dioxide, chlorine and hydrogen. Why?

The covalent bonds these molecules are but the bonds molecules are and easy to break.

What is the structure of a molecular solid?

A few substances that contain simple covalent molecules are at room temperature.

These are .

is a molecular solid at room temperature.

Two iodine atoms form a to become an iodine molecule.

The solid is formed because millions of iodine molecules are held together by to create a 3D molecular lattice.

What properties would you expect molecular solids to have with this type of structure?

What are the properties of molecular solids?

·

·

·

The between the molecules can be by a .

This means that the molecular solids are and and melt and boil at

Molecular solids are also because there are or ions to carry a charge.

What are giant covalent structures?

In some substances, such as , and , millions of atoms are joined together by bonds.

The covalent bonds in these substances do not form molecules but vast called

All the bonds are covalent, so giant covalent structures have and boiling points, and are usually .

What is the structure of sand?

Sand is mostly made of the mineral , which is . It has a giant covalent structure made up of and atoms.

Each silicon atom (2.8.4) is bonded to four oxygen atoms, and each oxygen atom (2.6) is bonded to two silicon atoms.

What are the allotropes of carbon?

Both diamond and graphite are made up of .

Different forms of the same element are called .

These allotropes of carbon have because the atoms are bonded in which create different giant structures.

What are the properties of diamond?

What are the properties of graphite?

In diamond, all the electrons in the outer shell of each carbon atom (2.4) are involved in forming covalent bonds.

This affects the properties of this allotrope of carbon:

In graphite, only three of the four electrons in the outer shell of each carbon atom (2.4) are involved in covalent bonds.

This affects the properties of this allotrope of carbon:

·

·

·

·

·

What is electronegativity?

In a between two different elements, the is

This is because different elements have .

This ability is called an element’s .

Electronegativity values for some common elements.

Values given here are measured on the Pauling scale.

Electronegativity and atomic radius

The electronegativity of an element depends on a combination of two factors:

1. Atomic radius

2. The number of unshielded protons

As radius of an atom , the bonding pair of electrons become further from the nucleus.

They are therefore to the positive charge of the nucleus, resulting in a .

The the number of

in a nucleus, the to the electrons in the covalent bond, resulting in .

However, energy levels of electrons the electrons in the bond from the increased attraction of the greater nuclear charge, thus electronegativity.

Types of Covalent Bonds:

We have discussed the two extreme cases of bonding: - ionic bonding

And covalent bonds with completely

Between these extremes are covalent bonds which involve electron sharing.

When atoms with form covalent bonds, those ΔEN values may be minimal or significant.

Non-polar bonds

If the electronegativity of both atoms in a covalent bond is , the electrons in the bond will be to both of them, and form a covalent bond.

This results in a around the two atoms.

Bonding in (for example O2 or Cl2) is because the electronegativity of the atoms in each molecule is .

Mostly Covalent bonds

If ΔEN is , the bonding electrons between the two atoms spend no more of their time nearer one nucleus than the other.

Such bonds are designated as being “” because ΔEN appears to be

Another way to characterize this is to say that these bonds have

Electronegativity and Covalent Bonds

As ΔEN increases , the pair of bonding electrons will be and closer to the nucleus of the atom with the.

This distribution of electron density will give that end of the bond a partially and the other a partially “pole.”

A “” is said to exist and the bond itself is known as a

ASSIGNMENT 3B: complete the following questions on a separate page

Hebden Questionspg 178 # 69-71 pg 179 # 72

Effect of electronegativity on polarization

The between the two atoms in a bond the of the bond.

This can be illustrated by looking at the hydrogen halides:

Ionic or covalent?

Rather than saying that ionic and covalent are two distinct types of bonding, it is more accurate to say that they are at the two .

Less polar bonds have more .

More polar bonds have more .

The atom the electrons in the bond enough to ionize the other atom.

Polar molecules

Molecules containing polar bonds are not always polar.

Practice Problems: Covalent Bonding

ASSGINMENT #3C: Complete the following Review Questions

SLIDE 165

1

21