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Dr. Marwa Eid

Chemical Bonds

Chemical Bonds

• Chemical Bonds

- attractive force that holds atoms or ions together

- Chemical bonding are classified into 3 types

ionic, covalent, metallic

Chemical Bonding

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

Hey! I find your electrons attractive!

Get lost, loser!

Electronegativity increases as you move from left to right.

Electronegativity decreases as you m

ove down each colum

n.

Valence Electrons

– electrons in the outermost occupied energy level.

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

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Atom – the smallest unit of matter

Heliumatom

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Electron Shells

a) Atomic number = number of Electrons

b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.

c) Electron shells determine how an atom behaves when it encounters other atoms

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Electrons are placed in shells according to rules:

The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

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Why are electrons important?

Elements have different electron configurations different electron configurations mean

different levels of bonding

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Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons

C would like to N would like toO would like to

Gain 4 electronsGain 3 electronsGain 2 electrons

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Bonding

• Elements that do not have a complete octet, tend to react.

• When the elements react bonds are formed.

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Some Common Ions

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Chemical bonds: an attempt to fill electron shells

1. Ionic bonds

2. Covalent bonds

3. Metallic bonds

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IONIC BOND

• A bond formed between two oppositely

ions by the transfer of electrons.• Each element (now an ion) will have a

complete octet after the transfer of electrons

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.

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IONIC BOND

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Formation of Ions from Metals

Ionic compounds result when metals react with nonmetals

Metals lose electrons to match the number of valence

electrons of their nearest noble gas

Positive ions form when the number of electrons are

less than the number of protons

Group 1 metals ion 1+

Group 2 metals ion 2+

• Group 13 metals ion 3+

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Some Typical Ions with Positive Charges (Cations)

Group 1 Group 2 Group 13

H+ Mg2+ Al3+

Li+ Ca2+

Na+ Sr2+

K+ Ba2+

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Learning Check

A. Number of valence electrons in aluminum1) 1 e- 2) 2 e- 3) 3 e-

B. Change in electrons for octet in aluminum1) lose 3e- 2) gain 3 e- 3) gain 5

e-

C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

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Solution

A. Number of valence electrons in aluminum3) 3 e-

B. Change in aluminum electrons for octet1) lose 3e-

C. Ionic charge of aluminum (13) 3) 3+

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FK

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FK

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FK

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FK

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FK

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FK

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FK

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FK+ _

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FK+ _

The compound potassium fluorideconsists of potassium (K+) ions

and fluoride (F-) ions

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FK+ _

The ionic bond is the attractionbetween the positive K+ ion

and the negative F- ion

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COVALENT BOND

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COVALENT BONDBond formed by the sharing of electrons

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Covalent Bond

• Between nonmetallic elements of similar electronegativity.

• Formed by sharing electron pairs• Stable non-ionizing particles.• Examples; O2, CO2, C2H6, H2O

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Covalent Bond

Non-polar Polar

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when electrons are shared equally

Non-polar Covalent Bonds

H2 or Cl2

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Cl Cl

circle the electrons foreach atom that completestheir octets

The octet is achieved byeach atom sharing theelectron pair in the middle

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Cl Cl

circle the electrons foreach atom that completestheir octets

It is a single bondingThis is the bonding pair

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Cl ClSingle bonds are abbreviated

with a dash

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Oxygen Atom Oxygen Atom

Oxygen Molecule (O2)

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Bonds in all the polyatomic ions and diatomics

are all covalent bonds

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when electrons are shared but shared unequally

Polar Covalent Bonds

H2O

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- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

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1. Define the following:a. Ionic bondb. Covalent bond

Compare between polar and non-polar covalent bond

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METALLIC BOND

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METALLIC BONDBond found in

metals; holds metal atoms together very strongly

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Metallic Bond

• A lattice of positive ions in a sea of electrons

• Formed between atoms of metallic elements• Electron cloud around atoms • Examples; Na, Fe, Al, Au, Co

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Sea of Electrons

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This electrostatic attraction is called metallic bonding and is the reason why the positive metal ions do not repel each other.

The outer shell electrons separate from their atoms and become delocalized, creating a ‘sea of electrons’. The atoms become positive ions and are attracted to these electrons.

metal atoms

sea of free electrons

metal ions

Metallic bonding

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Properties of Metallic Bonds• Good electrical conductors - free electrons

can move through the lattice carrying charge (GR).

• Conduct heat because of free electrons• Lusterous – absorb and emit light in regular

pattern due to free electrons

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• Malleable (can be hammered into different shapes) and ductile ( can be drawn into wires) – not in rigid position so ions can be shaped and drawn into wires

Properties of Metallic Bonds