Types of Chemical Bonds

Honors Chemistry/Biology10th grade - Ferguson

What is a Chemical Bond?• The interaction between

electrons of different atoms.• The electron cloud of an atom reacts to

any electric charge, not just that of its own nucleus.–Can even react to the positive charge of another atom’s nucleus.

• There are different kinds of interactions between atoms depending on the elements.

Electrons have a negative electric charge.

If negative charges repel each other,

how does an atom stay together?

proton: a tiny particle in the nucleus that has a positive charge.

neutral: having zero total electric charge.

Protons in the nucleus have a positive electric charge.

Electrons have a negative electric charge.

Because the electrons have energy and momentum

- The same reason why the Earth does not fall into the sun, but gravitates around it instead.

Why don’t the negative electrons “fall” into the positive nucleus?

Electrons are responsible for bond formation.

Electrons can be:

+-

Enthalpy of formation

∆Hf (kJ/mole)

Chemical bonds form because there is an advantage in energy.

Lower energy =

more stable

Metals are good conductors of electricity and heat

Density

Hardness

Elasticity

Transparency

Strength

Electrical conductivity

Thermal conductivity

Physical properties of Metals

Why?

Metallic bonding

Metallic bonding

Metallic bonding

Electrons are small, light, and therefore fast

They can carry energy quickly Thermal conductivity

They can carry charges quickly Electrical conductivity

Metallic bonding

Solo (unbonded) metal atom

Metals have low ionization energies;

valence electrons are not strongly bound

to their parent atoms.

A metal is like a fixed lattice of positive ions in a sea of free electrons

Ionic Bonds• Occurs between a metal and non-metal.• Happen when one or more electrons are

transferred between atoms.• Causes one atom to become positive, and one to

become negative.• The oppositely charged ions are now attracted to

each other.

In ionic compounds, electrons are NOT SHARED but TRANSFERRED.

1 electron

Sodium ion Chloride ion

Cl –1+1Na

Sodium atom Chlorine atom

Ionic bond

ClNa

Ionic Bond Example:

In ionic compounds, electrons are NOT SHARED but TRANSFERRED.

Magnesium chloride (MgCl2) is also an ionic compound.

Magnesium ion

1 electron 1 electron

+2Mg–1Chloride ion Cl Cl –1 Chloride ion

Chloride atomChloride atom Mg

Magnesium atom

Cl Cl

Ionic bondIonic bond

Covalent Bonds• Occurs between 2 non-metals.• When electrons are shared between

atoms to fill the outer shell of each.• As 2 atoms approach each other,

each nucleus begins to tug on the other’s electrons. Eventually, the orbitals overlap, forming a covalent bond.

Covalent Bond Example:

Covalent bondsA chemical bond is formed by sharing or transferring electrons.

covalent bond: a chemical bond that consists of two shared electrons.

molecule: a neutral group of atoms bonded together by covalent bonds.

There are two covalent bonds in a water molecule.

Polar Covalent Bonds• In polar bonds, electrons are not

shared equally between the atoms.

• Occur when there is a large difference in electronegativity.

• As a result, polar bonds have dipoles (positive and negative ends).

Non-Polar Covalent Bonds

• When there is little difference in the electronegativity.

• Electrons are equally shared between the atoms.

Single bonds

Double bond Triple bond

Some elements can share multiple electrons

with the same atom.

Multiple bonds

Determining Polarity• Electronegativity differences between

atoms sharing electrons can predict polarity.

Use numbers from pg 204 in textbookBond Type Electronegativity Difference

Non-polar covalent

Less than 0.5

Polar covalent

Between 0.5-1.7

Ionic Larger difference due to a bond between a metal and a non-metal atom

Polar and Non-Polar Bonds

• 4.0 – 4.0 = 0• Non-Polar

Bond

• 4.0 – 2.1 = 1.9

• Polar Bond

Valence Electrons and Bonding Patterns

• Only unpaired valence electrons bond.

• In a molecular compound, each unpaired electron can form one covalent bond.

• In the diagram to the right, the arrow shows which way the shared electrons are being pulled in the polar bond.

• The q+ and q- indicate the partial positive and negative ends of the molecule.

q+ q-

Determining if a Molecule has Polar Geometry

1. If all bonds in the molecule are non-polar, then the whole molecule is non-polar.

2. If there are polar bonds, but there is symmetry in the molecule, then the molecule is non-polar.

3. If there are polar bonds, but there is no symmetry, the molecule is polar.

Molecular Geometries

When all attached atoms are the same…

Symmetrical Not Symmetrical

Tetrahedral Trigonal Pyramidal

Trigonal Planar Bent

Linear

Carbon Dioxide

Each C-O bond is polar, however the symmetry of the molecule leads to the bonds cancelling each other out. Therefore, CO2 is a non-polar molecule.

Water

Each O-H bond is polar, and the molecule is not symmetrical, so water is a polar molecule.

CH4 CCl4 CH3F

Non-Polar Bonds

Polar Bonds C-F bond is polar

C-H bonds are not

Symmetrical Symmetrical Not Symmetrical

Non-Polar Molecule

Non-Polar Molecule

Polar Molecule

Learning Check1. Which electrons are involved in bonding?2. What is the difference between ionic and

covalent bonds?3. What determines polarity?4. Hydrogen and Carbon bond together. What kind

of bond is this?5. Sodium and Fluorine bond together. What kind

of bond is this?6. How many bonds does Potassium make?7. How many bonds does Aluminum make?8. How many bonds does Sulfur make?9. How many bonds does Neon make?