CHEM1101 Lecture Notes - Lecture 7: Matter Wave, Covalent Bond, Hydrogen

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19 May 2018

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Explain how electron sharing leads to lowering of electronic energy in terms of increasing the de Broglie

wavelength

Sharing of electrons

○

2 separate atoms

○

Atoms come together -> sharing of e- -> increased wavelength, decreased energy

○

Nuclei repel each other

○

Molecules contain 2 or more nuclei and 2 or more electrons

○

Covalent bond

•

Pair-wise interactions

•

Electrons and nuclei attract one another. Attractive interactions are energetically favourable, so an electron attracted to anucleus is at lower energy

than a free electron

Electrons repel each other, raising the energy and reducing the stability of a molecule

Nuclei repel each other, so these interactions also reduce the stability of a molecule

These interactions are balanced to give molecule its greatest possible stability

○

Balance is achieved when electron density is situated between the nuclei of bonded atoms

○

Electrons are shared between nuclei - known as shared electron density or covalent bond

○

In any covalent bond the attractive energy between nuclei and electrons exceeds the repulsive energy arising from nuclear-nuclear and

electron-electron interactions

○

Contains 2 nuclei and 2 electrons

As atoms approach, each nucleus attracts opposite electron, pulling 2 atoms closer together

BUT at same time, 2 nuclei repel each other, as do the 2 electrons

Repulsive interactions tend to drive atoms apart

For h2 to be stable, sum of the attractive energies must exceed the sum of the repulsive energies

e.g. Hydrogen molecule

nucleus

electron

attraction

repulsion

De Broglie reasoned that momentum (mv) of a particle should be related to its wavelength, like a proton ie. He

predicted that electrons are wave-like

Photon's momentum (p), related to its energy

Energy of photon --> E=hc/λ

Applying same 2 equations to a particular gives wavelength

P is momentum of the particle

7.1

Wednesday, 24 May 2017

6:43 PM

7. Bonding - MO theory Page 1

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Predict electron configurations and bond orders for diatomic molecules, given a molecular orbital (MO) energy

diagram

Electron figuration: 1s22s1

Bond order:

= 4-2

7.2

Wednesday, 24 May 2017

9:20 PM

7. Bonding - MO theory Page 2

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Document Summary

Explain how electron sharing leads to lowering of electronic energy in terms of increasing the de broglie wavelength. Atoms come together -> sharing of e- -> increased wavelength, decreased energy. Molecules contain 2 or more nuclei and 2 or more electrons. Attractive interactions are energetically favourable, so an electron attracted to a nucleus is at lower energy than a free electron. Electrons repel each other, raising the energy and reducing the stability of a molecule. Nuclei repel each other, so these interactions also reduce the stability of a molecule. These interactions are balanced to give molecule its greatest possible stability. Balance is achieved when electron density is situated between the nuclei of bonded atoms. Electrons are shared between nuclei - known as shared electron density or covalent bond. In any covalent bond the attractive energy between nuclei and electrons exceeds the repulsive energy arising from nuclear-nuclear and electron-electron interactions e. g. hydrogen molecule.

Related Questions

Chemistry 162 Lab Activity

Introduction Water has an amazing ability to adhere (stick) toitself and to other substances. Hydrogen bonds form when hydrogenatoms covalently bonded to nitrogen (N), oxygen (O), or fluorine(F) in the form of covalent compounds such as ammonia (NH3), water(H2O) and hydrogen fluoride gas (HF). In these molecules, thehydrogen atoms do not pull as strongly on the shared electrons asthe N, O, or F atoms. Therefore, the molecules are polar; thehydrogen atoms become positively charged and are able to formhydrogen bonds to negative ions or negatively charged parts ofother molecules (such as the N, O, and F atoms that becomenegatively charged in these compounds). Hydrogen bonds are not truebonds like covalent bonds or ionic bonds. Hydrogen bonds areattractions of electrostatic force caused by the difference incharge between slightly positive hydrogen ions and other, slightlynegative ions. These attractions are much weaker than true ionic orcovalent bonds, but they are strong enough to result in someinteresting properties.

In the case of water, hydrogen bonds form between neighboringhydrogen and oxygen atoms of adjacent water molecules. Theattraction between individual water molecules creates a bond knownas a hydrogen bond (Fig. 1).
Fig. 1: Hydrogen bonds shown as the dotted lines between watermolecules.
Cohesion Molecules of pure substances are attracted to themselves.This sticking together of like substances is called cohesion.Depending on how attracted molecules of the same substance are toone another, the substance will be more or less cohesive. Hydrogenbonds cause water to be exceptionally attracted to each other.Therefore, water is very cohesive.
Adhesion Adhesion is similar to cohesion, but it involves unlike(i.e. different) substances sticking together. Water is veryadhesive; it sticks well to a variety of different substances.Water sticks to other things for the same reason it sticks toitself â because it is polar so it is attracted to substances thathave charges. In this lab activity, you will be asked to use thematerials and procedures provided to explore the properties ofwater that involve both cohesion and adhesion. Be sure to writedown your observations and results as you progress. sults as youprogress.

Fig. 1

Hydrogen bonds shown as the dotted

lines between water molecules.

Part 1:

Exploring Water

Procedure

How many drops of water can you fit on the surface of a pennywithout the water spilling over?

Predict how many drops of water will fit on a penny. Record yourprediction.

Use the plastic pipette to drop water on the surface of a penny.Drop car

efully and slowly to fit as

many drops as possible on the penny. Count each drop until thewater spills over the side of the

penny and record your results.

Compare your results to those of your classmates. Record therange and calculate the average

number

of drops that fit on a penny.

Add more drops to the penny, without letting the water spillover. Carefully observe and draw the

water on the penny.

Record

a hypothesis for the behavior of water that you observed, usingthe language of cohesion

and adhesion

in relation to the water and the penny.

Record your results and

thinking in your notebook.

Can you

disturb

the water on the penny without spilling it?

dd drops of water to the penny, until the water is almost readyto spill over.

Predict what will

happen when you insert a toothpick into the surface of the waterpiled on the

penny. Record your prediction.

Insert the

toothpick

and carefully observe the surface of the water.

Try inserting the

toothpick

in various ways. Observe the surface of the water.

Pay special attention to

the water surface where the skewer enters the water.

Record your observations and draw what you see.

Repeat

these

procedures using a paper clip and the metal clip part of abinder clip. Try to indent the

pile of water as much as p

ossible without spilling it.

Record your observations and dra

w what you see, paying careful

attention to the surface of the

water.

Record

a hypothesis for the behavior of water that you observed usingthe language of cohesion

and adhesion in relation to the

toothpick

, the paperclip, the binder clip, and the water.

Record your results and

thinking in your notebook.would you please answer the questionfor me . Thanks

CHEM1101 Lecture Notes - Lecture 7: Matter Wave, Covalent Bond, Hydrogen

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