Pre-Class:Answer one of these two questions:

• What is the capacity of each of the first three energy levels?

• What does “valence” mean (in chemistry)?

Also, get your periodic tables.

Today is Thursday,September 17th, 2015

In This Lesson:Bonding

(Lesson 4 of 9)

Today’s Agenda

• Bonding– Aww… :)

• Forces sort of like bonding• Properties of water (the very basics)– Almost near the living stuff!

• Where is this in my book?– P. 22 and following…

By the end of this lesson…

• You should be able to describe three bonds and an intermolecular force that allow elements and compounds adhere to one another.

Bonding

• Bonding is what forms compounds.• Once a compound is formed and we write its

chemical formula, we can see how many atoms of each element are in it:– H2O – 2 Hydrogen, 1 Oxygen

– CO2 – 1 Carbon, 2 Oxygen

– H2SO4 – 2 Hydrogen, 1 Sulfur, 4 Oxygen

– C6H12O6 – 6 Carbon, 12 Hydrogen, 6 Oxygen

Things We Know

• After so much information recently, here’s some things we know, and that we’ll need for future information:– Ions are atoms out of balance. They either have

greater or fewer electrons than “normal.”– Valence electrons are the ones located in the

outermost energy level.– Atoms “want” to fill their valence shells, either

by dropping extra electrons or adding more.• This makes them STABLE.

Bonding

• There are three main kinds of bonds we’ll talk about briefly in this class, and here they are:– Ionic– Covalent– Hydrogen

• Plus one more thing that holds stuff together but really isn’t a bond.

Bonding

• Before we talk in detail about Ionic Bonding, let’s watch a short clip from NOVA about how the bonds work.– It’s a good overview for bonds in general.

Bonding

• Let’s start with Ionic Bonding.• Ionic bonding is when electrons are

transferred from one atom to another.• Involves oppositely charged atoms.– Positive atom meets negative atom.– Example: Na+ plus Cl- = NaCl (salt)– Animation on next slide…

BondsIonic

How to remember: Ions are selfish

Ionic Bonds• Sodium has 1 valence electron, Chlorine has 7.• Sodium is looking to lose an electron, Chlorine

to gain an electron.

Ionic Bonds

• So Sodium transfers an electron to Chlorine.

Ionic Bonds

• Another look at it:

Predicting Ionic Bonds

• Generally speaking, you can tell what kind of charge an atom likes to form by how many valence electrons it has.

Positive and Negative

• Think of Calcium. How many valence electrons does it have?• 2.

• Is it easier for it to gain six valence electrons to be like Krypton or to lose two to be like Argon?• Lose 2.

• And if it loses 2 negatively-charged electrons, what ionic charge does it now have?• 2+

http://chemicalelements.com/elements/ca.html

Positive and Negative

• Think of Nitrogen. How many valence electrons does it have?• 5.

• Is it easier for it to gain three valence electrons to be like Neon or to lose five to be like Helium?• Gain 3.

• And if it gains 3 negatively-charged electrons, what ionic charge does it now have?• 3-

http://chemicalelements.com/elements/n.html

Lose Electrons Gain Electrons

Form 1+ ions.Form 2+ ions. Form 3+ ions.Do Not IonizeForm 3- ions.Form 2- ions.Form 1- ions.Do Not Ionize

Ionic Bonds

• Summarizing Ionic Bonds:– Typically positive atom + negative atom.• Usually opposite ends of the Periodic Table.

– Electrons are transferred.– Bond is formed because of the attraction between

positive and negative.• Like the opposite poles of magnets.

Ionic Bonding Animation

• Ionic Bonding Animation – Teacher’s Domain

Covalent Bonds

• What does the word covalent sound like?– Think of it as co-valence.

• In a covalent bond, electrons are shared.• Both nuclei are pulling on the electrons being

shared, but neither can quite take it away.– This “tug of war” between the atoms is what

bonds them together.– Animation on next slide.

BondsCovalent

How to remember: covalent = cooperative

Covalent Bonds

• What it looks like:

Notice that eventhough only oneelectron is neededby each, theatoms share two.

http://www.ider.herts.ac.uk/school/courseware/materials/images/covalent_bonding.gif

Covalent Bonds• In this example, oxygen has 6 valence

electrons. It needs two electrons.• Each hydrogen has one valence electron. They

both need one electron each.

Important: Water is held together by

covalent bonds.

Covalent Bonds

• Covalent Bonding Animation – Teacher’s Domain

Another Covalent Bond Example

• Methane – CH4 – 1 Carbon, 4 Hydrogen

• Methane is a key ingredient in…?– Farts! (seriously)

Carbon

• Why is carbon special?– 4 valence electrons– Valence shell can hold 8 electrons– Carbon can bond to lots of other atoms/molecules

on each side.

C C CH H H

HH HH

H Propane

Carbon

• What you need to know:– Carbon is special because it can make long chains

or rings by bonding to other carbons and many other atoms.

– This is part of the reason carbon supports life. We’ll learn more about these carbon-based molecules in a few lessons.

Carbon’s Special

• CrashCourse – That’s Why Carbon is a Tramp

Double Bonds

• Covalent bonds can sometimes be double bonds.

• Notice how the atoms share two pairs of electrons (instead of just one pair).

Triple Bonds

• Sometimes there can also be triple bonds.• Three pairs of electrons are shared.

Covalent Bonds

• Summarizing Covalent Bonds:– Typically between two atoms that both have near-

capacity valence electrons.– Electrons are shared (or fought-over), and that

sharing (or fighting) is what keeps the atoms together.

– Double and triple bonds form when two atoms share more than one pair of electrons between them.

One last one…

• There’s also the hydrogen bond. It’s very simple.

• It’s actually a bond between molecules (not between atoms within one molecule).

• Here it is…

BondsHydrogen

How to remember: Hydrogen bonds are strong bonds between molecules involving hydrogen (and usually O, N, F). Just remember that.

It’s not quite a bond, but…

• There’s also this force called the van der Waals force.

• This is a force that holds molecules together due to weak forces between oppositely charged regions of different molecules.– In other words, the protons of one atom *slightly*

hold onto the electrons of another atom.– Generally a weak force, and not a conventional

bond.

Van der Waals Force

Van der Waals Forces

• Where do we see van der Waals forces in nature?– Geckos, for one!

http://duende.uoregon.edu/~hsu/blogfiles/gecko.jpg http://cdn.physorg.com/newman/gfx/news/2005/gecko.jpg

Geckos

Quia Activities

• One computer per pair.• Start with Battleship (1 player – work together):– Atomic Structure and Electron Configuration

Battleship• Move on to Battleship (1 player – work together):– Bond Battleship

• Move on to the Challenge Board (2 player):– Atomic Structure, Bonds, and Electron Configuration

Challenge Board

Closure

• Dogs Teaching Chemistry