Chapter 6

What holds a molecule together Why do the H’s & N in NH 3 stay together? Why do the O’s in O 2 stay together? Why do the H’s & O in H 2 O stay together?

The answer is that atoms can share or donate electrons to each other to form chemical bonds. The chemical bonds hold a molecule together! So the amount of electrons s/t has will explain how it bonds

Bonds & Energy If I want to break bonds between atoms in need to put in energy. This means breaking bonds is_________

When bonds are formed between atoms energy is given off.. This mean forming bonds is ___________

Lewis dot structures Since bonds are formed due to electrons we need a simple way to do electron accounting. This is called the lewis diagrams

The Lewis structure is the symbol of the atom surrounded by a dot (or an X) to symbolize the valence electrons If there is 1 valence electrons we will draw 1 dot. 2 valence electrons = 2 dots Etc. up to 8 dots.

Rules for Lewis structrue Each side must receive 1 dot before we double up a dot on a side. Except the first 2 dots can do on the same side.

The octet rule All atoms want to have 8 valence electrons. This is called the octet rule. Atoms will either gain, lose or share electrons to have 8 valence electrons.

Exception Helium (He) wants to have 2 valence electrons. And Hydrogen (H) wants to have either 2 or 0 (more on this later)

Covalent bonds The first type of bonding is when atoms share their valence electrons so that they can have a full octet.

Single covalent bonds If 2 chlorines combine they will both share 1 electron. This is an example of a single covalent bond.

Double covalent bond If 2 oxygens share electrons they will share 2 each. Making a double covalent bond

Triple covalent bond If 2 Nitrogen's share electrons they will share 3 each. Making a triple covalent bond.

RECAP Atoms can share electrons to get to a full octet. They can share 1 each, 2 each or 3 each. Making single, double or triple covalent bonds.

Not all sharing is done equal Just because 2 atoms share electrons, it doesn’t mean they will share the electrons evenly. Some atoms can ‘HOG’ electrons even when sharing.

HOGGING If chlorine shares an electron with a hydrogen, since chlorine has a higher ‘pull’ for electrons (electro negativity), it will hog the electrons.

HOGGING When electrons are shared, but unevenly it is called a POLAR COVANLENT BOND.

If the two atoms sharing have a difference in electro negativity it will always be polar. The stronger one always hogs electrons. The bigger the difference in EN, the more polar it is.

Non polar If two atoms share electrons and they have the exact same EN, they will share the electron exactly evenly.

Polar molecule Even when a substance has polar bonds, it is not automatically an overall polar molecule….

Can you see a difference?

Even when a molecule has polar bonds, if they cancel each other out the molecule will be non polar overall. But if the shape doesn’t cancel out it will be overall polar.

Use lewis structure and draw the following molecules, then decide if they are polar (unbalanced) or not polar (balanced) CO 2 CH 4 HCl NH 3

The rule If the middle atom is bonded to an odd number of molecules (1 or 3) it will be an uneven shape, and polar If the middle molecule is bonded to an even number of partners it will balance out and be not polar.

EXCEPTION!!!! H 2 O, has a weird shape, the hydrogen's are at angles, so it is not balanced, H 2 O is polar

More on covalent bonds When elements make covalent bonds they are called molecular substances. Molecular substances generally are soft, poor conductors of heat and electricity, and have low melting points.

Molecular substances Covalent bonds are formed between non metals only!

Ionic bonds Sometimes atoms will transfer electrons between themselves so that both atoms will have a full octet. For example if Na has 1 valence it will donate it, to get down to a full valence. And Cl has 7 valence it will accept the e- to get up to 8.

Ions When an atom gains or loses an electron it becomes an ION.

Metal Ions Look at the group 1, how many electrons will it want to lose to have an octet? What will its charge be when it becomes an ion?

Metal ions When a metal loses 1 electron it lost a negative charge-----to become positive. Ex: K starts with 19 protons (+) & 19 electrons (-). If it loses 1 electron it has 19 + and 18 – So overall it is +1

When metals lose electron their ions get smaller.

Non metals Non metals want to gain electrons to get a full octet. Sometime instead of sharing electrons (covalent) they will fully ‘steal’ electrons.

Non metal When a non metal becomes an ion it gains an electron. So it gains a negative charge, giving it a minus charge.

Non metal ions EX. Fluorine has 9 protons (+) and 9 electrons (-). If fluorine gains 1 electrons it will have 9 (+) and 10 (-) making it minus 1 overall.

When nonmetals gain electrons they get bigger

Metals Non Metals Lose electrons Gain electrons Become positive Become negative Have smaller radius Have larger Radius Have stable octet Have a stable octet

When atoms form ionic bonds, we can use Lewis diagrams to draw them. qjcCvzWwww

ex Use Lewis diagrams to draw the following ionic substances LiFNaICaOMgS

Polyatomic ions Many times groups of atoms can form big ions, but some of the atoms in the group have covalent bonds. These atoms are listed at the front of your table.

Ionic bonds Ionic bonds are formed only between metals (who lose e-) and non metals (who gain e-) They conduct electricity as a liquid (electrolytes) They have a high melting point.

Metallic bonding So far we have discussed covalent (non metals sharing) Ionic (metals and non metals transferring electrons) The last type is between metals and metals.

Metallic bonding When metals share electrons with other metals its called metallic bonding. In this type the electrons of all atoms are shared between all the atoms. There is a sea of electrons moving all over.

Metallic bonds This is why metals can always conduct electricity because the electrons can always move freely. jf9gMDP47s&feature=related

Intra-molecular forces Until now we have learnt about the bonds that hold 1 molecule together (covalent, ionic and metallic) These bonds are all intermolecular bonds (intra = within)

Intermolecular bonds But there also needs to be a connection that holds different molecules together. What makes all the zillions of molecules of H2O stick together in 1 drop?

Intermolecular bonds The bonds that hold molecules together are called intermolecular bonds (inter = in between)

Intermolecular bonds If a molecule is POLAR (aka lopsided) different sides have different charges (the side that hogs electrons is a little negative and the other is a little positive) These tiny charges can hold lots of molecules together.

Dipole on steroids When one of the molecules really hogs the electrons it becomes very negative. This means that the dipole forces it can form are even stronger regular

These super dipoles only happen when H shares e- with an N,O or F Because these hog electrons so much that the charges are bigger then usual

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Hydrogen bonds H-Bonds are very strong intermolecular forces. This is why water takes so long to boil----because the forces that connect the water are so strong!!

Intermolecular forces and boiling In general the stronger the intermolecular forces between molecules the more energy needed to break them. The stronger the intermolecular forces the higher the boiling point.

Explain the 3 types of intra molecular bonds