Ionic and Covalent Bonding Science 10

Valence e- what do we know…

• Which group on the periodic table, do you notice, always has all it’s valence electron shell full?

•  The Noble Gases. This is very significant… Why??

• Because every element wants to have a full outer shell of valence e- – because then it is completely stable and never has to react. Every element wants to be a noble gas

So what happens when atoms meet?

• When 2 atoms move close together, their valence electrons interact, and they form a chemical bond between them if they are a good pair (more stable together than apart)

• Having a full valence shell is what each element wants! So it will bind with other elements that make that happen!

Ionic Compounds2 or more elements bonded together where at least 1 is a metal and 1 is a non-metalEg. NaCl, LiF

Covalent Compounds2 or more elements bonded together where all are non-metals.Eg. CCl4, NiF2

IonsThey are Atoms that have a + or – charge (due to losing or gaining electrons) -they are no longer neutral.

• When atoms have the same # of protons and electrons – the atom is neutral. And it is called an ATOM.• When an atom loses or gains electrons from another element – it gets a charge and is now called an ION.• Ions form when a METAL and a NON-METAL combine to form a new compound. They create an IONIC BOND between them.• In an ionic bond, e- are transferred (not shared)

BERYLLIUM ATOM

BERYLLIUM ION

2 positive protons left over… so …

2+

Why might Beryllium want to only have 2 e- instead of

the original 4?

Let’s recap…

ATOM•No charge(Neutral)• Same # of protons as electrons

ION•Has a charge (Not Neutral)•Protons stay the same, but a different # of electrons

+Or -

So how did the Ion get a charge?• Every atom in the periodic table wants to be just like the nearest NOBLE GAS, because it has full outer shell of e- and is stable – that is what every atom wants.•Notice that the metals have more electrons than the stable noble gas, and that non-metals don’t have enough electrons to be a noble gas.

• Metals tend to give up e- to become more stable (metals are givers - positive elements)• Non-metals tend to gain or take e-

to become more stable. (non-metals are takers – negative elements)

P: 11N:12

What do you notice about these 2 elements??

P: 17N:19

Sodium Atom Chlorine AtomIf Sodium loses 1e-, it would look like Neon (a noble gas with 10e-)

If Chlorine gains 1e-, it would look like Argon (a noble gas with 18e-)

Atom 11 e-

Atom 17 e-

ION10 e-

ION18 e-

So why does Na get a + charge??

-Because it gave up an electron ( got rid of a “-” charge) – so it now has 1 more proton than e-, so 1+ charge!* Remember – Givers are happy (POSITIVE)*Sharing is caring!!

Chlorine is a taker – takers are selfish and are very negative. Chlorine has received an extra e-, so it’s got more e- than p+, so it’s 1-.

We form NaCl

P: 11N:12

What do they look like now that they have become IONS??

P: 17N:19

Sodium ION 1+

Chlorine ION 1-

Two types of Ions

•Metals that give up e- to form “+” charged IONS are called CATIONS•Eg. Mg2+, Li1+, Al3+, etc…

•Non-metals that take e- to form “-” charge IONS are called ANIONS•Eg. S2- , F1- , N3-, etc…

Let’s recap…• Givers of e-• They are losing e-• Become positive• The # of e- they lose, is the number of + charges they get.• Eg. Give up 3 e- = 3+ charge• Called Cations

• Takers of e-• They are gaining e-• Become negative• The # of e- they gain, is the number of - charges they get.• Eg. Take 3 e- = 3- charge• Called Anions

Take a look…

• Bohr model of a SODIUM “ATOM”

• All e- there (11).• Na

• Bohr model of SODIUM “ION”

• 1 valence e- gone (now 10 e-)

• Na 1+

P: 11N:12

P: 11N:12

+1

Now you try it…

• Bohr model of a Magnesium “ATOM”

• All e- there (12).

• Bohr model of Magnesium “ION”

• 2 valence e- gone (now 10e-) like Neon

• Mg 2+

P: 12N:12

P: 12N:12

+2

Try again…

• Bohr model of a Oxygen “ATOM”

• All e- there (8).

• Bohr model of Oxygen “ION”

• 2 valence e- added (now 10 e-) –like Neon!

• O 2-

P: 8N:8

P: 8N:8

-2

Let’s Recap…• All elements want to have a full outer shell of valence e-, just like their nearest noble gas.• If an element gives up e-, it becomes an ION with a + charge (CATION)• If an element takes an e-, it becomes an ION with a – charge (ANION)

• Notice that the ion charges of each element are given on your periodic table in the top right hand corner – called the COMBINING CAPACITY.• The combining capacity helps you predict the # of e- the element will gain or lose.

But wait a minute…• Notice on your

periodic table, that many of the transition metals have more that 1 charge/combining capacity. • That means that

they can form ions in more than 1 way. Elements with more than 1 charge are called MULTI-VALENT.

• Eg. Iron (Fe) is multivalent because it has a charge of 2+ or 3+, so it can either lose 2 e- or 3 e- to become Fe 2+ or Fe 3+

• It just depends on what it bonds with.

2+3+

Ions worksheet!

Can you answer these questions…• Can you draw the Bohr model of H2?

• Why would 2 Hydrogens be happy to bond together?

1p+0n

1p+0n

Try some for Lewis …• Remember, up to 4 e-, you put separately on each side of the

symbol, once you get to 5, you have to start pairing up.

1) Magnesium Ion 2) Nitrogen Ion

3) Fluorine Ion 4) Argon Ion?

Mg N

F Ar

2+ 3-

1-

Lewis Diagrams of ions• Lewis diagrams make drawing ions, and ionic bonds much less work

than Bohr diagrams.

Be Cl• •

•• •

• •

• •• •• •

• •

Each beryllium has two electrons to transfer

away, and each chlorine wants one more electron

BeCl Cl• •

• •• •

• •

•• •

• • BeCl Cl• •

•• •

• •

Since Be2+ wants to donate 2 electrons and

each Cl– wants to accept only one, two Cl– ions are

necessary

Beryllium chloride

2+ ––• •

• •• •

• •

• •• •• •

• •

• •• •• •

• •

Ionic Compounds

Mg + O OMg1.2+ 2-

Unpaired electronOr bonding pair

Lewis Diagrams of covalent bonds

• Lewis diagrams of covalent bonds are also very easy.• Like Bohr diagrams, valence electrons are drawn to

show sharing of electrons.• All atoms wish to have a full valence shell (1st orbit=2

e-, 2nd=8e-)• The shared pairs of electrons are usually drawn as a

straight line

SHARING IS CARING!!

Covalent Compounds

1. N + H NH HH

Bonding Pair

Lewis Diagrams of diatomic molecules

• •• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O

Several non-metals join to form diatomic

molecules

Valence electrons are shared, here in two

pairs!

This is drawn as a double bond

• Diatomic molecules: 2 of the same element are bonded

• Eg. Cl2, F2, O2, etc..• Try 2 Oxygens together (remember they both

want 8, so how are they going to share?)

Diatomic Compounds

+ F F F F

Remember when it’s a diatomic compound – you draw the 1 lines between them! (Symbolizing the 4 electrons sharing!!)

Practice Questions• Answer all the questions!