C3 Atoms,elements and compounds 3.4 Ions & ionic bonds

C3 Atoms,elements and compounds

3.4 Ions & ionic bonds

Learning objectives• Describe the formation of ions by electron loss or

gain.• Describe the formation of ionic bonds between

metals and non-metals as exemplified by elements from Group 1 and V11.

• Supplement:• Explain the formation of ionic bonds between

metallic & non-metallic elements.• Describe the lattice structure of ionic compounds

as a regular arrangement of alternating positive & negative ions, exemplified by the sodium chloride structure.

Which are atoms, ions or molecules?Put the following particles into the correct column of the table.

C H O H2O

CO2 Na+

Cl2 K+ OH– Mg CH4

atom ion molecule

C3b: How Atoms Combine – Ionic Bonding

IonsAn ion is a charged atom or group of atoms

For example:Cl-, Mg2+, Na+ , SO4

These are all ions because they carry a positive (+) or negative (-) charge.

2-

How are Ions formed?

• Ions are formed when atoms gain or lose electrons

• Positive ions are formed when atoms lose electrons

• Negative ions are formed when atoms gain electrons

Positive and Negative ions

• Positive ions are formed by the loss of electrons from atoms e.g.:

2+ ions form by the loss of 2 electrons

• Negative ions are formed by the gain of electrons by atoms:

2- ion formed by the gain of 2 electronsLook at the 2 following examples …

For e.g. Magnesium

• Mg has 12 electrons• Electron arrangement:• 2, 8, 2• Mg will lose two electrons to form 2, 8• Therefore Mg will have 12 protons and 10

electrons and will an overall +2 charge• Mg Mg+2

Mg

26

12

For e.g. Chlorine

• Cl has 17 electrons• Electron arrangement:• 2, 8, 7• Cl will gain one electron to form 2, 8, 8• Therefore Cl will have 17 protons and 18

electrons and will an overall -1 charge• Cl Cl-1

Cl17

35.5

IonsAn ion is formed when an atom gains or loses electrons and becomes charged:

If we “take away” the electron we’re left with just a positive charge:

This is called an ion (in this case, a positive hydrogen ion)

+-

+

The electron is negatively charged

The proton is positively charged

+

Na Bye!

The Electrons in a Sodium Ion

In the sodium atomatomAtomic number = number of protons = 11 Number of electrons = 11

Electron arrangement: 2.8.1 (Incomplete Shell)

Na+

Electron lost

Electron arrangement: 2.8 (Full Shells)

23

Na11

Stable octet

• When atoms gain or lose electrons to get a complete outer shell they are stable (a stable octet)

• They mimic a noble gas arrangement of electron configuration

Try to draw the formulae of the ion for each atom and then one person can check on the board

(Right click and zoom for bigger animation)

What do you notice? Any pattern?

Types of bonding

Atoms can be joined together in 3 possible ways

All three types involve changes in the electrons in the outermost electron shells of the atoms

Ionic Bonding

Metal and non-metal

Covalent Bonding

Non-metals only

Metallic Bonding

Metals only

IONIC BONDING

Support sheet for foundation: Collins’ Worksheet C3b 2 (Look in this sheet ‘O_C3b_1.doc’

Support sheet for higher: First 3 pages of Ionic and covalent bonding worksheet.doc

Ionic Bonding

• Happens between metals and non-metals• Involves electron transfer • This forms ions – positive & negative• Full outer shells are formed• Resulting in a stable structure

• The positive and negative charges (attractions) constitute the ionic bond

Consider this reaction:

Lithium + Fluorine Lithium Fluoride

How is Lithium Fluoride bonded ?

9p+

10n3p+

4n

Lithium - Li 7

3 Fluorine - F 19

9

Both atoms

are neutral

Same number of protons and electrons

3 protons +

3 electrons –

0 charge

9 protons +

9 electrons –

0 charge

3 protons +

2 electrons –

+1 charge

9 protons +

10 electrons –

-1 charge

FULL OUTER SHELLS ARE MADE, withNOBLE GAS CONFIGURATION

3p+

4n

Lithium ion (Li1+) has same electron configuration as Helium

He2

4(He:2)

9p+

10n

Fluoride ion (F1-) has same electron configuration as Neon

Ne10

20(Ne:2,8)

The ions are held together by electrostatic attraction:

3p+

4n

+ -

9p+

10n

Li+ F-

This is a stable ionic compound

“Dot and cross” model for the ionic bonding in sodium chloride

Formation of sodium chloride1. Formation of sodium ions

Sodium has 1 electron in its outer shell.

If it loses this it will have no partially filled shells.

Loses 1 electron

Sodium 1+ ion (2.8.0)Sodium atom (2.8.1)

This only happens if there is another atom able to accommodate the lost electron.

Na Na+

Formation of sodium chloride 2.Formation of Chloride ions

Chlorine has 7 electrons in its outer shell.

If it gains 1 electron it can achieve a full outer electron shell. It is, therefore, going to be able to accept the electron that the sodium wants to lose.

Chlorine atom (2.8.7)

Gains 1 electron(from sodium)

Chlorine I - ion (2.8.8)

Cl Cl

Formation of Sodium Chloride- the overall process.

ClNa

Na Cl

Sodium loses itsouter electron.Chlorine gains it.The result is both end up with full shells

Two oppositelycharged ionsare formed, which attract.Millions of such pairs form a giant lattice

Simpler electron diagrams

We can assume full inner electron shells. We can therefore sometimes shorten bonding diagrams by omitting to draw the inner electron shells.

Na Cl

Na Cl

Instruction

For each of the following slides state the ions involved. State how many electrons is/are gained/lost by each ion Higher Draw dot and cross diagram for these compounds after looking through these slides: (show charges clearly)sodium chloridemagnesium oxideSodium oxide magnesium chloride

Foundation

NaFLi2O

“Dot and cross” model for the ionic bonding in magnesium oxide

OMg

2.8.2. 2.6

Magnesium atom

Oxygen atom

Bonding in Magnesium Oxide

More than one electron may be transferred between atoms in ionic bonding.

Mg2+ O2-

2.82.8

Magnesium Oxide

Questions1) sodium chloride – done2) magnesium oxide – done3) sodium oxide4) magnesium chloride5) NaF6) Li2O

Draw dot & cross models for the bonding in sodium oxide and magnesium chloride

Sodium oxide ionic bondingSupplement learning objective!

The ions are held together by electrostatic attraction:

Na

+

- 2

O

Na2O

Na

+

Na= 2, 8 Na= 2, 8

O= 2, 8

Magnesium chloride ionic bonding

The ions are held together by electrostatic attraction:

+ 2

Mg

MgCl2Mg= 2, 8

Cl

-

Cl= 2, 8, 8

Cl

-

Cl= 2, 8, 8

Another way of showing it …

Mg

Magnesium chloride:

MgCl2

Cl

Cl

+ Mg

2+

Cl

-

Cl

-

Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:

1. Lithium (2.1) and fluorine (2.7)2. Sodium (2.8.1) and sulphur (2.8.6)3. Magnesium (2.8.2) and sulphur (2.8.6)4. Magnesium (2.8.2) and fluorine (2.7)5. Aluminium (2.8.3) and nitrogen (2.5)

Remember that the total number of electrons lost by the metal must equal the

total number of electrons gained by the non-metal

Activity

• Predict ionic charge from an element’s position in the Periodic Table.

• State the formulae for the ions NO3–; CO3

2–; SO42–; and

NH4+.

- Use these in making compounds (predicting formulae for ionic compounds)

Week 6

© Pearson Education Ltd 2008This document may have been altered from the original

The following table will help you to work out the name of some important compounds. Try the first table, which is easier than the second one. Fill in the formula of each compound in the table:

Chloride, Cl-

Bromide, Br-

Oxide, O2-

Sodium, Na+ NaCl

Magnesium, Mg2+

Aluminium, Al3+

Hint: Use brackets for ions made of group of atoms:

Hydroxide, OH-

Nitrate, NO3

-

Carbonate, CO3

2-Sulphate

, SO42-

Sodium, Na+

Magnesium, Mg2+

Aluminium, Al3+

Ammonium, NH4

+

Positive ions and negative ions attract one another

Ionic Bond Lattices are 3-Dimensional

Ions attract and build into a 2 dimensional sheet.

In fact the whole process will be going on in three dimensions to build up a giant 3-D lattice.

+ -+-

+

--+ +

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

+-+

-

- --+

+

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

+ -+-

+

--+ +

+-+

-

- --+

+

And so on to build a giant 3-D

lattice with millions of ions.

Ionic solids like NaCl and MgO form:

Giant Ionic lattices are held together by strong ionic bonds, which means:

• They have high melting & boiling pointshttp://www.avogadro.co.uk/structure/chemstruc/ionic/g-ionic.htm

Salt – Sodium Chloride

• Common salt contains two ions: sodium (+) and chlorine (-).

• These form giant ionic lattices in which positive ions are electrostatically attracted to negative ions.

Sodium Chloride structure

Properties of Sodium Chloride

• Has a high melting point – due to strong ionic bonds

• Dissolves in water

• When solid does NOT conduct electricity

• Sodium chloride solution conducts electricity.

Sodium chloride conducts electricity when dissolved in water

Magnesium Oxide

• Common salt contains two ions: Magnesium (2+) and Oxide (2-).

• Forms a giant ionic lattice in which positive ions are electrostatically attracted to negative ions.

Magnesium Oxide structure

Properties of Magnesium Oxide

• Has a very high melting point – strong ionic bonds

• When solid does NOT conduct electricity – ions cannot move

• Magnesium oxide and sodium chloride conduct electricity when molten

When ionic bonds in the lattices are broken, the solids MELT.

This means the ions are free to move & can conduct electricity.

Sometimes lattices can be broken by water molecules and the solids dissolve. Again the ions are free to move & can conduct electricity.

Explaining the properties of NaCl and MgO

•Why does MgO have a higher melting point than NaCl ?

•Why does NaCl dissolve in water, and MgO does not ?

NaCl = Na+ Cl-

MgO = Mg2+ O2-

•Greater force of attraction in MgO – 2+ & 2-

•Therefore lattice strength is greater.

QUESTION ?

Practical: C3b solubility and conductivity

• Experimental investigation of solubility and electrical conductivity of solids and solutions

Practical work F&H• (F&H) Do these experiments and record results

clearly in the work sheetsCollins’ Worksheet C3b 6 (two sheets)(H) Same as above but try to explain these:

– Explain the very high melting points of Sodium chloride and magnesium oxide

– Why solid ionic compounds do not conduct electricity

– When a solid ionic compound is melted or dissolved in water it conducts electricity

Answers for the Higher part– There is a very strong attraction

between the positive and negative ions in Sodium chloride and magnesium oxide. To melt these substances these strong attractive forces have to be broken by heating . This is why they have high belting points

– Ions cannot move in solid . This is why a solid ionic compounds do not conduct electricity

– When ionic compounds are melted or dissolved , the ions become free to move. so they conduct electricity

Higher only task • Describe the structure of sodium

chloride and magnesium oxide

Describing structure of solid sodium chloride and magnesium chloride:

The are made of ………….. ionic lattices in which ………… ions e…………………. attarct ………….. ions.

Describing structure of solid sodium chloride and magnesium chloride:

The are made of giant ionic lattices in which positive ions electrostatically attarct negative ions.

Challenge! A book of data gives the following information for two well known ionic compounds:

Compound Melting point (°C) Boiling point (°C)

sodium chloride 808 1465

magnesium oxide 2800 3600

a)Which compound has the higher melting and boiling points?b)Complete this table showing the charges on the ions.c) From your answers in part (b), suggest why magnesium oxide has a higher

melting and boiling point than sodium chloride.

sodium chloride magnesium oxide

Na+

Essential ideas• Ionic bonding is the e………… attraction between a

…………… ion and a negative ion• Ionic bonding is mostly between …………….. and non-

metals. Metals form the …………. ion and non-metals form ………… ions

• Charged particles are called ………………• Li+ is formed by lithium atom ……………… an electron• Cl- atom is formed by …………….. an electron• Solid Sodium chloride and magnesium oxide have very

………….. melting points • Solid sodium chloride and magnesium oxide do not

conduct ……………. as they do not contain freely moving ……….. when they are solids

• When melted or ………………. solid sodium chloride and magnesium oxide conduct electricity

Essential ideas- answers• Ionic bonding is the electrostatic attraction between a

positive ion and a negative ion• Ionic bonding is mostly between metals and

non-metals. Metals form the positive ion and non-metals form negative ions

• Charged particles are called ions • Li+ is formed by lithium atom losing an electron• Cl- atom is formed by gaining an electron• Solid Sodium chloride and magnesium oxide have very

high melting points • Solid sodium chloride and magnesium oxide do not

conduct electricity as they do not contain freely moving ions when they are solids

• When melted or dissolved solid sodium chloride and magnesium oxide conduct electricity

You should know these by now:

1. What is an ion?2. Sodium chloride and magnesium oxide

are examples of …………. Compounds and both have …………. melting points

3. Which one of the above ionic substances dissolves in water?

4. Why do they have very high melting points?

5. Why they do not conduct electricity when they are solids?

6. Why they conduct electricity when melted or dissolved in water?

1. Which of the following is not a sub-atomic particle?

A. Proton.

B. Isotope.

C. Neutron.

D. Electron.

2. The element Cobalt has a relative atomic mass of 59 and an atomic number of 27. Which of these is a true statement about each neutral cobalt atom?

A. It contains 59 neutrons.

B. It contains 27 electrons.

C. It contains 32 protons.

D. It contains equal numbers of neutrons and electrons.

3. The Periodic Table displays iron as shown below. This indicates that Fe atoms:

A. contain 56 neutrons.

B. contain 30 electrons.

C. contain 26 protons.

D. contains more protons than neutrons.

56Fe26

4. Bromine consists of a mixture of two isotopes: Bromine-79 and Bromine-81

• Which of the following is true:

A. Both isotopes contain 35 protons.

B. Bromine 79 contains 46 neutrons.

C. Bromine 81 contains 44 neutrons.

D. Bromine-81 is more reactive than bromine-79.

80Br35

6. Which answer best describes the shell arrangement of the electrons in a sodium atom?

A. 2,8,1.

B. 2,2,7.

C. 2,8,8,3.

D. 2,8,8,1.

23Na11

7. Which answer best describes the shell arrangement of the electrons in an oxygen atom?

A. 2,8,6.

B. 2,8,8.

C. 2,8.

D. 2,6.

16O8

8. Which of these elements will have electron shells that are either full or empty (i.e. not partially full)?

14N7

A 40Ar18

B

40Ca20

C 27Al13

D

9. Which answer best describes the shell arrangement of the electrons in an oxide ion O2-?

A. 2,8,6.

B. 2,8,8.

C. 2,8.

D. 2,6.

16O8