C3 Atoms, elements & compounds

C3 Atoms, elements & compounds

3.5: Molecules & Covalent bonds3.6: Giant Structures

Req-giant structure

3.5: Learning Objectives

• State that non-metallic elements form non-ionic compounds using a different type of bonding called covalent bonding.

• Describe the differences in volatility, solubility and electrical conductivity between ionic & covalent compounds. (H/W)


• Supplement:

• Draw dot-and-cross diagrams to represent the sharing of electron pairs to form single covalent bonds in simple molecules, exemplified by Cl2, H2O, CH4, HCl.

• Draw dot-and-cross diagrams to represent the multiple bonding in N2, C2H4 & CO2

Covalent bonding in hydrogen chloride

Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell.

H

(2)

Cl

(2,8,8)

H-ClCl

(2,8,7)

H

(1)

(H) Draw dot and cross diagrams for the following molecules and check your answers with the following slides (right click to zoom)

N2, C2H4 N2, C2H4

N2 C2H4

Chemical formula of elements• Each element has a symbol.

• Some elements exist as particular numbers of atoms bonded together.

• This fact can be represented in a formula with a number which shows how many atoms.

O

N

H H H

P

N N

FormulaMoleculeAtom

O O

P PP

P

O2

N2

H2

P4

The formula of molecular compounds

Water

Carbon dioxide

Methane

FormulaName

C H

H

H

H

CO O

H

HO

• Molecular compounds have formulae that show the type and number of atoms that they are made up from.

CH4

CO2

H2O

1. Octane• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

2. Propane• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

3. Ethanoic acid• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

4. Hydrogen peroxide• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

4. Ethene• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

5. Methanol• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

4.1

20.08.12 Bonding Answer the questions below

1. Write down the formula that contains 4 elements. 2. Write down the formula that is made up of 5 atoms. 3. Write down the formula that is a hydrocarbon.4. Write down the formula that is made up of two elements and two

atoms in total

Basic ideas- match up

Atom

Ion

Molecule

H2O

Na+

He

3. Ethanoic acid• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

4. Hydrogen peroxide• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

4. Ethene• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

5. Methanol• The molecular formula of this compound:• The number of different elements present in this compound:• Names of each element and how many atoms of each

element:

C3: Covalent bonding

Non-metals combine together by sharing electrons and this is called covalent bonding

How is HCl bonded?

• HCl



H

(2)

Cl

(2,8,8)

H-ClCl

(2,8,7)

H

(1)

Covalent compounds

• Covalent compounds are formed when non-metal atoms react together.

• As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms.

• The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells. (Duplet 2 ) (Octet 8)

Covalent bonds

• Covalent compounds are held together by this sharing of electrons.

• A pair of electrons shared in this way is known as a covalent bondcovalent bond..

• It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a pair of electrons (xx) or even just a line (see figure 2).

FX

X F FF-Figure 1 Figure 2



H

(2)

Cl

(2,8,8)

H-ClCl

(2,8,7)

H

(1)



• Supplement:

• Draw dot-and-cross diagrams to represent the sharing of electron pairs to form single covalent bonds in simple molecules, exemplified by Cl2, H2O, CH4, HCl.

• Draw dot-and-cross diagrams to represent the multiple bonding in N2, C2H4 & CO2

• HCl.

• Cl2• H2O,

• CH4

• N2

• C2H4

• CO2

Ionic & covalent bonding

• When an atom of a metal joins with an atom of a non-metal an ionic bond is formed.

• When 2 non-metals combine they share electrons to form a covalent bond. The atoms join to form a molecule.

Covalent Bonding

• This involves electrons being shared• Full outer shells are formed.

• Resulting in a stable structure• Covalent bonds are made between atoms

of non-metals

• Examples of molecules with covalent bonds include: Water and Carbon dioxide

Basic ideas1. Elements are chemically joined to make …………..2. The connection between the atoms in a compound is called a …………….. bond 3. There are two types of this: ……………… bonding and ...………… bonding 4. The type of chemical bonding between metals and non-metals is ……………. and the type of

chemical bonding between non-metals is …………………5. A substance that is made of two or more atoms bonded together is called a m……………..

Basic ideas1. Elements are chemically joined to make compound 2. The connection between the atoms in a compound is called a chemical bond 3. There are two types of this: covalent bonding and ionic bonding 4. The type of chemical bonding between metals and non-metals is ionic and the type

of chemical bonding between non-metals is covalent5. A substance that is made of two or more atoms bonded together is called a molecule

C3: Covalent bonding

Non-metals combine together by sharing electrons and this is called covalent bonding

Covalent compounds

• Covalent compounds are formed when non-metal atoms react together.

• As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms.

• The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells. (Duplet 2 ) (Octet 8)

Covalent bonds

• Covalent compounds are held together by this sharing of electrons.

• A pair of electrons shared in this way is known as a covalent bondcovalent bond..

• It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a pair of electrons (xx) or even just a line (see figure 2).

FX

X F FF-Figure 1 Figure 2



H

(2)

Cl

(2,8,8)

H-ClCl

(2,8,7)

H

(1)


Covalent bonding in hydrogen – H2

Hydrogen (1) needs 1 more electron to attain a full outer shell.

H

(2)

H-HH

(1)

H

(1)H

(2)

Covalent bonding in chlorine Cl2

Chlorine (2.8.7) needs 1 more electron to attain a full electron shell.

Cl

(2,8,7)

Cl

(2,8,7)

Cl

(2,8,8)

Cl

(2,8,8)

Cl-Cl

• Hydrogen (1) needs 1 more electron.

• How many does carbon (2,4) need?

• How many hydrogens per 1 carbon?

• Draw bonding diagrams for methane – CH4.

4

4

C H

H

H

H

C H

H

H

H

C OO

Represented as = C OO

Covalent bonding in Carbon dioxide – CO2

Carbon needs 4 more electrons but oxygen (2.6) needs 2 more. Therefore, we need 2 oxygen's.

4 electrons: Double covalent bond

4 electrons: Double covalent bond

Covalent bonding in water – H2O

Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more. Therefore, we need 2 hydrogen's.

O H

H

O H

H

O

H

H

Covalent bonding - multiple bonds

• Mostly electrons are shared as pairs.

• There are some compounds where they are shared in fours or even sixes.

• This gives rise to single, double and triple covalent bonds.• Again, each pair of electrons is often represented by a

single line when doing simple diagrams of molecules.

Cl-ClSingle bond

O=ODouble bond

N=NTriple bond

Task

• Can you draw a dot and cross diagram for Oxygen

• Nitrogen• Ethene C2H4

• HCl

Covalent bonding in oxygen

Oxygen (2.8.6) needs 2 more electrons to attain a full electron shell.

OO O=O

OO

4 electrons

(Higher) Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond.Draw a bonding diagram of nitrogen.

6 electrons

NN

N N

N=N

Nitrogen

Supplement• Ensure you can draw structures for the following:• Remember the exam is not restricted to using only

these! So practice and ensure you understand this!

• Chlorine• Water• Methane• Hydrogen Chloride• Nitrogen• Ethene• Carbon Dioxide

Covalent bonding animation

• sc_ocr_c3c2

http://www.gatewayscienceonline.co.uk/ctrl/science/preview/preview?cs=0&c=15&ct=c&node=a368&page=0

1. Hydrogen fluoride (HF)

2. Hydrogen sulphide (H2S)

3. Ethane (C2H6 and the carbons are joined by a single covalent bond)

4. Carbon dioxide (CO2 and the carbon oxygen bonds are double bonds)

H F

H HS

H

H

H H

H

HC C CO O

Draw ‘dot and cross’ type bonding diagrams for each of the following:

3.6 GIANT STRUCTURESLearning objectives

• Supplement only:

• Describe the giant covalent structures of graphite & diamond.

• Relate their structures to the use of graphite as a lubricant and of diamond in cutting.

• Describe the structure of Silicon (IV) Oxide (Silicon dioxide)

Research Task

• Research the following:

• Structures of Diamond, Graphite & Silicon (IV) Oxide (Silicon Dioxide).

• Relate the structure to the use of Diamond & Graphite.

Small covalent structures

• Sometimes just a few atoms join together in this way.

• This produces small covalent molecules – often known as simple molecular structures.

a simple molecularstructure

covalent bonds

Giant covalent structures

• Sometimes millions of atoms are joined together by covalent bonds.

• This produces a rigid 3-D network called a giant latticegiant lattice..

a giant lattice

covalent bonds

Giant covalent structures: diamond

• One form of carbon is diamond.

• Each diamond consists of millions of carbon atoms bonded into a single giant structure.

• It is veryvery hard.

Diamondstrong

covalentbonds

carbon atoms

Giant covalent structures: graphite

• A more common form of carbon is graphite.

• Millions of carbon atoms are bonded into a giant structure but within this structure the layers are only weakly joined.

Graphitestrong

covalentbonds

carbon atoms

weakattraction

Giant covalent structures: carbon footballs!

• During the last 20 years new forms of carbon have been discovered some of which have “closed cage” arrangements of the atoms.

• These are large but are not really giant molecules.

One of them contains 60 carbon atoms and bears remarkable similarities to a football!

Giant covalent structures: sand

• Sand is an impure form of silicon dioxide.

• Although it is a compound, it has a giant covalent structure with certain similarities to diamond.

silicon atoms

oxygen atoms

BONDING AND PHYSICAL PROPERTIES

Metallic bonding

• Metal atoms form a giant lattice similar to ionic compounds.

• The outermost electrons on each metal are free to move throughout the structure and form a “sea of electrons”.

• Having released electrons into this “sea” the metal atoms are left with a + charge.

= positively charged metal ion

Metallic bonding is the attraction of + metal ions for the “sea of electrons.”

Bonding and physical properties

These are things such as:

• Density• Conductivity• Malleability/ brittleness• Melting point

The type of structure that substances have has a huge effect upon physical properties.

The next few slides illustrate just a few of the general patterns.

Bonding & physical propertiesHARDNESS, WHY?

CONDUCT ELECTRICITY

MELTING POINT /BOILING POINT

DISSOLVE

IONIC

GIANT COVALENT

SIMPLE COVALENT

METALLIC

Simple covalent compounds

Carbon dioxide and water are simple covalent molecules

Carbon dioxide does not conduct electricity

Unlike ions, Carbon dioxide does not have a charge or free electrons and so does not conduct electricity

CO O

Covalent bonds

Water does not conduct electricity

Unlike ions, Water does not have a charge or free electrons and so does not conduct electricity

Intermolecular forces in CO2 and H2O

• Carbon dioxide and water have weak intermolecular forces between molecules.

• Understanding this can help explain the properties of CO2 and H2O

Intermolecular Forces

• First we must learn about intermolecular forces:

• Intermolecular forces are forces which act between whole molecules

• Look at the following slides

Intermolecular forces between Water molecules

Intermolecular forces between hydrocarbon molecules

Carbon dioxide is a molecule:•It has LOW MELTING &….

•BOILING POINT. (that’s why it’s a gas)

•This is because of the WEAK forces of attraction BETWEEN the molecules – WEAK INTERMOLECULAR BONDS

CO2

CO2

CO2

Carbon dioxide – CO2 – is a GAS at room temperature, with a low M.P, this is due to weak intermolecular bonds.

Water – H2O – is a LIQUID at room temperature, with a low M.P, this is due to weak intermolecular bonds, BUT stronger than CO2.

CO2

CO2

CO2

CO2

CO2

H2O H2O

H2OH2O

H2O

Relating the properties of carbon dioxide and water to their structure

• The weak intermolecular forces in CO2 and H2O mean these simple molecules have low melting points

• There are no free electrons so both do not conduct electricity.

• Generally substances with giant structures have high melting points and boiling points.

• Small molecules have melting points and boiling points that increase as the size of the molecule increases.

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

In giant structures all the atoms are tightly bonded together. Usually they are high melting-point solids.

Small molecules tend to be gas, liquid solids with low melting points.

weak forces

between molecules


• Ionic compounds are very brittle.

• Opposite charges attract, so neighbouring ions are pulled together.

• When something hits the substance a layer of ions will be pushed so that they are next to ions with the same charge.

Attraction becomes:

+ -

+-

+

-

-+ +

+-

+

-

- -

-

+

++ -

+-

+

-

-+ +

+ -

+-

+

-

-+ +Blow

+ -

+-

+

-

-+ +

repulsion!


• Metals are not brittle.

• The metal atoms are the same and exist in simple structures.

• If something hits the substance, it simply moves to the next layer along.

Blow


• Covalent substances do not conduct electricity.

• This is because in covalent substances the outer electrons are fixed (localised) between specific atoms.

• Metals conduct electricity.

• In metals the electrons can, given a potential, move anywhere throughout the structure.

H

H

H H

H

HC C

electrons fixed in

covalent bonds

electrons free to move


• Ionic substances do not conduct electricity as solids.

• When molten or dissolved they will conduct (and also undergo electrolysis).

• This is because the electricity is carried through the solution by the ions which are free to move when the ionic compound is molten or in solution.

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

Solid – not free to move Doesn’t conduct

-

++

- +-

Molten – mobile Does conduct


• Generally substances with giant structures do not dissolve easily (although many ionic compounds dissolve in water for a special reason).

• Again this is because in giant structures separating the particles involves breaking chemical bonds.

Small molecules usually dissolve in a range of solvents. We just separate one molecule from another.

weak forces

between molecules

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

Giant structures generally don’t dissolve easily.

strong bonds between the atoms/ions


Bonding & physical propertiesHARDNESS, WHY?

CONDUCT ELECTRICITY

MELTING POINT /BOILING POINT

DISSOLVE

IONICBRITTLE

WHEN molten or dissolved as electricity is carried through the solution by ions.Not when molten

HIGH-due to strong electrostatic attraction between ions.

DISSOLVE IN SOLVENTS LIKE WATER OR PETROL

SIMPLE COVALENT Usually gas of liquid at room temperature.

No-electrons are fixed between atoms.

Increase with size.Water unusual has high mp & bp for a small covalent molecule.

Dissolve in some solvents

GIANTCOVALENT HARD

NO- as electrons are fixed between atoms

HIGH DO NOT DISSOLVE EASILY-as it involves breaking chemical bonds

METALLIC NOT BRITTLE WHEN SOLID & LIQUID –as electrons can move freely.

High No

(H) Find and explain … 1. Find these physical properties of water and carbon

dioxide.– Melting points– Electrical conductivity (do they conduct electricity?)

2. Explain why some of the above have low melting points and others high? Use these ideas in your answer

• Intermolecular forces• Freely moving electrons or ions

Support sheet for foundation students

Information sheet for higher students

Recap activites

Copy the Table and fill in the blank columns.

YesYesLowNoE

Small or giant?

Yes

No

No

Yes

Conduct when

molten

NoHighNoD

NoHighNoC

NoLowYesB

YesHighNoA

Metal

Ionic

Small Mol

Giant Mol

Conduct as solid

Melting Point

Soluble in petrol

Giant Metal

Small Small Mol

Giant Giant Mol

Giant Ionic

Substance E is peculiar:

Can you suggest an actual substance that E could be?

Can you explain the low melting point?

MetalGiant

Activity

Substance

What type of bonding will the substances have?

Substance Bonding

Brass (Alloy copper + zinc)

Copper oxide

Sulphur dioxide

Iron

Sodium fluoride

Nitrogen chloride

Metallic

Ionic

Covalent

Metallic

Ionic

Covalent

Which of the following will have covalent bonding?

A. Sodium chloride

B. Iron

C. Bronze

D. Nitrogen dioxide

Which of the following will have metallic bonding?

A. Copper chloride

B. Graphite

C. Bronze

D. Phosphorus chloride

Which is a true statement about covalent bonds?

A. Usually formed between metals and non- metals

B. Involve transfer of electrons between atoms.

C. Form full electron shells by sharing of electrons.

D. Always involve 2 electrons per atom.

Which of the following exists as a giant molecular structure?

A. Water

B. Carbon dioxide

C. Sodium chloride

D. Diamond

What will be the formula of the compound formed by hydrogen and sulphur?

A.HS

B.H2S

C.HS2

D.H2S2

32

S16

1

H1

1 2.8.6

Which of these will conduct as both solid and liquid?

A. metal

B. ionic

C. small molecules

D. giant molecules

Which of these will conduct when liquid but not when solid?

A. small molecules

B. giant molecules

C. metal

D. ionic

Which of these will dissolve in solvents like petrol?

A. small molecules

B. giant molecules

C. metal

D. ionic

Which of these will not conduct at all and is hard to melt?

A. small molecules

B. giant molecules

C. metal

D. ionic

H He

Li Be B C N O F Ne

NaMg

Al Si P S Cl Ar

K Ca Fe Ni Cu Zn Br Kr

Ag I Xe

Pt AuHg

The Periodic TableAlkali

metals

Noble gases

HalogensThese elements

are metals

This line divides metals from non-metals These elements

are non-metals

Electronic Structure

1 72 3 4 5 6 8

Arrangement of Electrons

1

2

3

Click on action buttons to reveal how electron configuration is built-up.The transition metals

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3

2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

1 72 3 4 5 6 8

Electrons in Period 3

Elements in the third period have complete first and second shells. The third shell is completed one electron at a time as you cross the period from left to right.

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1 72 3 4 5 6 8

1


1 2

Skip this


1 72 3 4 5 6 8

2

2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8

This atom isspecial it has a complete outer shell

Elements in the second period contain 2 electrons in the first shell (complete) and the second shell is completed one electron at a time as you cross the period from left to right.

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3

2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

1 72 3 4 5 6 8


Elements in the third period have complete first and second shells. The third shell is completed one electron at a time as you cross the period from left to right.

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1

1

2

3

1

2,1

2,8,1

Group 1 Elements

Group 1 elements have 1 electron in the outermost shell which they lose in chemical reactions.The outer electron is further from the nucleus and so more easily lost as you go down the group. This is why reactivity increases going downwards

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2

2,2

2,8,2

Group 2 Elements

In chemical reactions metals tend to lose their outer shell electrons to form positive ions.

So, these elements all form ions with a 2+ charge.

The further the outer shell is from the nucleus the more easily electrons are lost.

CATIONS-form after loss of electron

Anions-gain of electrons

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3

2,3

2,8,3

Group 3 Elements

Metals lose their outer electrons to form ions. The charge on the ion produced by Group 3 metals will be +3.

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4

2,4

2,8,4

Group 4 Elements

The elements at the top of Group 4 are non-metals. They bond covalently, i.e. by sharing electrons with another atom.

Skip this

5

2,5

2,8,5

Group 5 Elements

The number of electrons in the outermost shell is the same as the group number.

They need 3 more electrons to achieve a full electron shell.

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6

2,6

2,8,6

Group 6 Elements

The atoms in Group 6 form negative ions (2-) by the addition of two extra electrons. This completes their outer most shell.

Skip this

7

2,7

2,8,7

Group 7 Elements

Group 7 elements form 1- ions by the addition of 1 extra electron.

They are most reactive at the top of the group because incoming electrons are pulled into shells that are closer to the nucleus.

Skip this

8

2,8

2,8,8

Group 0 Elements

The elements in Group 8 (or 0) have complete outer shells.

They are very unreactive and are called NOBLE (or inert) GASES.

2

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Mendeleev

Periodic table

Horizontal rows are called PERIODS

Vertical columns are called GROUPS

Hello. My name’s Dimitri Mendeleev. In the 19th century I arranged all the known elements

into a pattern according to their properties. This pattern is called “The Periodic Table”

Columns of elements

H

LiNaK

RbCsFr

BeMgCaSrBaRa

GaInTl

AlB

GeSnPb

SiC

SbBi

PN

As SeTePo

OS

He

Kr

NeAr

RnXe

Sc Ti V Cr Mn Fe Co Ni Cu ZnY Zr Nb Mo Tc Ru Pd Ag CdRh

Hf Ta W Re Os Ir Au HgLa PtRf Db Sg Bh Hs Mt ? ?Ac ?

Br

At

ClF

I

What are columns of elements called?

765432

GroupsGroups

1 0Group number

transition elements

Rows of elements

H HeLi Be N O F NeB C

Na Mg Al P S Cl ArSiK Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa KrAs

Rb Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh I XeCs Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt RnFr Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

PeriodsPeriodsWhat are rows of elements called?

1

2345

67

Period number

Tasks

• Starter after finishing both bonding imp.doc

• Structure and bonding information sheet.doc

• Bonding_card_sort or info sheet.doc

Plenary

• C3c_self assess quiz.doc• C3c_self assess answers.doc

• .

Don’t forget your homework!

• Describe the differences in volatility, solubility and electrical conductivity between ionic & covalent compounds. (H/W)

Documents

C3 Atoms, elements & compounds