08/05/2308/05/23

C4 Chemical C4 Chemical PatternsPatterns

M Barker

Shirebrook Academy

OCR 21OCR 21stst Century Century

08/05/23C4.1 What are the patterns in C4.1 What are the patterns in properties of elements?properties of elements?

08/05/2308/05/23Periodic Table IntroductionPeriodic Table IntroductionHow would you arrange these elements into groups?

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Mendeleev

Periodic tablePeriodic tableThe periodic table arranges all the elements in groups according to their properties.

Horizontal rows are called PERIODS

Vertical columns are called GROUPS

08/05/23Development of the Periodic Development of the Periodic TableTable

Li Be B C N O F Na Mg Al

Li Be B C N O F Na Mg Al

1869: Dimitri Mendeleev arranged the known elements in order of mass but he also left in gaps and was able to predict the properties of unknown elements:

1864: John Newlands arranged the known elements in order of atomic mass and found out that every 8th element had similar properties:

1817: Johann Dobereiner developed the law of “triads” – he put elements together in groups of 3 according to their properties.

1913: Henry Moseley proposed the use of atomic number rather than atomic mass.

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H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Fe Ni Cu Zn Br Kr

Ag I Xe

Pt Au Hg

The Periodic TableThe Periodic TableMost of the elements are metals:

These elements are metals

This line divides metals from non-metals

These elements are non-metals

08/05/2308/05/23Predicting Properties – the Noble Predicting Properties – the Noble GasesGases

He

Ne

Ar

Kr

Xe

Rn

08/05/23Properties of the Noble Properties of the Noble GasesGases

Element Melting Point (OC)

Boiling Point (OC)

Density (g/dm3)

Helium -272 -269 0.1786

Neon -249 -246 0.9002

Argon -189 -186 1.784

Krypton -157 -153 3.749

Xenon ? ? ?

What numbers would you expect Xenon to have?

08/05/2308/05/23Group 1 – The alkali metalsGroup 1 – The alkali metals

Li

Na

K

Rb

Cs

FrWatch video of these metals reacting with

water (from Sky One’s Brainiac)

08/05/23Group 1 – The alkali metalsGroup 1 – The alkali metals1) These metals are _____ when freshly cut but quickly tarnish due to reacting with water vapour

Some facts…

3) Reactivity increases as you go _______ the group. This is because the electrons are further away from the _______ every time a _____ is added, so they are given up more easily.4) They all react with water to form an alkali (hence their name) and __________. This means they need to be stored under oil.

Words – down, shiny, shell, hydrogen, nucleus, decreases

Potassium + water potassium hydroxide + hydrogen

2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

2) Density increases as you go down the group, while melting point ________

08/05/23Properties of the Alkali Properties of the Alkali MetalsMetals

Element Melting Point (OC)

Boiling Point (OC)

Density (g/cm3)

Lithium 180 1340 0.53

Sodium 98 883 0.97

Potassium 64 760 0.86

Rubidium 39 688 1.53

Caesium ?? ?? ??

08/05/23Trends in Group 1Trends in Group 1Consider a sodium atom:

Take away one

of the electrons

+

+Now consider a potassium atom:

Sodium ion

Potassium ion

Take away one

of the electrons

Potassium loses its electron more easily because its further away – potassium is MORE REACTIVE

08/05/2308/05/23Alkali Metals and ChlorineAlkali Metals and Chlorine1) Sodium and chlorine:

K

+

Cl

-

Na Cl+

2) Potassium and chlorine:

Cl+

Sodium + chlorine sodium chloride

Potassium + chlorine potassium chloride

K

Na

+

Cl

-

08/05/2308/05/23Hazard signs to learn…Hazard signs to learn…

h i

Acid

Harmful Irritant

Corrosive

Oxidising

Toxic

08/05/23Group 7 – The halogensGroup 7 – The halogens

F

Cl

Br

I

AtSome of the halogens are poisonous

gases so they need to be handled in a fume cupboard!!

08/05/23The Halogens - ChlorineThe Halogens - Chlorine

Each molecule has a strong force holding the atoms together (forming a “diatomic molecule”), but the forces between molecules are very weak so chlorine is a gas at room temperature and is pale yellow.

08/05/23The Halogens - BromineThe Halogens - Bromine

The forces between the diatomic molecules are slightly stronger so bromine is a liquid at room temperature. It is reddish-brown in colour.

08/05/23The Halogens - IodineThe Halogens - Iodine

Iodine is a solid at room temperature but with gentle heating it will melt. The atoms will remain in pairs. In solid form iodine is grey like metal but gaseous iodine is purple.

08/05/23PropertiesPropertiesElement Melting Point

(OC)Boiling Point

(OC)Density (g/cm3)

Flourine -220 -188 0.0016

Chlorine -101 -34 0.003

Bromine -7 59 3.12

Iodine 114 184 4.95

Astatine ?? ?? ??

08/05/23Trends in Group 7Trends in Group 7Consider a fluorine atom:

Add an electron

-

-Now consider a chlorine atom:

Flouride ion

Chloride ion

Add an electron

Chlorine doesn’t gain an electron as easily as fluorine so it is LESS REACTIVE

08/05/23Displacement reactionsDisplacement reactionsTo put it simply, a MORE reactive halogen will displace a LESS reactive halogen from a solution of its salt.

F

Cl

Br

I

Decreasing reactivity

Potassium

chloride KCl(aq)

Potassium

bromide KBr(aq)

Potassium iodide

KI (aq)

Chlorine Cl2

Bromine Br2

Iodine I2

08/05/23Common MoleculesCommon MoleculesChemical Diagram Formula

Hydrogen H2

Water H2O

Chlorine

Sodium Chloride

Potassium Bromide

Cl- Na+ Cl-Na+ Cl- Na+

Na+ Cl-Cl- Na+

08/05/23Balancing equationsBalancing equationsConsider the following reaction:

Na

OH H H H

Na

OH

Sodium + water sodium hydroxide + hydrogen

+ +

This equation doesn’t balance – there are 2 hydrogen atoms on the left hand side (the “reactants” and 3 on the right hand side (the “products”)

08/05/23Balancing equationsBalancing equationsWe need to balance the equation:

Na

OH H

H H

Na

OH

Sodium + water sodium hydroxide + hydrogen

+ +

Na

OH H

Na

OH

Now the equation is balanced, and we can write it as:2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

08/05/23Some examplesSome examples

Mg + O2

Zn + HClFe + Cl2

NaOH + HClCH4 + O2

Ca + H2ONaOH + H2SO4

CH3OH + O2

MgOZnCl2 + H2

FeCl3NaCl + H2OCO2 + H2OCa(OH)2 + H2

Na2SO4 + H2OCO2 + H2O

2 2 2 3

2 2

2 2

3

2

2

2

22 4

08/05/2308/05/23Balanced Equations for Alkali Balanced Equations for Alkali metals and halogensmetals and halogens

Na Cl+

Na(s) + Cl2(g) NaCl(s)

Na

+

Cl

-

2 2

08/05/23C4.2 Explaining the Patterns in C4.2 Explaining the Patterns in PropertiesProperties

08/05/2308/05/23The structure of the atomThe structure of the atom

ELECTRON – negative,

mass nearly nothingPROTON –

positive, same mass as neutron

(“1”)

NEUTRON – neutral,

same mass as proton

(“1”)

I did some experiments in 1808 that proved this and called these particles ATOMS. Most of an atom is empty space and the nucleus

is actually very small so this diagram is wrong:

Dalton

08/05/2308/05/23Mass and atomic numberMass and atomic numberParticle Relative Mass Relative ChargeProton 1 +1

Neutron 1 0Electron Very small -1

MASS NUMBER = number of protons + number of neutrons

SYMBOLPROTON NUMBER = number of protons (same as the number of

electrons) - this number stays the same for a given element

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Mendeleev

Periodic tablePeriodic table

1 2

3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

19 20 21 22 etc

Notice that elements in the Periodic Table are arranged in order of proton number:

Proton number

08/05/23Flame testsFlame testsCompounds containing lithium, sodium, potassium, calcium and barium ions can be recognised by burning the compound and observing the colours produced:

LithiumRed

SodiumYellow

Potassium

Lilac

CalciumBrick red

BariumGreen

08/05/23SpectroscopySpectroscopySpectroscopy is kind of like a flame test but using a “spectroscope” to see the results: Using this spectroscope

I can see this:

Each different element has a different “signature” when viewed through a spectroscope. This analysis enables us to the discovery of new elements including rubidium and caesium and these discoveries depended on these new techniques.

08/05/2308/05/23Mass and atomic numberMass and atomic numberHow many protons, neutrons and electrons?

08/05/2308/05/23Electron structureElectron structureConsider an atom of Potassium:

Potassium has 19 electrons. These electrons occupy specific energy levels “shells”…

Nucleus

The inner shell has __ electronsThe next shell has __ electronsThe next shell has __ electronsThe next shell has the remaining __ electron

Electron structure = 2,8,8,1

08/05/2308/05/23Electron structureElectron structureDraw the electronic structure of the following atoms:

Electron structure = 2,8,8,2

Nucleus

Electron structure

= 2,8,2

Nucleus

Electron structure

= 2,5

Nucleus

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H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Fe Ni Cu Zn Br Kr

Ag I Xe

Pt Au Hg

Electron Structure and The Periodic Electron Structure and The Periodic TableTable

Looking at their position in the Periodic Table gives us the key to work out an element’s electron structure:

For example, group 1 elements all have 1 electron in their outer shell

How many electrons do the noble gases and halogens have in their outer shell?

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H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Fe Ni Cu Zn Br Kr

Ag I Xe

Pt Au Hg

The Periodic TableThe Periodic TableThe chemical properties of each element

are determined by its electron arrangement, e.g:

Potassium has 19 electrons in the configuration __,__,__,__

Sodium has 11 electrons in the configuration 2,8,1

Potassium is more reactive as it’s outer electron is further away from the nucleus.

The halogens have 7 electrons in their outer shell so they have totally different properties!

08/05/23C4.3 Explaining the Properties of C4.3 Explaining the Properties of CompoundsCompounds

08/05/23IonsIonsAn 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

+

08/05/23Dissolving Ionic StructuresDissolving Ionic StructuresWhen an ionic structure like sodium chloride is dissolved it enables the water to conduct electricity – this gives evidence of the existence of ions:

Cl- Na+ Cl-

Na+ Cl- Na+

Cl- Na+ Cl-

Na+ Cl- Na+

08/05/2308/05/23Balancing ionsBalancing ions

Determine the formula of these compounds:

1) Sodium chloride2) Magnesium oxide3) Magnesium chloride4) Ammonium chloride5) Sodium sulphate6) Sodium oxide

Some common ions:Sodium – Na+

Potassium – K+

Magnesium – Mg2+

Ammonium – NH4+

Chloride – Cl-

Bromide – Br-

Oxide – O2- Sulphate – SO4

2-

Answers:

1) NaCl2) MgO3) MgCl24) NH4Cl5) Na2SO4

6) NaO

08/05/23Some examples of ionic Some examples of ionic saltssalts

Mg

Magnesium chloride:

MgCl2

Cl

Cl

+ Mg

2+

Cl

-

Cl

-

Calcium oxide:

CaO

OCa + Ca

2+

O

2-

08/05/23Giant Ionic StructuresGiant Ionic StructuresWhen many positive and negative ions are joined they form a “giant ionic lattice” where each ion is held to the other by strong electrostatic forces of attraction (ionic bonds).

Cl- Na+ Cl- Na+ Cl- Na+

Na+ Cl- Na+ Cl- Na+

Cl- Na+ Cl- Na+ Cl- Na+

Na+ Cl- Na+ Cl- Na+

Cl-

Cl-

If these ions are strongly held together what affect would this have on the substance’s:

1) Melting point?2) Boiling point?3) State (solid, liquid or gas) at room temperature?

08/05/2308/05/23Alkali Metals and Chlorine Alkali Metals and Chlorine revisionrevision

1) Sodium and chlorine:

K

+

Cl

-

Na Cl+

2) Potassium and chlorine:

Cl+

Sodium + chlorine sodium chloride

Potassium + chlorine potassium chloride

K

Na

+

Cl

-

Notice that these compounds are

“ionic”