materials atomic structure and the periodic table modul03a(iii)

Materials Atomic structure and the Periodic Table Modul03a(iii)

Compounds and mixtures - Mixtures http://www.bbc.co.uk/schools/ks3bitesize/sci ence/chemical_material_behaviour/compoun ds_mixtures/revise7.shtml http://www.bbc.co.uk/schools/ks3bitesize/sci ence/chemical_material_behaviour/compoun ds_mixtures/revise7.shtml Look at this site as an introduction

Describe the structure of an atom in terms of electrons and a nucleus containing protons and neutrons At the centre of an atom is a nucleus containing protons and neutrons. Electrons are arranged around the nucleus in energy levels or shells. Make sure you can label a simple diagram of an atom http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/ato mic/atomstrucrev1.shtml http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/ato mic/atomstrucrev1.shtml http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm

Atoms are made up of 3 types of particles electrons, protons and neutrons. Electrons are tiny, very light particles that have a negative electrical charge (-). Protons are much larger and heavier than electrons and have the opposite charge, protons have a positive charge (+). Neutrons are large and heavy like protons, however neutrons have no electrical charge.

Define proton number and nucleon number. PROTON NUMBER (also called ATOMIC NUMBER) The proton number is equal to the number of protons in the nucleus of an atom. The proton number is also equal to the number of electrons in orbit around a neutral atom. NUCLEON NUMBER (also called MASS NUMBER) The nucleon number is equal to the total number of nucleons (protons and neutrons) in the nucleus of an atom. This gives an idea of the total mass of the atom

Representing atoms Atoms/elements can be represented like this: A X Z Where X is the chemical symbol for the element, Z is the number of protons ie the atomic number,atomic number A is the number of neutrons and protons combined ie the mass number.

State the relative charges and approximate relative masses of protons, neutrons and electrons PARTICLERELATIVE CHARGE RELATIVE MASS proton+1 1 neutron0 1 electron-1 0 ENERGY LEVEL OR SHELLMAXIMUM NUMBER OF ELECTRONS first2 second8 third8

Describe the build-up of electrons in shells and understand the significance of the noble gas electronic structures and of valency electrons http://www.bbc.co.uk/schools/gcsebitesize/sc ience/add_aqa_pre_2011/atomic/atomstrucre v2.shtml http://www.bbc.co.uk/schools/gcsebitesize/sc ience/add_aqa_pre_2011/atomic/atomstrucre v2.shtml

Electron Shells Electrons are added in order Begin adding to the first shell When this is full (2 electrons) start on the next shell When the second shell is full (8 electrons) start on the third shell A full outer shell means the atom /particle is very stable and wont react with other atoms/particles

A Carbon atom has 6 protons

A nitrogen atom has 7 protons

ELEMENTS Elements are made of atoms, which are extremely small. Sometimes in elements 2 or more atoms join together to form molecules Because all the atoms are the same though it is still an element All atoms of a given element have the same chemical properties and contain the same number of PROTONS The number of PROTONS tells us which element the atom/particle has come from

Use proton number and the simple structure of atoms to explain the basis of the Periodic Table (see C9), with special reference to the elements of proton number 1 to 20. http://www.bbc.co.uk/schools/gcsebitesize/scie nce/add_ocr_pre_2011/periodic_table/element srev1.shtml http://www.bbc.co.uk/schools/gcsebitesize/scie nce/add_ocr_pre_2011/periodic_table/element srev1.shtml http://www.ptable.com/ You should be able to draw out the electronic structures for the first 20 elements if you know the proton and nucleon number

Define isotopes Atoms of the same element can have different numbers of neutrons These are called isotopes Adding neutrons makes the atom heavier Some isotopes are radioactive because they are very heavy and spontaneously break down Not all isotopes are radioactive http://www.colorado.edu/physics/2000/isotopes /index.html http://www.colorado.edu/physics/2000/isotopes /index.html

Ions and ionic bonds

CHEMICAL BONDS H hydrogen will form one bond O - oxygen will form two bonds C carbon will for four bonds N nitrogen will form three bonds Atoms will form bonds by sharing electrons (covalent bonds) Atoms will form bonds by losing or gaining electrons (ionic bonds) The number of bonds an atom will form is called its valency http://www.colorado.edu/physics/2000/periodic_table/valences.html

Describe the formation of ions by electron loss or gain. Some atoms need to gain 1 or 2 electrons to fill up their outer shell These form new positively charged particles called ions Other atoms need to lose electrons to leave the next full shell exposed as the outer shell These form new negatively charged particles called ions http://www.bbc.co.uk/schools/gcsebitesize/science/ add_edexcel/ionic_compounds/ionicrev1.shtml http://www.bbc.co.uk/schools/gcsebitesize/science/ add_edexcel/ionic_compounds/ionicrev1.shtml

IONIC BONDING A giving and taking of electrons Positively or negatively charged particles called ions are formed

Describe the formation of ionic bonds between metals and non-metals as exemplified by elements from Groups I and VII. Metals usually have 1 or 2 (sometimes 3 eg Al)electrons in the outer shell If they can donate these to another element then they are left with a full outer shell (8 electrons or 2 if it is the first shell) They form positively charged ions Non-metals usually have 3 or more electrons They need to fill up this shell by accepting or sharing electrons from other elements If they have 6 or more then they can accept electrons and for negatively charged ions

THE IONIC BOND formed between elements whose atoms need to lose electrons and those which need to gain electrons electrons are transferred from one atom to the other.

Sodium + Chlorine Sodium Chloride Sodium needs to lose one electron and Chlorine needs to gain one electron This leaves both Na and Cl with a full outer shell

FORMATION OF MAGNESIUM CHLORIDE Mg needs to lose two electrons Each Cl needs to gain 1 electron This produces one Mg 2+ ion and two Cl - ions Mg Cl e

IONIC BONDING Animations

SODIUM CHLORIDE Cl SODIUM ATOM 2,8,1 Na CHLORINE ATOM 2,8,7

SODIUM CHLORIDE Cl SODIUM ION 2,8 Na CHLORIDE ION 2,8,8 both species now have full outer shells; ie they have the electronic configuration of a noble gas +

SODIUM CHLORIDE Cl SODIUM ION 2,8 Na CHLORIDE ION 2,8,8 NaNa + + e 2,8,1 2,8 ELECTRON TRANSFERRED Cl + e Cl 2,8,7 2,8,8 +

MAGNESIUM CHLORIDE Cl MAGNESIUM ATOM 2,8,2 Mg CHLORINE ATOMS 2,8,7 Cl

MAGNESIUM CHLORIDE Cl MAGNESIUM ION 2,8 Mg CHLORIDE IONS 2,8,8 Cl 2+

IONS Charged particle formed during ionic bonding Positively charged ions have lost electrons Negatively charged ions have gained electrons

COMPOUNDS Compounds are formed by the chemical combination of two or more different kinds of atoms. (Whole numbers only) Covalent compounds are made up of molecules Ionic compounds are made up of ions

Explain the formation of ionic bonds between metallic and non-metallic elements. Metallic elements generally need to lose small numbers of electrons to gain a full outer shell Non-metallic elements usually need to gain a small number of electrons to gain afull outer shell In reacting together electrons are donated by the metal and accepted by the non-metal

FORMATION OF MAGNESIUM CHLORIDE Mg needs to lose two electrons Each Cl needs to gain 1 electron This produces one Mg 2+ ion and two Cl - ions Mg Cl e

Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions, exemplified by the sodium chloride structure. GIANT IONIC CRYSTAL LATTICE NaCl sodium chloride Oppositely charged ions held in a regular 3-dimensional lattice by electrostatic attraction The Na + ion is small enough relative to a Cl ion to fit in the spaces so that both ions occur in every plane. Cl - Chloride ion Na + Sodium ion

Each Na + is surrounded by 6 Cl and each Cl is surrounded by 6 Na +

Physical properties of ionic compounds Melting point - very high A large amount of energy must be put in to overcome the strong electrostatic attractions and separate the ions. Strength - Very brittle Any dislocation leads to the layers moving and similarly charged ions being next to each other. The repulsion splits the crystal. Electrical Do not conduct when solid - ions are held strongly in the lattice. Conduct when molten or in aqueous solution - the ions become mobile and conduction takes place. Solubility Insoluble in non-polar solvents but soluble in water. Water as it is a polar solvent and stabilises the separated ions.

IONIC COMPOUNDS - ELECTRICAL PROPERTIES Solid ionic compounds do not conduct electricity Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Ions are held strongly together Positive ons cant move to the cathode Negative ions cant move to the anode Molten ionic compounds do conduct electricity Ions have more freedom in a liquid so can move to the electrodes Solutions of ionic compounds in water do conduct electricity Cl - Na + CATHODE ANODE

Molecules and covalent bonds

State that non-metallic elements form non-ionic compounds using a different type of bonding called covalent bonding. Covalent bonding is a sharing of electrons to give full outer shells This occurs if larger numbers of electrons are needed to fill the outer shell Or the element is not reactive enough to donate or accept the electrons Its all to do with the amount of energy required and how tightly the electrons are held to the atom

COVALENT BONDING A sharing of electrons

MOLECULES Molecules are made when two or more atoms bond covalently A molecule of water is made of two hydrogen atoms and one oxygen atom Its formula is H 2 O

A covalent bond Consists of a shared pair of electrons with one electron being supplied by each atom either side of the bond. atoms are held together because their nuclei which have an overall positive charge are attracted to the shared electrons + +

Formation between atoms of the same element; N 2, O 2, diamond, graphite between atoms of different element CO 2, SO 2 CCl 4, SiCl 4 BeCl 2

In covalent bonding atoms share electrons to get the nearest noble gas electronic configuration ie to gain a full outer shell 2 electrons if its the first shell Or 8 electrons if its any other shell

HYDROGEN H Another hydrogen atom also needs one electron to complete its outer shell Hydrogen atom needs one electron to complete its outer shell atoms share a pair of electrons to form a single covalent bond A hydrogen MOLECULE is formed H H H WAYS TO REPRESENT THE MOLECULE

HYDROGEN CHLORIDE Cl H Hydrogen atom also needs one electron to complete its outer shell Chlorine atom needs one electron to complete its outer shell atoms share a pair of electrons to form a single covalent bond H Cl WAYS TO REPRESENT THE MOLECULE

METHANE C Each hydrogen atom needs 1 electron to complete its outer shell A carbon atom needs 4 electrons to complete its outer shell Carbon shares all 4 of its electrons to form 4 single covalent bonds H H H H H C H H H H H WAYS TO REPRESENT THE MOLECULE

AMMONIA N Each hydrogen atom needs one electron to complete its outer shell Nitrogen atom needs 3 electrons to complete its outer shell Nitrogen can only share 3 of its 5 electrons otherwise it will exceed the maximum of 8 A LONE PAIR REMAINS H H H H N H H H WAYS TO REPRESENT THE MOLECULE

WATER O Each hydrogen atom needs one electron to complete its outer shell Oxygen atom needs 2 electrons to complete its outer shell Oxygen can only share 2 of its 6 electrons otherwise it will exceed the maximum of 8 2 LONE PAIRS REMAIN H H H O H H WAYS TO REPRESENT THE MOLECULE

HYDROGEN H H HHH both atoms need one electron to complete their outer shell atoms share a pair of electrons to form a single covalent bond DOT AND CROSS DIAGRAM

METHANE C H H HH C H H H H H C H H H H H Each hydrogen atom needs one electron to complete its outer shell Carbon atom needs four electrons to complete its outer shell Carbon shares all 4 of its electrons to form 4 single covalent bonds DOT AND CROSS DIAGRAM

AMMONIA N H H H N H HH H N H H H Each hydrogen atom needs one electron to complete its outer shell Nitrogen atom needs three electrons to complete its outer shell Nitrogen can only share 3 of its 5 electrons otherwise it will exceed the maximum of 8 A LONE PAIR REMAINS

WATER O H H O H H Each hydrogen atom needs one electron to complete its outer shell Oxygen atom needs two electrons to complete its outer shell Oxygen can only share 2 of its 6 electrons otherwise it will exceed the maximum of 8 TWO LONE PAIRS REMAIN H O H H

OXYGEN O Each oxygen atom needs two electrons to complete its outer shell each oxygen shares 2 of its electrons to form a DOUBLE COVALENT BOND OO O O

Draw dot-and-cross diagrams to represent the sharing of electron pairs to form single covalent bonds in simple molecules, exemplified by (but not restricted to) H 2, Cl 2, H 2 O, CH 4 and HCl Try Cl 2 for yourself

SIMPLE COVALENT MOLECULES BondingAtoms are joined together within the molecule by covalent bonds ElectricalDont conduct electricity as they have no mobile ions or electrons Solubility Tend to be more soluble in organic solvents than in water

Boiling point Low because intermolecular forces (van der Waals forces) are weak; as the intermolecular forces are weak, little energy is required to separate molecules from each other so boiling points are low these forces increase as molecules get larger e.g. CH 4 -161C;C 2 H 6 - 88C; C 3 H 8 -42C; some boiling points are higher than expected for a given mass because you can get additional forces of attraction eg in water

Draw dot-and-cross diagrams to represent the multiple bonding in N 2, C 2 H 4 and CO 2 Try these for yourselves

Answers http://www.chemprofessor.com/bonding.htm http://chemwiki.ucdavis.edu/Organic_Chemistry/Hydrocarbons/Alkenes/S tructure_and_Bonding_in_Ethene-The_Pi_Bond http://chemwiki.ucdavis.edu/Organic_Chemistry/Hydrocarbons/Alkenes/S tructure_and_Bonding_in_Ethene-The_Pi_Bond

Describe the differences in volatility, solubility and electrical conductivity between ionic and covalent compounds. Try to set up a table comparing ionic and covalent compounds

Ionic and molecular (covalent) compounds

Giant structures

COVALENT NETWORKSCOVALENT NETWORKS GIANT MOLECULESGIANT MOLECULES MACROMOLECULESMACROMOLECULES They all mean the same!They all mean the same!

Describe the giant covalent structures of graphite and diamond. Many atoms joined together in a regular array by a large number of covalent bonds

DIAMOND, GRAPHITE MELTING POINTVery high structures are made up of a large number of covalent bonds, all of which need to be broken if the atoms are to be separated. ELECTRICALDont conduct electricity have no mobile ions or electrons but... Graphite conducts electricity

Graphite consists of layered planes of carbon atoms The hexagonal carbon rings provide the delocalised electrons, allowing easy conduction within the planes.

DIAMOND, GRAPHITE STRENGTH Diamond is Hard exists in a rigid tetrahedral structure Graphite is soft In the form of hexagonal layers which move over each other

DIAMOND MELTING POINTVERY HIGH many covalent bonds must be broken to separate the atoms STRENGTHSTRONG each carbon is joined to four others in a rigid structure ELECTRICALNON-CONDUCTOR No free electrons - all four carbon electrons are used for bonding

GRAPHITE MELTING POINTVERY HIGH many covalent bonds must be broken to separate the atoms STRENGTHSOFT each carbon is joined to three others in a layered structure layers are held by weak van der Waals forces can slide over each other ELECTRICALCONDUCTOR Only three carbon electrons are used for bonding which leaves the fourth to move freely along layers layers can slide over each other used as a lubricant and in pencils

DIAMOND GRAPHITE

Relate their structures to the use of graphite as a lubricant and of diamond in cutting. Graphite lubricant Layers of atoms slide over each other Diamond cutting Atoms strongly bonded gives a very strong, hard substance

Describe the structure of silicon(IV) oxide (silicon dioxide). Crystalline silicon has the same structure as diamond. To turn it into silicon dioxide, all you need to do is to modify the silicon structure by including some oxygen atoms.

SILICON DIOXIDE MELTING POINTVERY HIGH many covalent bonds must be broken to separate the atoms STRENGTHSTRONG each silicon atom is joined to four oxygen atoms - each oxygen atom are joined to two silicon atoms - ELECTRICALNON-CONDUCTOR - no mobile electrons

METALLICBONDING

METALLIC BONDING

Involves a lattice of positive ions surrounded by delocalised electrons Metal atoms achieve stability by off- loading electrons to attain the electronic structure of the nearest noble gas. These electrons join up to form a mobile cloud which prevents the newly-formed positive ions from flying apart due to repulsion between similar charges.

Atoms arrange in regular close packed 3- dimensional crystal lattices. The outer shell electrons of each atom leave to join a mobile cloud or sea of electrons which can roam throughout the metal. The electron cloud binds the newly- formed positive ions together.

Stoichiometry

Use the symbols of the elements to write the formulae of simple compounds http://www.chemicalformula.org/basic-chemistry/writing- chemical-formula http://www.chemicalformula.org/basic-chemistry/writing- chemical-formula This is a relatively simple way to write formulae This site helps you learn the chemical symbols http://www.chemicalformula.org/chemistry-drill/elements-of- the-periodic-table-1 http://www.chemicalformula.org/chemistry-drill/elements-of- the-periodic-table-1

Complete the table Element or polyatomic group CompoundChemical formula Chemical name NaClSodium chloride MgCl 2 Sodium sulphate Al 2 (SO 4 ) 3 Aluminium sulphate

Deduce the formula of a simple compound from the relative numbers of atoms present http://www.acceleratedstudynotes.com/2012 /02/04/igcse-coordinated-science- stoichiometry/ http://www.acceleratedstudynotes.com/2012 /02/04/igcse-coordinated-science- stoichiometry/ This may be useful to you

Deducing chemical formulae It is possible to work out the chemical formulae of a compound when given the elements present. For example, if we are told that a certain compound contains both sodium and chlorine, we can deduce its formulae to be NaCl. Remember when working out the chemical formulae to take into consideration the valency of the elements present.

Determine the formula of an ionic compound from the charges on the ions present http://www.chemicalformula.org/basic- chemistry/writing-chemical-formula-ionic- charges http://www.chemicalformula.org/basic- chemistry/writing-chemical-formula-ionic- charges You can also use the charges on the ions to write the formulae

Charges/valency on ions Group12 345678 Valency1+2+ 3+43-2-1-0 Periodic table H LiBeTransition block BCNOFNe First 20 elements NaMgvariableAlSiPSClAr KCavalencies

Chemical compound Make the simplest neutral compound from the ions Chemical formula (ignore ions) Sodium chloride Na + Cl - Check: + 1 + -1 = 0 NaCl Magnesium chloride Mg 2+ Cl - Cl - Check: 2+ + 2- = 0 MgCl 2 Aluminum chloride Al 3+ Cl - Cl - Cl - Check: 3+ + 3- = 0 AlCl 3 Calcium oxide Ca 2+ O 2- Check: 2+ + 2- = 0 CaO Sodium oxide Na + O 2- Na + Check: 2+ + 2- = 0 Na 2 O Lithium phosphide Li + P 3- Li + Li + Check: 3+ + 3- = 0 Li 3 P Aluminum oxide Al 3+ O 2- Al 3+ O 2- O 2- Check: 6+ + 6- = 0 Al 2 O 3

Deduce the formula of a simple compound from a model or a diagrammatic representation You should be able to write down the formula from structural diagrams eg C 8 H 18 Try these

Define relative atomic mass, Ar http://www.bbc.co.uk/schools/gcsebitesize/sc ience/add_gateway_pre_2011/chemical/react ingmassesrev1.shtml http://www.bbc.co.uk/schools/gcsebitesize/sc ience/add_gateway_pre_2011/chemical/react ingmassesrev1.shtml The relative atomic mass is a measure of the mass of one atom of the element

Define relative molecular mass, Mr, as the sum of the relative atomic masses (relative formula mass or Mr will be used for ionic compounds). To calculate the relative formula mass: Write the formula of the compound. Write the numbers of each atom in the formula. Insert the relative atomic mass for each type of atom. Calculate the total mass for each element. Add up the total mass for the compound.

Calculate the relative formula mass of the compound with the formula: H 2 SO 4 Answer (H = 1, S = 32, O = 16) H 2 SO 4 (2 x H) (1 x S) (4 x O) (2 x 1) (1 x 32) (4 x 16) 2 32 64 2 + 32 + 64 = 98

Define the mole in terms of a specific number of particles called Avogadros constant. (Questions requiring recall of Avogadros constant will not be set.). 1 mole of a pure substance has a mass equal to its molecular mass expressed in grams.molecular mass This is known as the molar mass, M, and has the units g mol -1 One mole of any substance conatins the same number of molecules or atoms This is called Avogadro's number = 6.0221415 10 23 One mole of gas occupies 24 litres at room temperature and pressure

So 2 moles of a substance would have a mass = 2 x molar mass How many molecules would it contain? 2x(6.0221415 10 23 ) 3 moles of a substance would have a mass = 3 x molar mass etc How many molecules would it contain? 3 x(6.0221415 10 23 ) http://www.ausetute.com.au/massmole.html If you search this site there are quizzes etc you might like to do

This leads to the formula: mass = moles x molar mass If we let: m = mass of substance in grams, n = moles of pure substance, M = molar mass of the pure substance in g mol -1 we can write the equation: n = m x M This equation can be rearranged to give the following: n = m M (moles = mass molar mass) M = m n (molar mass = mass moles)

Calculate the mass of 0.25 moles of water Write the equation: m (in grams) = n x M Extract the data from the question: n = 0.25 mol Calculate the molar mass of the substance using the periodic table: M(H 2 O) = (2 x 1.008) + 16.00 = 18.016 g mol -1periodic table Substitute the values into the equation and solve: mass = 0.25 x 18.016 = 4.504 g

Use the molar gas volume, taken as 24 dm 3 at room temperature and pressure. http://www.docbrown.info/page04/4_73calcs 09mvg.htm http://www.docbrown.info/page04/4_73calcs 09mvg.htm

What is the volume of 3.5g of hydrogen? [A r (H) = 1] hydrogen exists as H 2 molecules, so M r (H 2 ) = 2, 1 mole or formula mass in g = 2g Number of moles of hydrogen = 3.5/2 = 1.75 mol H 2 volume H 2 = mol H 2 x molar volume = 1.75 x 24 = 42 dm 3 (or 42000 cm 3 )

Calculate stoichiometric reacting masses and reacting volumes of solutions; solution concentrations will be expressed in mol/dm 3. (Calculations involving the idea of limiting reactants may be set.) http://www.bbc.co.uk/schools/gcsebitesize/sc ience/add_gateway_pre_2011/chemical/react ingmassesrev2.shtml http://www.bbc.co.uk/schools/gcsebitesize/sc ience/add_gateway_pre_2011/chemical/react ingmassesrev2.shtml Look at this website and the following pages it shows you how to do some of the calculations You may find your textbook useful here

Given the equation MgCO 3(s) + H 2 SO 4(aq) ==> MgSO 4(aq) + H 2 O (l) +CO 2(g) What mass of magnesium carbonate is needed to make 6 dm 3 of carbon dioxide? [A r 's: Mg = 24, C = 12, O = 16, H =1 and S = 32] since 1 mole = 24 dm 3, 6 dm 3 is equal to 6/24 = 0.25 mol of gas From the equation, 1 mole of MgCO 3 produces 1 mole of CO 2, which occupies a volume of 24 dm 3. 0.25 moles of MgCO 3 is need to make 0.25 mol of CO 2 formula mass of MgCO 3 = 24 + 12 + 3x16 = 84 required mass of MgCO 3 = mol x formula mass = 0.25 x 84 = 21g

You might find some other useful stuff in here http://www.docbrown.info/page01/ElCpdMix /EleCmdMix3.htm http://www.docbrown.info/page01/ElCpdMix /EleCmdMix3.htm

materials atomic structure and the periodic table modul03a(iii)

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