18 QUESTIONS - ATOMIC STRUCTURE

1. Which of the following particles contain more electronsthan neutrons?

I. ~H

A. lonly

B. II only

II. ~~CI- III. ~~K+

C. I and II only

D. II and III only

2. The atom with the same number of neutrons as 54Cr is

A. 50Ti B. 51V C. 53Fe

3. All isotopes of tin (Sn) have the same

I. number of protons

II. number of neutrons

III. mass number

A. lonly

B. II only

C. III only

D. I and III only

4. Which one of the following sets represents a pair ofisotopes?

A. l:C and l;N

B. 02 and 03

c.~~S and f~S2-

D. 2~~Pb and 2~~Pb

5. The atomic and mass numbers for four different nuclei aregiven in the table below. Which two are isotopes?

atomic number mass numberI. 101 258II. 102 258

III. 102 260

IV. 103 259

A. I and II C. II and IV

B. II and III D. III and IV

6. Which species contains 16 protons, 17 neutrons and 18electrons?

7. Spectra have been used to study the arrangements ofelectrons in atoms. An emission spectrum consists of aseries of bright lines that converge at high frequencies.Such emission spectra provide evidence that electrons aremoving from

A. lower to higher energy levels with the higher energylevels being closer together.

B. lower to higher energy levels with the lower energylevels being closer together.

C. higher to lower energy levels with the lower energylevels being closer together.

D. higher to lower energy levels with the higher energylevels bei ng closer together.

8. Which electron transition in a hydrogen atom releases themost energy?

A. n = 2 ~ n = 1B. n = 4 ~ n = 2

C. n=6~n=3

D. n = 7 ~ n = 6

9. An element has the electronic configuration 2.7. Whatwould be the electronic configuration of an element withsimilar chemical properties?

A.2.6 B.2.8 C. 2.7.1 D.2.8.7

10.An element with the symbol Z has the electronconfiguration 2.8.6. Which species is this element mostlikely to form?

A. The ion Z2+ C. The compound H2Z

D. The compound Z6FB. The ion z6+

The following diagram should be used to answer question 11.

Abundance

20Mass

11. According to the mass spectrum above, the relative atomicmass of the element shown is best expressed as

A.20.0. C. 21.0.

B. between 20.0 and 21.0. D. between 21.0 and 22.0.

12. The first four ionization energies (k] mol-l) for a particularelement are 550, 1064, 4210 and 5500 respectively. Thiselement should be placed in the same Group as

A. Li C.B D.CB. Be

11 IB questions - Atomic structure

13.Which ionization requires the most energy?

A. Na(g) ~ Na+(g) + e

B. Na+(g) ~ Na2+(g) + e

C. Mg(g) ~ Mg+(g) + e

D. Mg+(g) ~ Mg2+(g) + e

14.Which one of the following atoms in its ground state hasthe greatest number of unpaired electrons?

A. AI B. Si c.P D. S

15.All of the following factors affect the value of theionization energy of an atom except the

A. mass of the atom.

B. charge on the nucleus.

C. size of the atom.

D. main energy level from which the electron is removed.

The Periodic Table and physical properties (1)THE PERIODIC TABLE

G

In the Periodic Table elements are placed in order ofincreasing atomic number. Elements with the same number ofvalence electrons are placed vertically in the same group. Thegroups are numbered from 1 to 8 (or 0). Some groups havetheir own name:• Group 1 - alkali metals• Group 7 - halogens• Group 8 or 0 - noble gases (sometimes also called rare

gases or inert gases).

Elements with the same outer shell of valence electrons areplaced horizontally in the same period. The transitionelements are located between groups 2 and 3.

I roupillilJ'

~2 3 4 5 6 7 He

Li Be B C N 0 F Nef-- I--

Na Mg Transition elements AI Si P 5 CI Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Br

5 Rb I

6 Cs

ATOMIC RADIUS

Io152

(0112

CD88

©77

@70

@66

The atomic radius is the distance from thenucleus to the outermost electron. Sincethe position of the outermost electron cannever be known precisely, the atomicradius is usually defined as half thedistance between the nuclei of two bondedatoms of the same element.G G0000

186 160 143 117 110 104

•• atomic radius/JO''? m

®64

@99

As a group is descended the outermostelectron is in a higher energy level, wh ichis further from the nucleus, so the radiusincreases.

Cationsatom ion

8 ONa+

186 982.8.1 2.811 protons 11 protons11 electrons 10 electrons

231

244

114 Across a period electrons are being addedto the same energy level, but the numberof protons in the nucleus increases. Thisattracts the energy level closer to thenucleus and the atomic radius decreasesacross a period.

IONIC RADIUSIt is important to distinguish between positiveions (cations) and negative ions (anions). Bothcations and anions increase in size down agroup as the outer level gets further from thenucleus.

Cations contain fewer electrons than protons sothe electrostatic attraction between the nucleusand the outermost electron is greater and the ionis smaller than the parent atom. It is also smallerbecause the number of electron shells hasdecreased by one. Across the period the ionscontain the same number of electrons(isoelectronic), but an increasing number ofprotons, so the ionic radius decreases.

Anions contain more electrons than protons soare larger than the parent atom. Across a periodthe size decreases because the number ofelectrons remains the same but the number ofprotons increases.

Periodicity 12

133

Qu+68

I

Anionsatom ion

@ B99 1812.8.7 2.8.817 protons 17 protons17 electrons 18 electrons

0133

(3 0190 181

G196

8219

ONa+98

OAi3+ 045 ~

212

()vlg2+

65

8133 ionic radiusl1(j12m

The Periodic Table and physical properties (2)PERIODICITYElements in the same group tend to have similar chemical and physicalproperties. There is a change in chemical and physical propertiesacross a period. The repeating pattern of physical and chemicalproperties shown by the different periods is known as periodicity.

These periodic trends can clearly be seen in atomic radii, ionic radii,ionization energies, electronegativities and melting points.

electrons increases.• Silicon in the middle

of the period has amacromolecularcovalent structure with very strong bonds resulting in a very high melting point.

• Elements in groups 5, 6, and 7 (P4' S8' and C12) show simple molecular structures with weak van der Waals' forces ofattraction between the molecules.

• The noble gases (Ar) exist as monatomic molecules (single atoms) with extremely weak forces of attraction between the atoms.

Within groups there are also clear trends:• In group 1 the melting point decreases down the group as the atoms become larger and the strength of the metallic bond

decreases.Li Na K Rb Cs

M. pt! K 454 371 336 312 302• In group 7 the van der Waals' attractive forces between the diatomic molecules increase down the group so the melting points

MELTING POINTSMelting points depend 5000both on the structure ofthe element and on the Ctype of attractive forces 4000holding the atomstogether. Using period

:L

3 as an example: c 3000'0Q.

• At the left of the OJ)c

period elements·z

20000;

exhibit metallic E

bonding (Na, Mg,AI), which increases 1000

in strength as theH Henumber of valence

o2 4

increase.

M. pt! K

ELECTRONEGATIVITYElectronegativity is a relative measure of the attractionthat an atom has for a shared pair of electrons when itis covalently bonded to another atom. As the size ofthe atom decreases the electronegativity increases, sothe value increases across a period and decreasesdown a Group. The three most electronegativeelements are F, N, and O.

H2.1 ILi Be B C N 0 F1.0 1.5 2.0 2.5 3.0 3.5 4.0

Na CI0.9 3.0

K Br0.8 2.8

I2.5

Si

N 0

Ca

Kp S CI ArNe

5 6 8 10 12 14 15 17 19 2016 187 9 11 13

atomic number

FIRST IONIZATION ENERGYThe defi n ition of fi rst ion ization energy has been given on page 9.The values decrease down each group as the outer electron is furtherfrom the nucleus and therefore less energy is required to remove it,e.g. for the group 1 elements, Li, Na and K.

Element:Electron arrangementFirst ionization energy (k] mol "l

Li2.1519

Na2.8.1494

K2.8.8.1

418

Generally the values increase across a period. This is because theextra electrons are filling the same energy level and the extraprotons in the nucleus attract this energy level closer making itharder to remove an electron, e.g. for the third period.

Element Na Mg AI Si P S CI ArNumber of

11 12 l3 14 15 16 17 18protonsElectronarrangement 2.8.1 2.8.2 2.8.32.8.4 2.8.5 2.8.6 2.8.7 2.8.8

First ionizationenergy (kJ mol ") 494 736 577 786 1060 1000 12601520

Periodicity 13

The Periodic Table and chemical propertiesCHEMICAL PROPERTIES OF ELEMENTS IN THE SAME GROUPGroup 1 - the alkali metals

Lithium, sodium, and potassium all contain one electron in their outer shell. They are all reactive metals andare stored under liquid paraffin to prevent them reacting with air. They react by losing their outer electron toform the metal ion. Because they can readily lose an electron they are good reducing agents. The reactivityincreases down the group as the outer electron is in successively higher energy levels and less energy isrequired to remove it.

Li 10>>-Na .~.-e=(J) >

K gl'DRb t; glCs .s ~

They are called alkali metals because they all react with water to form an alkali solution of the metal hydroxide and hydrogengas. Lithium floats and reacts quietly, sodium melts into a ball which darts around on the surface, and the heat generated fromthe reaction with potassium ignites the hydrogen.

2Li(s) + 2HP(I) -- 2Li+(aq) + 20H-(aq) + H2(g)

2Na(s) + 2HP(I) -- 2Na+(aq) + 20H-(aq) + H2(g)

2K(s) + 2Hp(I) -- 2K+(aq) + 20H-(aq) + H2(g)

They all also react readily with chlorine, bromine and iodine to form ionic salts, e.g.

2Na(s) + CI2(g) -- 2Na+CI-(s)

2K(s) + Br2(1) -- 2K+B,(s)

2Li(s) + 12(g) --> 2Li+I-(s)

Group 7 - the halogensThe halogens react by gaining one more electron to form halide ions. They are good oxidizing agents. Thereactivity decreases down the group as the outer shell is increasingly at higher energy levels and further fromthe nucleus. This, together with the fact that there are more electrons between the nucleus and the outer shell,decreases the attraction for an extra electron.

Chlorine is a stronger oxidizing agent than bromine, so can remove the electron from bromide ions in solution to form chlorideions and bromine. Similarly both chlorine and bromine can oxidize iodide ions to form iodine.

CI2(aq) + 2B,(aq) -- 2CI-(aq) + Br2(aq)

CI2(aq) + 2I-(aq) -- 2CI-(aq) + 12(aq)

Br2(aq) + 2I-(aq) --> 2B,(aq) + 12(aq)

Test for halide ionsThe presence of halide ions in solution can be detected by adding silver nitrate solution. The silver ions react with the halide ionsto form a precipitate of the silver halide. The silver halides can be distinguished by their colour. These silver halides react withlight to form silver metal. This is the basis of photography.

Ag+(aq) + X-(aq) -- AgX(s) where X = CI, Br, or I

light jAg(s) +iX2

AgCI white

AgBr cream

AgI yellow

CHANGE FROM METALLIC TO NON-METALLIC NATURE OF THE ELEMENTS ACROSS PERIOD 3Metals tend to be shiny and are good conductors of heat and electricity. Sodium, magnesium, and aluminium all conductelectricity well. Silicon is a semi-conductor and is called a metalloid as it possesses some of the properties of a metal andsome of a non-metal. Phosphorus, sulfur, chlorine, and argon are non-metals and do not conduct electricity. Metals can alsobe distinguished from non-metals by their chemical properties. Metal oxides tend to be basic, whereas non-metal oxides tendto be acidic.

Sodium oxide and magnesium oxide are both basic and react with water to form hydroxides,

MgO(s) + H20(I) -- Mg(OH)2e.g.

Aluminium is a metal but its oxide is amphoteric, that is, it can be either basic or acidic depending on whether it is reacting withan acid or a base.

The remaining elements in period 3 have acidic oxides. For example, sulfur trioxide reacts with water to form sulfuric acid, andphosphorus pentoxide reacts with water to form phosphoric(V) acid.

14 Periodicity

Oxides of the third period (sodium ~ argon)• 'i5eTh ~~~_~rF~

OXIDES OF PERIOD 3 ELEMENTSThe oxides of sodium, magnesium, and aluminium are all ionic. This accounts for their high melting points and electricalconductivity when molten. Silicon dioxide has a diamond-like macromolecular structure with a high boiling point. At the otherend of the period the difference in electronegativities between the element and oxygen is small, resulting in simple covalentmolecular structures with low melting and boiling points.

The acid-base properties of the oxides are also linked to their structure. The oxides of the electropositive elements are very basicand form solutions that are alkaline.

Nap(s) + H20(I) -- 2Na+(aq) + 20H-(aq)

MgO(s) + H20(I) -- Mg(OH)2

The amphoteric nature of aluminium oxide can be seen from its reactions with hydrochloric acid and sodium hydroxide.

Acting as a base: AI203(s) + 6HCI(aq) -- 2AICI3(aq) + 3H2O(I) •Acting as an acid: AI203(s) + 2NaOH(aq) + 3H20(I) -- 2NaAI(OH)4(aq)

sodium aluminate

Silicon dioxide behaves asa weak acid. It does not react with water but will form sodium silicate with sodium hydroxide.

Si02(s) + 2NaOH(aq) -- Na2Si03(aq) + H2O(aq)

The oxides of phosphorus, sulfur, and chlorine are all strongly acidic.

S02(g) + H20(I) -- H2S03 sulfurous acid

p4010(S)+ 6H20(l) -- 4H3P04(aq) phosphoric acid

CI207(1) + H20(I) --> 2HCI04(aq) perchloric acid

Oxides of period 3 elements

Formula Na20 MgO AI203 Si02P40,0 S03 CI207

(P406) (S02) (CIP)

State at 25°C Solid Solid Solid SolidSolid Liquid Liquid(Solid) (Gas) (Gas)

Melting point / °C 1275 2852 2027 1610 24 17 -92

Boiling point / °C - 3600 2980 2230 175 45 80

Electrical Good Good Good Very poor None None Noneconductivityin molten state

\. .) \. )

Y Covalent yStructure Ionic macromolecular Simple covalent molecular

Reaction with water Forms Forms Does Does P4O,0 S03 forms Cl207

NaOH(aq), Mg(OH)2' not react not react forms H2S04, a formsan alkaline weakly H3P04, strong acid HCl04,solution alkaline an acidic an acidic

Isolution solution

~

\. )V

Nature of oxide Basic Amphoteric Acidic

L- __• .rMm:.~'" LJJtii1.~~~ • Iii. S1m~_ • .twf. -.~

Periodicity 15

Chlorides of the third period (sodium ~ argon)

CHLORIDES OF PERIOD 3 ELEMENTSThe physical properties of the chlorides are related to the structure in the sameway as the oxides. Sodium chloride andmagnesium chloride are ionic - they conduct electricity when molten and have high melting points. Aluminium chloride iscovalent and is a poor conductor. Unlike silicon dioxide, silicon tetrachloride hasa simple molecular structure as do theremaining chlorides in the period. These molecules are held together by weak van der Waals' forces, which results in lowmelting and boiling points.

Sodium chloride dissolves in water to give a neutral solution, magnesium chloride gives a slightly acidic solution with water.All the other chlorides including aluminium chloride react vigorously with water to produce acidic solutions of hydrochloricacid together with fumes of hydrogen chloride.

2AICI3(s) + 3H20(I) --...AI203(S) + 6HCI(aq)

SiCI4(1)+ 4H20(I) -+ Si(OH)4(aq) + 4HCI(aq)

PCI3(1)+ 3H20(I) --...H3P03(aq) + 3HCI(aq)

Chlorine itself reacts with water to some extent to form an acidic solution.

CI2(aq) + H20(I) = HCI(aq) + HCIO(aq)

Chlorides of period 3 elements

Formula NaCI MgCI2 AI2CI6 SiCI4PCl3 (S2CI2) CI2(PCls)

State at 25 °C Solid Solid Solid Liquid Liquid (Solid) Liquid Gas

Melting point / °C178801 714 (sublimes) -70 -112 -80 -101

Boiling point /oC 1413 1412 - 58 76 136 -35Electrical Good Good Poor None None None Noneconductivityin molten state

Structure Ionic Simple covalent molecular

Reaction Somewith reactionwater Dissolve easily Fumesof HCI produced with water

Nature of solution NeutralWeakly

Acidicacidic,,.. • • • • • . iliii&& l\i.~ • .~~ __ 1$. 1 ~~ il.}"'~

16 Periodicity

d-block elements (first row)

ElementElectronconfiguration [Ar] 4s23d1

Ti Mn Fe Co CuTHE FIRST ROW TRANSITION ELEMENTS

(Sc) v Cr Ni (Zn)

A transition element is defined as an element that possesses an incomplete d sub-level in one or more of its oxidation states.Scandium is not a typical transition metal as its common ion Sc3+ has no d electrons. Zinc is not a transition metal as it containsa full d sub-level in all its oxidation states. (Note: for Cr and Cu it is more energetically favourable to half-fill and completely fillthe d sub-level respectively so they contain only one 4s electron).~~~~'~~..:~~~..:~~

Cu(+1) Cu20 copper(l) oxide

f- •• ".- Jl ~ ,, CHARACTERISTIC PROPERTIES, OF TRANSITION ELEMENTS'-------.-I------~~~~~

~~.~~~Variable oxidation statesThe 3d and 4s sub-levels are very similar inenergy. When transition metals lose electronsthey lose the 4s electrons first. All transitionmetals can show an oxidation state of +2.Some of the transition metals can form the +3or +4 ion (e.g. Fe3+, Mn4+) as the ionizationenergies are such that up to two d electronscan also be lost. The M4+ ion is rare and inthe higher oxidation states the element isusually found not as the free metal ion buteither covalently bonded or as the oxyanion,such as Mn04-. Some common examples ofvariable oxidation states in addition to +2 are:

Cr(+3) CrCI3 chromium(lIl) chloride

Cr(+6) Cr2°l- dichromate(VI) ion

Mn(+4) Mn02 manganese(IV) oxide

Mn(+7) Mn04- manganate(VII) ion

Fe(+3) Fe203 iron(llI) oxide

, ~ •• amr

Formation of complex ionsBecause of their small size d-block ions attract species that are rich inelectrons. Such species are known as ligands. Ligands are neutral moleculesor anions which contain a non-bonding pair of electrons. These electronpairs can form co-ordinate covalent bonds with the metal ion to formcomplex ions.

A common ligand is water and most (but not all) transition metal ions existas hexahydrated complex ions in aqueous solution, e.g. [Fe(H20)613+.Ligands can be replaced by other ligands. A typical example is the additionof ammonia to an aqueous solution of copper(ll) sulfate to give the deepblue colour of the tetraaminecopper(ll) ion. Similarly if concentratedhydrochloric acid is added to a solution of Cu2+(aq) the yellowtetrachlorocopper(ll) anion is formed. Note: in this ion the overall chargeon the ion is -2 as the four ligands each have a charge of -1.

CI- NH3[CuCI4j2- = [Cu(H20)412+ ~- [Cu(NH3)4j2+

H20 H20

The number of lone pairs bonded to the metal ion is known as the co-ordination number. Compounds with a co-ordination number of six areoctahedral in shape, those with a co-ordination number of four aretetrahedral or square planar, whereas those with a co-ordination numberof two are usually linear.

6[Fe(CN)6j3-

[Fe(OH)}(H20)3]

Co-ordination numberExamples

Coloured complexesIn the free ion the five d orbitals are degenerate (of equalenergy). However, in complexes the d orbitals are split intotwo distinct levels. The energy difference between the levelscorresponds to a particular wavelength or frequency in thevisible region of the spectrum. When light falls on thecomplex, energy of a particular wavelength is absorbed andelectrons are excited from the lower level to the higher level.

Cu2+(aq) appears blue because it is the complementarycolour to the wavelengths that have been absorbed. Theamount the orbitals are split depends on the nature of thetransition metal, the oxidation state, the shape of thecomplex, and the nature of the ligand, which explains whydifferent complexes have different colours. If the d orbital iscompletely empty, as in Sc3+, or completely full, as in Cu"or Zn2+, no transitions within the d level can take place andthe complexes are colourless.

.1~ .1.1i reflected light

energy absorbecJ ~ complementaryIl E as electron promoted colour to

t t 1~ l t t 1 absorbedlight

--;:.~M3do ~corr~p;:d:;-;;' particularcomplex wavelength in visible region

white light~

4[CuCI4]2-

[Cu(NH3)4]2+

Catalytic behaviourMany transition elements and their compounds are veryefficient catalysts, that is, they increase the rate of chemicalreactions. This helps to make industrial processes, such asthe production of ammonia and sulfuric acid, more efficientand economic. Platinum and palladium are used incatalytic converters fitted to cars. In the body, iron is foundin haem and cobalt is found in vitamin B12. Other commonexamples include:

Iron inthe Haberprocess

Vanadium(V)oxide in theContact process

Nickel inhydrogenationreactions

Manganese(IV)oxide withhydrogen peroxide

Mn02(s)2H202(aq) , 2H20(I) + °2(g)

Periodicity 17

18 QUESTIONS - PERIODICITY

1. In the periodic table, elements are arranged in order ofincreasing

A. atomic number. C. number of valence electrons.

B. atomic mass. D. electronegativity.

2. Which one of the following series is arranged in order ofincreasing value?

A. The first ionisation energies of: oxygen, fluorine, neon.

B. The radii of: H- ion, H atom, H+ ion.

C. The electronegativities of: chlorine, bromine, iodine.

D. The boiling points of: iodine, bromine, chlorine.

3. Which property increases with increasing atomic numberfor both the alkali metals and the halogens?

A. lonisation energies

B. Melting points

C. Electronegativities

D. Atomic radii

4. Which set of reactants below is expected to produce themost vigorous reaction?

A. Na(s) + CI2(g)

B. Na(s) + Br2(g)

C. K(s) + CI2(g)

D. K(s) + Br2(g)

5. Which one of the following statements about the halogengroup is correct?

A. First ionisation energies increase from F to I.

B. Fluorine has the smallest tendency to be reduced.

C. CI2 will oxidise I-(aq).

D. 12 is a stronger oxidising agent than F2.

6. Strontium is an element in Group 2 of the Periodic Tablewith atomic number 38. Which of the following statementsabout strontium is NOT correct?

A. Its first ionisation energy is lower than that of calcium.

B. It has two electrons in its outermost energy level.

C. Its atomic radius is smaller than magnesium.

D. It forms a chloride with the formula SrCI2.

7. Which one of the following elements has the lowest firstion isation energy?

A. Li

B. Na

C. Mg

D.AI

8. Which element is most similar chemically to the elementwith 14 electrons?

A. AI

B. As

C. Ge

D. P

9. 0.01 mole samples of the following oxides were added toseparate 1 dm ' portions of water. Which will produce themost acidic solution?

A. AI203(s)

B. Si02(s)

C. Na20(s)

D. S03(g)

10. Which reaction occurs readily?

I. Br2(aq) + 2I-(aq) ~ 12(aq) + 2 Br-(aq)

II. Br2(aq) + 2CI-(aq) ~ CI2(aq) + 2Br-(aq)

A. lonly

B. II only

C. Both I and II

D. Neither I nor II

11. In which region of the Periodic Table would the elementwith the electronic structure below be located?

1s22s22p63s23p63dlo4s24p64d65s2

A. group 6 C. s block

B. noble gases D. d block

12. A certain element has the electronic configuration1s22s22p63s23p64s23d3 Which oxidation state(s) wouldthis element most likely show?

A. +2 only

B. +3 only

C. +2 and +5 only

D.+2,+3,+4,+5

13. Which ion is colourless?

A. [Cr(H20)613+

B. [Fe(CN)614-

C. [Cu(NH3)412+

D. [Zn(H20)412+

18 IB questions - Periodicity

14. Which of the following chlorides give neutral solutionswhen added to water?

I. NaCI

II. AI2CI6

III. PCl3

A. lonly

B. I and II only

C. II and III only

D.I, II and III

15. Based on melting points, the dividing line between ionicand covalent chlorides of the elements Mg to S liesbetween

A. Mg and AI.

B. AI and Si.

C. Si and P.

D. P and S.

16.The colours of the compounds of d-block elements are dueto electron transitions

A. between different d orbitals.

B. between d orbitals and s orbitals.

C. among the attached ligands.

D. from the metal to the attached ligands.