UNIT 3 - Periodicty

Question 1

Define electron affinity.

Answer 1

energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions

usually exothermic reaction but it might be endothermic if the added electron is repelled by the negatively charged ion
(e.g. oxide ion O-)

noble gases do not have it.

Question 2

Determine how the melting point changes in the period and what does it depend on.

Answer 2

on the type of bonding and the structure of it -> high melting point = ionic or covalent giant structures, low = molecular covalent

Decrease down group 1 as the elements have metallic structure held together by attractive forces between delocalized outer electrons and positively charged ions.

Decreases with distance.

Increases down group 17 as its elements are held together by London dispersion forces.

Question 3

Define transition metals.

Answer 3

Elements of block d with the exception of group 12 that has specific transition metal properties.

Question 4

Name the group 15 of the periodic table.

Answer 4

Pnictogens

Question 5

List the properties of transition metals.

Answer 5

• many oxidation states
• catalytic properties
• form coloured compounds
• form complex compounds with ligands
• magnetic properties depend on oxidation - - - states and coordination no
• high electrical and thermal conductivity
• high melting point
• malleable
• high tensile strength
• ductile

Question 6

Define a metallic bond.

Answer 6

Electrostatic attraction between cations and sea of delocalized electrons.

Question 7

Define malleable.

Answer 7

Easily bent into shape.

Question 8

Define halogens.

Answer 8

Reactive non-metals of group 17.

Question 9

Define high tensile strength.

Answer 9

Can hold large loads.

Question 10

Write reaction of Cl2 with water.

Answer 10

Cl2 + H2O -> HCl + HClO

Question 11

Define ductile.

Answer 11

Can easily be drawn into wires.

Question 12

Define noble gases.

Answer 12

Very unreactive non-metal family of group 18.

Question 13

Define electronegativity and state what does a change of it relate to.

Answer 13

Measure of the ability of an atom to attract electrons in a covalent bond.

High electronegativity->strong pulling power
change in it relates to the attraction of the nucleus.

again doesn’t apply to group 18.

Question 14

Characterize the noble gases.

Answer 14

• colourless
• gases
• monatomic - exist as single atoms
  very unreactive - due to inability to lose or gain electrons -> form stable octet (complete valence energy levels with eight electrons)

Question 15

List the processes (4) and name them where transition metals are the catalysts.

Answer 15

contact process: 2SO2+O2–V2O5->2SO3

decomposition of H2O2: 2H2O2–MnO2 -> H2O+O2

Haber process: N2+3H2-Fe-> 2NH3

Hydrogenation: H2C=CH2+H2–Ni,Pt,Pd->CH3-CH3

Question 16

Define London dispersion forces.

Answer 16

The weakest intermolecular force.

The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles.

This force is sometimes called an induced dipole-induced dipole attraction.

London forces are the attractive forces that cause nonpolar substances to condense to liquids and to freeze into solids when the temperature is lowered sufficiently.

Question 17

Explain why transition metals can easily form alloys.

Answer 17

Because of the similarity in the atomic radii and thus the atoms of one d-block metal can easily be replaced by atoms of another without too much disruption to the solid structure.

Question 18

Name the group 16 of the periodic table.

Answer 18

Chalcogens

Question 19

Explain why transition metals form strong metallic bonds and are good electricity conductors.

Answer 19

3d and 4s are close in energy and are involved in bonding so they form parts of delocalized sea of electrons which holds the metal together.
Therefore the large numbers of electrons involved accounts for the strength of the bond and high electrical conductivity.

Question 20

State how and why the atomic radii changes in the periodic table.

Answer 20

Increases down a group as the number of electron increases.

Question 21

Define a ligand.

Answer 21

Molecule/ion that has a lone pair of electrons that forms a coordinate bond to a central atom and together forms a coordination compound.

Question 22

Define lanthanoides & actinoides.

Answer 22

Metals which make up the first and second row of the f block.

Question 23

Define denticity.

Answer 23

The number of coordinate bonds the ligands can form.

Question 24

Define a displacement reaction.

Answer 24

The more reactive element displaces the ions of the less reactive one from its compounds.

Question 25

Define coordinate number.

Answer 25

The number of bonds that all the ligands create with the transition metal.

Question 26

Determine why do metals conduct electricity.

Answer 26

Because their valence electrons are able to move away from the atomic nucleus
usually assisted by low electronegativity and low ionization energies.

Question 27

State what charges can a ligand have with examples.

Answer 27

• neutral e.g. H20, NH3
• negative e.g. EDTA 4-

Question 28

Distinguish the chemical character of period 3 oxides, what does it depend on.

Answer 28

Acid-base properties depend on the bonding and structure.

• ionic oxides, metallic elements = basic
• non-metal oxides, covalent = acidic
• ionic oxide, covalent character = amphoteric

Basic oxides: dissolve in water forming alkaline solutions, reacts with and acid forming salt and water.

Acidic oxide: reacts with water to produce acidic solution.

Amphoteric oxide: Al2O3 - doesn’t affect the pH when added to water, insoluble in water, behaves as a base with acids but as an acid with bases (forms complexes).

Question 29

Define what is a crystal field theory.

Answer 29

Electrostatic model where ligands are considered as point charges that surround metal cation.

Question 30

Define metalloids.

Answer 30

Characteristics of both metal and non-metal, physically more metals, chemically more non-metals.

Question 31

List factors influencing the crystal field splitting energy.

Answer 31

• identity of a metal (higher energy = down group)
• oxidation state of a metal (the higher energy = higher oxidation state)
• geometry
• nature of a ligand

Question 32

State what are the chemical properties determined by.

Answer 32

The number of valence electrons in their outer energy levels.

Question 33

Explain why do complex ion form.

Answer 33

Transition metals have high charge density and attract water molecules which form coordinate bods with the positive ions to form a complex.

Question 34

Name the group 2 of the periodic table.

Answer 34

Alkaline-earth metals.

Question 35

Explain where and why transition metals act as heterogenous catalysts.

Answer 35

Where catalyst is in a different state grom reactants.

Because their 3d and 4s electrons form weak bonds to reactant molecules providing a surface for the reactants to come together with the correct orientation.

e.g. Haber process, nickel in conversion of alkenes to alkanes.

Question 36

Define alkali metals.

Answer 36

Reactive group of group 1s block metals.

Question 37

Explain where and why transition metals act as homogenous catalysts.

Answer 37

Catalysts and reactants are in the same state.

Because of their variable oxidation states especially in redoxes.

e.g. Fe2+ in heme, Co3+ in vit B12

Question 38

Define a chelate and provide and example and its use in real life.

Answer 38

Complex containing at least one polydentate ligand (name derived from Greek “claw”)

e.g. EDTA4– food additive, DNA preserver, detoxification of patients with heavy metal food poisoning.

Question 39

List and define the magnetic properties.

Answer 39

• diamagnetism - property of all materials, v weak opposition to any applied magnetic field
• paramagnetism - only in substances with unpaired electrons, stronger, magnetization proportional to applied field
• ferromagnetism - largest effect, long range ordering of unpaired electrons, able to retain its own magnetic field e.g. Fe, Ni, Co

Question 40

State by what is the nuclear charge given and how does it change successively in the periodic table.

Answer 40

By the atomic number.

Increases by one as the proton is added to the nucleus.

Question 41

Define domains in the context of ferromagnetism.

Answer 41

Regions with large numbers of atoms lined up with unpaired d electrons with parallel spins, remains even after the external magnetic field is applied.

Question 42

Is Si(OH)4 an acid or a base?

Answer 42

Acid

Question 43

When do degenerated d orbitals split into two sublevels?

Answer 43

In the presence of ligands lone pair of electrons and the electric field produced.

Question 44

Characterize the alkali metals, with distinction to physical and chemical properties, how and why their properties change in the periodic table and how they behave in chemical reactions.

Answer 44

• silvery metals
• name because the resulting solution is alkaline
• too reactive to be found in nature -> stored in oil usually to prevent contact with air and water
• form single charged ions M+
• conductivity because outer electrons are mobile

PHYSICAL:
- good conductors of electricity and heat
- have low density
- have grey shiny surfaces when freshly cut with a knife

CHEMICAL:
- very reactive
- form ionic compounds with non-metals

• reactivity increases down the group -> high atomic number=low ionization energy
• react with water and produce hydrogen and the metal hydroxide.

Question 45

Characterize the halogens, with distinction to physical and chemical properties, how and why their properties change in the periodic table and how they behave in chemical reactions.

Answer 45

• exist in diatomic molecules X2

PHYSICAL:
- are coloured
- show gradual change from gases (F2 and Cl2), to liquid (Br2) and solids (I2 and At2)

CHEMICAL:
- very reactive non-metals - because they are ready to accept electrons because their nuclei have high effective charge of +7 = exert strong pull on any electron from other atoms
- form ionic compounds with metals and covalent compounds with other non-metals.

Their reactivity decreases down the group.

Form halides with group one metals, usually will be exothermic.

Question 46

What does the colour of the complex ion depend on?

Answer 46

• nuclear charge and identity of the central metal ion - strength of coordinate bond, high nuclear charge=better interaction
• the charge density of the ligand - high charge density=large split of d orbitals
• geometry of the complex ion - relative orientation of the ligand and d-orbitals
• number of electrons, oxidation of the central ion

Question 47

Define and list example of the shielding.

Answer 47

Outer electrons are partially shielded from the attractive force of the protons in the nucleus by inner electrons. Increases up the periods.

To explain how shielding works, consider a lithium atom. It has three protons and three electrons—two in the first principal energy level and its valence electron in the second. The valence electron is partially shielded from the attractive force of the nucleus by the two inner electrons. Removing that valence electron becomes easier because of the shielding effect.

There is also a shielding effect that occurs between sublevels within the same principal energy level. Specifically, an electron in the ss sublevel is capable of shielding electrons in the pp sublevel of the same principal energy level. This is because of the spherical shape of the ss orbital. The reverse is not true - electrons in the pp orbitals do not shield electrons in ss orbitals.

Question 48

Explain why do transition metals have many oxidation states?

Answer 48

Because of the energetic instability and thus close ionization energies.

Question 49

Write a reaction of NO2 with water.

Answer 49

NO2 + H2O -> HNO2 + HNO3

Question 50

Explain why do oxidation above +3 mean covalent character.

Answer 50

Because the ions of higher energy have such large charge that they polarize negative ions and increase covalent character.

Question 51

Define periodicity.

Answer 51

Repeating pattern of physical and chemical properties.

Question 52

State when is the solution with transition metals colourless.

Answer 52

When the d sub-level of the metal is full or empty.

Question 53

Characterize the period 3 oxides, the structures they form, what does it depend on.

Answer 53

Only conduct electricity in ion state when they are free to move.

They illustrate the transition from metallic to non-metallic character.

The bonds go as follows:
- giant ionic structure - Na-Al oxides
- molecular covalent - P, S, Cl oxides
- giant covalent structure - Si oxide

It all depends on the difference in electronegativity between elements.

Question 54

Explain why are the transition metal solutions colourful.

Answer 54

Metals with not-fully filled d orbitals -> d orbital splits into two energy levels under ligands influence -> visible light passes through sample -> d-to-d transitions occur absorbing specific energy -> colour complementary to the energy absorbed is SEEN.

Question 55

Determine how do halogens react with silver.

Answer 55

Form insoluble salts therefore if a solution containing silver ions is added to a solution containing the halide ions a precipitate is produced which is useful in identifying the halide ion.