Classification of Matter

what is periodicity?

the trends observed across periods and down groups

atomic radius trend across a period

• generally decreases

• atomic number increases = increased nuclear charge

• additional electrons added in same shell so shielding between nucleus and outer electrons roughly the same

• increased nuclear charge = stronger attraction between nucleus and outer shell electrons = decreasing atomic radius

atomic radius trend down a group

• generally increases

• down a group the number of shells increases = outer shell electrons further from nucleus = weaker attraction

• electrons in inner shells repel outer electrons = increased shielding

what occurs to the ionic radius of a cation

• decreases compared to parent atom

• loss of electrons, often loss of outer shell = fewer repulsions so greater attraction to nucleus

what occurs to the ionic radius of anions?

• generally increases compared to parent ion

• extra electrons gained = increased repulsion = decreased attraction to nucleus

what is the ionic radius trend across a period?

• for cations it decreases

• where anions form it sharply increases and then decreases again as nuclear charge increases

what is the ionic radius trend down a group?

increases

what is the ionization energy?

amount of energy required to remove one mole of electrons from one mole of atoms of an element in the gaseous state to form one mole of ions

what are the units of ionization energy?

kJmol^-1

what is the ionization energy trend across a period?

• generally increases

• nuclear charge increases, shielding remains rougly constant

• so stronger attraction to nucleus

• so more energy needed to overcome stronger attraction

what happens to the ionization energy between the last element in one period and the first in the next?

rapid decrease due to increased distance between nucleus and outer shell electrons and increased shielding

what is the ionization energy trend going down a group?

• generally decreases

• number of energy levels increases so outer shell electrons are farther from nucleus

• experience increased shielding

• so attraction between nucleus and outer shell electrons decreases

• so less energy required to remove outermost electron

what is electron affinity?

amount of energy released when one mole of electrons is gained by one mole of atoms of an element in the gaseous state to form one mole of ions

what are the units of electron affinity?

kJmol^-1

what are the electron affinity trends across a period?

• becomes more negative (more exothermic)

• nuclear charge increases, atomic radius decreases

• so stronger attraction to nucleus

what are the electron affinity trends down a group?

• less negative (less exothermic)

• number of shells increases, atomic radius increases, shielding increases

• so electrons are further from the nucleus and have less attraction

what is electronegativity?

the ability of an atom to attract a pair of electrons towards itself in a covalent bond

what is the trend of electronegativity across a period?

increases

• nuclear charge increases

• shielding is constant

• atomic radius decreases

• so stronger attraction to nucleus

what is the trend of electronegativity down a group?

decreases

• nuclear charge increases

• increased shielding (more shells)

• larger atomic radius

• weaker attraction to nucleus

physical properties of group 1 metals

• soft, easy to cut

• shiny when cut

• conduct heat and electricity

• low melting points

• low densities

chemical properties of group 1 metals

• react readily with oxygen and water vapour

• react vigorously with water to form an alkaline metal hydroxide solution and hydrogen gas

what is the equation for group 1 metal + water?

group 1 metal + water → group 1 metal hydroxide + hydrogen

what would be observed in a reaction between lithium and water?

• floats and reacts slowly

• bubbles of hydrogen gas

• clear, colourless solution formed

what would be observed in a reaction between sodium and water?

• reacts more vigorously than lithium but less than potassium

• bubbles of hydrogen gas

• sodium melts to form a silvery ball that moves on the surface

• clear, colourless solution formed

what would be observed in a reaction between potassium and water?

• reacts more violently than sodium and lithium

• hydrogen gas released rapidly

• potassium melts into a shiny ball that dashes around on the surface

• produces a lilac flame

• forms a clear, colourless solution

what is the trend in reactivity down group 1?

increases

• atoms get larger

• outermost electron further from the nucleus

• more shielding

• so weaker attraction

• so outer shell electron lost more easily

what is the state and colour of fluorine at room temperature?

yellow gas

what is the state and colour of chlorine at room temperature?

pale green gas

what is the state and colour of bromine at room temperature?

orange-brown liquid, readily evaporates to form brown gas

what is the state and colour of iodine at room temperature?

grey-black solid that sublimes to form a purple vapour

what is the colour of chlorine in water?

green-blue

what is the colour of bromine in water?

orange

what is the colour of iodine in water?

dark brown

what is the trend in reactivity down group 17?

decreases

• atomic radius increases

• number of shells + shielding increases

• electron affinity becomes less negative

• attraction between nucleus and outer shell electrons decreases so less reactive

what occurs in displacement of halogens with halide ions?

a more reactive halogen will displace a less reactive halogen from an aqueous solution of its halide

what does amphoteric mean?

a substance can act as an acid and a base

what causes acid rain?

non-metal oxides dissolving in atmospheric water

how does ocean acidification occur?

CO₂ dissolves in seawater to form carbonic acid, which dissociates to hydrogen carbonate ions and hydrogen ions, increased hydrogen ions lowers pH

what are the characteristic properties of transition elements?

• variable oxidation states

• high melting points

• magnetic properties

• catalytic behaviour

• formation of coloured compounds

• ability to form complex ions with ligands

how does transition metal magnetism arise?

• unpaired electrons in d orbitals

• each spinning electron generates a tiny magnetic dipole

• paired electrons spin in opposite directions cancelling the dipole

• where they are unpaired they can become aligned in an external magnetic field and produce magnetism

how do you form a permanent magnet?

• by heating and cooling iron, nickel or cobalt in a magnetic field

• magnetic dipoles align and the material retains its magnetism

why can transition elements catalyse redox reactions?

• variable oxidation state means they can accept and lose electrons

• they can be oxidised and reduced repeatedly so catalysing redox reactions

what is a hetergenous catalyst?

one in a different state to the reactants

what is a homogenous catalyst?

one in the same state as the reactants

what do catalytic converters do?

reduce air pollution in car exhausts

what is a ligand?

a molecule or ion that donates a lone pair of electrons

why do transition metal compounds appear coloured?

• in an octahedral complex there is d-orbital splitting

• a wavelength of visible light is absorbed

• this excites an electron

• and the complementary colour is observed

what does the structural formula show?

the spatial arrangement of atoms and bonds in a molecule

what is a skeletal formula?

simplified way of representing organic molecules

• carbon-carbon bonds shown as straight lines

• hydrogen atoms bonded to C omitted unless part of a functional group

what is a stereochemical formula?

shows the three dimensional arrangement of atoms or groups around a chiral carbon

what is a chiral carbon?

bonded to four different groups or atoms creating a tetrahedral shape with bond angles of 109.5º

what is the functional group name of an alkane?

alkyl

what is the functional group name and formula of an alkene?

alkenyl

what is the functional group name and formula of an alkyne?

alkynyl

what is the functional group name and formula of an halogenoalkane?

halogeno

F-, Cl-, Br-, I-

what is the functional group name and formula of an alcohol?

hydroxyl

what is the functional group name and formula of an aldehyde?

carbonyl

what is the functional group name and formula of a ketone?

carbonyl (ketone)

what is the functional group name and formula of a carboxylic acid?

carboxyl

what is the functional group name and formula of an ether?

alkoxy

what is the functional group name and formula of an amine?

amino

what is the functional group name and formula of an amide?

amido

what is the functional group name and formula of an ester?

ester

what is the functional group name and formula of an aromatic?

phenyl

what is a homologous series?

a family of similar compounds with the same functional group and similar chemical properties

what are the characteristic features of a homologous series?

• each member has the same functional group

• same general formula

• similar chemical properties

• each member differs by -CH₂-

• gradually changing physical properties

what is the trend in melting point/boiling point for a straight chain homologous series?

as the number of carbon atoms increases so does the bp and mp

why does bp/mp increase in a straight chain homologous series?

• each member differs by CH₂

• increases molecular size and area so stronger london dispersion forces

• stronger forces = more energy required to separate molecules

what are structural isomers?

compounds with the same molecular formula but different structural formulae

what are the three types of structural isomerism?

• functional group isomerism

• positional isomerism

• branched chain isomerism

what is functional group isomerism?

where different functional groups result from the same molecular formula

what is positional isomerism?

where isomers have the same molecular formula and the same functional group, but the functional group is in a different place in the chain

what is branched chain isomerism?

compounds have the same molecular formula but their longest hydrocarbon chain is not the same

what are stereoisomers?

compounds with the same atoms bonded to each other but arranged differently in space

what are the two types of stereoisomerism?

• conformational

• configurational

what is conformational isomerism?

compounds with the same atoms bonded to each other but different spatial arrangement due to free rotation around a single sigma bond

what is configurational isomerism?

compounds with the same atoms bonded to each other but different spatial arrangements that cannot be interconverted by rotation due to a pi bond

what is a cis isomer?

has two functional groups on the same side of a carbon-carbon double bond

what is a trans isomer?

has two functional groups on opposite sides of a carbon-carbon double bond

what are optical isomers?

chemical that contain a chiral carbon (a carbon with four different atoms or groups attached)

what are enantiomers?

a pair of chiral molecules that are non-superimposable mirror images of each other

what are diastereomers?

compounds with more than one chiral centre

what are the chemical properties of enantiomers?

optical isomers have different smells

what are the physical properties of optical isomers?

identical physical properties except

• enantiomers can rotate the plane of polarised light (optically active)

• diastereomers are not optically active

how can you determine between enantiomers?

by the rotation of plane polarised light

what is a racemic mixture?

mixture containing a 50:50 ratio of enantiomers

is a racemic mixture optically active?

no because each enantiomer will cancel the other’s effect on plane polarised light

what is detected on a mass spectrum?

only positively charged fragments

what does the highest peak of a mass spectrum show?

the parent ion or the Mr of the whole compound

what does IR spectroscopy measure?

changes in vibrations of atoms when they absorb IR

what must a molecule have to be IR active?

a permanent dipole