semester 1 exammm

Question 1

what is atomic radius

Answer 1

distance from outermost electron to nucleus

atomic radius decreases left to right across a period due to:

atom’s increasing nuclear charge &

high nuclear charge increases attraction of electrons, bringing them closer to the nucleus therefore decreasing atomic radius

Question 2

what is ionisation energy

Answer 2

amount of energy needed to remove an electron from a neutral atom in the gaseous state

e.g. metals like lithium have low ionisation energy

non metals have high ionisation energy as they almost have a full valence shell

ionisation energy increases from left to right across a period

Question 3

what are the 3 factors that explain the trends of the periodic table

Answer 3

1. atom’s nuclear charge: great nuclear charge the more strongly electrons are attracted to the nucleus
2. atomic radius: as the distance between the nucleus and outermost electron increases, the strength of electron attraction decreases
3. sheilding by inner shell electrons: electrons in the inner shell repel other electrons between the nucleus and the outer electrons, blocking some of the atom’s electronegativity to the outer electrons

Question 4

what is effective nuclear charge

Answer 4

number of protons in nucleus - number of inner shell electrons

increases left to right: as nucleus becomes more positive attraction between nucleus and electrons becomes stronger (increasing effective nuclear charge.)

more energy needed

decreases down group: electrons get further from nucleus and are less strongly bound - sheilding effect is greater

Question 5

what is successive ionisation energy

Answer 5

energy needed to remove subsequent electrons

values become larger because electrons are being removed from ions which have increasing positive charges

Question 6

explain electronegativity

Answer 6

definition: the electron attracting power of an atom in a molecule

metals have low electronegativity values

non metals have high electronegativity values

increases across a period:

decreases down a group:

Question 7

what is emission spectra

Answer 7

when atoms absorb energy e.g. heat they become exited & can move up to a higher energy level (an e- shell thats further away)

when the e- moves back into its original position it releases light energy in all different directions

the light will have a specific wavelength unique to each element

for each particular element, all atom energy levels are identical

Question 8

what are the 3 different types of spectra

Answer 8

emission spectroscopy

atomic absorption spectroscopy (AAS)

mass spectrometry

Question 9

explain what atomic absorption spectroscopy (AAS) is

Answer 9

used to perform quantitative analysis (find amount of element present)

relies on electron transfer between atomic energy levels

uses the absorption of light by the atoms electrons to measure how much of an element is present

the lamp used for this process is made out of the same element being tested

e.g. if you were testing for zinc, you would use a zinc lamp

the light emitted has a unique set of wavelengths unique to the element.

Question 10

what is the best analytical technique for determining the isotopic concentration of a sample

Answer 10

atomic absorption spectroscopy

Question 11

explain the process of an atomic absorption spectrometer

Answer 11

1. an electric current is passed through a gaseous sample of the element so it will emit light
2. the light emitted has a unique set of wavelengths
3. the sample is vaporised
4. the light from the lamp is passed through the vaporised sample
5. the element being tested for will absorb the light
6. light enters the monochromator which focuses on 1 wavelength by the detector
7. detector measures amount of light passed through the sample that is not absorbed

Question 12

what is an isotope

Answer 12

atoms that have the same atomic number but different mass number (number of protons)

share the same chemical properties (due to same number of valence electrons)

physical properties (mass) will differ

Question 13

what is relative atomic mass

Answer 13

actual atomic mass is too small to calculate

it is the mass of the atom compared to 1 twelfth of the mass of a carbon-12 atom

its an average of all naturally occurring isotopes present

Question 14

list the properties of metal

Answer 14

good conductors of heat and electricity in solid & liquid state

shiny surface

hard

malleable

ductile

insoluble in water

reasonably high MP

very high BP

Question 15

describe metallic bonding

Answer 15

particles arranged as a lattice of positive cations surrounded by a sea of delocalised electrons

delocalised: can move around atoms and through the lattice

Question 16

explain the metallic property of heat/electricity conduction

Answer 16

when heated energy of cations and delocalised electrons increases

this energy is conducted along metals as cations and electrons collide, transferring electricity

when metals conduct electricity, electrons from one end of the metal cause a similar number of e- to be displaced from the other end

in sold: only electrons move
liquid: both cation and e- carry charge

Question 17

explain the metallic property of malleability and ductility

Answer 17

bonding in metals is NON DIRECTIONAL

layers of atoms can slide over each other without destroying metallic bond

Question 18

explain the metallic property of MP & BP

Answer 18

MP and BP indicate strength of intermolecular forces

relatively high MP and BP due to strong attraction between positive cations and mobile electrons

Question 19

explain the metallic property of hardness

Answer 19

strength of bond is related to charge of positive cations in lattice

metals in group 2 are stronger because atoms release 2 valence electrons (instead of 1 in group 1) and form ions with a +2 charge

Question 20

list the ionic properties

Answer 20

non conductors of electricity in solid state

good electrical conductors in molten or liquid state

hard

brittle

relatively high MP

relatively high BP

varying solubilities in water, insoluble in non-polar solvents

Question 21

describe ionic bonding

Answer 21

ionic solid:
positive and negative ion are arranged in an orderly 3D lattice

each positive ion is surrounded by negative ions and vice versa

ions are held in fixed positions by strong ionic bonds

Question 22

Explain the ionic property of conducting heat/electricity

Answer 22

solid: non conductors because ions are held in a fixed lattice, no mobile charged particles
molten: ions are now mobile, both positive and negative ions carry charge
aqueous: ions dissociate and are able to carry charge

Question 23

Explain the ionic property of MP and BP

Answer 23

high MP and BP:

ionic bonding has large electrostatic forces of attraction between holding atoms together in a lattice

large amount of energy is required to overcome strong ionic bonds

Question 24

Explain the ionic property of hardness

Answer 24

strong ionic bonding extends throughout lattice solid

scratching requires overcoming strong ionic bonds

Question 25

Explain the ionic property of brittleness

Answer 25

ionic lattice doesn't withstand distortion when lattice is distorted, like charges align and repel, shattering lattice

Question 26

Describe covalent molecular substances

Answer 26

exist only as discrete molecules non metals only solid, liquid or gaseous state intramolecular forces: strong covalent bond hold atoms together within a molecule intermolecular forces: weak forces of attraction between molecules

Question 27

list the properties of CMS

Answer 27

non conductors of electricity in solid and liquid some are weak/good conductors in aqueous solutions malleable soft low Mp and BP mostly insoluble in water, soluble in non-polar compounds examples: F2, H2O, O2

Question 28

explain the covalent molecular property of electricity conduction

Answer 28

non conductors in aq, s or l: molecules are uncharged electrons are held tightly within covalent bonds **exception: some CMS react with water to form ions, and become conductors in aqueous solutions

Question 29

explain the covalent molecular property of softness

Answer 29

weak intermolecular forces require little effort to overcome: easy to separate molecules strong covalent bonds aren't disrupted

Question 30

explain the covalent molecular property of malleability

Answer 30

molecules can easily slide or be pushed only weak intermolecular forced exist between them, these can easily be reformed

Question 31

explain the covalent molecular property of BP and MP

Answer 31

low BP and MP: when CMS are heated, little energy is needed to overcome weak intermolecular forces

Question 32

Describe covalent network substances

Answer 32

solid state only non metals only carbon with different structures are called allotropes: diamond and graphite examples of CNS substances: silicon, silicon dioxide, carbon

Question 33

List the properties of covalent network substances

Answer 33

non conductors of heat and electricity in solid and liquid state **exception: graphite extremely brittle extremely hard high MP and BP insoluble in water and most other solvents reasonably chemically inert

Question 34

Describe the bonding of covalent network substances

Answer 34

arranges in an infinite lattice structure

Question 35

explain the CNS property of electricity/heat conduction

Answer 35

non conductors: no mobile electrons because all valence electrons are tied up in covalent bonds **exception: graphite

Question 36

explain the CNS property of brittleness

Answer 36

if some bonds are broken, the rest of the lattice is placed under stress and shatters

Question 37

explain the CNS property of hardness

Answer 37

extremely hard: breaking strong covalent bonds requires a very large amount of energy

Question 38

explain the CNS property of MP and BP

Answer 38

high MP and BP: each atom is held in place by strong covalent bonds breaking these bonds requires a very large amount of energy

Question 39

explain the CNS property of solubility

Answer 39

insoluble in water & most other solvents: vary large amount of energy is required to re-arrange existing bonds in any dissolving process

Question 40

explain the CNS property of chemical inertness

Answer 40

reasonably chemically inert: all bonding requirement are fulfilled very large amounts of energy required to re-arrange existing bonds

Question 41

Briefly describe the structure and property of diamond

Answer 41

structure: each carbon atoms is attached to 4 other atoms in a 3D arrangement called a tetrahedron ``` properties: high MP (>3550˚C) non conductor of electricity brittle extremely hard ```

Question 42

Briefly describe the structure and property of graphite

Answer 42

structure: each carbon atoms is covalently bonded to 3 other atoms to form flat 2D sheets called graphene one valence electrons from each carbon remain delocalised properties: high MP good conductor of electricity soft

Question 43

what does the mole represent in mole/mass calculations

Answer 43

measure of the number of particles in a substance 1 mole of any substance contains 6.022 x 10(23) particles

Question 44

what does molar mass represent in mole/mass calculations

Answer 44

equal to atomic, molecule and formula masses in grams

Question 45

What is mass spectrometry used for

Answer 45

determines mass and relative abundance of each isotope present in a sample of an element

Question 46

describe the process of mass spectrometry

Answer 46

``` involved 4 steps: vaporisation ionisation acceleration detection ``` 1. sample is vaporised 2. electrons are fired at the sample and are used to knock off electrons from the atoms, forming ions 3. ions are accelerated and are deflected through a magnetic field (heavier ions are deflected less than lighter ions) 4. Ions are detected and produces a mass spectrum

Question 47

list 3 separation techniques

Answer 47

sieving filtration evaporation

Question 48

Briefly describe the separation technique of filtration

Answer 48

liquid passes through filter paper (filtrate) ad solid residue is left behind used for: separating very fine solid particles from liquids and gases

Question 49

Briefly describe the separation technique of sieving

Answer 49

mixture is passed through a sieve, a series of sieves may be used based on different sizes of components, smaller particles will pass through the hole, larger particles will get caught used for: separating solids from liquids e.g. straining pasta

Question 50

what are the classifications of matter

Answer 50

pure substances: contain 1 type of particle - elements: contain 1 type of atom e.g. Ca, O2 - compounds: contain 2 or more different types of atoms e. g. H2O, NaCl mixtures: contain 2 or more different types of particles - homogenous * uniform composition * e.g. air, soft drinks - heterogenous * non uniform composition * e.g. dirty water, paints

Question 51

what determines the shape of molecules

Answer 51

the arrangement of electrons pairs surrounding the central atom

Question 52

what does VSEPR stand for and what does this theory state

Answer 52

stands for valence shell electron pair repulsion theory states that electrons pairs in the valence shell of an atom repel each other, and are arranges as far apart as possible

Question 53

what does polarity refer to

Answer 53

related to the sharing of the bonding electrons between atoms

Question 54

what is the difference between a polar and non polar bond

Answer 54

non polar: electrons are shared evenly between atoms, equal charge distribution polar: electrons are not shared evenly between atoms because different atoms have different electronegativities

Question 55

explain what a polar bond is

Answer 55

occurs between atoms with 2 different electronegativities electrons spend more time moving around the atom with the greatest electronegativity this leads to an uneven charge distribution in the bond the region near the more electronegative atoms has a partial negative bond the region near the less electronegative atoms has a partial positive bond this is called a bond dipole

Question 56

what is an extreme polar bond

Answer 56

occurs between non metal atoms with large differences in electronegativities e.g. F and H

Question 57

what are intermolecular forces

Answer 57

weak attractive forces existing between molecules

Question 58

list the different types of intermolecular forces

Answer 58

dispersion: attraction between all types of particles resulting in instantaneous dipoles dipole-dipole: attraction between polar molecules hydrogen bonds: attraction between polar molecules containing OH, NH or FH groups ion-dipole: attraction between polar solvent water molecules and dissolved ions

Question 59

explain what dispersion forces are

Answer 59

temporary dipoles form between molecules in order for them to change shape temporary polarity: electrons are constantly moving around atoms and are not always symmetrically distributed across the atom this temporary asymmetrical distribution produces a temporary/instantaneous dipole if it is close to another molecule w/ a temporary dipole, it will cause polarity in the neighbouring atom these two temporary dipoles will be attracted to one another this force between molecules is dispersion force

Question 60

how can you predict the strength of dispersion forces

Answer 60

increase in strength with increasing number of electrons - as ayomic radius increases, e' have greater space to mover and greater chance to arrange asymmetrically molecular shape the larger the surface area over which the electrons can develop an instantaneous dipole and the closer molecules can fit next to each other, the strogner the dispersion force

Question 61

explain what dipole-dipole forces are

Answer 61

weak attractive forces between polar molecules molecule that has a partial negative charge is attracted to neighbouring molecule with partial positive charge the more polar the molecules, the stronger the force will be

Question 62

explain what hydrogen bonding is

Answer 62

dipole-dipole forces containing NH, OH or FH as they're the most electronegative atoms very polar bond --> stronger dipole dipole forces more energy required to overcome bonds: higher BP atomic radii are smaller - high charge density at the end of each molecule e- are attracted more strongly toward N, O or F

Question 63

what are the requirements for hydrogen bonding

Answer 63

presence in 1 molecules of at least 1 NH OH or FH covalent bond presence of another polar molecule containing at least 1 N, O or F atoms with a non-bonding pair of electrons

Question 64

define hydrogen bond

Answer 64

the attractive force between the lone pair of electrons on the N, O of F atom on on of the polar molecules and the partially positive charge of the H bonded to N, O of F on the second polar molecule

Question 65

what are the unique properties of water

Answer 65

relatively high MP (O˚) and BP (100˚) density of water in the solid phase is lower than its density in liquid phase high surface tension

Question 66

explain water's property of its density

Answer 66

water has a maximum density of 1.0g ML-1 as a liquid at 4˚ when freezed it expands significantly and density drops by 8% reduced density is why ice floats on water and freezes top down providing a layer of insulation preventing the rest of the water from freezing this is because of the crystal lattice formed when water freezed - each water molecule can form 4 hydrogen bonds, maximising hydrogen bonding but takes up more space

Question 67

explain water's property of its high surface tension

Answer 67

water has strong intermolecular forces imbalance of these forces at waters surface causing water molecules to be pulled inward toward the bulk of the liquid as a result the surface tries to contract to minimise surface area

Question 68

what is chromatography

Answer 68

separates compounds in a solution with the same properties paper chromatography: separates a mixture of solutes with difference solubilities of absorption

Question 69

explain the process of chromatography

Answer 69

uses paper and a solvent that can move over the medium samples are placed along chromatography paper and paper is dipped in a solvent and left to dry solvent will run up the paper, dissolving the samples different solubilities cause some samples to run further up the paper than others liquid with the lowers BP is first to evaporate and be distilled out of the paper and collected

Question 70

what are the physical properties of intermolecular forces

Answer 70

changing phase solubility equilibrium vapour pressure

Question 71

explain the physical property of changing phase for intermolecular forces

Answer 71

MP and BP of substances increases as intermolecular force strength increases as molecular mass increases (number of e'), MP and BP increases substances that have dipole-dipole forces have a slightly higher MP and BP substances that have hydrogen bonding have a slightly higher MP and BP

Question 72

explain the physical property of solubility for intermolecular forces

Answer 72

a solute and solvent can only form a solution if the attractive forces between molecules are comparable in strength e,g, non polar molecules (dispersion forces) can't be soluble in polar substances (dipole-dipole)