property and stucture of atoms / materials

Question 1

two things that affect ionisation energy

Answer 1

• increased nuclear charge (number of protons) = increased ionisation energy
• increased distance from nucleus = decreased ionisation energy

Question 2

what is electronegativity

Answer 2

the ability of an atom to attract and form bonds with electrons (from nearby atoms)

Question 3

what is atomic radius

Answer 3

distance between the nucleus and outer boundary shell (valence)

Question 4

explain the trends as you go across the periodic table

Answer 4

• decrease atomic radius
• decrease atomic size
• decrease in metallic nature
• increase ionisation energy
• increase electronegativity

Question 5

explain the trends as you go down the periodic table

Answer 5

• increase atomic radius
• increase atomic size
• increase metallic nature
• decrease ionisation energy
• decrease electronegativity

Question 6

explain the function of mass spec

Answer 6

• measures the masses and relative concentration of atoms and molecules
• determines elements / isotopes that are present and isotope concentration / relative abundance

Question 7

explain the process of mass spec

Answer 7

• substance to be analysed is vaporised and ionised (overall positive charge)
• ions are accelerated
• pass through a velocity selector and then enter the magnetic field
• particles are separated based on mass / charge ratio

Question 8

explain the analysis of results for mass spec

Answer 8

• mass / charge ratio and relative abundance are recorded on the output chart

Question 9

explain the function of the flame test

Answer 9

• identifies a range of metal ions due to the characteristic colours produced when their salts are burnt

Question 10

explain the process of flame tests

Answer 10

• samples placed in a hot non-luminous flame give characteristic colours
• due to the electrons moving from ground to excited state and the amount of energy

Question 11

explain the function of AES

Answer 11

• a more efficient and quantitative method of analysing elements in a flame

Question 12

explain the process of AES

Answer 12

• intense heat of flame atomises and vaporises sample
• excited atoms emit light
• dispersed through a prism into its characteristic spectra with the monochromator allowing each wavelength to be detected and recorded separately

Question 13

explain the analysis of results for AES

Answer 13

• produces a series of electron energy levels (wavelengths) where the darkness and intensity of the wavelengths allows us to identify more metalloid elements

Question 14

explain the function of AAS

Answer 14

• used to determine how much of an element is present in a sample of a substance

Question 15

explain the process of AAS

Answer 15

• light from the hollow cathode lamp has the specific wavelengths that the metal being analysed can absorb
• the detector effectively measures the amount of light which is absorbed
• this indicates the concentration of the metal atoms in the sample

Question 16

explain the analysis of results for AAS

Answer 16

• produces a calibration curve
• absorbance value of known concentrations can be placed on the curve, the a.v of the unknown is compared
• properties and structure of materials is identified

Question 17

what are pure substances

Answer 17

• uniform on composition
• element: made up of only one atom, can’t be separated into simpler substances
• compound: made up of two or more different elements chemically combined into a fixed ratio

Question 18

what are mixtures

Answer 18

• various compositions / impure substances
• homogenous: uniform composition and properties (becomes one / equal amounts when distributed)
• heterogenous: variable composition and properties (different amounts of substances when distributed)

Question 19

what is a physical property

Answer 19

• properties that can be determined without changing the chemical composition of a substance
• examples: melting / boiling point, hardness, electrical conductivity, hardness, malleable, ductile, strength, state

Question 20

what is a chemical property

Answer 20

• relate to the ability of a substance to react to form new substances
• example: decomposition by heat, effect of light, reactions with: water, acids, bases, oxygen etc

Question 21

what is nanotechnology

Answer 21

• field deals with matter at the atomic and molecular scale, used in medicine, materials fabrication, energy production and electronics

Question 22

what are nano-materials

Answer 22

• materials that have particles between 1-100 nanometers (nm) in size
• made of nanoparticles and nanoatoms (nano = x10^-9)

Question 23

what is a nanometre

Answer 23

• 1 billionth of a metre, cannot be seen with the naked eye or by light microscopy
• small particle size results in unexpected and unique properties, different to those of bulk materials

Question 24

what does delocalised mean

Answer 24

• electrons that are detached from their atoms

Question 25

what does non-directional mean

Answer 25

- electrons of metallic bonds are free to move around between cations

Question 26

what does malleable and ductile mean

Answer 26

- malleable: able to be beaten into another shape or flattened into a thin sheet without breaking - ductile: able to be drawn into a wire

Question 27

describe the structure of metallic bonding

Answer 27

- electrostatic attraction between the positive metal ions and the delocalised negative electrons

Question 28

describe the properties of metallic bonding

Answer 28

- conduct electricity - conduct heat - ductile / malleable - high melting / boiling point - lustrous - hard

Question 29

describe the structure of ionic bonding

Answer 29

- 3D lattice of alternating positive and negative ions, which vibrate about their fixed positions, with a strong electrostatic attraction between positive and negative ions

Question 30

describe the properties of ionic bonding

Answer 30

- hard - brittle - high melting / boiling point - electrical conductivity: solid (no), molten state / solution (yes)

Question 31

explain the structure of covalent bonding

Answer 31

- electrostatic attraction between shared electrons and their positively charged nuclei (held together by mutual attraction of shared electrons)

Question 32

describe the properties of covalent bonding

Answer 32

- low melting and boiling point - soft - electrical conductivity: solid / liquid (no), solution (yes)

Question 33

what are two types of electron pairs in covalent bonding

Answer 33

- lone pairs: remaining electrons that are not involved in bonding - bonding pairs: electrons shared between the two atoms (covalent bond)

Question 34

what are dative / coordinate bonds

Answer 34

- bonds formed when an atom shares lone pair electrons with other atoms that have completely vacant valence orbitals

Question 35

explain the structure of covalent network substances

Answer 35

- 3D lattice of atoms that are covalently bonded with other atoms, with no intermolecular or intramolecular forces (no molecules)

Question 36

explain the properties of covalent network substances

Answer 36

- high melting / boiling point - doesn't conduct electricity - hard - brittle - inert

Question 37

what is an allotrope

Answer 37

- different forms (structure) of the same element, results in different properties

Question 38

what are the allotropes of carbon

Answer 38

- diamond - graphite - amorphous carbon - carbon fibre - fullerenes

Question 39

explain the structure of diamond

Answer 39

- each carbon atom is covalently bonded to 4 other carbon atoms in a tetrahedral shape

Question 40

explain the properties of diamond

Answer 40

- doesn't conduct electricity - hard - brittle

Question 41

explain the structure of graphite

Answer 41

- each carbon atom is covalently bonded to 3 other carbon atoms forming layers of hexagonal sheets, with 1 delocalised electron

Question 42

explain the properties of graphite

Answer 42

- conduct electricity - high melting / boiling point - soft

Question 43

what is ionisation energy

Answer 43

the amount of energy needed to remove the most loosely bound electrons from an atom or ion in gaseous state