Materials & Atoms Flashcards
(101 cards)
1
Q
What are materials
A
Substances used to make objects
Eg. Wood, Paper, Nylon
2
Q
What are Properties of Materials
A
Melting Point: Temperature to change state to liquid
Boiling Point: Temperature to change state to gas
Reactivity: Tendency of substance to undergo chemical reactions
Hardness: Ability of material to resist deformation from force
Density: Measure of materials mass per volume
3
Q
What are Pure Substances
A
Made up of one type of substance
Cannot be physically separated
Uniform & Definite composition throughout substance
4
Q
What are Elements
A
Made up of one type of atom
Cannot be separated by chemical processes into simpler substances
Eg. Carbon (C), Gold (Au), Silver (Ag)
5
Q
What are Compounds
A
Two or more atoms chemically combined
Formula indicates number of atoms of each element in compound
Name and formula depend on bonding type
6
Q
What are Mixtures
A
Two or more substances physically mixed, can be separated
7
Q
What are Homogenous Mixtures
A
Same proportions of components throughout mixture
Eg. Solution
8
Q
What are Heterogenous Mixtures
A
Composition not uniform throughout mixture
Eg. Vegetable Soup
9
Q
What are Properties of Metals
A
High tensile strength, ductility, malleability, shiny lustre, high melting points, thermal & electrical conductivity
10
Q
What are Alloys
A
Mixture with other metals, or small amounts of non-metals
Refine physical properties of metal
11
Q
What are Properties of Polymers
A
Low density, corrosion resistant, electrical insulators, biological polymers have good compatibility with human tissue
Molecular structure of repeating smaller units bonded together
12
Q
What are Properties of Ceramics
A
Hard, high compressive strength, withstand high temperatures
Metal, non-metal, metalloid elements held together by ionic & covalent bonds
13
Q
What are Properties of Composites
A
Combination of two or more distinct metals, with different physical & chemical properties
Resultant material has range of properties
Eg. Reinforced concrete, steel bars counter low tensile strength of concrete
14
Q
What is Filtration
A
Separate insoluble solids from liquid or gas
Depends on components of mixture having different solubilities
15
Q
What Properties Does Filtration Use to Separate
A
Particle Size, Solubility
16
Q
What is gravitational filtration
A
Uses weight of mixture to push through filter paper
Paper catches larger particles, smaller particles pass through
17
Q
What is sieving
A
Mesh screen, allows smaller materials through, leaving larger particles
Eg. Flour sieve
18
Q
What is decantation
A
Pour liquid from one container to another, leaving sediment behind
Difficult for complete separation
Eg. Pouring clean water from muddy water
19
Q
What properties does decantation use
A
Insolubility, Density
20
Q
What is centrifugation
A
Spins mixture rapidly, separates finer particles
21
Q
What is solvent extraction
A
Two unmixable liquids shaken to disperse one in the other
- Solutes migrate from one solvent to other
Requires separation funnel to drain solution separately
22
Q
What properties does centrifugation use
A
Density
23
Q
What properties does solvent extraction use
A
Density
24
Q
What is crystallisation
A
Solvent boiled off, recovering solute (Was dissolved)
Water lost to atmosphere
Faster the liquid boiled = Smaller crystals
Eg. Evaporating sea water for sea salt
25
What properties does crystallisation use
Boiling Point
26
What is distillation
Solvent boiled off, recovering solute (Was dissolved)
Vapor collected & cooled, pure liquid (Distillate)
Example: Perfume
27
What properties does distillation use
Boiling point
28
What is fractional distillation
Separate mixable liquids with similar boiling points
29
What is chromatography
Substances in mixture are dissolved in solvent, travel with solvent through medium
- Different solutes chemically attracted to medium by varying amounts
- Move at different sppeds through medium
- Each component moves different amount over time period
30
What properties does chromatography use
Adsorption, Solubility
31
What is gas chromatography
Separates organic mixtures
Separated components pass out at different times, detected in ionisation chamber
32
What did John Dalton do
Revised concept of atoms
Based theory on others' experimental data
In chemical reactions, atoms are rearranged not changed
Atoms of different elements combine in simple proportions to make compounds
Made billiard ball model
- Each element is uniform, indivisible, solid sphere (Atom)
33
What did JJ Thomson do
Discovered electrons
- Mass smaller than hydrogen, is negative particles within atoms
Did Cathode Ray Tube experiment:
- Shined a beam of negative particles (Beta), which bent towards positive plate
- Proposed atoms must have positive particles to cancel negative
34
What did Ernest Rutherford do
Discovered nucleus
- Dense, positive charge in center
- Majority of mass
- Tiny
Did Gold Foil experiment
- Hit positive alpha ray into thin gold foil
- Some rays bounced back, means atoms have positive part
- Majority of atoms went through = Empty space
Made Nuclear Model:
- Dense, positive nucleus, surrounded by negative electrons
35
What did Niels Bohr do
Discovered energy levels:
- Electrons exist in specific energy levels
- Make up electron shells
Did Bright-Line Spectrum experiment
- Where there was presence of specific colours in Hydrogen's emission spectrum
- Each line was a different energy level
Made Planetary Model:
- Electrons in circular orbits, in electron shells
36
What did James Chadwick do
Discovered neutrons:
- Z, A values didn't match
- Bombarded neutrons into Nitrogen gas, found the mass
- Found neutrons were from nucleus
STILL NEED TO FINISH
37
What is the structure of an atom
Cloud of negatively charged electrons, which is most of the volume
Nucleus, which holds protons & neutrons
38
What are the three subatomic particles, their charge, and relative mass
Neutron, neutral, 1
Proton, positive, 1
Electron, negative, 1/1836
39
What is the nucleus
Protons & neutrons, held together by nuclear force
Positive charge in center of atom
99.9% mass, is 100,000x smaller then whole atom, dense
40
How is the nucleus held together
Electrostatic forces push protons away from each other
Nuclear force attracts nucleons together, regardless of charge (Only a short distance)
To be stable, there needs to be a balance of the two forces
41
What is the electron cloud
Where the electrons move, large space
Negatively charged, move around nucleus by electrostatic forces
Each shell holds fixed number of electrons (Eg. 2,8,8,2)
42
What is atomic number
Atom identity determined by number of Protons in nucleus
Neutral atom, number of protons = number of neuytrons
Periodic table, elements sorted by atomic number
43
What is mass number
Mass Number = n(Protons) + n(Neutrons)
Lighter atoms, number of protons = number of neutrons
Heavier atoms, more neutrons than protons
44
What are isotopes
Same atomic number, different number of neutrons
45
What are the properties of isotopes compared to other isotopes
Same chemical properties (Eg. Same number of electrons)
Different physical properties (Eg. Density, Boiling Point), due to different mass
Larger isotopes have unstable nucleus, therefore radioactive
46
What is the nuclear notation for isotopes
AZX
A = mass number
Z = atomic number
X = chemical symbol
47
What is mass spectrometry
Determines abundancy of each isotope in element
48
What are the steps in mass spectrometry
Vaporisation
Ionisation
Acceleration
Deflection
Detection
49
What is vaporisation in mass spectrometry
Where a sample is heated to a gas
50
What is ionisation in mass spectrometry
Electron gun hits atom/molecule, removes some electrons, cation forms
51
What is acceleration in mass spectrometry
Where the atoms are accelerated by negatively charged plates
52
What is deflection in mass spectrometry
Ions deflected by magnetic field, greater mass : charge ratio deflected more
Lighter mass = Deflected more, higher charge = Deflected more (Mass : Charge)
53
What is detection in mass spectrometry
Particular mass : charge, detected by device, counts number of ions (Abundancy)
Records proportions of each isotope
54
Why does mass spectrometry happen under vacuum
Ions have free run through machine without hitting air molecules
If hit air molecules, alter pathway of some ions, could go undetected, giving inaccurate result
55
What is relative atomic mass
Mass of an atom, compared to (1/12) the mass of a Carbon-12 atom
Unitless
56
What is the formula for relative atomic mass
Ar = ( (% abundance of isotope a) * Ar(a) + (% abundance of isotope b) * Ar(B) ) / 100
57
How are the electrons in the bohr model of an atom
Orbit the nucleus in fixed, circular orbits
Orbits correspond to fixed energy levels / shells
Large the radii, higher the energy
Cannot exist between energy levels
58
What is the outermost electron shell in an atom
Valence shell
Electrons in valence shell = Valence electrons
- Involved in chemical reactions
Atoms with full valence shell = Very stable (Octet Rule)
Is possible to move between shells, by absorbing / emitting energy
59
What is electron configuration
Number of electrons in each shell, separated by a comma
Starts with lowest energy shell
60
What is atomic radii
Distance between adjacent atomic nuclei, divided by 2
Is the radius of an atom
61
What are the patterns of atomic radii
Atomic radii increasing as it goes to left of periodic table
Atomic radii increasing as it goes down periodic table
62
What are the two principles to explain the trend in atomic radii
Principal Quantum Number
Effective Nuclear Charge
63
What is principal quantum number
Number of electron shells
64
What is effective nuclear charge
Net charge experienced by valence electrons towards nucleus
More shells = Less electrostatic attraction to nucleus than core electrons (Electrons closer to nucleus)
Zeff = Atomic Number - (# of core electrons)
65
What is the trend down a group in periodic table of atomic radii
More electron shells down a group = Increasing atomic radii
66
What is the trend across a period in periodic table of atomic radii
More protons in nucleus, means more pull on valence electrons towards nucleus, decreasing atomic radii
67
What are ions
Where n(Protons) doesn't equal n(Electrons)
Atoms lose/gain electrons in chemical reactions, to have full outer shell
Lose electrons = Cation (Positive)
Gain electrons = Anion (Negative)
When lose/gained, written as power, followed by charge
68
What is quantisation of energy
Where every energy level / shell is quantised
Cannot exist between energy levels
Can move between energy levels by absorbing / emitting electromagnetic radiation
69
What is an electron in ground state
Lowest energy state, in first shell
70
What is an electron in excited state
Atom absorbed electromagnetic radiation, moved to higher energy level
Unstable, exists for short amount of time, then back to ground state, releasing electromagnetic radiation
71
What is electromagnetic radiation
Visible light on electromagnetic spectrum
Described with frequency, wavelength, energy
Observed through emission spectra / absorption spectra
72
What is absorption spectra
Electron excited through electromagnetic radiation
- Jumps to higher energy level
Atoms only absorb certain colours = Absorption lines
- All absorbed lines on full spectrum = Absorption spectrum
73
What is emission spectra
Excited electron returns to lower energy level shortly after through various possible transitions
- Photon / light emitted, energy equal to amount initially absorbed
- Different jumps between energy levels produce different colours
Individual colours of light emitted = Emission lines
- All emission lines = Emission spectrum
74
How is emission spectrum different to every atom
Different number of electrons, different number of electron shells
Photon emitted energy equal to difference in energy between levels
Therefore photons emitted unique to each element (Characteristic)
75
What is spectroscopy
Study of interaction between matter and electromagnetic radiation
76
What is flame test
Determines metallic elements in compound
Shown by emission spectrum
77
What is process for flame test
Sample heated, electrons in metal atom excited, moves to higher energy level
- Returns ground state shortly after, releases photons unique to element
- Causes flame to change colour
78
What is atomic absorption spectrum
Finds amount of element in a substance
79
What is process for atomic absorption spectrum
Lamp made out of element being tested for
Substance vaporised in flame to produce free atoms (Gaseous element)
Light shined through sample from lamp, element being tested for absorbs light, electrons in it become excited state
The light is focused through a slit, which enters monochromator that separates wavelengths
1 wavelength is analysed, where intensity is measured to see amount of light not absorbed = Absorbance value
80
What is Beer's Law
Linear relationship between absorbance value & concentration
Used to determine concentration of element
81
What is ionisation energy
Energy (Joules) required for complete removal of 1 mole of electrons from 1 mole of gaseous atom/ion
- Knocks out most weakly held electron (Valence electron)
82
What is pattern of ionisation energy down a group
Decreases down a group
- Shells increase down group, so valence electrons further from nucleus, decreasing attraction
- Easier to remove electrons
83
What is pattern of ionisation energy across a period
Increases across a period
- Valence electrons pulled closer, as there are more protons, so atom more positively charged
- Harder to remove electrons
84
What is the explanation of trend of ionisation energy
Related to atomic radii (Opposite)
Energy used to remove electron, must overcome attraction to nucleus, related to atomic radius
Uses same two principles
1) Principal Quantum Number (n)
2) Effective Nuclear Charge (Zeff)
85
What is successive ionisation energies
Removing more moles of electrons after 1st one
Requires more energy, removing negative electron from positive cation
Massive jump in energy for next shell, as it's closer to nucleus
86
What is electronegativity
Relative scale of ability of atom to attract shared electrons in covalent bond (Unitless, baseline hydrogen)
More electronegative = Stronger pull of shared electrons
87
What is pattern of electronegativity down a group
Decreases down a group
- Effective nuclear charge lower
- Tendency to attract electrons decreases, decreasing electronegativity
88
What is pattern of electronegativity across a period
Increases across a period,
- Effective nuclear charge higher
- Tendency to attract electrons increases, increasing electronegativity
89
What is explanation of trend of electronegativity
Inversely related to its size
If its tendency to attract electrons is larger, then it would attract the shared electrons more
90
What is periodic table
Arrangement of elements by atomic number
91
What is the rows in periodc table
Periods
Same row = Same number of shells
Valence electrons increase left to right
92
What are the columns in periodic table
Groups
Same valence electrons
Electron shells increase down a group
Similar chemical properties
93
Why are neutrons last to be discovered
As they have no charge, so they couldn't use the same method they used to discover protons & neutrons
94
Why does each element have unique absorption/emission spectrum
Different atoms have different number of Protons, and different electron arrangement, so need different amounts of energy for the atom's electrons to move between energy levels.
Different wavelengths have different amounts of Energy, therefore have different absorption spectras.
95
What are properties of alkali metals
Solft, silvery colored metals
Very reactive
96
What are properties of alkaline earth metals
Silvery-White metals
Fairly reactive
97
What are properties of transition metals
Most good conductors of electricity
Malleable (Easily bent/hammered into wires/sheets)
98
What are properties of metalloids
Share properties with metals & non-metals
99
What are properties of non-metals
Brittle
Don't conduct electricity
100
What are properties of halogens
Fairly reactive
Salt-Forming
101
What are properties of noble gases
Unreactive
Gases at room temperature
Exist in Earth's atmosphere
