Elements of Life Flashcards
What is an atomic structure made of?
- 3 sub atomic particles
- protons and neutrons form the nucleus
- electrons occupy energy levels/shells orbiting the nucleus
What is the relative atomic mass of each sub-atomic particle?
protons: 1
neutrons: 1
electrons: 0.00055 (1/1836)
What is the relative charge of each sub-atomic particle?
protons: +1
neutrons: 0 (no charge)
electrons: -1
What is the atomic number?
the number of protons in the nucleus of an atom
What is the mass number?
the number of protons and neutrons in the nucleus of an atom
What are isotopes?
atoms of the same element with different mass numbers
same no. of protons identifying the element with different no. of neutrons
What does mass spectrometry do?
measures atomic or molecular mass of different particles in a sample as well as relative abundance of different isotopes in an element
What happens in a mass spectrometer?
sample atoms/molecules are ionised into positively charged cations which are separated according to mass m to charge z ratios
separated ions are detected together with relative abundance
How do you calculate relative atomic mass from a mass spectra?
- %abundance of each ion (isotope) calculated by height of peak
- (relative isotopic mass x relative abundance) … add together each isotope and then divide all by 100
What is nuclear fusion?
when 2 light atomic nuclei fuse together to form a single heavier nucleus of a new element, releasing an enormous amount of energy
What are the required conditions for nuclear fusion?
- must be very close together
- very high temperature (e.g. star) so that nuclei move quickly and collide with more energy to overcome repulsive forces of nucleus
What does the absorption spectra look like?
- a series of black absorption lines on a coloured background
- missing frequencies of light where they have been absorbed by particles in the chromosphere
What does the emission spectra look like?
- a series of coloured lines on a black background
- correspond to emitted frequencies
What does the emission spectrum show?
the frequencies of emitted electromagnetic radiation where electrons of atoms/molecules/ions are raised from their ground state to higher energy states (excited states)
particles lose extra energy when emitting EM radiation
What is the name of the characteristic emission spectrum in the ultraviolet of the EM spectrum called?
the lyman series
What is the name of the hydrogen emission spectrum in visible light?
the balmer series
Is light seen from stars continuous?
no - consists of lines corresponding to absorption or emission of specific frequencies of light - atomic spectra
What are the 2 theories used to describe behaviour of light?
wave theory
particle theory
What is the speed of light? c
a constant
3.00 x 10(8) ms-1
when travelling in a vacuum
What is the formula relating frequency and wavelength?
speed of light c (ms-1) = wavelength λ (m) x frequency v (s-1)
What happens as the wavelength increases?
the frequency decreases (c remains the same)
What is the particle theory of light?
- light regarded as steady stream of photons (energy)
- energy of photons related to position in EM spectrum
- linked
What is the formula used in the particle theory of light?
energy of a photon E (J) = planck constant h (Js-1) x frequency v (s-1)
What is the value of the planck constant?
6.63 x 10(-34) Js-1
Bohr’s theory: how is an emission spectrum given off?
- when an atom is excited, electrons jump to higher energy levels
- later drop back into lower levels emitting extra energy as EM radiation and give off emission spectrum
Bohr’s theory: how is an absorption spectrum given off?
- electrons have been raised to higher levels without then dropping down again
- correspond to light absorbed by atoms in sample (and with coloured lines of emission spectrum of that element)
What are the main points of Bohr’s theory?
- the electron in the hydrogen atom exists only in certain definite energy levels or electron shells
- a photon of light is emitted or absorbed when the electron changes from one energy level to another
- the energy of the photon is equal to the difference between the 2 energy levels (deltaE)
- since E=hv it follows that the frequency of the emitted or absorbed light is related to deltaE by deltaE=hv
What are quanta?
definite quantities of energy possessed by electrons (can only change to specific values and not continuously)
What happens to the energy levels as you move further away from the nucleus of an atom?
- they get higher
- they become closer together (frequency)
What are the maximum numbers of electrons that can be in each shell (up to 7) and what is its principal quantum number n label?
- 1st shell: (n=1) 2 electrons
- 2nd and 3rd shells: (n=2) (n=3) 8 electrons
- 4th and 5th shells: (n=4) (n=5) 18 electrons
- 6th and 7th shells: (n=6) (n=7) 32 electrons
What are the different types of sub-shell and how many electrons can be held in each one?
S : 2
P : 6
D : 10
F : 14
Split the number of electrons held in each shell into sub-shells for: n=1
- 2 electrons in s sub-shell
- total = 2
Split the number of electrons held in each shell into sub-shells for: n=2
- 2 electrons in s sub-shell
- 6 electrons in p sub-shell
- total = 8
Split the number of electrons held in each shell into sub-shells for: n=3
- 2 electrons in s sub-shell
- 6 electrons in p sub-shell
- 10 electrons in d sub-shell
- total = 18
Split the number of electrons held in each shell into sub-shells for: n=4
- 2 electrons in s sub-shell
- 6 electrons in p sub-shell
- 10 electrons in d sub-shell
- 14 electrons in f sub-shell
- total = 32
Flame test: colour of Li+ ion flame?
bright red
Flame test: colour of Na+ ion flame?
yellow
Flame test: colour of K+ ion flame?
lilac
Flame test: colour of Ca2+ ion flame?
brick red
Flame test: colour of Ba2+ ion flame?
apple green
Flame test: colour of Cu2+ ion flame?
blue green
How many orbitals does an s sub-shell always contain?
1
How many orbitals does an p sub-shell always contain?
3
How many orbitals does an d sub-shell always contain?
5
How many orbitals does an f sub-shell always contain?
7
What is the maximum number of electrons each atomic orbital can hold? (how are they shown?)
2
each electron spins at same rate in opposite direction so drawn with opposing arrows
What 4 pieces of information are required when describing an electron?
- the electron shell it’s in
- the sub-shell
- its orbital within the sub-shell
- its spin
What is the electronic configuration of an atom?
the arrangement of electrons in shells and orbitals
filled in specific order to produce lowest energy arrangement possible
How are orbitals filled?
- in order of increasing energy
- orbitals first occupied singly by electrons which keeps electrons as far apart as possible (spins are parallel)
What is significant about the 3d sub-shell and the 4s sub-shell?
the 4s sub-shell is filled first
still write 3d before 4s
How did Mendeleev arrange elements in the periodic table and why did he leave gaps?
- arranged elements in order of increasing atomic mass and so elements with similar properties were in the same vertical group
- he left gaps for undiscovered elements in order to keep elements with similar properties in the same group
How is the periodic table arranged today?
- in order of atomic number
- in blocks s d p and f (similarities)
- vertical columns groups = no. of electrons in highest energy level
- horizontal rows periods = no. of energy levels
What is periodicity?
the occurrence of periodic patterns
What are the arrangements of noble gases called?
closed shell arrangements
all sub-shells fully occupied
What ions do groups 1 2 6 and 7 form?
1: +1
2: +2
6: -2
7: -1
What are dot and cross diagrams used for?
used to represent the way that atoms bond together
What is covalent bonding?
when 2 non-metals share electrons to bond together
What are lone pairs?
pairs of electrons not involved in bonding
What are bonding pairs?
electron pairs that form bonds
What is a dative covalent bond?
this is when both bonding electrons come from the same atom (shown by an arrow)
What are the physical properties of covalently bonded simple molecules?
- strong intramolecular forces
- intermolecular forces weak (electrostatic forces between molecules)
- low melting/boiling points (not much energy required to break intermolecular forces)
- do not conduct electricity (no charged particles)
- do not dissolve readily in water
For a linear shape molecule…
how many bond pairs are there?
what are the bond angles?
what is an example?
- 2 bond pairs
- 180 degree bond angles
- e.g. BeCl2
For a trigonal planar shape molecule…
how many bond pairs are there?
what are the bond angles?
what is an example?
- 3 bond pairs
- 120 degree bond angles
- e.g. BF3
For a tetrahedral shape molecule…
how many bond pairs are there?
what are the bond angles?
what is an example?
- 4 bond pairs
- 109.5 degree bond angles
- e.g. CH4
For a trigonal bipyramidal shape molecule…
how many bond pairs are there?
what are the bond angles?
what is an example?
- 5 bond pairs
- 120 degree and 90 degree bond angles
- e.g. PF5
For a octahedral shape molecule…
how many bond pairs are there?
what are the bond angles?
what is an example?
- 6 bond pairs
- 90 degree bond angles
- e.g. SF6
What is the order of repulsion between lone pairs and bond pairs?
lone pair-lone pair > lone pair-bond pair > bond pair-bond pair
(lone pairs have greater repulsion)
For a pyramidal shape molecule…
how many bond/ lone pairs are there?
what are the bond angles?
what is an example?
- 3 bond pairs, 1 lone pair
- 107 degree bond angles
- e.g. NH3
For a angular shape molecule…
how many bond/ lone pairs are there?
what are the bond angles?
what is an example?
- 2 bond pairs, 2 lone pairs
- 104.5 degree bond angles
- e.g. H2O
For a square planar shape molecule…
how many bond/ lone pairs are there?
what are the bond angles?
what is an example?
- 4 bond pairs, 2 lone pairs
- (90 degree bond angles?)
- e.g. XeF4
What is relative atomic mass? Ar
the mass of an atom relative to carbon-12
Ar have no units
What is the formula for amount in moles?
amount in moles n (mol) = mass m (g)
————————-
molar mass M (gmol-1)
What is a mole?
a unit for measuring the amount of each substance
contains as many particles as there are in atoms in 12g of carbon-12
What is molar mass?
the mass of one mole
What is the relative formula mass? Mr
the sum of the relative atomic masses of the elements making it up
What are formula units?
basic units/building blocks atoms/molecules/ion groups that match the formulae of the substances
What does the amount in moles of formula units equal?
molar mass
What is the avogadro constant?
the number of formula units in one mole of substance
it’s a constant NA
value: 6.02 x 10(23) formula units per mole
What does the molecular formula tell you?
the actual numbers of different types of atom
What is the empirical formula?
the simplest ratio for the moles of atoms
What is water of crystallisation?
when crystals of ionic lattices include molecules of water which are fitted into attic regularly
What is the difference between hydrous and anhydrous?
- hydrous means water molecules are present
- anhydrous means water molecules are removed
What factors can reduce %yield?
- loss of products from reaction vessels
- side-reactions occurring, producing unwanted by-products
- impurities in reactants
- changes in temperature and pressure
- if reaction is reversible in an equilibrium system
How do you calculate % yield?
experimental yield
—————————– x100
theoretical yield
What are the state symbols for a solid, liquid, gas and aqueous solution?
solid : s
liquid: l
gas: g
aqueous solution: aq
What is ionic bonding?
when a metal and a non-metal bond by transferring electrons (from M to NM)
cations and anions formed held together by electrostatic forces
What are the 4 salt making equations?
- acid + alkali –> salt + water
- acid + base –> salt + water
- acid + carbonate –> salt + water + carbon dioxide
- acid + metal –> salt + hydrogen
What ionic substances are soluble and which ones aren’t?
soluble:
- all G1 compounds
- ammonium compounds
- nitrates
insoluble:
- barium, calcium, lead and silver sulfates
- silver and lead halides (chlorides/bromides/iodides)
- all metal carbonates
- metal hydroxides (excluding G1 and aluminium)
How can ionic substances conduct electricity?
- when in a solution or molten
- ions become differentiated, acting independently of each other and spread out
- ions can carry charge and therefore conduct
What are spectator ions?
ions not involved in the reaction
Why must ionic equations always have state symbols?
help identify precipitates etc e.g. ionic precipitation (a suspension of solid particles produced by a chemical reaction in a solution)
What do you use sodium hydroxide to test for (when it forms a precipitate)?
metal ions e.g. Cu2+ (blue) , Fe(ii) 2+ (dirty green), Fe(iii) 3+ (orange/brown)
What do you use potassium iodide to test for (when it forms a precipitate)?
Pb2+ ions (bright yellow)
What do you use silver nitrate to test for (when it forms a precipitate)?
halide ions e.g. Cl- (white), Br- (cream), I- (pale yellow)
What do you use barium chloride to test for (when it forms a precipitate)?
sulfate ions (white)
What are the physical properties of ionic compounds?
- solid at room temperature and pressure
- have regular lattices of positive and negative ions in 3D (regularly shaped crystals)
- high melting/boiling points because of strong electrostatic forces requiring lots of energy to be broken
- conduct electricity when dissolved or molten
How does metallic bonding work?
a giant lattice structure of metal cations is held together by a sea of delocalised valence electrons which are free to move
What are the properties of metallic lattices?
- conduct electricity due to delocalised electrons free to carry charge
- relatively high melting/boiling points
- insoluble
- relatively hard but malleable
What are covalent networks and what properties do they have?
e.g. diamond and silicon dioxide
large covalent networks formed from strong covalent bonds between networks
- high melting/boiling points because it takes a lot of energy to break intramolecular forces but intermolecular forces still weak
- insoluble
- do not conduct electricity (exception graphite with a free delocalised electron each carbon atom)
What is first ionisation enthalpy?
the first ionisation enthalpy of an element is the energy needed to remove one electron from every atom in one mole of isolated gaseous atoms of the element - a mole of gaseous ions with one positive charge are formed
How does reactivity change across the s block of metals?
- elements become more reactive down a group
- become less metallic across a period left to right (G1 more reactive than G2 of same period)
What are the general patterns of first ionisation energies of elements 1-20?
- as you cross the period it becomes harder to remove an electron so ionisation enthalpy increases
- going down a group, it becomes easier to remove an electron (more shielding from nucleus) so next period increases less
- group 1 have the lowest ionisation enthalpies whilst the noble gases have the highest ionisation enthalpies
Why is there a decrease in ionisation enthalpy between beryllium and boron?
Be) 1s2 2s2
B) 1s2 2s2 2p1
the s sub-shell is lower in energy than the p sub-shell therefore less energy is needed to remove the outer electron of boron despite increased nuclear charge because the p electron can more strongly resist the nucleus (the s sub-shell is stable)
Why is there a decrease in first ionisation enthalpies between nitrogen and oxygen?
the extra repulsion from the paired electron sub-shell in oxygen means less energy is needed to remove one of the paired electrons despite increased number of protons
As you go down group 2, what is the trend of reactivity with water? What does it form?
- increases
- form hydroxides and hydrogen
As you go down group 2, what is the trend in thermal stability of carbonate? What does it form?
- decomposes at increasingly higher temperature
- form oxides and carbon dioxide
As you go down group 2, what is the trend in pH of hydroxide in water? What does it form?
- increasing pH
- form alkaline solutions (not very soluble)
As you go down group 2, what is the trend in solubility of hydroxide and carbonate? What does it form?
- hydroxide - increase in solubility
- carbonate - decrease in solubility
What is thermal stability?
how much energy / temperature needed to start decomposition
measured in terms of charge density (smaller=higher density and less stable)
What is an acid?
a compound that disassociates in water to produce hydrogen H+ ions
What is a base?
a compound that reacts with an acid - a proton acceptor- to produce water and a salt
What is an alkali?
a base that dissolves in water to produce hydroxide OH- ions
When a solution is made, what will its concentration depend on?
- the amount of solute
- the final volume of solution
How do you find the concentration in MOLdm-3?
molar mass (g mol-1)
How do you work out the amount of solute in a particular volume?
amount (mol) = concentration of solution (mol dm-3) x volume of solution
How many cm3 is in 1dm3?
1000cm3
What is the equation relating amount of moles, concentration and volume?
amount n (moles) = concentration c (mol dm-3) x volume v (dm3)
