elements of life Flashcards
What are isotopes?
Atoms with the same number of protons but different numbers of neutrons.
What was Dalton’s model of the atom?
A solid sphere.
What was JJ Thomson’s model of the atom?
The plum pudding model: a positively charged sphere with embedded electrons.
What was Rutherford’s contribution to atomic theory?
Fired alpha particles at gold foil; some reflected, suggesting a dense nucleus.
What are the 4 principles of the Bohr model?
- Electrons exist in fixed orbits. 2. Shells have fixed energy levels. 3. Electrons absorb/emit energy when moving between shells. 4. Radiation has a fixed frequency.
What are the stages of mass spectrometry?
- Vaporisation 2. Ionisation 3. Acceleration 4. Detection.
What is measured in mass spectrometry?
Time taken to reach the detector; lighter, highly charged ions arrive first.
What is a mole?
6.022 × 10²³ particles (Avogadro constant).
What is the formula for moles?
Moles = mass / Mr.
What are ionic equations?
Equations showing only the reacting particles and products formed.
What is the empirical formula?
The simplest whole number ratio of atoms in a compound.
What is water of crystallisation?
Water chemically bonded in hydrated compounds that is lost when heated.
What is the formula for percentage yield?
(Actual yield / Theoretical yield) × 100.
What is a standard solution?
A solution of known concentration.
How do you dilute a solution?
Final conc. / Initial conc. × Volume of new solution.
What is the purpose of a titration?
To determine how much acid is needed to neutralise an alkali.
What colour change is shown by methyl orange in titration?
Red (acid) to yellow (alkali).
What colour change is shown by phenolphthalein in titration?
Colourless (acid) to pink (alkali).
What are the subshell capacities for s, p, d, and f?
s = 2, p = 6, d = 10, f = 14.
What is spin pairing?
Two electrons in the same orbital spin in opposite directions.
What shapes are s and p orbitals?
s = spherical, p = dumbbell shaped.
What are the s, p, and d blocks?
s-block: groups 1–2, p-block: groups 3–8, d-block: transition metals.
What is ionic bonding?
Electrostatic attraction between oppositely charged ions.
What is the structure of ionic compounds?
Giant ionic lattice; conduct electricity when molten or dissolved, high melting points.
What is covalent bonding?
Shared pair of electrons; balance between attraction and repulsion.
What are properties of simple covalent compounds?
Low melting points, don’t conduct electricity, usually insoluble.
What is dative covalent bonding?
A covalent bond where one atom donates both electrons.
What are properties of giant covalent structures?
Very high melting points, hard, good heat conductors, insoluble, don’t conduct electricity.
What is metallic bonding?
Positive metal ions in a sea of delocalised electrons.
What are properties of metallic structures?
High melting point, malleable, ductile, good conductors of heat and electricity, insoluble.
What determines the shape of a molecule?
Electron pairs repel; lone pairs repel more than bonding pairs.
How do lone pairs affect bond angles?
Each lone pair reduces bond angle by about 2.5°.
What is the shape of a molecule with 4 bonding pairs?
Tetrahedral.
What is the shape with 3 bonding pairs, 1 lone pair?
Trigonal pyramidal.
What is the shape with 2 bonding pairs, 2 lone pairs?
Bent or non-linear.
What is the shape with 3 bonding pairs?
Trigonal planar.
What is the shape with 2 bonding pairs?
Linear.
What is the shape with 6 bonding pairs?
Octahedral.
What is the shape with 5 bonding pairs, 1 lone pair?
Trigonal bipyramidal (distorted).
How does melting point change across a period for metals?
Increases due to more delocalised electrons and higher charge density.
Why do noble gases have the lowest melting points?
They exist as single atoms with very weak forces between them.
What is first ionisation enthalpy?
Energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms.
What affects ionisation enthalpy?
Atomic radius, nuclear charge, and electron shielding.
Why does first ionisation energy decrease down a group?
More shielding and greater atomic radius outweigh increased nuclear charge.
Why does first ionisation energy increase across a period?
More protons in nucleus, same shielding, so stronger attraction to electrons.
How does thermal stability of carbonates change down group 2?
Increases due to decreasing cation charge density.
Why are large cations less polarising?
Lower charge density causes less distortion of carbonate ion.
What colour is copper carbonate?
Blue-green.
What colour is silver carbonate?
Yellow.
What colour are most other carbonate precipitates?
White.
Which salts are always soluble?
Group 1 salts, nitrates, most halides (except Ag⁺, Pb²⁺), and group 1 hydroxides.
Which salts are mostly insoluble?
Most carbonates, hydroxides (except group 1), and some halides like AgCl, PbI₂.
How do you carry out a flame test?
Dip nichrome loop in HCl, then compound, hold in flame and observe colour.
What colour is the silver hydroxide precipitate?
Brown.
What colour is calcium hydroxide precipitate?
White.
What colour is copper(II) hydroxide precipitate?
Blue.
What colour is iron(II) hydroxide precipitate?
Green.
What colour is iron(III) hydroxide precipitate?
Reddish brown.
What colour is zinc or aluminium hydroxide precipitate?
White, redissolves in excess NaOH to form colourless solution.
How do you test for carbonates?
Add dilute HCl and bubble gas through limewater; turns cloudy.
How do you test for sulfates?
Add HCl then barium chloride; white precipitate forms.
How do you test for ammonium ions?
Add NaOH and heat gently; ammonia gas turns damp red litmus blue.
How do you test for hydroxide ions?
Red litmus turns blue in solution.
How do you test for halides?
Add dilute nitric acid then silver nitrate.
What is the result for chloride ions?
White ppt, dissolves in dilute ammonia.
What is the result for bromide ions?
Cream ppt, dissolves in conc. ammonia.
What is the result for iodide ions?
Yellow ppt, doesn’t dissolve in ammonia.
How do you test for nitrates?
Warm with NaOH and Al foil; ammonia gas turns damp red litmus blue.
What is the ground state of an electron?
The lowest energy level.
What happens when an electron is excited?
It absorbs energy and jumps to a higher level.
What happens when an electron drops to a lower energy level?
It releases energy as radiation.
What does absorption spectra show?
Dark lines where frequencies are absorbed by a gas.
What does emission spectra show?
Coloured lines showing frequencies emitted as electrons fall.
What is the equation linking energy and frequency?
ΔE = h × f
What is the equation for wave speed?
Speed = frequency × wavelength.
What is nuclear fusion?
Two small nuclei combine under high temperature and pressure to form a larger nucleus.
Where does nuclear fusion occur?
In stars; hydrogen nuclei fuse to form helium.
What happens when hydrogen runs out in a star?
Temperature and pressure rise, forming heavier elements.
