Chemistry Exam November

How many protons & neutrons in Helium-3

2 Protons, 1 Neutron

Two reagents to test for phosphate ions in aqueous solution

Ammonium Molybdate, Nitric Acid

Explain energy levels

Fixed energy / Quantised energy / Energy in an orbit / Energy in a shall of an electron

Distinguish between ground and excited states in hydrogen’s electron

Ground = Lowest energy / n = 1 / Stable
Excited = Greater Energy / n > 1 / Unstable

What happens when an electron goes from excited to ground

Energy is released: _{(only 1 necessary)}
as a photon
as light
as em radiation
at a specific frequency
E_m - E_n = hf

Name the instrument used to examine the line spectrum of an element

Spectrometer / Spectroscope

Explain: Uncertainty Principle

Impossible to measure position & velocity at the same time

S, P, D electron config of Neon (10)

1s² 2s² 2px² 2py² 2pz²

Distinguish between an energy sublevel and an atomic orbital

Sublevel: 2p
Orbital: 2p_x
Sublevels are regions of space such as S, P, D whilst orbitals are specific regions like 2p_x

Neon is unreactive, explain this through its electron config

full outer shell / full p sublevel / satisfies octet rule

Explain how successive ionisation energy values of Ne provide evidence of energy levels

Ninth (ionisation energy) significantly greater than the eighth

Draw the shape of a p orbital

dumb-bell shape

Draw a dot and cross diagram to show valence electrons in BF₃ Boron (5) Fluorine (9)

Image

Would you expect a B-F bond to be polar or non-polar? Justify your answer

Polar because of a large electronegativity difference

Would you expect a BF₃ molecule to be polar or non-polar

non-polar

Phosphane (PH₃) is colourless, flammable, highly toxic and gaseous. Predict the shape of a molecule.

Pyramidal: three bond pairs and one lone pair (on P)

Neither BF₃ nor PH₃ is very soluble in water, explain

non-polar / little hydrogen bonding / little intermolecular forces

Define: Atomic Number

number of protons in nucleus of an atom

Define: Mass Number

number of protons and neutrons in nucleus of an atom

Taking the valency of gallium (Ga) as 3, write the formula formed from Gallium and Nitrogen

GaN

Taking the valency of gallium (Ga) as 3, write the formula formed from Gallium and Oxygen

Ga₂O₃

Predict the two possible shapes of a molecule AB_n where n = 2

V - Shaped & Linear

What is diffusion?

Spreading (movement) of a substance (compound, molecules) from high to low concentration to fill a container (volume)

Identify stages 2 & 4 of this mass spectrometer

2: Ionisation
4: Separation

How did Thomson account for the fact that atoms are electrically neutral

Plum pudding model of atom where electrons (negatives) were embedded in a sphere of positive matter balancing the charges

State one piece of evidence for the existence of energy levels in atoms

Atomic Spectra
Flame Tests
Periodic Table Layout

State Two limitations of Bohr’s atomic theory that led to its modification

Only works for hydrogen
Wave-like motion not included
Uncertainty Principle not included
Did not explain sublevels

Define: an atomic orbital

a region in space where there is a relatively high probability of finding an electron

Write the S P D config for bromine (35) in its ground state

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4px² 4py² 4pz¹