Atomic Structure
What is the definition of an isotope?
Atoms of the same element with the same number of protons but different numbers of neutrons
In which group of the Periodic Table are the noble gases found?
Group VIII (Group 0)
What is meant by the term "compound"?
A substance formed when two or more different elements are chemically combined in fixed proportions.
What property does distillation make use of to separate substances?
Boiling point
What causes Brownian motion of smoke particles?
Molecules in the air hitting the smoke particles.
An atom of element X has 5 protons and 6 neutrons. What is element X?
Boron
What is a typical property of transition elements?
They can act as catalysts (also: high melting points, high density, good electrical conductivity, form coloured compounds).
How many outer electrons does a carbon atom have, and how many bonds can it form?
4 outer electrons; it can form 4 covalent bonds.
Which apparatus is used to measure 2.00 g of calcium carbonate and 50.0 cm³ of hydrochloric acid?
Balance (for calcium carbonate) and burette (for hydrochloric acid).
Which gas has the fastest rate of diffusion: Ar, C₂H₆, HCl, or H₂S?
C₂H₆ (ethane, Mr = 30)
Why do isotopes of the same element have identical chemical reactions?
They have the same number of outer shell electrons.
Which set shows the change from metallic to non-metallic character across a period?
A) beryllium → magnesium → calcium
B) sodium → silicon → chlorine
C) fluorine → bromine → iodine
B) sodium → silicon → chlorine
Which two particles have the same electronic structure?
A) C and O²⁻
B) F⁻ and Na
C) K⁺ and S²⁻
D) Mg and Na⁺
B) F⁻ and Na (both have 10 electrons: 2,8)
What is the correct order of processes to separate sodium chloride from a mixture of sand and salt?
1. Dissolving (add water), 2. Filtration (to remove sand), 3. Crystallisation/Evaporation (to obtain salt crystals).
Which two gases will diffuse at the same rate at the same temperature?
A) carbon monoxide and carbon dioxide
B) carbon monoxide and nitrogen
C) chlorine and fluorine
D) nitrogen and oxygen
B) carbon monoxide and nitrogen (both have Mr = 28)
An atom has 18 electrons, 20 neutrons, and 18 protons. What is its nucleon number?
38 (protons + neutrons = 18 + 20)
As you descend Group VIII (noble gases), what happens to boiling point and density?
Both boiling point and density increase.
In a CO₂ molecule, what type of bonds are present, and how many electron pairs are shared between carbon and each oxygen?
Covalent bonds; 2 electron pairs (double bonds) are shared between carbon and each oxygen.
In chromatography, what are the two correct statements about Rf values?
Rf values are always less than 1.0
Rf = distance travelled by solvent ÷ distance travelled by substance
Higher Rf means substance travels further
Rf is not affected by solubility
1 and 3
As ice melts, what happens to the temperature and energy?
Temperature stays the same; energy is used to overcome attractive forces between particles.
Particle A has 10 electrons, 13 neutrons, and 11 protons. Is this an atom or an ion? If an ion, what charge does it have?
It is a positive ion with a 1+ charge (Na⁺) because it has 11 protons but only 10 electrons.
A new element "Oxforium" (Ox) is insoluble in water, does not conduct electricity, and has the formula Ox₂ with bonding Ox≡Ox. Which group should it be placed in?
Group V (it forms a triple bond and exists as a diatomic molecule, similar to nitrogen).
Identify the ion pairs that could form a compound with formula XY₂ from the electronic structures shown
B = 2
C = 2,8,2 with 2+ charge
D = 2,8,8 with 3- charge
E = 2,8,1 with 1+ charge
F = 2,8,8 with 2- charge
G = 2,8 with 1- charge
C (2,8,2 → C²⁺) and G (2,8,8 with 1- charge → G⁻) would form CG₂. Alternatively, any +2 ion paired with a -1 ion.
In paper chromatography of amino acids, what is the purpose of propanol and the locating agent?
Propanol moves the amino acids up the chromatography paper (it is the solvent/mobile phase); the locating agent makes the individual amino acids visible.
Which substances can be separated by filtration?
A) insoluble liquid and water
B) insoluble solid and water
C) solution of soluble liquid in water
D) solution of soluble solid in water
B) insoluble solid and water