Atomic theory 1 Flashcards
Naturally occurring chlorine consists of 75.5% of (35)Cl and 24.5% of (37) Cl. Calculate the relative atomic mass (Ar) of chlorine. (L.C)
- 75.5 x 35 = 2642.5
- 24.5 x 37 = 906.5
100 atoms = 3549
1 atom = 35.49 (Ar)
A dipositive ion, M2+, has 25 electrons and 32 neutrons. What is (i) the atomic number, (ii) the mass number, of M (L.C)
i) 27
ii) 59
What are isotopes? (L.C)
Atoms with the same atomic number (Z) but different mass numbers (A)
How many (i) electrons, (ii) neutrons, has the aluminium ion (13 - bottom, 27 - top) Al³+ (L.C)
i) 10
ii) 14
Explain why relative atomic masses are rarely whole numbers. (L.C)
As it is the average of mass numbers of the isotopes of an element
Define (i) mass number, (ii) relative atomic mass (L.C)
(i) number of protons and neutrons in the atoms of an isotope
(ii) Average mass of atoms of element relative to 1/12 of mass of carbon-12 atom
A sample of the element gallium is composed of 60.1% gallium-69 and 39.9% gallium-71. Calculate the relative atomic mass of gallium from this information. (L.C)
69 x 60.1 = 4146.9
71 x 39.9 = 2832.9
100 atoms = 6979.8
Ar = 69.798 (69.8)
Define relative atomic mass (L.C)
Average mass of atoms of element relative to 1/12 mass of carbon-12 atom
Define relative atomic mass (L.C)
Average mass of atoms of element relative to 1/12 mass of carbon-12 atom
Define (a) atomic number, (b) relative atomic mass (L.C)
a) Number of protons in the nucleus of an atom of the element
b) Average mass of atoms of element relative to 1/12 mass of carbon-12 atom
What are isotopes? (L.C)
Atoms with the same atomic number (Z) but different mass numbers (A)
What are isotopes? (L.C)
Atoms with the same atomic number (Z) but different mass numbers (A)
What is the principle of the mass spectrometer? (L.C)
Positive ions separated based on relative mass when moving in a magnetic field
Calculate, to two decimal places, the relative atomic mass of a sample of neon shown by mass spectrometer to be composed of 90.5% of neon-20 and 9.5% of neon-22. (L.C)
90.5 x 20 = 1810
9.5 x 22 = 209
100 atoms = 2019
Ar = 20.19
What are isotopes? (L.C)
Atoms with the same atomic number (Z) but different mass numbers (A)
Define relative atomic mass, Ar (L.C)
Average mass of atoms of element relative to 1/12 mass of carbon-12 atom
Calculate the relative atomic mass of a sample of lithium, given that a mass spectrometer shows it consists of 7.4% (6)Li and 92.6% (7)Li (L.C)
7.4 x 6 + 92.6 x 7 = 692.6
100 atoms = 692.6
1 atom = 6.926
What is the principle on which the mass spectrometer in based? (L.C)
Positive ions separated based on relative masses when moving in a magnetic field.
Identify an element that is a non-metal and is a liquid at room temperature.
Br
Identify an element that is a divalent metal.
Be (anyone from group 2)
In the periodic table identify an element in the same period as magnesium but with larger atoms. (L.C)
Sodium / Na
In the periodic table identify an element in the same period as magnesium but with smaller atoms. (L.C)
Beryllium / Be
Define electronegativity
The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.
Describe using dot and cross diagrams the bonding in the ammonia molecule.
Drawn.
Use electron pair repulsion theory to determine the shape of the ammonia molecule. Which of the following angles: 104°, 107°, 109°, 120° or 180° would you expect to be closest to the bond angle in the ammonia molecule? Explain your answer.
- Three bonding and one non-bonding (lone) pair giving bond arrangement (shape of molecule) to be pyramidal
- 107°
- Greater repulsion of lone pair and lone pair pushes bonds closer together
Defineelectronegativity.
The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.
Accountfortheincreaseinelectronegativityvaluesacrossthesecondperiodoftheperiodictable.
- Effective nuclear charge increasing
- More protons
- Atomic number (Z) increasing /
- Atomic radius decreasing
Useelectronegativityvaluestopredictthetypeofbondinginoxygendifluoride (OF₂).
Slightly polar covalent
StateandaccountfortheshapeoftheOF₂molecule.
State - V-shaped planar
Account - 2 bond pairs electrons and 2 lone pairs
180.0° 109.5° 120.0° 103.0° Select,giving your reasons,whichofthese anglesis the most probable valueforthebondangleinoxygendifluoride.
xx
WhatismeantbytheperiodicsysteminthecontextofMendeleev’s1869periodictableoftheelements?
Elements listed according to relative atomic mass and in groups with similar properties
Commentonthepositioningoftellurium(Te)andiodine(I)inthe1869table.
Chemical properties matched (fitted) better when order reversed.
Whydidthe1869tablenotincludeanynoblegases?
They were undiscovered in 1869.
Modernperiodictablesarrangetheelementsinorderof atomicnumberandnot in orderofrelativeatomic mass.Define the terms atomic number and relative atomic mass.
A.N - The number of protons present in the nucleus of an atom, (this equals the number of electrons in an atom).
R.A.M - The average mass of an atom of an element compared to 1/12 the mass of the carbon - 12 isotope, taking relative abundances of isotopes into account.
Explain whyalltheelementsof Group 18inthe periodic table are chemicallyinert.
Stable arrangement of electrons.
Explain how andwhythe reactivity ofthe halogens
changes downGroup17.
How : Less reactive down group
Why : Increasing (greater) atomic radius (number of shells)
Howwouldyouexpectasmallsampleoffranciumto reactinwater?Justifyyouranswer. Predicttheproductsofthisreaction.
How : violently / explosively
Justify : reactivity increases down group
Predict : FrOH (francium hydroxide) and H₂ (hydrogen)
Stateandgivethereasonforthetrendinatomicradiiacrossthesecondperiodoftheperiodictable.
State : decrease
Give : nuclear charge increasing and atomic number increasing
Define(i)massnumberofanatom,(ii)relativeatomicmassofanelement.
(i) The number of protons plus neutrons in the nucleus of an atom.
(ii) The average mass of an atom of an element compared to 1/12 the mass of the carbon - 12 isotope, taking relative abundances of isotopes into account.
Asampleofmagnesiummetalwasintroducedintoamassspectrometerandvaporised.Whatwerethenextthreefundamentalprocessesthatoccurredinthespectrometer?
- ionisation
- acceleration
- separation
Defineelectronegativity.
The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.
PredictthetypeofbondformedbetweencarbonandchlorineatomsinaCCl₄molecule.
Polar covalent
Whatisthevalencyofcarbonintetrachloromethane?
4
Stateandaccountfortheshapeofatetrachloromethanemolecule.
State : tetrahedral
Account : four pairs electrons and no lone pairs.
DrawadotandcrossdiagramtoshowthearrangementofallthevalenceshellelectronsinaCS₂molecule.
Drawn.
Why did Mendeleev place tellurium before iodine in his periodic table of elements?
x
Define electronegativity.
The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.
Why is there an increase in electronegativity value moving from gallium to germanium in the periodic table?
- nuclear charge increasing
- atomic radius decreasing
Mendeleev predicted the properties of the elements gallium and germanium years before either of them was discovered. Explain the basis for his predictions.
Predicted the properties from properties of known elements.