Atomic theory 9 Flashcards
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
Predict the type of bond formed between carbon and chlorine atoms in a CCl₄ molecule (L.C)
Polar covalent
State and account for the shape of a tetrachloromethane molecule. (L.C)
- Tetrahedral
- Four pairs electrons and no lone pairs
Define electronegativity (L.C)
The relative power of attraction an atom of an element has 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? (L.C)
- Nuclear charge increasing
- Atomic radius decreasing
Use electron pair repulsion theory to predict the shape of a molecule of boron trifluoride. (L.C)
- Trigonal planar
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
Define electronegativity (L.C
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
How many (i) sigma bonds, (ii) pi bonds, result from sharing of the valence electrons between the atoms in a molecule of nitrogen. (L.C)
(i) 1 sigma
(ii) 2 pi
Distinguish between intramolecular bonding and intermolecular forces. (L.C)
Intramolecular : forces between atoms in molecules
Intermolecular : forces between molecules
Explain in terms of intramolecular bonding and intermolecular forces, why the boiling point of hydrogen (20 K) is significantly lower than that of oxygen (90.2 K). (L.C)
- hydrogen smaller
- weaker intermolecular forces
Explain in terms of intramolecular bonding and intermolecular forces, why iodine has a very low solubility in water. (L.C)
- Iodine is pure covalent
- Water is a polar solvent
Explain in terms of intramolecular bonding and intermolecular forces, why when a charged rod is held close to a thin stream of water flowing from a burette, the stream of water is deflected. (L.C)
Charge on rod attracts opposite charge on polar water molecule.
Distinguish between sigma (σ) and pi (π) covalent bonding. (L.C)
Sigma - When orbitals overlap ‘head-on’. This can occur between two s orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals.
Pi - When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only.
Give one reason why electronegativity values exhibit general increase across the second period of the periodic table. (L.C)
Increase in nuclear charge / decrease in atomic radius
Show that the ammonia molecule has polar covalent bonding. (L.C)
- There is an electronegativity difference between N and H.
- N with greater attraction
- H with smaller attraction
Describe the processes involved when ammonia dissolves in water. (L.C)
- Hydrogen bonds between slightly negative O of water and H of ammonia and between slightly positive H of water and N of ammonia.
- Breaking of hydrogen bonds in water
- Forming of hydrogen bonds between ammonia and water.
Distinguish between sigma (σ) and pi (π) covalent bonding. (L.C)
Sigma - When orbitals overlap ‘head-on’. This can occur between two s orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals.
Pi - When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only.
State two factors that cause electronegativity values to increase across a period in the periodic table of the elements. (L.C)
- Increasing effective nuclear charge
- Decreasing atomic radius
State which of the following compounds contain intermolecular hydrogen bonds, HCl, H₂O, NH₃. Justify your answer. (L.C)
H₂O and NH₃
- Hydrogen bonded to a small highly electronegative element (bonded to F, O or N)
Suggest a reason why the boiling point of ammonia (-33°C) is significantly lower than that of water (100 °C) (L.C)
- Weaker hydrogen bonding in ammonia
- Stronger hydrogen bonding in water
Explain the term intermolecular forces (L.C)
Attractive forces (repulsive) between molecules
A thin stream of liquid is flowing from the burette. A stream of water is deflected towards a positively charged rod whereas a stream of cyclohexane is undeflected. Account for these observations. (L.C)
- Polarity of water causes attraction to charged rod
- Non-polarity of cyclohexane means it is not affected by charged rod
Use electronegativity values to predict the type of bond expected between hydrogen and sulphur. (L.C)
- Weakly polar
- Almost non-polar
- Covalent bond
Write the chemical formula for hydrogen sulphide. (L.C)
H₂S
Distinguish between sigma and pi covalent bonding.(L.C)
Sigma - When orbitals overlap ‘head-on’. This can occur between two s orbitals, an ‘s’ and a ‘p’ orbital or two ‘p’ orbitals.
Pi - When orbitals overlap ‘side-ways’. This can occur between two ‘p’ orbitals only.
Define atomic covalent radius. (L.C) (same as atomic radius)
The atomic radius is obtained by getting half the distance between the centres of singly bonded atoms of the same element
Under what circumstances can ionic compounds conduct electricity? (L.C)
In water / in the molten state
A thin stream of liquid is flowing from the burette. A stream of water is deflected towards a positively charged rod whereas a stream of cyclohexane is undeflected. Explain what would happen in the case of the stream of water if the positively charged rod were replaced by a negatively charged rod. (L.C)
Stream of water still attracted to rod as molecules arrange themselves with positive pole towards rod.
What is the valency of carbon in tetrachloromethane?
4
Suggest a reason why ammonia has the highest boiling point of the three hydrides. (L.C)
Hydrogen bonding in ammonia is stronger than the other intermolecular forces.
Suggest a reason why phosphine’s boiling point is lower than that of arsine. (L.C)
Phosphine molecules are smaller.
