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
