Unit 1-4 Flashcards
(67 cards)
What happens to atomic radius across a row?
Decreases because there’s a greater nuclear attraction as proton number increases, pulling the shell slightly inwards
What happens to atomic radius down a group?
Increases since successive elements have an extra shell
Why are cations smaller than the parent atom
Has lost electrons and has less shells
Why are anions larger than the parent atom?
Less effective nuclear charge as there are more electrons for the same number of protons
Where are repulsive forces present in an ionic bond?
Ions of the same charge
Inner shells of electrons in the ions
Positive nuclei (to a lesser extent)
What are isoelectronic ions?
Different ions with the same electronic configuration and number of electrons
Note: Different atomic radii
Example: O2−, F−, Na+, Mg2+and Al3+ all have 10 electrons
What is an ionic bond?
Electrostatic force of attraction between two oppositely charged ions
Formed by transfer of one or more electrons from a metal to nonmetal
Note: Individual molecules don’t exist
Why do ionic lattices have a high melting temperature?
Large amount of energy needed to break strong electrostatic attraction
Why are ionic lattices soluble in water?
Polar solvents stabilise the separated ions
All group 1, nitrate and most halide compounds are soluble in water
Note: Insoluble in non-polar solvents
Why are ionic lattices electrolytes when molten or dissolved in water?
Because the ions are free to move and carry the charge
Why are ionic lattices very brittle?
Repulsion of similarly charged ions splits the crystal after dislocation
What is a normal covalent bond?
Electrons are shared
Attractive forces exist between positively charged nuclei and the negative charge cloud of the shared electron pair
What is a coordinate covalent bond?
All electrons are donated by a single atom with a lone pair
Bonds are delocalised
The charge of the ions involved is distributed across the molecule
Note: Impossible to distinguish between bonds of the same atom
Where are repulsive forces present in a covalent bond?
Inner shells of electrons on each atom
Each of the positively charged nuclei
The electron shells and charge cloud
Why are covalent molecules liquids and gases at room temperature?
Low melting point as bonds are easy to break
Where is electron density in a covalent bond?
Bulk of electron density will surround the nuclei
Some will occur in the inter-nuclear region
Why are covalent molecules non-conductive?
No free ions or electrons
What does electron deficient mean?
Didn’t gain enough electrons after bonding and still don’t have a full outer shell
What is a lone pair of electrons?
Unbonded electrons in the outer shell
Can be donated with electron deficient atoms to form coordinate bonds
What is electronegativity?
The ability of an atom to pull electron density towards itself within a covalent bond
Note: Shown by the Pauling scale
Why does electronegativity increase across a row?
Nuclear charge increases for only a slight or no increase in shielding
Why does electronegativity decrease down a group?
Less effective nuclear charge due to increased shielding and distance from the nucleus
How is polarity determined?
By the difference in electronegativity in atoms
What is a pure covalent bond?
0 difference in electronegativity
Electrons are shared equally
Only occurs between identical atoms
