1.3- Bonding Flashcards
What makes ionic bonding stronger and melting points higher?
Smaller ions
Higher charges
What is an ionic bond?
Electrostatic force of attraction between oppositely charged ions formed by electron transfer
What is a covalent bond?
A shared pair of electrons
What is a dative covalent bond?
When the shared pair of electrons in the covalent bond come from only one of the bonding atoms
What is a metallic bond?
Electrostatic force of attraction between the positive metal ions and the delocalised electrons
Three factors affecting the strength of a metallic bond?
Number of protons/strength of nuclear attraction
Number of delocalised electrons per atom
Size of ion
What are the properties of ionic bonding?
High melting and boiling points because of giant lattice of ions with strong electrostatic forces between oppositely charged ions
Generally good solubility in water
Poor conductors when solid as ions can’t move/fixed in the lattice
Good conductors when molten as ions are free to move
Usually crystalline solids
What are the properties of simple molecular substances?
Low melting and boiling points because of weak intermolecular forces between molecules (specify type of bonding)
Generally poor solubility in water
Poor conductors when solid as there are no ions to conduct and electrons are localised
Poor conductors when molten as there are no ions
They are mostly gases and liquids
What are the properties of macromolecular substances?
High melting and boiling points because of many strong covalent bonds in the macromolecular structure. Take a lot of energy to break the many strong bonds
They are insoluble in water
Diamond and sand are poor conductors when solid because electrons are localised
Graphite is a good conductor when solid because there are delocalised electrons between layers
Poor conductors when molten
Generally solids
What are the properties of metallic substances?
High melting and boiling points as strong electrostatic forces between positive ions and sea of delocalised electrons
Insoluble in water
Good conductors when solid as the delocalised electrons can move through the structure
Good conductors when molten
Malleable as the positive ions in the lattice are all identical so the planes of ions can slide easily over one another. Attractive forces in the lattice are the same whichever ions are adjacent
Generally shiny metals
Linear shape?
2 bonding pairs, 0 lone pairs
180°
Trigonal planar?
3 bonding pairs, 0 lone pairs
120°
Tetrahedral shape?
4 bonding pairs, 0 lone pairs
109.5°
Trigonal pyramidal?
3 bonding pairs, 1 lone pair
107°
Bent/Angular?
2 bonding pairs, 2 lone pairs
104.5°
Trigonal Bipyramidal?
5 bonding pairs, 0 lone pairs
120° and 90°
Octahedral shape?
6 bonding pairs, 0 lone pairs
90°
How to explain the shapes of molecules?
State the number of bonding and lone pairs of electrons
State that electron pairs repel and try to get as far apart as possible (position of minimum repulsion)
If there are no lone pairs state that the electron pairs repel equally
If there are lone pairs state that the lone pairs repel more than bonding pairs (reduce bond angles by 2.5° per lone pair)
State the actual shape and bond angle
Steps to work out shapes of molecules?
Count number of outer shell electrons of the central atom
Add that to number of electrons the bonding atoms bring
Add/remove electrons depending on the charge of the molecule
Divide total number by two to find electron pairs
Look at molecule to decide how many bonding and lone pairs and then decide the shape
What is electronegativity?
The relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself
What are the trends in electronegativity?
Increases across a period as the number of protons increases and the atomic radius decreases because the electrons in the same shell are pulled in more
Decreases down a group because the distance between the nucleus and the outer electrons increases and the shielding of inner shell electrons increases
What is a polar bond?
A covalent bond in which the electron pair is not shared equally. Thus creating partial charges (dipoles)
What is a non-polar bond?
A covalent bond in which the electron pair is shared equally
What are intermolecular forces?
A physical attraction between molecules
Permanent dipole-dipole bonding?
Attraction between two polar molecules (dipoles)
What are van der Waals forces?
Attraction between temporary dipoles caused by the movement of electrons in the atoms of a molecule
What is hydrogen bonding?
Attraction between polar molecules that contain hydrogen atoms bonded to one of these atoms:
F, O, N, Cl
Central atom must have an available lone pair of electrons
