Bonding Flashcards
What happens in ionic bonding?
Atoms loose and gain electrons to give them noble gas configuration. (some block elements may not achieve this) The electrostatic attraction between cations and anions is the ionic bond. Always mention how many electrons are lost from one and gained by another in a bond -> therefore each ions charge.
Define lattice
The regular repeated 3D arrangement of atoms, ions or molecules in a metal or other crystalline solid.
Why do ionic compounds have a high mp and what affects this?
There are a large number of electrostatic attractions within a crystal, so lots of energy is required to overcome the ES forces.
Smaller size -> stronger ionic bond -> higher mp
Higher charge -> stronger ionic bond -> higher mp
How does ion size compare to atom size in +ve and -ve ions?
Positive ions are normally smaller as metal ions will have one less energy level occupied. The effective nuclear charge increases, pulling electrons closer to the nucleus.
Negative ions are normally larger as the repulsion between the electrons moves the, further apart. Also, the effective nuclear charge decreases.
Why are ionic compounds usually soluble in water?
The polar water molecules are attracted to the charged ions and will hit into the molecule as they move, knocking off ions and surrounding them. Some ionic substances have too strong ES attraction and so water cannot break them, e.g. Al2O3
Why do ionic compounds conduct electricity?
When liquid or aqueous, the ions are free to move and carry charge.
What is a covalent bond?
A shared pair of electrons between atoms. An unpaired electron in an orbital can be shared with an unpaired electron in an orbital of another atom. Atoms can also promote electrons to unoccupied orbitals to allow more bonds to form.
What is a coordinate/dative bond?
A covalent bond where both electrons are supplied by one atom.
What is a metallic bond?
The electrostatic attraction between the sea of delocalised electrons and the layers of positive metal atoms in the lattice.
Why can metals conduct heat?
The delocalised electrons can flow and carry charge.
Why can metals conduct heat?
The delocalised electrons in a metal are close enough together to pass heat energy to each other.
Why are metals ductile and malleable?
The structured layers of the lattice can slide over each other without disrupting the bonding. This means it can be drawn out into wires (ductile) and hammered into shape (malleable).
Why do metals have high mp and what impacts this?
Lots of energy is required to overcome the electrostatic forces of attraction between the sea of delocalised electrons and the positive ions. The metallic bonding is stronger for multiple charged ions as more electrons and smaller sized +ve ions.
What are the two main types of covalent substances?
molecular (simple covalent)
macromolecular (giant covalent)
How many other C atoms is every C in diamond bonded to and what is the shape and angle?
4
tetrahedral -> 109.5
What is the structure and bonding of graphite?
Each carbon forms 3 covalent bonds with other carbons (trigonal planar -> 120) and delocalised its last electron. This forms a sea of delocalised electrons between the planar layers of carbons. These causes weak forces between the layers and conductivity. The weak forces between layers mean they can slide over each other but the strong covalent bonds means lots of energy is required to break.
What do you call going from a solid -> gas on heating?
Subliming
Define electronegativity
power of an Atom the attract the pair of electrons in a covalent bond.
What does electronegativity depend on?
(3)
- Distance of bonding electrons from the attractive power of the nucleus
- Size of nuclear charge
- Shielding of inner electrons
Trend in electronegativity across a period and down a group.
Increases across a period:
Atomic rad decreases as the size of nucleus increases
Nuclear charge increases
Electronegativity decreases down a group:
Atomic rad increases
More sheilding
Why do van der Waals forces arise?
All atoms have electrons which are in constant random motion around the nucleus. So, at any one time, there will be be a slight imbalance causing an electronegative side of the molecule. his will induce a dipole in neighbouring atoms causing attractive forces between the oppositely charged sides. These dip[oles and forces are constantly forming and disappearing.
What is evidence for van der Waals?
Halogen’s (simple covalent) bp increases down the group as size of molecules increases. So do the bps of noble gases as you descend the group.
How do permanent dipole-dipole forces arise?
Molecules with a permanent dipole will have ES attraction between the electro+ve side and the electro-ve side of another.
How do hydrogen bonds arise?
An electropositive H atom within a polar covalent bond is attracted to the lone pair on a N,O, or F atom.
What properties of water does hydrogen bonding explain?
- Fluidity - H bonds can break and reform allowing the molecules to move around one another.
- Higher BP than expected for Group 6 hydride as H bonding is stronger then VDW or PD.
- Ice’s lower density than water - when the water molecules must organise in a crystalline structure, the H bonds mean the molecules form a more open tetrahedral arrangement.
What properties of ethanol does hydrogen bonding explain?
- Solubility in water - water can form H bonds with ethanol
- Higher bp than expected
What properties of propane does hydrogen bonding explain?
- Solubility in water - H bonds can form between water and the electronegative C=O
- Higher bp than expected.
Explain why both SO2 and SO3 have polar bonds, but only SO2 has polar molecules?
There is a difference in electronegativity between S and O, meaning the bonds are polar. The unbalanced shape of SO2 means these dipoles do not cancel;, whereas the symmetrical shape of SO3 mean they do.
