Chemical structure and bonding Flashcards
(47 cards)
Properties of metal
- high melting point
- good conductors of electricity and heat
- malleable and ductile
Metallic bonding
and what increases its strength
Strong electrostatic attraction between metal cations and delocalised electrons
Strength increased by:
- more delocalised electrons
- smaller ion size
Metallic structure
Giant lattice of metal cations with delocalised electrons
Why metal conducts electricity
and what makes it better at conducting
Delocalised electrons can carry negative charge through the metal
Conductivity increased by:
- more delocalised electrons
- smaller ion size (for higher electron density)
Why metal is a good thermal conductor
Delocalised electrons quickly transfer kinetic energy around the metal
Why metal is malleable and ductile
- metallic bonding relies on delocalised electrons so it is non-directional
- if layers of the lattice slide over each other, bonding stays intact
Ionic bonding
and what increases its strength
Strong electrostatic attraction between oppositely charged ions
Strength increased by:
- larger ion charges
- smaller ion size
Properties of ionic compounds
- high melting point
- conducts electricity when molten or dissolved
- brittle
- soluble in water
Why ionic compounds conduct electricity only when molten or dissolved
- solid ionic compounds have charged particles, but they are not free to move
- as part of a liquid, the ions can move freely and carry charge
Why ionic compounds are brittle
- ionic bonding is between oppositely charged ions
- if layers of the lattice slide over each other, ions with the same charge repel, breaking the bonding
Why ionic compounds are soluble in water
- water is a polar molecule
- poles of water molecules surround oppositely charged ions, pulling them out of the lattice
Demonstration of the existence of ions
Electrolysis of green copper chromate solution separates blue copper ions from yellow chromate ions
Covalent bonding
and what increases its strength
Strong electrostatic attraction between two nuclei and a bonding pair of electrons
Strength increased by:
- shorter bond length (smaller atomic radii)
Sigma bond
- covalent bond formed by the overlap of two orbitals directly between the nuclei
- the first type of covalent bond to form
- stronger than a pi bond
Pi bond
- covalent bond formed by a sideways overlap of two p orbitals
- only forms after a sigma bond is present
- present in double or triple covalent bonds
- weaker than a sigma bond
Electronegativity
and what increases it
An element’s ability to attract a bonding pair of electrons
Increased by: - higher nuclear charge - smaller atomic radius - less electron shielding (highest in top right of table)
Polar covalent bond
- covalent bond between atoms of different electronegativity (different elements)
- EN diff causes a dipole to form
Dative covalent bond
- covalent bond where both bonding electrons are from the same atom
- functionally the same as any other covalent bond
Octet rule
- atoms usually want 8 electrons in their outer shell
- C, N, O, and F always follow this
- H, Be, B, and elements past period 3 do not follow
Polarising power of a cation
Ability of a cation to distort an anion’s electrons (increases as EN increases)
Polarisability of an anion
Tendency of an anion to be distorted by a cation (increases as EN decreases)
London forces
- occurs in all molecules
- electron density constantly moves around in molecules
- when it is higher on one side, a dipole is formed
- this induces more dipoles on neighbouring molecules, which are then attracted
What makes london forces stronger
- more electrons (larger molecule)
- more points of contact (flatter molecule / less branches)
Permanent dipole forces
- occurs only in polar molecules
- attraction between the dipoles of polar molecules
