3.1.3: Bonding Flashcards
Why do elements bond to have a full outer shell?
- to become more stable
- to be inert and unreactive
- like noble gases
What is ionic bonding?
- ions attatched due to an electrostatic attraction between opposing charges
- between metals and nonmetals
- lose or gain electrons
- metal= positive ion/cation
- non-metal= negative ion/ anion
What are properties of ions?
- dissolve in polar solvents
- always solid at room temperature due to strong ionic bonds and electrostatic forces
- in a fixed position when solid, can vibrate but can’t carry current /electricity.
- when molten, ions are free to move and carry electrical current
- brittle as layers can move in alternating positive/negative ions that can repel to break apart the ion
- high melting and boiling point
What is covalent bonding?
- bond between 2 nonmetals
- share electrons
- single covalent bond= one shared electron pair
What are properties of covalently bonded molecules?
- held by electrostatic attraction between nucleus of atom and shared electrons
- low melting and boiling points due to weak intermolecular forces so little energy is needed to break them apart
- strong coval nt bonds
- poor conductors of energy due to neutral charge
What’s a co-ordinate/ dative bond?
- a type of covalent bond
- both electrons from a pair come from one atom, represented by an arrow
- atom that accepts electrons doesn’t have a full outer shell and is electron deficient
- donating atom donates non-bonding pair of electrons (lone pair)
What is a metallic bond?
- metal merges the main levels of its atoms
- electrons aren’t associated with a single atom but shared
- positive ions surrounded by delocalised electrons
What’s the arrangement of metallic structures?
- arranged metal ion in latttice
- results in giant metallic structure of positively charged ions
- sea of delocalised electrons
What are the properties of metallic structures?
- good conductor of heat/ electricity (have delocalised electrons which can vibrate and carry charge).
- very strong (the greater charge, the more delocalised electrons, the more it vibrates)
- malleable and ductile (even aftervsmall distortion, layers still in same place)
- high melting and boiling point (giant with strong attraction)
- +ionic charge, -ion size,+no. valence electrons, +attraction, +mp. and bp.
What is periodicity?
The electrons on the outer shell and reaction patterns across elements.
What is electronegativity?
the ability and power of an atom to attract a pair of electrons and towards it
the greater electronegativity the more electrons it attracts
What are factors affecting electronegativity?
- nuclear charge (greater charge, increases attraction of electrons due to opposing charge)
- distance of the valence shell from the nucleus
- electron shielding (less shielding, less distance)
- the more electronegative, the greater share of electrons in polar atoms (e.g. Cl is more e.n. so in HCl electrons pull towards Cl)
- so HCl is a polar covalent bond as its not a symmetrical distribution of charge (permanent as Cl is always more e.n. than H)
- greater diffence in e.n., greater permanent dipole
Who is Linnaeus Pauling?
The scientist who made the Pauling scale used to measure electronegativity based on trends in shielding, shells, attraction and distance.
What is VSEPR theory?
(valence shell) electron pair repulsion theory
- as electron pairs in the same outer shell have the same charge, they repel and spread as far apart as possible
- one spins upwards, other spins downwards, minimising the repel
What is electron domain?
- each pair of shared electrons behaves as a single unit in terms of repulsion as they’re found together.
- single, double, triple and lone pairs act as one domain
- the total no. of electron domains determines molecule shape
What is the effect of lone pairs?
- slightly more electron dense than a bonded pair
- repel more than bonding pairs
- reduce bond angle by 2.5° per lone pair
What are the differnt types of bonds based on differences in electronegativity?
- no difference in electronegativity= non-polar covalent
- small difference in electronegativity= polar covalent
- large difference in electronegativity= ionic bond
What’s the difference between molecular and electron domain geometry?
Molecular geometry- considers bonded domains only
Electron domain geometry- considers all domains
if there’s lone pairs on the central atom, eg and mg won’t be the same
VSEPR GEOMETRY
molecular geometry of 2 domains
linear= 180°
VSEPR GEOMETRY
molecular geometry of 3 domains
trigonal planar= 120°
- 1 lone pair- bent(117.5°)
VSEPR GEOMETRY
molecular geometry of 4 domains
tetrahedral= 109.5°
- 1 lone pair- trigonal pyramidial (107°)
- 2 lone pairs- bent (104.5°)
VSEPR GEOMETRY
molecular geometry of 5 domains
trigonal bipyramidial= 120° & 90°
- 1 lone pair- seesaw
- 2 lone pairs- T shape
- 3 lone pairs- linear (180°)
VSEPR GEOMETRY
molecular geometry of 6 domains
octahedral= 90°
- 1 lone pair- square pyramidial
- 2 lone pairs- square planar
- 3 lone pairs- T shape
- 4 lone pairs- linear (180°
What are intermolecular forces?
- forces that hold atoms together, to do with attraction between positive and negative
- in ionic compounds, this is caused by the complete transfer of electrons.
- not all i.m. forces are equal
- VDW, dipole, hydrogen bonds (increase in strength)
intermolecular forces are weaker than cova!ent bonds
What are Van Der Walls forces?
instantaneous, induced, temporary dipole
- uneven distribution of electrons (as electrons are constantly moving)
- if more happen to be on one side than the other, a temporary/ instantaneous dipole is created (one more electronically charged than the other/ electron distortion)
- this can induce the neighbouring atom
- the more electrons, the greater charge, the stronger the VDW
occur between all molecules, even if there’s other intermolecular forces
What is a permanent dipole?
- there’s only permanent dipole-dipole attraction between polar molecules
- molecules with polar bonds but are non-polar don’t have this attraction
e.g. HCl
What’s a polar molecule?
- a molecule that contains polar bonds that are arranged asymmetrically around the central atom so the charge is unevenly distributed
- therefore polar molecules have a permanent dipole, in addition to the weaker VDW forces by a temporary dipole
What is polarity?
- an unequal sharing of electrons in a bond, if the electron sharing is equal, the bond is described as non-polar
- this increases melting and boiling point
What is hydrogen bonding?
a special case of permanent dipole-dipole attraction
- A hydrogen (H) atom bonded to a very electronegative atom (e.g. F,O and N)
- the polar bond between the H and electronegative atom leaves the H nucleus exposed as H only has one electron
- therefore, there’s a strong attraction from the lone pair on the electronegative atom of one molecule to the exposed H nucleus of another molecule
Hydrogen- slightly positive, Electronegative molecule- slightly negative
What is a melting and boiling point?
melting- temperature where a solid melts to be liquid
boiling- temperature where liquid changes and boils to be a gas
(this can be represented on a graph with specific heat of fusion and vapourisation)
Solid properties
arrangement, spacing, movement
ARRANGEMENT- fixed regular arrangement, crystal shaped have straight edges/ definite shapes.
SPACING- compact and close, not easily compressed
MOVEMENT- vibrate around a point
Liquid properties
ARRANGEMENT- random, changes shape to fit container, compact
SPACING- close, not easily compressed
MOVEMENT- rapid ‘jolting’
Gas properties
ARRANGEMENT- random, changes shape to sealed container
SPACING- far apart, easily compressed
MOVEMENT- rapid, gases exert pressure
What is a crystal?
- solid particles with a regular arrangement, held together by forces of attraction
-the strength of the forces of attraction between particles in the crystal affects their physical properties
forces can be strong (ionic, covalent or metallic) or weak (VDW,d-d,h)
What’s an example of a crystal?
- graphite- high m.p., soft due to VDW, conductor, graphene layers that slide, delocalised electrons
- diamond- very high m.p., strong, rigid
- silica (SIO4)
all crystals joined by covalent bonds have a high m.p. due to lots of covalent bonds and don’t conduct electricity (except graphite) as there’s no free electrons
covalent, giant, macro = all th same giant molecules
