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Valency
Atoms form chemical bonds to obtain a full valence shell to become chemically stable.
Metallic Bonding Model
Metals tend to become cations. The cations are arranged in a closely packed 3D lattice arrangement.
The valence electrons are DELOCALISED and are free to move throughout the lattice. The remaining electrons are localised.
Model = A lattice of cations surrounded by a sea of delocalised electrons. They are held together by electrostatic forces of attraction (+/- charges) or METALLIC BONDS in a 3D LATTICE
Metallic bonding is the strong attraction between closely packed positive metal ions (cations) and a 'sea' of delocalised electrons in a 3D lattice
Properties of Metal: Hard + High MP
Metallic Bonding Model
A higher amount of energy is required to overcome the strong electrostatic attraction between cations and delocalised Electrons in the 3D lattice
Properties of Metal: Conductor of Heat + Electricity
Metallic Bonding Model
The 3D delocalised electrons are free to overlap and carry charge/kinetic energy through the 3D lattice.
Properties of Metal: Malleable + Ductile
Metallic Bonding Model
When a FORCE IS APPLIED cations are able to move past each other because they are stabilised by the 'sea' of delocalised electrons
Properties of Metal: Lustrous
Metallic Bonding Model
Delocalised e- on the surface of the metal reflect light waves
Ionic Bonding Model
The electrostatic attraction between a 3D lattice of positive and negatively charged Ions. Brittle
Properties of Ionic Bonds: Hard + High MP
Ionic Bonding model
A LOT of energy is required to overcome the ELECTROSTATIC ATTRACTION between ions in the 3D lattice
Properties of Ionic Bonds: Conductive in Molten State and Solution
Ionic Bonding model
In liquid state, ions are free to move over eachother. THEREFORE, there are mobile charge carriers present and conudctive
In solutions, ions are separated and evenly distributed in water solvent
NOT CONDUCTIVE IN SOLIDS => ions are in fixed postions => no mobile charge carriers.
Properties of Ionic Bonds: Brittle
Ionic Bonding model
When force is applied, like charged ions move closer together and repel
Lattice Fractures
VSEPR theory
Valence-shell electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible
Number of e- domains
Linear VSEPR shape
a molecule in which atoms are deployed in a straight line (under 180° angle)
3 Electron Domains
trigonal planar, 120 degrees
3 electron domains, 1 lone pair
bent, <120 degrees
4 electron domains
tetrahedral, 109.5 degrees
4 electron domains, 1 lone pair
pyramidal, <109.5 degrees
4 electron domains, 2 lone pairs
Bent 109.5
Electronegativity
a measure of the tendency of an atom to attract a bonding pair of electrons
An atoms attraction for bonding a pair of e-
Polarity
A lack of electrical symmetry in a molecule. Charge differences on opposite ends of a structure.
Delta negative/Delta positive
Partially positive / partially negative
Polar bonds
a type of covalent bond between atoms that differ in electronegativity. the shared electrons are pulled closer to the more electronegative atom. making one slightly negative and the other slightly positive
Polar molecule
molecule with an unequal distribution of charge, resulting in the molecule having a positive end and a negative end
Atomic Radius Trend Down A Group
Atomic radius increases down a group as there is an increased number of electron shells inside each atom putting more and more distance to the nucleus. There is also a lesser attraction of valence electrons to nuclear charge, (shielding from inner shell e-)
) Atomic Radius increases
) Increased number of e- Shells
) Further from the nucleus
) Less attraction of valence e- to nuclear charge (Shielding from inner shell e-)
Atomic Radius Trend Across A Period
Atomic radius decreses (left to right)
Valence e- are added to the same shell
Nuclear charge increases across a period
Greater attraction of valence e- to nuclear charge
electronegativity trend down a group
EN decreases
The binding pair of e- are in a shell further from the nuclear charge
Less attraction of valence e- to nuclear charge (Shielding from inner shell e-)
electronegativity trend across a period
EN increases
across a period bonding e- are in the same shell
Nuclear charge is increasing
Greater attraction from nuclear charge on bonding e-
Covalent Molecules
Are discrete and have a start + endpoint
Allotropes
elements can exist w/ their atoms in several different structural arrangements which are bonded in specific ways
allotropes of carbon
diamond and graphite
Diamond
Brittle, very hard, non cunductive.
Each C is bonded to 4 other C in a tetrahedral 3D lattice
Graphite
Each C bonds 3 other C in a trigonal planar 2D sheet called graphene. Each C has 1 delocalised electron spread throughout the sheet
Graphite properties
- soft and slippery
- good conductors of electricity
-high melting and boiling point
