Chemistry Covalent Bonding + Structure

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