Bonding And Structure Flashcards
Ionic bonding
The electrostatic force of attraction between oppositely charged ions, formed by electron transfer
It holds together cations and anions in ionic compounds
Common cations?
Metal ions- Na + and Al 3+
Ammonium ions -NH3+
Common anions
Non metal ions - cl- or o2-
Polyatomic ions ( no3-, so42-)
What are ionic compounds
Ionic bonding leads to GIANT IONIC STRUCTURES/ LATTICES
CLOSEly packed, regular arrangements of positive and negative ions - where there are strong forces of attraction between the oppositely charged ions in ALL directions
Describe a lattice of Na and Cl ions
Each Na+ is surrounded by 6 cl-
And each cl- is surrounded by 6 Na+
Properties of ionic compounds
High melting and boiling points
Solubility
Electrical conductivity
What are the melting and boiling points liked in ionic compiunds and why ?
Almost all ionic compounds are solids at room temperature-there is INSUFFICIENT energy to overcome strong electrostatic forces of attraction between oppositely charged ions
High temperatures are needed to overcome this attraction
IONIC BONDIGN IS STRONGER AND M+BP IGHER , WEN IONS ARE SMALLER OR HAVE JIGHER CHARGES
Solubility of ionic compounds
Many ionic compounds dissolve polar solvents , such as water
Polar h20 molecules brea down the lattice and surround each ion is solution
In a compound Mae of IONS with LARGE charges, the ionic attraction may be TOO strong for water to be able to break down the lattice structure- the compound will then not be very soluble
What does solubility mean
The ionic lattice must be broken down
Water molecules must attract and surround the ions
The solubility therefore depends on relative strengths of attraction WITHIN the giant ionic lattice and the attractions between ions and h20 molecules
Electrical conductivity - ionic compounds
Melted or dissolved in water
- solid lattice breaks down
- ions free to move as mobile charge carries
Covalent bonding?
The strong electrostatic attraction between SHARED pair of electrons and the nuclei of the bonded atom
Covalent BONDiNG occurs between atoms in..
Non metallic elements e.g. H2 and c2
Compounds of non metallic elements e.g. H2o and co2
Polyatomic ions e.g. NH4+
What is a polyatomic ion?
Created when many atoms come together to form a group
Positive or negative charge
Can be cation or anion
What is orbital overlap ( covalent bonding)
A covalent bond is the overlap of atomic orbitals each containing 1 electron, to give a shared pair of electrons
E.G. H + H – h2
The shared pair of electrons is attracted to the nuclei of BOTH the bonding atoms, the bonded atoms often have other shells with the same electron structure on the nearest noble gas
A covalent bond is .. LOCALISED?
The attraction is localised
Acting solely between the shared pair of electrons and the nuclei of the 2 bonded atoms
The result is a small unit called a molecule
Double covalent bond
Electrostatic attraction between 2 shared pairs of electrons and the nuclei of the bonding atoms
E,g, h20 and o2
Triple covalent bond
The electrostatic attraction is between 3 shared pairs of electrons and the nuclei of the bonding atoms
Dative covalent bonds /coordinate bond
Forms when the shared pair of electrons in the covalent bond come from ONLY ONE of the bonding atoms
The shared electron pair was originally a lone pair of electrons on one of the bonded atoms
E.g. NH4+ —- NH3 and a H+ ion
What is average bond enthalpy?
Measure of covalent bond strength
Giant adn simple covalent
***(
What is the electron pair repulsion theory
An electron has a negative charge, so electron pairs repel one another
The electron pairs surrounding a centeral atom determine the shape of the molecule or ion
The electron pairs repel one another so they are arranged as far apart as possible
The arrangement of electron pairs minimises repulsion and thus holds the atoms in place
Different numbers o electron pairs result in different shape
What shape do you get , when there are 2 electron bondingpairs around centeral atom ?
LINEAR
180 degrees
What shape and angle for 3 bonding pairs around centeral atom
TRIGONAL PLANAR
120
What shape and angle for 4 bonding pairs around centeral atom
Tetrahedral
109.5
What shape and angle for 6 bonding pairs around centeral atom
Octahedral
90 degrees
What are lone pairs and how do they affect bond Angels
Lone pairs are closer to the nucleus and occupies MORE SPACE- repel more strongly
Reduce bond angles by 2.5 per lone pair
H20 bond angle size
104.5
NH3 bond angle size
107
1 lone pair + 3 bonded =
Pyramidal
107 degrees
E.g. NH3
2 lone pairs + 2 bonded pair
Non linear
104.5
E.g. H20
Multiple bonds?
Each multiple bond is treated as a bonding region or pair
Co2- 2 bonding regions - linear
Drawing 3D structures- what are the 3 different lines
- solid line
- solid wedge
- dotted wedge
Solid line ?
Bond in the plane of the paper
Solid wedge
Comes out of the plane of the paper
Dotted wedge
Goes into the plane of the paper
