Topic 3- Chemical Bonding Flashcards
What are the types of bonds?
Chemical and physical
What is a chemical bond?
When elections are gained lost or shared between atoms
What are the types of chemical bonds?
A) ionic bonds (electrovalent)
B) Covalent and dative covalent bonds
C) Metallic bonds
What are the types of physical bonds?
a) Hydrogen bonds
b) Permanent dipole - permanent dipole interaction
c) Induced dipole - induced dipole interaction
What are physical bonds?
Bonds produced from changes of state that are broken if you go back the other way
Van der Waals bonds and Intermolecular bonds
How do you identify ionic bonds?
Formula should have metallic and non metallic elements
Formula should have polyatomic ions (SO4^2-)
How are ionic bonds produced?
- The metallic element loses its valency electrons to form cations (ionisation)
2 . The non-metallic elements gain electrons into their valency shells whereby the number gained is equivalent to their valency, to form anions
3 . The oppositely charged ions electrostaticaly attract each other to form ionic bond. This is an exothermic reaction and the energy given out is known as lattice energy
What are isoelectric ions?
Ions that have the same number of electrons
How do you identify ionic compounds practically?
1 . All ionic compounds are soluble in water
2 . All ionic compounds conduct electricity when in molten state or aqueous phase
3 . Ionic compounds have high melting points due to strong electrostatic forces
4 . They are hard but brittle
What is an ionic bond?
A strong electrostatic bond between oppositely charged ions
Metallic bonding
The electrostatic attraction between positive ions and delocalised electrons
Covalent bonding
Electrostatic attraction between the nuclei of two atoms and a shared pair of electrons
How to identify ionic compounds practically
- Soluble in water
- Conduct electricity only when molten or aqueous
- High melting points
- Hard
- Brittle - when ions with the same charge get close, repulsion causes breakage without warning
Define
Electronegativity
The ability or affinity for an atom to attract electrons to itself
Explain the reactivity of free radicals
they have one electron to be readily lost to allow for pairing
Why are pi bonds easier to break than sigma bonds?
Electrons in a pi bond are farther from the nucleus than sigma bonds, therefore they are less strongly held
Describe
Excited state
when one electron gains energy and jumps to a higher energy level
What are degenerate orbitals?
Orbitals at the same energy level
Conditions for a Dative Covalent bond
- One species mus have a lone pair
- The other species must have an empty orbital
- the atoms must have opposite charges
What are ligands?
a species that donates lone pairs of electrons into a single metal cation
What is a polar bond?
A covalent bond with ionic charachter
Relate Nuclear Charge to Electronegativity
the higher the nuclear charge the more stronger the attraction to electrons therefore the higher the electronegativity
electronegativity increases across the period
Relate the shielding effect to electronegativity
The more shells, the more that nuclear charge is shielded, therefore the lower the electronegativity
electronegativity reduces down the group
Conditions for Polar bonds
- Must have polar bonds (covalent with charges)
- must be asymmetrical so that dipoles do not cancel out
difference in electronegativity value between 04 and 1.7
all polar molecules are soluble in water
Conditions for non-polar molecules
- Must have non-polar bonds
- symmetrical if they have polar bonds
all hydrocarbons; insoluble in water
Parts of metallic bonds
- Layers of cations
- Sea of delocalised valency electrons
- network of stong electrostatic forces
Metallic Bonding
Evidence of layers of cations
Metals are malleable and ductile because the layers can slide over each other
Metallic bonding
Evidence of delocalised electrons
Metals are very good conductors of electricity as the electrosn become mobile when a current is applied
Conditions
Hydrogen Bonds
- Must contain one of the highly electronegative elements ( N O F )
- Hydrogen must be directly attached to one of the above
- Higly electronegative elements must have a lone pair
Why is ice less dense than water?
Ice forms a network of permanent hydrogen bonds with air molecules trapped within
Factors affecting the strength of Induced dipole - Induced dipole interactions
Size of the molecule
length of the moleule
increase in both leads to stronger bonds
VSEPR Theory
Valence Shell Electron Pair Repulsion Theory
What is the VSEPR theory?
- Cental atom is the one in the molecule that forms the most covalent bonds
- Must have bonding pairs
- BPs and LPs repel echother for maximum separation for minimal repulsion
- Double and triple bonds are treated as one centre of negative charge
Define
Bond energy
the energy required to break one mole of a particular covalent bond in the
gaseous state
Define
Bond length
the internuclear distance of two covalently bonded atoms
