Topic 4 Chemical Bonding and Structure (4.1, 4.2, 4.3, 4.4) Flashcards
4.1 What is the octet rule?
Noble gases have a full energy level of electrons and are stable because of it so atoms lose or gain electrons or share them to achieve electron configurations of noble gases
4.1 What are some exceptions to the octet rule?
H, He, B, Be, and S are stable without 8 outer electrons
4.1 What is the relationship between electronegativity difference and bonding?
0-0.4 non polar covalent, 0.5-1.7 polar covalent, >1.7 ionic
4.1 How are ions formed?
Losing electrons would create positive ions (cations)
Gaining electrons would create negative ions (anions)
It is determined by the electron configuration- their valence electrons
4.1 What is ionic bonding?
It is the electrostatic attraction between oppositely charged ions, occurring between metal and non-metals with a EN difference greater than 1.7 units.
4.1 What are the properties of ionic compounds? 6 points
- They have a lattice structure help together by the oppositely charged ions
- Solid under standard conditions
- High mp and bp
- Low volatility
- Insoluble in non-polar substances
- Can’t conduct electricity in solid but aqueous solutions of ionic compounds can conduct
4.1 How are ionic compounds dissolved?
Hydration: when ions leave the crystal and is surrounded by water molecules (oppositely charged ends of the compound attracts water, breaking the crystal into smaller pieces)
Dissociation: when ions separate from their crystal form, molecules completely broken into ions
4.2 What is covalent bonding?
It is the electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
4.2 What are lewis structures?
It shows all the valence electrons in a molecule- the bonding and non-bonding electrons.
4.2 What is the relationship between bond length and bond strength?
Decreasing length= increasing strength, triple bonds are the strongest because they are the shortest in length
Bonds in smaller atoms are also harder to break because the bonds are shorter in length
4.2 What are pure covalent bonds?
Electrons are shared equally between the two atoms eg. H2, O2, Cl2, N2, CH4
4.2 What are polar covalent bonds?
Unequal sharing of electrons results in a dipole- an imbalance of charge across the bond. Partial negative charge at the most electronegative atom, partial positive on the least
4.2 How to identify polar covalent compounds? 3 points
Unsymmetrical, has lone pairs, elements around central atom is not the same
4.2 What are allotropes and what are the 4 allotropes of carbon?
Different forms of the same element in the same physical state.
Diamond, graphite, fullerene C60, graphene
4.2 Describe bonding, structure and properties of graphite.
C atoms are sp2 hybridised, covalent bonded to 3 others, forms hexagons in parallel layers with bond angles of 120 (van der waals’ forces between layers)
They are good electrical conductors but not thermal, soft and slippery, brittle, very high melting point.
4.2 Describe bonding, structure and properties of diamond.
C atoms are sp3 hybridised, covalent bonded to 4 others, tetrahedrally arranged with bond angles of 109.5
They don’t conduct electricity but are thermal conductors, hard, brittle, very high melting point.
4.2 Describe bonding, structure and properties of fullerene C60.
C atoms are sp2 hybridised, covalent bonded to 3 others, forms a sphere with 12 pentagons and 20 hexagons with bond angles of 120.
They are semi electrical conductors and low thermal conductors, light and strong, low melting point.
4.2 Describe bonding, structure and properties of graphene.
Covalent bonded to 3 other carbons, forms hexagons with bond angles of 120.
They are good electrical and thermal conductors, very thin but strong, flexible, high melting point.
4.2 What are resonance structures?
When there are more than one position for a double bond in a molecule. The bond lengths become equal, bond order is average of all the bonds present in the molecule.
4.3 Outline the principles of the VSEPR theory
Find no. of electron pairs/ charge centres in valence shell of central atom, electron pairs repel each other and will therefore take up positions to minimise repulsions, non bonding pairs repel more than bonding pairs.
4.3 Name all molecular geometry shapes, electron domains and their bond angles.
2 bonding pairs, 0 lone pairs linear 180 - 3,0 trigonal planar 120 2,1 bent <120 - 4,0 tetrahedral 109.5 3,1 trigonal pyramidal 107 2,2 bent 105 - 5,0 trigonal bipyramidal 90&120 4,1 seesaw 90&120 3,2 t shaped 90 2,3 linear 180 - 6,0 octahedral 90 5,1 square pyramidal 90 4,2 square planar 90
4.3 What is the mnemonic for molecular geometry shapes? (:
LTBTTBTSTLOSS
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4.3 What are coordinate covalent bonds/ dative covalent bonds?
Type of covalent bond where both electrons come from the same atom
4.4 Difference between intermolecular and intramolecular, which one is weaker
Intermolecular- between molecules
Intramolecular- holds atoms together in a molecule
Intermolecular forces are generally weaker
