topic 2: bonding and structure
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what is the shape and bond angle of a molecule with 2 bonding pairs and 0 lone pairs and some examples
shape: linear bond angle: 180 examples: CO2, CS2, HCN, BeF2
what is the shape and bond angle of a molecule with 3 bonding pairs and 0 lone pairs and some examples
shape: trigonal planar bond angle: 120 examples:BF3, AlCl3, SO3, NO3-, CO3 2-
what is the shape and bond angle of a molecule with 4 bonding pairs and 0 lone pairs and some examples
shape: tetrahedral bond angle: 109.5 examples: SiCl4, SO42-, ClO4-, NH4+
what is the shape and bond angle of a molecule with 3 bonding pairs and 1 lone pairs and some examples
shape: trigonal pyramidal bond angle: 107 examples: NCl3 ,PF3,ClO3 ,H3O+
what is the shape and bond angle of a molecule with 2 bonding pairs and 2 lone pairs and some examples
shape: bent bond angle: 104.5 examples: OCl2, H2S, OF2, SCl2
what is the shape and bond angle of a molecule with 5 bonding pairs and 0 lone pairs and some examples
shape: trigonal bipyramidal bond angle: 120 and 90 example: PCl5
what is the shape and bond angle of a molecule with 6 bonding pairs and 0 lone pairs and some examples
shape: octahedral bond angle: 90 example: SF6
what is ionic bonding
strong electrostatic force of attraction between oppositely charged ions formed by electron transfer
why are positive ions smaller in comparison to their atoms
because it has one less shell of electrons and the ratio of protons to electrons has increased so there is greater net force on remaining electrons holding them more closely
why are anions larger than their atoms
the negative ion has more electrons than the corresponding atom but the same number of protons. so the pull of the nucleus is shared over more electrons and the attraction per electron is less, making the ion bigger
does the ionic radius increase or decrease from N3- to Al3+ and why
decrease because there are increasing numbers of protons from N to F and then Na to Al but the same number of electrons. the effective nuclear attraction per electron therefore increases and ions get smaller
does the ionic radius increase or decrease down the group and why
increases down group because as one goes down the group the ions have more shells of electrons
what are the physical properties of ionic compounds
*high melting points ( there are strong attractive forces between the ions) *non conductor of electricity when solid (ions are held together tightly and can not move) *conductor of electricity when in solution or molten. ( ions are free to move) *brittle / easy to cleave apart
what is covalent bond
strong electrostatic attraction between 2 nuclei and the shared/ bonding pair of electrons
what is the strength of covalent bond demonstrated by
high melting points
why do giant covalent structures have high melting points
because they contain many strong covalent bonds in a macromolecular structure. it takes a lot of energy to break the many strong bonds
what is the effect of multiple bonds on bond strength and length
nuclei joined by multiple (i.e. double and triple) bonds have a greater electron density between them. this causes an greater force of attraction between the nuclei and the electrons between them, resulting in a shorter bond length and greater bond strength
what is a dative bond and examples
when the shared pair of electrons in the covalent bond come from only one of the bonding atoms. a dative covalent bond is also called co-ordinate bonding eg. NH4+, H30+, NH3BF3
what is electronegativity
the relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself is measured on the Pauling scale
why do electronegativity increases across a period
the number of protons increases and the atomic radius decreases because the electrons in the same shell are pulled in more
why do electronegativity decreases down the group
because the distance between the nucleus and the outer electrons increases and the shielding of inner shell electrons increases
what does a small electronegative difference mean
purely covalent
what would the electronegative difference when ionic
very large electronegativity difference (> 1.7)
describe the formation of a permanent dipole
a polar covalent bond forms when the elements in the bond have different electronegativities . (Of around 0.3 to 1.7) When a bond is a polar covalent bond it has an unequal distribution of electrons in the bond and produces a charge separation, (dipole) δ+ δ- ends