bonding alevel chemistry

ionic bonding

electrostatic force of attraction between oppositely charged ions formed by electron transfer.

how can ionic bonds be stronger

stronger and the melting points higher when the ions are smaller and/ or have higher charges

giant ionic lattice and ionic bonds reaction in water

-regular structure -cubic shape -giant repeating pattern -most ionic compounds dissolve in water as water is polar -attracts the + and - charges break up structure

ionic bonds conduct electricity and have high melting points because?

-molten or dissolved as ions are free to move around -there are many electrostatic forces between ions -lots of energy to overcome these forces

Covalent bonding

sharing of outer electrons to form a full outer shell -electrostatic attraction between nucleus and shared electrons

electrons in covalent bonds

pair to form multiple covalent bonds

dative covalent bonds

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.

metallic bonding

electrostatic force of attraction between the positive metal ions and the delocalised electrons

the factors affecting metallic bonding

-Number of protons/ Strength of nuclear attraction. -Number of delocalised electrons per atom -Size of ion

there are 4 types of crystal structure

ionic, metallic, simple molecular, macromolecular

molecular properties

low bp because of weak intermolecular forces between molecules -poor solubility -poor conductivity no ions -mostly liquids and gases -electrons localised

macromolecular properties

-high melting points -many strong covalent bonds in macromolecular structure -lot of energy to break many strong bonds -insoluble -conductivity poor (not graphite) -poor when molten -solids

metallic bonding properties

-high mp/bp strong electrostatic forces between + ions and negative sea electrons -good conductivity -delocalised electrons and molten

description of metallic bonding

shiny metal -Malleable as the positive ions in lattice are all identical -planes of ions can slide easily over one another -attractive forces in the lattice are same whichever ions are adjacent

Shapes of molecules

-bond pairs and lone pairs -specific shape specific angles -bond pairs repel each other equally -electrons repel -lone pair repel bonding pairs more as they are attracted to same nucleus -2.5 degrees -and repel bonding bonding pairs

rules shapes of molecules

maximum repulsion -minimum separation

Lone pair repulsion

-lone pairs around central atom provides additional repulsive forces, because the lone pair closer to nucleus of atom, while bp is attracted to other nucleus
-for every lone pair there is a reduction of 2.5 degrees

Molecule shape

-linear -trigonal planar -tetrahedral -trigonal pyramidal -bent -trigonal bipyramidal -octahedral

Tetrahedral

109.5 bp: 4

trigonal pyramidal

3 bonds, 1 lone pair, 107 bond angle

trigonal bipyramidal

90-120 bp: 5

octahedral

bp: 6 90 degrees

Linear

BP: 2 LP: 0 ANGLE: 180

V-shaped (bent)

BP:2 LP:2 ANGLE:104.5

Trigonal planar

BP:3 LP: 0 120

Electronegativity

tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself.

how is it measured

Electronegativity is measured on the Paulings scale(ranges from 0 to 4) F, O, N, CL are the most electronegative -most en is fluorine

how is electronegativity affected?

-increases across a period as the number of protons increases and the atomic radius decreases because the electrons in the same shells
-distance between the nucleus and the outer electrons increases and the shielding of inner shell electrons increases

intermediate bonding

Ionic and covalent bonding are the extremes of a continuum of bonding type. Differences in electronegativity between elements can determine where a compound lies on this scale

elements of similar electronegativity and hence a small electronegativity difference will be

will be purely covalent

elements in a compound with a large electronegativity difference

>1.7 ionic

polar covalent bond

-different electronegativities -unequal distribution of electrons -produces charge separation -dipole -unsymmetric

symmetric molecules

non-polar as dipoles cancel out -not net dipole moment

vaan der waals occur in

-all molecular substances and noble gases-do not occur in ionic substances -transient, induced dipole-dipole interactions -occur between all simple covalent molecules and the separate atoms in noble gases

van der Waals forces

a slight attraction that develops between the oppositely charged regions of nearby molecules

Why do van der Waals interactions occur?

electrons are moving constantly, randomly -electron density can fluctuate -parts of the molecule become more or less negative i.e. small temporary or transient dipoles form.

factors affecting van der waals?

-more electrons there are in the molecule the higher the chance that temporary dipoles will form. -Van der Waals stronger between the molecules and so boiling points will be greater

Van der waal in branched vs straight chained alkanes

-Long chain alkanes -larger surface area of contact between molecules -Van der Waals to form than compared to spherical shaped branched alkanes and so have stronger Van der Waals

Permanent dipole-dipole force

between polar molecules -stronger than Van der Waals and so the compounds have higher boiling points -Polar molecules have a permanent dipole

polar molecules are

asymmetrical and have a bond where there is a significant difference in electronegativity between the atoms -permanent dipoles have electrostatic forces between them

hydrogen bonding

hydrogen atom attached to one of the three most electronegative atoms of nitrogen, oxygen and fluorine -an available lone pair of electrons -large electronegativity difference between the H and the O,N,F

all intermolecular forces must

have van der waals as well

ice

-forms a regular structure -held by hydrogen bonding -molecules further apart -less dense then water

graphite (macromolecule giant covalent)

-pencil lead -layers slide easily (weak forces) -delocalised electrons -conduct electricity -low density -layers are far apart -insoluble high mp -covalent bonds

diamond

-tightly packed rigid arrangement -allows heat to conduct well -doesn't conduct electricity -insoluble and high mp because of covalent bonds -gemstones -no delocalized electrons