Chemical Bonding 2 Flashcards Part 2

substance made up of two or more elements chemically combined

When bonding occours, atoms tend to reach an electron arrangement with eight electrons in the outermost shell

Transition elements dont obey the octet rule and often have more or less than 8 electrons in the outer shell
Elements near helium tens to have 2 electrons in the outer shell

the valency of an element js the number of atoms of hydrogen in which an atom of the element can bond

the number of atoms of different elements in which a certain element can combine with.

A charged atom/ group of atoms

Cations

Anions

its charge

Ionic boning
Covalent bonding

The electrostatic attraction between a postive and negative ion.

Bohr diagrams, dot and cross diagrams

crystal lattice structure ( ionic compounds do not form individual molecules )

Very high melting and boiling points - the electrostatic attractions require a lot of energy to be broken

exist as solid crystalline structures.
Most ionic compounds are white

do not conduct electricity in the solid state are ions are not free to move- held in a crystal lattice structure.
Will conduct electricity when molten or dissolved- ions- free to move

Sodium chloride- essential in diet
salt used on food as preservative
hydrated sodium carbonate- washing soda tablets- clean clothes- remove hardness from water

bond that forms when two atoms share a pair of electrons

two or more atoms chemically combined

low melting and boiling points - weak intermolecular forces between covelent molecules

most covelent molecules are liquids or gasses and solids are soft in apperance

will NOT conduct electriity as there are no ions avliable

region in space around the nucleus where there is a high probability of finding and electrons.

head on overlap of two orbitals

sideways overlap of p or d orbitals

There is less overlap between orbitals in a pi bond, therefore it is weaker than a sigma bond

1 sigma bond

1 sigma and 1 pi bond

1 sigma and two pi

Sigma bonds
formed by the head on overlap of atomic orbitals
Stronger bonds- not easily broken

Pi bonds
sideways overlap of p or d orbitals
weaker bonds- more easily broken

the measure of relative attraction that an atom has for a shared pair of electrons

Delta δ

Non-polar covalent bond (pure covalent)
Polar covalent bond

type of bond that forms when two atoms share a pair of electrons equally.
e.g Cl2

type of bond that formes when two atoms share a pair of electrons unequally

The differnce in electronegativity values involved is 0 or so small that the shared pair of electrons are shared equally

the difference in electronegativity calues in the elemets is significant so the pair of electrons are pulled towards the more electronegative atom, are shared unequally.

Polarity of covalent bonds
perdict which compounds are ionic and which ones are covalent

Ionic bonding

Polar Covalent bond

Non polar covalent bond

the more electronegative atom acquired a partially negative charge / negative diople
the less electronegative atom acquires a partially postive charge/ postive dipole

0-0.39

0.4- 1.69

1.7 <

Boron trifluoride (BF3)
Hydrogen fluoride (HF)

you think they would have ionic bonding but they actually have polar colvalent bonding

to show if a compund (usually a liquid)is polar.Water is polar. ( has tempoary postive charges associated) water will deflect when a postively or negativily charged rod comes near. The H postive will be attracted towards the negativily charged rod.Similarly, the O (negative) will be sttracted to th negativitly charged rod.
Cyclohexane is an organic compound that is non-polar (no deflection)

the polar molecules in the liquid will turn and arrange themselves so..
for a negatively charged rod- the postive dipoles will be attracted to it.
for a postively charged rod- the negative dipoles of the molecule will be attracted

Valence shell electron pair replusion theory

to perdict the same of a molecule

the number of pairs of electrons in the valence shell of the central atom.
the type of these pairs (Bond pair or lone pair)

This theory is used to perdict the shape of a molecule.
The shape of a molecule depends on the number of pair of electrons in the valence shell of the central atom, and the type of these pairs.
electron pairs repel eachother.
A lone pair and lone pair of electrons (stongest )repel each other more strongly than a lone pair and bond pair of electrons (moderate )which repel each other more strongly than a bond pair and bond pair of electrons (weakest)

Both electrons come from the same atom

each electron comes from a different atom

Special type of covalent bond where one atom supplies both the electrons
Eg. NH4+

Tetrahedral

Trigonal planer

Linear

Pyramidial

V-shaped / bend

109.5

120

180

107

104.5

Pyramidial and v-shaped

covalent molecule

If the molecule is highly symmetrical
the centres of postive and negative charge coincide
the molecule as a whole is non polar despite having polar bonds.

Intramolecular bonds- Type of bond inside the molecule
Intermolecular bond - forces of attraction that exist between one molecule and another

Van der waals
Dipole-Dipole
Hydrogen bonding

between a non-polar molecule and another non-polar molecule- caused by tempoary dipoles formedin the atoms.
Low melthing and boiling points- gas at room temp.
As the molecules molecular mass increases, the stenght of the van der waals increases.

form between polar molecules- caused by permanent dipoles in the atoms.
partially pos atom attracted to partially neg atom.
Stronger than van der Waals forces

attaction between a partially postive hydrogen in one molecule and a partially negative N,O or F in another molecule.
Strongest intermolecular forces

Nitrogen, oxygen and fluorine are small and highly electronegative atoms

explains why the three hydrides H2), hf and nH3 have higher boiling points than other hydrides
explais how H2O has a very large relative boiling point
explains surface thension on water

Ensures water is liquid at room temp so life can exist on earth.
Synthetic clothing- bullet proof vests/protective clothing.
hydrogen bonds in wool help it absorb water. hydrogen bonds in water give it a high surface tension.

CHECK:
1 - type of intermolecular force…hydrogen stronger than dipole-dipole stonger than Van der waals
2 - the molecular mass of the molecule….heavier molecules have higher boiling points
3 - how polar the molecule is… more polar molecules have higher boiling points

ionic compounds are very soluble in water
the partial negative charge in the polar water is attreacted to the postive ion in the ionoc compound
the partial postive charge in the polar water is sttracted to the negative ion in the ionic compounds. The crystalline structure can be pulled apart

ionic compounds are not soluble in non-polar solvents. No partial charges in the non polar solvent to pull the ionic crystal apart

Like dissolves like

water molecules are polar, amonia molecules are polar
hydrogen bonds form between the molecules and ammonia dissoves

Iodine is not soluble/sparingly soluble in water
Iodine molecules are non-polar, water molecules are polar
Little or no Intermolecular forces form between the molecules, so the iodine does not dissolve