Chemical Bonding.2 Flashcards
What is a compound
substance made up of two or more elements chemically combined
what is the octet rule?
When bonding occours, atoms tend to reach an electron arrangement with eight electrons in the outermost shell
What are expections to the Octet rule
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
What is ment by the valency of an element
the valency of an element js the number of atoms of hydrogen in which an atom of the element can bond
Variable valancy
the number of atoms of different elements in which a certain element can combine with.
What is an ion
A charged atom/ group of atoms
What is a postive ion called
Cations
What is a negative ion called
Anions
What is the valency of an ion equal to?
its charge
What are the two types of bonding
Ionic boning
Covalent bonding
Define an ionic bond
The electrostatic attraction between a postive and negative ion.
What do you use to show the formation of ionic bonding
Bohr diagrams, dot and cross diagrams
Comment of the structure of ionic compounds
crystal lattice structure ( ionic compounds do not form individual molecules )
Discuss the melting and boiling points of ionic compounds
Very high melting and boiling points - the electrostatic attractions require a lot of energy to be broken
Discuss the apperance of ionic compounds
exist as solid crystalline structures.
Most ionic compounds are white
Discuss the conduction of electricity of ionic compounds
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
Give three uses of ionic compounds
Sodium chloride- essential in diet
salt used on food as preservative
hydrated sodium carbonate- washing soda tablets- clean clothes- remove hardness from water
Define a covalent bond
bond that forms when two atoms share a pair of electrons
what is a molecule
two or more atoms chemically combined
Discuss the melthing and boiling point of covalent compounds
low melting and boiling points - weak intermolecular forces between covelent molecules
Discuss the apperance at room temp of covalent compounds
most covelent molecules are liquids or gasses and solids are soft in apperance
Discuss the conduction of electricity of covalent compounds
will NOT conduct electriity as there are no ions avliable
Atomic orbital
region in space around the nucleus where there is a high probability of finding and electrons.
What is a sigma bond
head on overlap of two orbitals
What is a pi bond
sideways overlap of p or d orbitals
Are Sigma bonds stronger or Pi bonds stronger
There is less overlap between orbitals in a pi bond, therefore it is weaker than a sigma bond
What does a single covalent bond consist of
1 sigma bond
What does a double covalent bond consist of
1 sigma and 1 pi bond
What does a triple covalent bond consist of
1 sigma and two pi
Give two differences between sigma bonds and pi bonds
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
Electronegativity
the measure of relative attraction that an atom has for a shared pair of electrons
What is a charge indicted by?
Delta δ
Name the two types of covalent bond
Non-polar covalent bond (pure covalent)
Polar covalent bond
what is a non-polar covalent bond (pure covalent) name an example
type of bond that forms when two atoms share a pair of electrons equally.
e.g Cl2
What is a polar covalent bond. Name an example
e.g HCl
type of bond that formes when two atoms share a pair of electrons unequally
Why are the electrons shared equally in non-polar covalent bonding
The differnce in electronegativity values involved is 0 or so small that the shared pair of electrons are shared equally
why are the electrons shared unequally in polar covalent bonding
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.
What can electronegivity be used to predict
Polarity of covalent bonds
perdict which compounds are ionic and which ones are covalent
What does a EN difference of >1.7 indicate?
Ionic bonding
What does a EN difference of 0.4 -1.7 indicate?
Polar Covalent bond
What does a EN difference of < (or equal) 0.4 indicate?
Non polar covalent bond
What is the significance of a molecule having polar covalent bonds
the more electronegative atom acquired a partially negative charge / negative diople
the less electronegative atom acquires a partially postive charge/ postive dipole
what is the electronegativity differnce of non-polar covalent bonding?
0-0.39
what is the electronegativity differnce of polar covalent bonding
0.4- 1.69
what is the electronegativity differnce of od Ionic bonding
1.7 <
what two compounds are expections to the electronegativity rules
Boron trifluoride (BF3)
Hydrogen fluoride (HF)
you think they would have ionic bonding but they actually have polar colvalent bonding
What is the demostrating polarity used to show
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)
In the demostating polarity, explain why a polar liquid will also be attracted to a rod regardless of if the rod is charged, negativily or postively.
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
Whats does VSEPRT stand for
Valence shell electron pair replusion theory
what is VSEPRT used for
to perdict the same of a molecule
what does the shape of a molecule depend on?
the number of pairs of electrons in the valence shell of the central atom.
the type of these pairs (Bond pair or lone pair)
Describe VSEPRT
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)
What is a loan pair
Both electrons come from the same atom
What is a bond pair of electrons
each electron comes from a different atom
What is a dative corrdinate bond
Special type of covalent bond where one atom supplies both the electrons
Eg. NH4+
A molecule has 4 electron pairs,4 bond pairs,0 loan pairs what shape it it?
Tetrahedral
A molecule has 3 electron pairs,3 bond pairs,0 loan pairs what shape it it?
Trigonal planer
A molecule has 2 electron pairs,2 bond pairs,0 loan pairs what shape it it?
Linear
A molecule has 4 electron pairs,3 bond pairs,1 loan pairs what shape it it?
Pyramidial
A molecule has 4 electron pairs,2 bond pairs,2 loan pairs what shape it it?
V-shaped / bend
What is the bond angle of a tetrahedral
109.5
What is the bond angle of a trigonal planer
120
What is the bond angle of a linear
180
What is the bond angle of a pymidial
107
What is the bond angle of a v-shaped
104.5
Which molecule shapes are not symmetrical
Pyramidial and v-shaped
What type of molecule does VSEPRT only apply to
covalent molecule
Explain why certain molecules can be non-polar molecules despite having polar bonds within their 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.
Distinguish between intramolecular bonds and intermolecular forces
Intramolecular bonds- Type of bond inside the molecule
Intermolecular bond - forces of attraction that exist between one molecule and another
Name the three types of intermolecular forces
Van der waals
Dipole-Dipole
Hydrogen bonding
Describe Van der waals
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.
describe Dipole-Dipole forces
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
describe Hydrogen Bonding
attaction between a partially postive hydrogen in one molecule and a partially negative N,O or F in another molecule.
Strongest intermolecular forces
Why does hydrogen bonding only occur between molecules with partially negative nitrogen, oxygen, or fluorine atoms?
Nitrogen, oxygen and fluorine are small and highly electronegative atoms
Give three effects of hydrogen bonding
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
Hydrogen bonding in everyday life
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.
How to compare boiling points of different substances
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
compare the solubilities of ionic compounds in water
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
compare the solubilities of ionic compounds in cytohexane
ionic compounds are not soluble in non-polar solvents. No partial charges in the non polar solvent to pull the ionic crystal apart
General rule for dissolving substances
Like dissolves like
Explain why ammonia is readily soluble in water?
water molecules are polar, amonia molecules are polar
hydrogen bonds form between the molecules and ammonia dissoves
Would you expect iodine to be soluble in water? Explain
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
