Bonding Flashcards
Define ionic bonding
Ionic bonding involves electrostatic attraction between oppositely charged ions in a lattice
What is the compound formula for sulfate?
SO4^2-
What is the compound formula for sulfate?
SO4^2-
What is the formula for hydroxide ?
OH-
What is the formula for carbonate ?
CO3^2-
What is the formula for ammonium?
NH+4
Define covalent bonding
A single covalent bond contains a shared pair of electrons
Held by electrostatic attraction
What do multiple bonds contain ?
Multiple bonds contain multiple pairs of electrons
Define a coordinate /dative covalent bond
Contains a shared pair of electrons with both electrons supplied by one atom
What happens in a coordinate covalent bond ?
-atom accepts the electron pair is an atom that doesn’t have a filled outer main level of electrons-atom is electron deficient
-the atom is donating the electrons has a pair of electrons that is not being used in a bond called a lone pair
What are the similarities with an ordinary covalent bond and coordinate bonds?
Coordinate bonds have exactly the same strength and length as ordinary covalent bonds between the same pair of atoms
Define metallic bonding
Metallic bonding involves attraction between delocalised electrons and positive ions arranged in a lattice
What does the number of delocalised electrons depend on ?
Number of delocalised electrons depends on how many electrons have been lost by each metal atom
What are the properties of metals?
Good conductors of electricity
Good conductors of heat
Malleable
Ductile
High mpg and bpt
Why are metals good conductors of electricity?
Delocalised electrons move freely throughout the structure enabling current to flow
Why are metals good conductors of heat?
Closely packed ions enables efficient spread of energy through vibrations
Why are metals malleable and ductile ?
Layers of positive ions can slide over each other
Why do metals have high mpt and bpt?
Strong electrostatic attraction between positive ions and delocalised electrons
Define electronegativity
Electronegativity is the power of an atom to draw electron density in a covalent bond towards itself
What scale shows how electronegative an atom is?
Pauling scale=0-4 the greater the number the more electronegativite the atom the noble gases have no number because they do not in general form covalent bonds
What does electronegativity depend on?
Nuclear charge
Distance between the nucleus and the outer shell electrons
Shielding of nuclear charge by electrons in inner shell
Describe nuclear charge in electronegativity terms
Attraction between positive protons in the nucleus and electrons .an increase in protons means increased attraction for electron number in outer shells thus increased nuclear charge means increased electronegativity
Describe atomic radii in terms of electronegativity
Electrons closer to nucleus are more strongly attracted to positive nucleus electrons further away are less attracted so higher atomic radii means decreased electronegativity
Describe shielding of nuclear charge by electrons in inner shells through electronegativity
Filled energy levels can shield the effects of nuclear charge outer electrons are less attracted to nucleus thus adding extra shells/sub shells in atom will cause electrons to feel less attractive force higher number of inner shells and sub shells decreases electronegativity
What does a smaller atom mean in terms of electronegativity?
Smaller atom =closer nucleus is to shared outer main level electrons -greater electronegativity
What happens to electronegativity down a group?
-decrease in electronegativity down the group
-nuclear charge increases (more protons added to nucleus)
-however each element has an extra filled electron shell increasing shielding
-addition of extra shell increase distance between nucleus and outer shell electrons =larger atomic radii
What happens to electronegativity down a group?
-decrease in electronegativity down the group
-nuclear charge increases (more protons added to nucleus)
-however each element has an extra filled electron shell increasing shielding
-addition of extra shell increase distance between nucleus and outer shell electrons =larger atomic radii
What happens to electronegativity across a period?
-electronegativity increased
- nuclear charge increase with addition of protons
-shielding remains constant as no new shells added to atoms
- nucleus has increasingly strong attraction for bonding pair of electrons the period of the per table
Why don’t noble gases share electrons?
Noble gases don’t share electrons full outer shell doesn’t form bonds
What bond is it if both atoms have electronegativities less than 1.6 to 1.9?
If both atoms have electronegativities less than 1.6 1.9 then the bond is metallic
What wonders it is if eva atom has an electronegativity greater than 1.9 and the difference is less than 0.5
If eva atom has an electronegativity greater than 1.9 and the difference is less than 0.5 the bond is covalent
What molecule is a molecule if it contains polar bonds but it’s symmetrical?
If a molecule contains polar bonds but it’s symmetrical it’s a nonpolar molecule. This is due to the dipole which are directional and will council out if they are equal and the opposite directions.
What makes intermolecular forces different from covalent and ionic?
Intermolecular forces are weaker than covalent and ionic bonds
What are the three types of intermolecular forces?
Van der waals – act between all atoms and molecules (even noble gases)
Dipole – dipole – act only between certain molecule types (changes properties)
Hydrogen bonding – act only between certain molecule types
What is the relative strength of ionic and covalent bond hydrogen bond dipole – dipole forces and van der waal forces?
Ionic &covalent=1000
Hydrogen=50
Dipole-dipole forces=10
Van der waals forces=1
Describe van der waals between atoms
Roughly vertical atoms of an ideal gas shouldn’t be attracted or repelled by one another (if this were really the case, the noble gases couldn’t be liquified
In a real gas atom, electrons are constantly moving and any one time it can have an instantaneous dipole due to an uneven distribution of these electrons
This atom can vent induced dipole in a neighbour molecule. There’s then an attraction between these molecules – there’s a temporary induced dipole – dipole attraction.
Describe VanderWaal forces between molecules
The electron density is spread equally throughout the molecule
At any given time it’s possible for the electron density to be anywhere in this case the electron density is located mainly on the right generating a temporary dipole which has a fleeting existence
If two hydrogen molecules are separated by a large distance dipole can’t be induced. If two hydrogen molecules are in close proximity and temporary dipole can be induced.
What is the boiling point of noble gases increased down the group?
Noble gases have a larger number of electrons larger electron density, larger dipole so the boiling point of noble gases increases down the group
Describe a polar bond
Polar bond is a covalent bond in which the bpt of electrons are unequally shared and there’s a separation of charge between end and the other eg HCL
It occurs because of a significant difference in electronegativity between the two atoms of the covalent bonds
Describe van der waals
Present in all molecular substances
Electrons are constantly moving around and there will be an uneven electron distribution at any given moment in time
Causing a temporary dipole within a molecule
This temporary dipole induces a temporary dipole in a neighbouring molecule
There’s then an attraction between molecules -temporary induced dipole dipole attraction
The larger the molecule I e more electrons the larger the induced dipole the greater the van der waals forces so the higher the boiling point
Van der waals forces are the only attractions between non polar molecules
Non polar molecules
Molecules that don’t have any electrical charges or partial charges
What are dipole dipole attractions only between
Only between polar molecules -some molecules are non polar but contain polar bonds these don’t have permanent dipole dipole attraction
Why do polar bonds occur?
Polar bonds occur because of a significant difference in electronegativity between the two atoms of the covalent bonds
Describe the hydrogen bond
Dipole dipole attractions - some of a covalent bond
Consists of a hydrogen atom between two very electronegative atoms
What are the conditions for hydrogen bonding
Very electronegative atom with lone pair of electrons covalently bonded to a hydrogen atom
(Water molecular fulfill these conditions- oxygen is more electronegative than hydrogen so water is polar
Why is the intermolecular bonding of hydrogen atoms strong?
Would expect weak dipole dipole attraction but there aren’t because
Oxygen atoms in water have lone pairs of electrons
In water the hydrogen atoms are highly electron deficient (why?-
Oxygen is very electronegative and attracts shared electrons in the bond towards it
Hydrogen atoms in water are positively charged and very small exposed protons have a very strong electric field due to their small size
Where is the lone pair in a water molecule and what is it attracted to ?
The lone pair of electrons on the oxygen atom of another water molecule is strongly attracted to the electron deficient hydrogen atom the strong intermolecular force is called a hydrogen bind
In terms of structure, what are hydrogen bonds?
Always linear the pair of electrons in the covalent bond repels those in the hydrogen bond
How strong are hydrogen bonds?
Stronger than dipole – dipole
Weaker than covalent
Which atoms can form hydrogen bonds?
Only atoms electronegative enough to form hydrogen bonds are oxygen nitrogen and fluorine
What must happen to form a hydrogen bond?
Hydrogen is that bonded to a very electronegative atom (will produce a strong partial positive charge on the hydrogen atom)
Very electronegative atom with a lone pair of electrons will be attracted to partially charged hydrogen atoms in the molecule and form the bond
Describe the boiling points of hydrides
Noble gases – gradual increase in boiling points due to the early forces acting between the atoms being van der waals forces – increase the number of electrons present
Water, hydrogen fluoride ammonia -higher than those of the hydrides of the other elements in the group due to the hydrogen bonding being present between the molecules in each of those compounds and these stronger intermolecular forces of attraction make the molecules more difficult to separate
Why are hydrogen bond significant?
Hydrogen bonds are weaker than covalent bonds and can make or break under conditions where bonds are unaffected– makes them very significant
Describe the structure and bonding in ice
In water, the liquid state of ice hydrogen bonds break and reform easily as molecules are moving about
When water freezes water molecules are no longer free to move out and hydrogen bonds molecules in fixed position
Why is ice less dense than water ?.
Molecules are slightly less closely packed in liquid water – means ice is less than water and forms on top of pond rather than at the bottom this insulates the ponds and enables fish to survive through the winter helps to continue in the relative warmth of water under ice
Describe the electron pair repulsion theory
Each pet of electrons around an atom will repel all other electron pairs
Pairs of electrons will thus take up positions as far apart as possible to minimise repulsion
What does a shape of a single molecule depend on ?
Shape of molecule depends on the number of pairs of electrons that surround the central atom to work out the shape of any molecule first draw a dot and cross diagram to find the number of pair of electrons
Describe what the molecule would be if it has two pairs of electrons
Molecule will be linear
Furthest away from each other, the two can get is 180 degrees apart
Describe what the molecule would be if they had three pairs of electrons
120° apart
Trigonal planar
Three pairs central atom
Describe what’s the molecule would be if it had four pairs of electrons
Furthest apart when arranged
Tetrahedral
109.5°
Three dimensional, so some of angles can be more than 360°
Ion has an overall charge that doesn’t affect shape
Describe what molecule would be if it had five pairs of electrons
Trigonal by pyramid
120°
Describe a molecule would be had six pairs of electrons
Octahedral
90°
Describe molecules with lone pairs electrons
Not a part of covalent bonds
Lone pairs affect the shape of molecules, for example, ammonia and water as well offering
Describe ammonia in terms of its lone pair
Four pairs of electrons and one of the groups is alone pair
Shape based on a tetrahedron
Only three arms so shape is a triangular pyramid
Describe lone pair repulsion
Repulsion between lair and electrons and abundant pair electrons is greater than that between two bonding pairs
Approx rule of thumb is 2.5 per lone pair
How does repulsion increase ?
Bonding pair bonding pair
Lone pair bonding pair
Lone pair lone pair
