topic 3: bonding

Question 1

ionic bonding

Answer 1

-ionic bonds are oppositely charged ions in a lattice, held together by electrostatic for of attraction, occurs between metals and non metals, electrons transfer from metal to non metal
-metals form positive ions and non metals form negative ions

Question 2

what determines the shape of molecules (2 types of electron pairs)

Answer 2

2 TYPES OF ELECTRON PAIRS
-BONDING PAIRS: 2 shared electrons in a covalent bond
-LONE PAIRS: 2 electrons not involved in bonding on one atom
-REPULSION STRENGTH: lone pairs repel more than bonding pairs as they are closer to the nucleus of the central atom than the bonding pairs and reduce the bond angle to a small extent and therefore compact

Question 3

biggest angle, second biggest angle and smallest angle

Answer 3

-lone pair/ lone pair - biggest angle
-lone pair/ bonding pair - second biggest angle
-bonding pair/ bonding pair - smallest angle

Question 4

what is the the shape of a molecule a consequence of?

Answer 4

the shape of any molecule or ion is a consequence of the number of electron pairs which repel eachother as far as possible

Question 5

work out the shape of a molecule

Answer 5

1. work out central atom - atoms bonded to it
2. work out number of outer electrons in central atom
3. add one to this number for every atom bonded to central (add for - and substract for +)
4. divide by 2 to find the number of electron pairs on the central atom
5. the number of atoms bonded to central atom is the bonding pairs and the rest are lone pairs

Question 6

electronegativity definition

Answer 6

the power of an atom to attract the pair of electron in a covalent bond

Question 7

trends in electronegativity

Answer 7

-increases across a period
-decreases down a group

Question 8

electronegativity increases across a period

Answer 8

-the atoms have the same shells and similair shielder
-the atoms have more protons so they have a stronger force of attraction to the pair of electrons in the covalent bond
-fluorine is the most electronegative elements

Question 9

electronegativity decreases down a group

Answer 9

-the atoms have more shells and more shielding
-so there is a weaker force of attraction to the pair of electrons in the covalent bond

Question 10

electronegativity in noble gases

Answer 10

noble gases do not have electronegativity values because they have a full outer shell, so they do not normally form covalent bonds

Question 11

bond polarity

Answer 11

the unequal distribution of electrons between atoms in a covalent bond, therefore there is a difference in electronegativity

Question 12

dipole

Answer 12

difference in charge between two atoms caused by an electron shift

Question 13

permanent dipole

Answer 13

in a polar bond the difference in electronegativity between the two atoms

Question 14

polar bonds in a covalent bond - when does it occur? + example

Answer 14

-when two different atoms are covalently bonded, so there are different electronegativityes so unequal sharing of electrons, this s a dipole moment
-delta (d+) and delta (d-)
-the greater the difference in electronegativity between the atoms, the more polar the bond

examle: H (d+) —– Cl (d-) chlorine is much more electronegative than hydrogen, so hydrogen chloride has a permanent dipole (different electronegatives)

Question 15

non polar bonds in a covalent bond - when does it occur? + example

Answer 15

-when two of the same atoms are covalently bonded, so they have the same electronegativity as electrons are both shared equally as there is an equal attraction to both atoms

example: hydrogen and carbon (hydrocarbons) have similair electronegativites
all hydrocarbons are non polar
Cl-Cl and C-H

Question 16

polarity of molecules - polar bonds when does it occur?

Answer 16

-has polar bonds, which do not cancel out since it has an uneven distribution of charge across the molecule - asymmetrical shape, so it has a permanent dipole

Question 17

what bonds are present in polar molecules?

Answer 17

VAN DER WALLS, DIPOLE-DIPOLE or HYDROGEN BONDS

examples: H2o the end of the molecule is negatively charged and other end is positively charged
this is an asymmetrical shape so there is an uneven distribution of charge which do not cancel out

Question 18

non polar bonds - when does it occur?

Answer 18

the polar bonds are arranged symmetrically in the molecule, then the (dipole) charges cancel out and there is no permanent dipole

Question 19

non polar bond - what bonds are present

Answer 19

VAN DER WALLS

examples: CO2
o-c-o the positively and negative charges are spread evenly (symmetrical shape) across the molecule so the charges cancel out and there is no permanent dipole

Question 20

intermolecular forces

Answer 20

weak forces of attraction between molecules

Question 21

3 types of intermolecular forces - order from the weakest to strongest (increasing strength(

Answer 21

1. van der walls (induced dipole-dipole forces) - weakest
2. permanent dipole-dipole forces
3. hydrogen bonding - strongest

Question 22

van der waal forces

Answer 22

-van der waals are caused by the constant movement of electrons, this causes an uneven distribution of electrons and charge within the molecules
-this induces ( gives rise to) a temporary dipole in the neighbouring molecule
-this causes a weak force of attraction between delta + and - charged molecules
—> induced dipole-dipole
-van der waals are found between all molecular substances and only forces in non-polar bonds
-van der waals forces can hold molecules in a lattice

Question 23

stronger van der waals forces have higher boiling piints

Answer 23

bigger molecules have more electrons so there are stronger van der waals (larger induced dipoles) therefore the boiling point increases

Question 24

permanent dipole-dipole attraction + example

Answer 24

-permanent dipole-dipole forces are found ONLY IN POLAR MOLECULES, but not in non polar molecules even if they have dipole bonds
-substances made up of molecules that have PERMANENT DIPOLES (in polar bonds), there will be WEAK ELECTROSTATIC FORCES OF ATTRACTION between the d+ and d- charges on neighbouring molecules
-molecules with permanent dipole dipole attraction have a HIGHER BOILING POINT than induced dipole-dipole/ van der waals

example: hydrogen chloride gas has polar molecules:

H(d+) - Cl(d-)—-H(d+) - Cl(d-)—-H(d+) - Cl(d-)
the d- chlorine is attracted to the d= hydrogen on the next neighbouring molecule (drawn with a dotted line)

Question 25

hydrogen bonding + example

Answer 25

-the STRONGEST intermolecular force
-occurs when hydrogen is covalently bonded to only fluorine, nitrogen or oxygen
-fluorine, oxygen and nitrogen are VERY ELECTRONEGATIVE so attract the electrons, they draw the electrons away from the hydrogen atom - the bond is so POLARISED

-hydrogen has a HIGH CHARGE DENSITY since it is so small
-a hydrogen bond is formed between a H(d+) atom and a lone pair of electrons on the fluorine, oxygen or nitrogen on the next neighbouring molecule, this forms WEAK BONDS BETWEEN THE MOLECULES

example: a lone pair of electron on the oxygen is attracted to the d+ hydrogen

Question 26

boiling points of hydrogen bonding

Answer 26

boiling points of compounds like H2O, HF and NH3 are the highest as they have hydrogen bonding
-hydrogen bonds have HIGH BOILING POINTS as they have stronger bonds between molecules which require more energy to overcome these bonds

Question 27

importance of hydrogen bonding in ice

Answer 27

-as a liquid, water forms hydrogen bonds which break and reform easily as the molecules are moving about
-when frozen the molecules cant move, so the hydrogen bonds hold the molecules in a fixed position
-in order to fit, the molecules are slightly less closely packed together, this mean the ice is less dense than and floats on top of it, this is why there is life (fish surviving in ponds during winter) beneath an icy surface which acts as an insulator