2.2.2-Bonding and structure

Question 1

ionic bonding

Answer 1

strong electrostatic force of attraction between oppositely charged ions

Question 2

describe which compound will have a higher charge Sodium chloride or Magnesium oxide

Answer 2

-The greater the charge
on the ions, the stronger the forces holding them together
-Sodium chloride is made from Na+ ions and Cl– ions and has a melting point of 801°C
-Magnesium oxidemade from ions with two charges (Mg2+ and O2–) and so has a much higher melting point of 2,852°C.

Question 3

covalent bonding

Answer 3

the strong electrostatic force of attraction between a shared pair of electrons and nuclei of bonded atoms

Question 4

dative(coordinate bonding)

Answer 4

when both electrons come from same atom

Question 5

define average bond enthalpy

Answer 5

measurement of covalent bond strength

Question 6

electronegativity

Answer 6

the ability of an atom to attract bonding electors I a covalent bond

Question 7

the three types of intermolecular forces are:

Answer 7

-the permanent dipole-dipole interactions
-induced dipole-dipole interactions
-hydrogen bonding

Question 8

hydrogen bonding

Answer 8

-bonding between N,O or F

Question 9

describe two anomalous properties due to hydrogen bonding

Answer 9

-ice is less dense than liquid water due to water molecules pushed further apart forming an open lattice structure
-has relatively high melting and boiling point due to the hydrogen bonding

Question 10

describe what are simple molecular lattices

Answer 10

-covalently bonded molecules attracted by London forces

Question 11

structure of ice

Answer 11

-simple molecular lattice
-the covalently bonded molecules are attracted by the hydrogen bonds

Question 12

metallic bonding

Answer 12

strong electrostatic attraction between cations(positive metal ions) and a sea of delocalised electrons

Question 13

describe the structure of diamond graphite graphene and silicon

Answer 13

• a network of atoms bonded by strong covalent bonds
  -giant covalent lattice

Question 14

describe a polar bond

Answer 14

-occurs within molecules containing covalently bonded atoms with a permanent dipole due to the large difference in electronegativities

Question 15

compound

Answer 15

two or more elements that are chemically bonded together

Question 16

describe why noble gases are stable

Question 17

lone pair

Answer 17

an unshared pair of electrons that is not involved in bonding

Question 18

outline why ionic compounds are naturally soluble in water

Answer 18

-they are both polar and so is water

Question 19

what do the Pauling values represent

Answer 19

non-polar= 0
polar= 0-1.8
ionic= more than 1.8

Question 20

describe why a compound is non-polar

Answer 20

-it is symmetrical
-has an even distribution of charge

Question 21

describe why simple covalent molecules have relatively low melting and boiling points

Answer 21

-the intermolecular forces between covalent molecules are weak-london forces
-do not require much energy to break
-low melting and boiling points and are generally liquids and gases at rtp

Question 22

what is broken in giant covalent molecules

Answer 22

the strong covalent bonds

Question 23

where are London forces found

Answer 23

found between all molecules

Question 24

why can water form two hydrogen bonds per molecule

Answer 24

oxygen very electronegative
and has two lone pairs of electrons
molecules ae held further apart than in liquid so lower denisty in ice

Question 25

why are permanent dipole -dipole forces strronger than london forces

Answer 25

-permanent dipole-dipole forces occur betwen polar molecules -they are asymmetrical and due to the significant difference in electronegativity ina ddition to london forces it makes it stronger -so higher boiling points

Question 26

Explain why I2 solid but Cl2 gas

Answer 26

-the increasing boiling points as you go down group -due to increasing number of electrons in bigger molecules causing an increase in size of induced dipole-dipole interactions between molecules

Question 27

explain why CO2 is symmetrical

Answer 27

molecule is non-polar all dipoles on bonds 'cancel out' due to symmetrical shape of molecule there is no net dipole movement -molecules is non polar

Question 28

what determines shape of a molecule

Answer 28

-by the number of electron pairs around central atom and repulsion between them -each electron pair naturally repel -so largest bond angle possible exists

Question 29

why are double and triple bonds stronger than a single covalent bond?

Answer 29

-the length of a covalent bond is strongly linked to its strength -shorter bonds stronger as aroms held closer together forces of attraction greater higher levels of enrgy to break

Question 30

Graphene

Answer 30

Bonding- has strong covalent bonds between atoms and delocalised electrons across its surface E.C-Yes,as the delocalised electrons can move T.B- High,strong covalent bonds between atoms require a lot of energy to break

Question 31

Graphite

Answer 31

Bonding-strong covalent bonds between carbon atoms and weak London forces between layers, Also has delocalised electrons which can move between layers Trigonal planar-120 E.C-Yes,as delocalised electrons can move T.B- High, as covalent bonds between atoms require a lot of energy to break layers of carbon atoms that are arranged in 6-membered, hexagonal rings.

Question 32

Diamond

Answer 32

Bonding-strong covalent bonds between the carbon atoms, every carbon has 4 carbons attached so tetrahedral-109.5 electrical conductivity-no, there are no delocalised electrons melting and boiling point-high,strong covalent bonds between atoms require a lot of energy to break

Question 33

what are simple molecular substances?

Answer 33

-Made up of molecules containing a few atoms joined together by covalent bonds -in non-metals

Question 34

Simple molecular -e.g.I2

Answer 34

Bonding-strong covalent bonds between atoms ,weak intermolecular forces between molecules E.C-No,there are no delocalised electrons Melting point and boiling point-low, as there are weak intermolecular forces between molecules

Question 35

Giant metallic lattice-e.g Na

Answer 35

Bonding-positive metal ions attracted to a sea of delocalised electrons Electrical conductivity-Yes, as the delocalised electrons are free to move Tm and Tb-High,due to the strong electrostatic forces of attraction between the positive ions and delocalised electrons

Question 36

Giant ionic lattice-e.g LiCl

Answer 36

Bonding-strong electrostatic force of attraction between oppositely charged ions Electrical conductivity-Yes, only when molten or dissolved as ions are free to move No,when solid as ions cannot move Tm and Tb-High due to strong electrostatic forces of attraction between oppositely charged ions

Question 37

what do non-metals in periodic table form?

Answer 37

-covalent bonding 1-giant molecule or macromolecular-covalent bonding- throughout the structure-diamond,graphite,silicon dioxide 2-simple molecule molecular-weak intermolecular forces-carbon dioxide and water

Question 38

Properties of compounds with Hydrogen Bonding

Answer 38

*They have higher boiling points compared to compounds the other types of intermolecular forces *They tend to be soluble in other compounds with hydrogen bonds (water, ethanol) eg ammonia, HF, carboxylic acids will dissolve in water and ethanol. *They can have higher viscosity: the stronger the hydrogen bonding the more viscous the liquid. *Higher surface tension

Question 39

Why does hydrogen bonding explain why water has a high surface area tension and viscosity?

Answer 39

water molecules are less capable to slide over each other so that water has a high viscosity. The hydrogen bonds at the surface of water gives rise to surface tension

Question 40

why are hydrogen bonds stronger than the other two types of intermolecular bonds?

Answer 40

-The small size of the hydrogen atom and the oxygen,nitrogen, fluorine atoms allow the atoms to approach eachother closely, which makes the force of attraction strong. -The force of attraction is also made strong because the difference in electronegativity is significant.

Question 41

what are permanent dipole-dipole forces

Answer 41

the weak intermolecular forces of attraction that arise between permanently polar molecules for example Hal

Question 42

how do induced dipoles-london forces occur

Answer 42

- movement of electrons within orbital can trigger dipoles in a molecule - instantaneous dipoles will exist but it will be constantly shifting - instantaneous dipole induces a dipole in a neighbouring molecule - induced dipole induces further dipoles

Question 43

Why is the CF4 molecule nonpolar even though it contains polar bonds?

Answer 43

All bond dipoles are painting away from C toward F because F is the more electronegative atom .These dipoles cancel out

Question 44

Factors that affect size of London forces

Answer 44

1-more electrons there are in the molecule the higher the chance that temporary dipoles will form. This makes the London forces stronger between the molecules and more energy is needed to break them so boiling points will be greater. 2-The shape of the molecule can also have an effect on the size of the London forces. Long straight chain alkanes have a larger surface area of contact between molecules for London forces to form than compared to spherical shaped branched alkanes and so have stronger London forces .

Question 45

How do London forces occur?

Answer 45

-In any molecule the electrons are moving constantly and randomly. - As this happens the electron density can fluctuate and parts of the molecule temporarily become more or less negative i.e. small temporary or transient dipoles form.

Question 46

intermolecular forces

Answer 46

forces of attraction between molecules

Question 47

bond enthalpy

Answer 47

the energy required to break a bond present in a compound.

Question 48

Why do lone pairs repel more than bonding pairs?

Answer 48

-lone pairs are not shared by two atoms, so they are held closer to the nucleus -this means they repel further than a bonded pair of electrons