Bonding

Question 1

what is ionic bonding?

Answer 1

Metals lose outer electrons to non-metals to form positive and negative ions

Question 2

how are ions attracted to each other + other oppositely charged ions?

Answer 2

electrostatic forces

Question 3

what do ionic compounds always exist as?

Answer 3

lattices

Question 4

what are the properties of ionic lattices?

Answer 4

• always solids at room temperature
• giant structures so high melting points (lots of energy required to break up lattice of ions
• conduct electricity when motel or aqueous solution due to ions being free to move to carry a current
• brittle and shatter easily due to being a lattice of alternating positive and negative ions which if distorted, can cause contact between ions with like charges

Question 5

what does the strength of an ionic bond depend on?

Answer 5

• charge on the ions, ions with higher charges will have a greater electrostatic attraction
• distance between the ions, smaller ions have smaller internuclear distance so electrostatic attraction is greater

Question 6

what is covalent bonding?

Answer 6

between non-metals which share outer electrons to create a stable noble gas arrangement

Question 7

what are covalent bonds held by?

Answer 7

held together by electrostatic attraction between nuclei and shared electrons which takes place in the molecule - these forces balance when the nuclei are a certain distance apart

Question 8

what is a double covalent bond?

Answer 8

4 electrons are shared

Question 9

what are the properties of substances with molecular structures?

Answer 9

• low melting points because strong covalent bonds are only between atoms within the molecules but there is a weak attraction between the molecules so they do not need a lot of energy to move apart
• poor conductors as no charged particles to carry the current

Question 10

what is a dative covalent bond?

Answer 10

one atom provides both electrons in the covalent bond (represented by an arrow to atom accepting pair of electrons)

• the atom that accepts the electron pair is an atom that does not have a filled outer main level of electrons (electron deficient)
• atom that is donating the electrons has a pair not being used in a bond (lone pair) e.g NH3 ammonia, in its ion (NH4+) Nitrogen uses lone pair to form a dative covalent bond with H+ ion

Question 11

what is metallic bonding?

Answer 11

metals consist of a lattice of positive ions within a sea of electrons which are delocalised

Question 12

what are the properties of metallic bonds?

Answer 12

• giant structures
• good conductors of electricity and heat due to delocalised electrons/sea of electrons
• strength depends on charge and size of ion (greater the charge, greater number of delocalised electrons and stronger electrostatic attraction between positive ions and electrons) + (the smaller the ion the closer the electrons are to the positive nucleus and the stronger the bond)
• metals are strong as delocalised electrons extend through the solid so there are no individual bonds to break
• high melting points as are giant structures
• malleable and ductile due to ions being able to slide/move past each other

Question 13

what is electronegativity?

Answer 13

The power of an atom to attract the electron density in a covalent bond towards itself

Question 14

what is electron density?

Answer 14

How negative charge is distributed in the molecule

Question 15

what is the pauling scale?

Answer 15

Pauling scale measures electronegativity from 0-4, the greater the number the more electronegative

Question 16

what does electronegativity depend on?

Answer 16

Electronegativity depends on:

• nuclear charge
• distance between the nucleus and the outer shell electrons
• the shield of the nuclear charge by the the electrons in inner shells

Question 17

therefore the _____ the atom, the _____ the nucleus is to the outer main level electrons and _____ its electronegativity

Answer 17

1. smaller 2. closer 3. greater

Question 18

What happens to electronegativity as you go up a group?

Answer 18

Going up a group, electronegativity increases (atoms get smaller) and there is less shielding by electrons in inner shells

Question 19

What happens to electronegativity as you go across a period?

Answer 19

Going across a period, electronegativity increases. the nuclear charge increases but the number of inner levels stay the same and atoms become smaller.

Question 20

Where are the more electronegative atoms found?

Answer 20

More electronegative atoms found in top right corner of periodic table e.g fluorine, oxygen, nitrogen and chlorine

Question 21

What is polarity?

Answer 21

Polarity - unequal sharing of electrons between atoms that a bonded covalently (represented by partial negatives and partial positives)

Question 22

How are electrons shared in a covalent bond with two of the same atoms? + what is the polarity of the bond

Answer 22

electrons in the bond are shared equally, so both have same electronegativity and bond is non-polar

Question 23

How are electrons shared in a covalent bond with two different atoms? + what is the polarity of the bond

Answer 23

electrons will not be shared equally, e.g one might be slightly positive and one might be slightly negative (HF) as a result it is polar. the greater the difference in electronegativity, the more polar the covalent bond

Question 24

What are the 3 types of intermolecular forces?

Answer 24

• van der waals : act between all atoms and molecules
• dipole-dipole : only between some
• hydrogen : only between some

Question 25

What are the properties of van der waals forces?

Answer 25

van der waals → produce weak electrostatic attractions between all atoms and molecules

→ distribution of charge is constantly changing

Question 26

What are the properties of dipole-dipole forces?

Answer 26

dipole-dipole → slightly positive on one side and slightly negative on the other (+ of one molecule will attract - of another) they are only found in polar molecules

Question 27

What are the properties of hydrogen bonds?

Answer 27

hydrogen bonds → very strong permanent dipole-dipole, formed when H bonds to O, N or F e.g water of ammonia

→ develops a strong delta+ charge

Question 28

What is the electron pair repulsion theory?

Answer 28

pairs of electrons around atoms will repel other electron pairs therefore the pairs of electrons will take up positions as far as possible to minimise repulsion

Question 29

what are the names of the different shapes of molecules from 1-6 pairs of electrons + bond angles?

Answer 29

two pairs of electrons - linear (180 degrees)

three pairs of electrons - trigonal planar (120 degrees)

four pairs - tetrahedral (109.5 degrees)

five pairs - trigonal bipyrimidal

six pairs - octahedral (90 degrees)

Question 30

what do electron pairs do in the outer shell to minimise repulsion?

Answer 30

arrange themselves as far apart as possible

Question 31

what is the difference between bonding pairs and lone pairs in terms of repulsion?

Answer 31

Bonding pairs repel each other equally. While lone pairs repel other pairs more because they are more electron dense.