structure and bonding

Question 1

what is an ion?

Answer 1

an electrically charged atom or group of atoms formed by the loss or gain of electrons

Question 2

what are cations and how are they formed?

Answer 2

• Positive ions that form when atoms lose electrons, meaning they have more protons than electrons
• they are formed when they lose electrons

Question 3

what are anions and how are they formed?

Answer 3

• Negative ions that form when atoms gain electrons, meaning they have more electrons than protons
• they are formed when they gain electrons

Question 4

what do all metals do to become positively-charged ions?

Answer 4

lose electrons

Question 5

what do all non-metals do to become negatively charged ions?

Answer 5

gain electrons

Question 6

why do ions gain or lose electrons?

Answer 6

to obtain a full outer shell of electrons

Question 7

how to deduce the charge of an ion

Answer 7

• find the number of electrons in the outer electron shell
• find out if it is easier for the atom to gain electron or to donate electron
• atoms that gain electrons become negative ions and atoms that donate electron forms positive ion

Question 8

charge of each group of metals

Answer 8

• group 1 - 1+
• group 2 - 2+
• group 3 - 3+
• group 5 - 3-
• group 6 - 2-
• group 7 - 3-

Question 9

charge of silver

Answer 9

Ag+

Question 10

charge of copper (II)

Answer 10

Cu2+

Question 11

charge of iron (II)

Answer 11

Fe2+

Question 12

charge of iron (III)

Answer 12

Fe3+

Question 13

charge of lead (II)

Answer 13

Pb2+

Question 14

charge of zinc (II)

Answer 14

Zn2+

Question 14

charge of hydrogen

Answer 14

H+

Question 14

charge of ammonium

Answer 14

NH +
4

Question 15

charge of hydroxide

Answer 15

OH-

Question 15

charge of carbonate

Answer 15

CO 2-
3

Question 15

charge of nitrate

Answer 15

NO -
3

Question 16

charge of sulphate

Answer 16

SO 2-
4

Question 16

charge of ionic compounds overall

Answer 16

no overall charge, because the size of a positively charged ion is equal to the size of the negatively charged ion

Question 17

how to find the formula of simple ionic compounds (direct comparison)

Answer 17

• the formula of an ionic compound can be determined by directly comparing the charges of the ions:
• for example, iron(II) sulfate
• the iron(II) ion is Fe2+, which means that it has a 2+ or +2 charge
• the sulfate ion is SO42–, which means that it has a 2– or –2 charge
• the charges cancel each other out
• mathematically, (+2) + (–2) = 0
• this means that one SO42– ion is needed to cancel the +2 charge on Fe2+
• therefore, the formula of iron(II) sulfate is FeSO4

USE THIS WHEN THEY HAVE THE SAME CHARGE

Question 18

how to find the formula of simple ionic compounds (swap and drop method)

Answer 18

• when the ions in the ionic compound have different charges, it can be easier to use the swap-and-drop method
• for example, copper(II) chloride:
• the copper(II) ion is Cu2+, which means that it has a 2+ or +2 charge
• the chloride ion is Cl–, which means that it has a 1– or –1 charge
• the size of the charge on the copper(II) ion indicates the number of chloride ions needed, and the size of the charge on the chloride ion indicates the number of copper(II) ions needed

Question 19

example of how to do a dot and cross diagram

Answer 19

• sodium is a Group 1 metal so will lose one outer electron to another atom to gain a full outer shell of electrons
• a positive sodium ion with the charge 1+ is formed
• chlorine is a Group 7 non-metal so will need to gain an electron to have a full outer shell of electrons
• one electron will be transferred from the outer shell of the sodium atom to the outer shell of the chlorine atom
• a chlorine atom will gain an electron to form a negatively charged chloride ion with a charge of 1-

-the formula of sodium chloride is NaCl

Question 20

how are ionic compounds held together?

Answer 20

Between positive and negative ions there are strong electrostatic forces of attraction which act in all directions, which holds ionic compounds together

Question 21

what are ionic lattices?

Answer 21

• thousands of positive and negative ions in an ionic compound form a giant lattice structure
• compounds with giant ionic lattice have high melting points

Question 22

why do ionic compounds have high melting and boiling points?

Answer 22

• they have giant ionic lattices
• there are strong electrostatic forces of attraction between oppositely charged ions in all directions
• the forces need lots of energy to overcome them

Question 23

why are Ionic compounds poor conductors in the solid state?

Answer 23

• for electrical current to flow there must be freely moving charged particles such as electrons or ions present
• the ions are in fixed positions in the lattice
• they are therefore unable to move and carry a charge

Question 24

why are ionic compounds good conductors of electricity in the molten state or in solution?

Answer 24

when the ionic compound is melted or dissolved in water, the ions are able to move and carry a charge

Question 25

what are covalent bonds?

Answer 25

• non-metal atoms can share electrons with other non-metal atoms to obtain a full outer shell of electrons
• when atoms share pairs of electrons, they form covalent bonds
• covalent bonds between atoms are very strong

Question 26

what are shared electrons?

Answer 26

• they are called bonding electrons and occur in pairs
• electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons

Question 27

what are the electrostatic forces of attraction like in a covalent bond?

Answer 27

• there is a strong electrostatic attraction between the shared pair of electrons and the nuclei of the atoms involved, since the electrons are negatively charged and the nuclei are positively charged

Question 28

why do simple molecular structures have low melting and boiling points?

Answer 28

• there are weak intermolecular forces between the molecules
• these forces require little energy to overcome

Question 29

what happens when simple molecular structures increase in size?

Answer 29

as the molecules increase in size, the melting and boiling points generally increase because the strength of these intermolecular forces increases and so more energy is needed to break them

Question 30

do simple molecular structures conduct electricity?

Answer 30

Simple molecular structures are poor conductors of electricity (even when molten) because:

• there are no free ions or electrons to move and carry the charge.
• most covalent compounds do not conduct at all in the solid state and are thus insulators

Question 31

features of giant covalent bonds (giant lattices)

Answer 31

• solids
• high melting points as they have strong covalent bonds between them, requiring more energy to break them apart

Question 32

properties of diamond

Answer 32

• contains only carbon atoms
• in diamond, each carbon atom bonds with four other carbons, forming a tetrahedron
• each covalent bond is very strong

Diamond is very hard because:
- each carbon atom is covalently bonded to four other carbon atoms
- the covalent bonds are very strong

Question 33

why does diamond have a high melting point?

Answer 33

• it has a giant covalent structure
• there are strong covalent bonds between atoms which need lots of energy to break

Question 34

properties of graphite

Answer 34

• each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom
• graphite is soft and slippery
• the layers are free to slide over each other because there are only weak forces between the layers, not covalent bonds
• graphite can conduct electricity and heat
• due to each carbon atom only forming three bonds, one electron from each carbon atom is delocalised. the delocalised electrons are free to move

Question 35

why does graphite have a high melting point?

Answer 35

• it has a giant covalent structure
• there are strong covalent bonds between atoms which need lots of energy to break

Question 36

properties of C60 Fullerine

Answer 36

• a group of carbon allotropes which consist of molecules that form hollow tubes or spheres
• fullerenes can be used to trap other molecules by forming around the target molecule and capturing it, making them useful for targeted drug delivery systems
• have a huge surface area and are useful for trapping catalyst molecules onto their surfaces making them easily accessible to reactants so catalysis can take place
• some are excellent lubricants
• the first fullerene to be discovered was referred to as a “buckyball”
• 60 carbon atoms are joined together forming 20 hexagons and 12 pentagons which produce a hollow sphere that is the exact shape of a soccer ball

Question 37

why does C60 Fullerine have a high melting point?

Answer 37

• C60 fullerene has a high melting point because:
  It has a giant covalent structure
• there are strong covalent bonds between atoms which need lots of energy to break