Ionic And Covalent Bonding

Question 1

What is a compound give an example

Answer 1

It is when two or more elements combine in a chemical reaction eg, hydrogen gas is burned in oxygen gass, water is formed

Question 2

Give one difference between elements and compounds?

Answer 2

Elements cannot be broken down into simpler substances whereas compounds can eg, if electricity is passed through water it breaks down into hydrogen and oxygen

Question 3

What does a chemical formula tell you?

Answer 3

What elements are present and in what relative proportions

Question 4

What is water of crystallisation?

Answer 4

It’s water chemically combined in definite proportions in a crystalline compound

Question 5

Give an example of noble gas uses

Answer 5

Helium - wearer balloons and blimps

Argon - in light bulbs

Question 6

What is the octet rule?

Answer 6

Atoms on reaction tend to reach an electron arrangement with eight electrons in the outermost energy level

Question 7

What are exceptions to the octet rule?

Answer 7

Beryllium and boron have few electrons in the outer levels so they cannot gain enough electrons to reach eight in the outer level
The d block elements don’t usually obey the octet rule
Hydrogen and lithium atoms tend to reach electronic structure of helium but unable to gain large number of electrons

Question 8

What is the valency?

Answer 8

It’s the number of reactions an atom of the element forms when it reacts

Question 9

What does valency measure?

Answer 9

The combining power of an atom

Question 10

Where will you normally find ionic bonds?

Answer 10

Compounds that contain metals with non-metals.

Question 11

What is an ionic bond?

Answer 11

It’s the electrostatic force of attraction between oppositely charged ions

Question 12

What does ionic bonding result in?

Answer 12

Not a compound, but a lattice

Question 13

What is a lattice

Answer 13

Each ion in a lattice is surrounded by others of opposite charge

Question 14

How is the structure of crystal lattices determined?

Answer 14

By X-ray technique

Question 15

Characteristics of ionic substances

Answer 15

High melting points - the strong forces of attraction means there is a lot of energy needed to break up the lattice - solids at room temp
Conduct electricity when in molten state - ions have been freed
Most dissolve in water, water is polar are attracted to ions

Question 16

What’s the test for carbonate and hydrogen carbonate?

Answer 16

Both react : dilute hydrochloric acid
Reagent : magnesium sulfate
On heating : hydrogen carbonate turns into carbonate
White ppt : carbonate

Question 17

What is the test for sulfate and sulfite?

Answer 17

Both react : barium chloride
Reagent : hydrochloric acid [barium sulfite]
White ppt : sulfite

Question 18

What is the test for chloride?

Answer 18

Silver nitrate = white ppt = dissolved in ammonia

Question 19

What is the test for nitrate?

Answer 19

Iron II sulfate + conc sulfuric acid = brown ring

Question 20

Test for phosphate

Answer 20

On heating w/ ammonium molybdate = yellow ppt = dissolved by ammonia

Question 21

Test for anions procedure

Answer 21

1. Add 2cm3 of solution to a test tube and then add they both react with
2. White ppt indicates presence of sulfate/sulfite ions/ c02 is produced = limewater
3. Add reagent and what is white ppt
4. Repeat and for hco3 remember to mention heating

Question 22

What is a covalent bond?

Answer 22

It is formed when two atoms share a pair of electrons

Question 23

What are lone pairs?

Answer 23

Pairs of electrons not involved in the bonding

Question 24

How are the strengths of covalent bonds measured?

Answer 24

Measuring energy needed to break the bond

Question 25

What occurs in a single covalent bond

Answer 25

Atomic orbitals overlap end on to eachother [ two s orbitals, two p orbitals or an s and a p orbital]

Question 26

What occurs in a double bond?

Answer 26

Sideways overlap between two p atomic orbitals each containing one electron = pi bond

Question 27

What occurs in a triple covalent bond?

Answer 27

2 pi bonds and 1 sigma bond overlapping sideways

Question 28

What is a non polar molecule?

Answer 28

Its a pure covalent bond where electrons are equally shared

Question 29

What factors dictate where the shared electrons are attracted to

Answer 29

The size of the atom - stronger attraction than larger atoms so shared electrons can get closer
Nuclear charge - atoms with bigger charge in nucleus will have a greater charge

Question 30

What are polar covalent bonds?

Answer 30

When electrons are shared unequally

Question 31

In a polar covalent bond, what becomes positively/negatively charged?

Answer 31

The atom with lesser share of electrons = slightly positively charged
Atom with more = slightly negatively charged

Question 32

What are the characteristics of covalent substances?

Answer 32

Low melting and boiling points - gases at room temp
Do not conduct electricity - neutral molecules
Do not dissolve readily in water

Question 33

Give examples of polar materials in every day life

Answer 33

Polar - water [washing clothes] + glucose [lucozade]

Non polar - Petrol

Question 34

What is electronegativity?

Answer 34

It’s the relative attraction of an atom for shared pairs of electrons in a covalent bond

Question 35

The higher the electronegativity value, what effect does it have?

Answer 35

It better it is at attracting the shared electrons

Question 36

Where does the electronegativity increase on the periodic table and why?

Answer 36

Across

• atomic number increases, nuclear charge
• no screening since extra electrons are added to the same outer shell therefore atomic radius decreases
• both these = the greater the attraction

Question 37

Where does the electronegativity decrease and why?

Answer 37

Down the group

• extra energy levels cause shielding of outer electrons from nucleus = increase in atomic radius
• although the nuclear charge is increasing, not attracted strongly
• greater screening, increased atomic radius reduces attraction for shared pairs of electrons