Bonding & Structure

Question 1

What are positive and negative ions called?

Answer 1

+ve - cations
-ve - anions

Question 2

What is an ionic bond?

Answer 2

Strong electrostatic attraction between positive & negative ions

Question 3

How would you describe the structure of an ionic compound?

Answer 3

Giant ionic lattice
Giant - many, many ions
Lattice - a repeatin 3D arrangement of particles

Question 4

Why do ionic compounds have high melting and boiling points?

Answer 4

• Giant ionic lattice structure - many strong attractions between positive & negative ions
  Lots of energy needed to break the bonds

Question 5

In what conditions can ionic compounds conduct electricity?

Answer 5

When molten or dissolved in solution e.g. water - the ions are free to move
DO NOT CONDUCT WHEN SOLID CAUSE THE IONS CANNOT MOVE

Question 6

Why are ionic compounds soluble in water?

Answer 6

The ions make attractions to the H+ and O- atoms in the water molecules

ions are pulled apart and mix with the water molecules

Delta symbol means a partial charge

Question 7

Which factors affect the strength of ionic bonding?

Answer 7

• Ionic charge
• Ionic radius/ size of ions

Question 8

Typically are there ions in a covalent bond?

Answer 8

No - refer to them as atoms

Question 9

What is a covalent bond?

Answer 9

A strong electrostatic attraction between a shared pair of e- and the nuclei of two bonded atoms

Simply a shared pair of e-

Question 10

What is the Octect rule?

Answer 10

Tendency of atoms to prefer to have 8 e- in the outer shell

NOTE: this rule is not always followed

Question 11

What is a Lone pair and Vacant orbital?

Answer 11

LP - Any pairs of e- that are not shared (not bonding)
VO - space where e- are meant to be

Question 12

How many bonds do carbon, oxygen and nitrogen form?

Answer 12

1. C - 4
2. O - 2
3. N - 3

Question 13

Give examples of elements which break the octect rule?

Answer 13

Boron, Aluminium, Berylium - happy with less e- than 8
Phosphorus & Sulfur - expand the octect

Question 14

What is a dative covalent bond?

Answer 14

Where both e- are shared by the same atom

dative bond represented with an arrow on displayed formula

Question 15

If you have a third element or e- from elsewhere how do you present it in a dot and cross diagram?

Answer 15

A third symbol e.g. triangle or square

Question 16

TRUE OR FALSE: Bonding pairs repel more than lone pairs

Answer 16

FALSE - lone pairs repel more than bonding pairs and decrease the bond angle by 2.5 degrees

Question 17

What are all the names and angles of the bond shapes that you need to know?

Answer 17

Question 18

Do multiple bonds (double or triple) affect the shape of the molecule?

Answer 18

NO - however refer to them as bonding regions

Question 19

What is electronegativity?

Answer 19

The ability of an atom to attract the shared pair of electrons in a covalent bond

Question 20

What is the trend for electronegativity?

Answer 20

As you go down a group electronegativity decreases & as you go across a period electronegativity increases

Question 21

What are the most electronegative atoms?

Answer 21

• Fluorine
• Oxygen
• Chlorine
• Nitrogen

Question 22

What factors affect the electronegavitity of an atom?

Answer 22

1. the nuclear charge on the atom (no. of protons)
2. size of the atom
3. the shielding (no. of shells)

Question 23

What is meant by a non-polar bond?

Answer 23

If the covalent bond is between atoms of the same element or atoms with electronegativity <0.5 of each other - electrons are shared equally

Question 24

What is a bond that is always non-polar?

Answer 24

C-H

Question 25

What is an electron density cloud?

Answer 25

The region around a nucleus in which electrons are dispersed ## Footnote **This definition is not needed but helps to understand**

Question 26

What is meant by a **polar bond** ?

Answer 26

When there is an **uneven distribution of electron charge density** - described as an overall dipole ## Footnote difference in electeronegativity between two bonded atoms is >0.5 - **the electrons are shared unequally**

Question 27

Which atom in a covalent bond attracts the electrons **more strongly**?

Answer 27

The more electronegative atom

Question 27

Which ends are **slightly more positive** and **slighlty more negative** in a covalent bond?

Answer 27

The **more electronegative** atom is **slightly negative** and the **less electronegative** atom is **slightly positive** ## Footnote *positive end can also be called electron defficient*

Question 28

What is the separation in charge called?

Answer 28

a **dipole**

Question 29

What is an example of a polar molecule?

Answer 29

**water**

Question 30

If a molecule contains **polar bonds** but is **symmetrical** is it polar?

Answer 30

**No** - it is non-polar because the dipoles cancel each other out ## Footnote **If not symmetrical the dipoles do not cancel each other out and the molecule is polar**

Question 31

How can you tell if a molecule is **symmetrical**?

Answer 31

* If there is only bonding pairs **(no lone pairs)** * All atoms surrounding the central atom are the same

Question 32

How to tell if a molecule is **asymmetrical** (not symmetrical)?

Answer 32

* If any atom surrounding the central atom is different to the others * if there are any lone pairs on the central atom

Question 33

What 2 types of structure form from a covalent bond?

Answer 33

1. **Giant covalent** 2. **Simple molecular** - most covalent substances

Question 34

**TRUE or FALSE:** Are intermolecular forces in giant covalent structures?

Answer 34

**No** - they are always/only in simple molecular substances

Question 35

What are the 3 IMFs you need to know? What is their **strength** compared to ionic and covalent bonds?

Answer 35

1. Hydrogen bonds, Permanent dipole-dipole & London forces 2. **They are relatively weak** - Hydrogen bonds are the strongest then PDD & London forces

Question 36

What IMF do all molecular substances have?

Answer 36

**London forces** ## Footnote In noble gases but not ionic substances

Question 37

When will substances have PDD forces or hydrogen bonds?

Answer 37

1. Will have PDD forces if the molecules are **polar** 2. Will have hydrogen bonds if they contain: **N-H, O-H or F-H bonds** ## Footnote N,O & F are the most electronegative and have at least one lone pair

Question 38

How do **London forces arise**?

Answer 38

* In a molecule e- are constantly moving randomly * the e- charge density can flucctuate, parts of the molecule can become less negative - **forms a temporary dipole in the molecule**

Question 39

What can a temporary dipole cause?

Answer 39

* Causes a dipole to form in a neighbouring molecule - **called an induced dipole** * Attraction between a positive side on one molecule & negative side on an adjacent molecule - **this is a London force or induced dipole-dipole force**

Question 40

What **factors** affect the **strength/size** of London forces?

Answer 40

* **No. of electrons** - more e- higher chance a temporary dipole will form, makes stronger London forces * **surface area contact** - straight chains, to do with alkanes

Question 41

How do PDD forces form?

Answer 41

* **Polar molecules have a permanent dipole** - *difference in electronegativity* * attraction between positive side of one molecule and negative side of a neighbouring molecule

Question 42

How do Hydrogen bonds form?

Answer 42

* Big difference in electronegativity between the H and the N,O or F *(there is a large dipole)* * attraction between the **lone pair** on N, O or F and the H+ partial charge of a neighbouring molecule

Question 43

What are the features of a Hydrogen Bonding diagram?

Answer 43

* All dipoles * Lone pair on N, O or F * Hydrogen bond shown clearly with dashed line **(between the lone pair and the partial positive charge on the H on the other molecule)**

Question 44

What are the anomalous properties of water?

Answer 44

**Ice is less dense than liquid water** * water can form two H2 bonds per molecule cause O is very electronegative & has 2 lone pairs * The H2 bonds hold the water molecules further apart in ice than in liquid water

Question 45

What are the properties of simple molecular substances?

Answer 45

1. **Low melting & boiling points** - weak IMFs require little energy to overcome, molecules separate and are no longer attracted to each other 2. **Electrical conductivity** - Will not conduct electricity in solid or molten state **(there are no charged particles free to move)** 3. **Solubility** - non-polar molecules will not generally dissolve in water, if the simple molecules can form H2 bonds then they can become more soluble ## Footnote molecules that form H2 bonds dissolve more easily in H20