Chemical Changes and Structure

Question 1

General Knowledge Of Periodicity

Answer 1

Elements are arranged in the periodic table in order of increasing atomic number.

The chemical and physical properties of an element can be predicted from its position in Periodic Table
* the Alkali Metals in group 1 are reactive elements where reactivity increases down the group
* the Halogens in Group 7 are reactive elements where reactivity decreases down the group
* the Noble Gases in Group 0 are unreactive elements
* the Transition Metals are in the middle section of the Periodic Table between Groups 2&3.

-groups: vertical columns within the table contain elements with similar chemical properties resulting from a common number of electrons in the outer shell
-periods: rows of elements arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from metallic to non-metallic characteristics

Question 2

20 elements categorization

Answer 2

-metallic (Li, Be, Na, Mg, Al, K, Ca)
-covalent molecular — H2, N2, O2, F2, Cl2, P4, S8 and fullerenes (eg C60)
-covalent network — Boron, Carbon (diamond, graphite), Silicon
-monatomic (noble gases)

Question 3

Covalent Radius/Atomic Size

Answer 3

-The covalent radius is a measure of the size of an atom.
-The atomic size is the distance from the centre of the atom to its edge

Question 4

Atomic Size Trend Along A Period

Answer 4

atomic size decreases due to the increased nuclear charge/more protons pulling the electrons within the same shell closer.

Question 5

Atomic Size Trend Down A Group

Answer 5

atomic size increases due to addition energy levels and electron shielding effect, the inner electrons shield the outer electrons from the pull of of the positive nucleus, therefore the outer electrons are further away

Question 6

Ionisation energy

Answer 6

The first ionisation energy is the energy required to remove one mole of electrons from one
mole of gaseous atoms. The second and subsequent ionisation energies refer to the
energies required to remove further moles of electrons.

Question 7

I.E along a period

Answer 7

ionisation energy becomes greater due to the increase in nuclear charge/more protons attracting the electrons within the same energy level. The energy therefore increase

Question 8

I.E down a group

Answer 8

ionisation energy decreases due to the electron energy levels and shielding effect. The outer electrons therefore experience less of the positive pull of the nucleus.

Question 9

Electronegativity

Answer 9

-Atoms of different elements have different attractions for bonding electrons.
-Electronegativity is a measure of the attraction an atom involved in a bond has for the electrons of the bond.

Question 10

Electronegativity along a period

Answer 10

Electronegativity increases along a period, due to the the greater nuclear positive charge, due to an increase in protons, increases the pull on the outer electrons. The outer electrons are therefore more difficult to remove.

Question 11

Electronegativity down a group

Answer 11

Electronegativity decreases down a group as there are more energy levels and the outer electrons are further away form the nuclear positive charge. The pull on the outer electrons is less,hence Electronegativity decreasing.

Question 12

General Covalent Bonds

Answer 12

In a covalent bond, atoms share pairs of electrons. The covalent bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.

Question 13

Polar Covalent Bonds

Answer 13

Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding
electrons is different. Delta positive (δ+) and delta negative (δ-) notation can be used to indicate the partial charges on atoms, which give rise to a dipole.

Question 14

Ionic Bonds

Answer 14

Ionic bonds are the electrostatic attraction between positive and negative ions. Ionic compounds form lattice structures of oppositely charged ions.

Question 15

Pure covalent bonding and ionic bonding

Answer 15

-Pure covalent bonding and ionic bonding can be considered as opposite ends of a bonding continuum, with polar covalent bonding lying between these two extremes.
-The difference in electronegativities between bonded atoms gives an indication of the ionic character. The larger the difference, the more polar the bond will be. If the difference is large, then the movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions.

Question 16

Ionic compound

Answer 16

Compounds formed between metals and non-metals are often, but not always, ionic

Question 17

Intermolecular forces

Answer 17

Intermolecular forces acting between molecules are known as van der Waals forces. There are several different types of these:
London dispersion forces
Permanent dipole-Permanent dipole attraction
Hydrogen Bonding

Question 18

London Dispersion Forces

Answer 18

London dispersion forces are forces of attraction that can operate between all atoms and molecules. These forces are much weaker than all other types of bonding. They are formed as a result of electrostatic attraction between temporary dipoles and induced
dipoles caused by movement of electrons in atoms and molecules.
The strength of London dispersion forces is related to the number of electrons within an atom or molecule.

Question 19

How is London Dispersion Forces Affected?

Answer 19

the bigger the atom due to an increase in total number of electrons, the greater the London forces due to larger dipoles formed. Therefore increasing the energy required to desperate these molecules, hence increase in mp and bp

Question 20

Spatial Arrangement Symmetrical

Answer 20

when the polar bond’s spatial arrangement is symmetrical then the molecules is non-polar

Question 21

Spatial Arrangement Unsymmetrical

Answer 21

when the polar bond’s spatial arrangement is unsymmetrical then the molecule is polar

Question 22

Permanent dipole-permanent dipole interactions

Answer 22

-Permanent dipole-permanent dipole interactions are additional
electrostatic forces of attraction between polar molecules.
-the electrostatic attraction between the oppositely charged dipole ends of two or more polar molecules.
-Permanent dipole-permanent dipole interactions are stronger than
London dispersion forces for molecules with similar numbers of
electrons

Question 23

Hydrogen Bonding

Answer 23

Bonds consisting of a hydrogen atom bonded to an atom of a
strongly electronegative element such as fluorine, oxygen or
nitrogen are highly polar. Hydrogen bonds are electrostatic forces
of attraction between molecules that contain these highly polar
bonds. A hydrogen bond is stronger than other forms of permanent
dipole-permanent dipole interaction but weaker than a covalent
bond.

Question 24

Melting point of polar and non-polar molecule

Answer 24

The melting and boiling points of polar substances are higher than
the melting and boiling points of non-polar substances with similar
numbers of electrons.

Question 25

High mp and bp in ammonia, water, hydrogen

Answer 25

The anomalous boiling points of ammonia, water and hydrogen
fluoride are a result of hydrogen bonding.

Question 26

Hydrogen Bonding in ice

Answer 26

Hydrogen bonding between molecules in ice results in an expanded structure that causes the density of ice to be less than that of water at low temperatures.

Question 27

Solubility

Answer 27

-Ionic compounds and polar molecular compounds tend to be soluble in polar solvents such as water, and insoluble in non-polar solvents.
-Non-polar molecular substances tend to besoluble in non-polar solvents and insoluble in polar solvents.

Question 28

To predict the solubility of a compound

Answer 28

-presence in molecules of O-H or N-H bonds, which implies hydrogen bonding
-spatial arrangement of polar covalent bonds, which could result in a molecule possessing a permanent dipole

Question 29

Metallic Elements

Answer 29

Contain metallic bonding.
As the number of delocalized outer electrons increase, the hardness, mp and bp also increase. The strength of the metallic bond increases with the increases attraction between the positive core and increasing number of delocalised electrons

Question 30

Covalent Networks

Answer 30

-solid at room but insoluble in water
-graphite conducts due to only 3 out of 4 electrons bonding
-Strong covalent bonds inside and outside

Question 31

Reduction

Answer 31

Reduction is a gain of electrons by a reactant in any reaction.

Question 32

Oxidation

Answer 32

Oxidation is a loss of electrons by a reactant in any reaction.

Question 33

Redox Reaction

Answer 33

In a redox reaction, reduction and oxidation take place at the same
time.

Question 34

Oxidising Agent

Answer 34

An oxidising agent is a substance that accepts electrons.
-Elements with high electronegativities tend to form ions by gaining
electrons and so act as oxidising agents.

Question 35

Reducing Agent

Answer 35

A reducing agent is a substance that donates electrons.
-Elements with low electronegativities tend to form ions by losing
electrons and so act as reducing agents.

Question 36

Identification

Answer 36

You should be able to identify oxidising and reducing agents in a reaction.

Question 37

Strongest Reducing and Oxidising Agents

Answer 37

In the periodic table, the strongest reducing agents are in group 1,
and the strongest oxidising agents are in group 7.

Question 38

Examples of Oxidising Agents

Answer 38

-hydrogen peroxide is a molecule that is an oxidising agent
-dichromate and permanganate ions are group ions that are
strong oxidising agents in acidic solutions

Question 39

Examples of Reducing Agent

Answer 39

carbon monoxide is a gas that can be used as a reducing agent

Question 40

Uses of Oxidising Agents

Answer 40

Oxidising agents are widely used because of the effectiveness with
which they can kill fungi and bacteria, and can inactivate viruses.
The oxidation process is also an effective means of breaking down
coloured compounds, making oxidising agents ideal for use as
‘bleach’ for clothes and hair

Question 41

Electrochemical Series

Answer 41

-The electrochemical series represents a series of reduction
reactions.
-The strongest oxidising agents are at the bottom of the left-hand
column of the electrochemical series.
-The strongest reducing agents are at the top of the right-hand
column of the electrochemical series.
-An ion-electron equation can be balanced by adding appropriate
numbers of water molecules, hydrogen ions and electrons.
-Ion-electron equations can be combined to produce redox
equations.